الجزءالثالث عشر من معجم الاجهزة M

MAC Media Access Con­ trol. A media-specific access-control protocol within IEEE 802 specifica­ tions (lower sublayer of layer 2 of ISO mode!), which includes variations for token ring, token bus, and CSMA/CD. mach See machine.

Mctch angle The angle between the path of a bodJ that is moving with supersonic velocity and a corresponding path that the body would take when moving at sonic velocity (the Mach line). The speed of sound divided by the body's velocity equals the sine of the Mach angle. machine Any device that is capable of per­ forming useful work, especially a device for producing controlled motion or for regulat­ ing the effect of a given force. machine address An absolute, direct, unin­ dexed address that is expressed as such or that is the result when indexing and other processing have been completed. machine code The lowest level of computer language; digital code that can be directly executed by the computer. machine code instruct A code that defines a particular computer operation and that can be used without further translation. machine-dependent program A program that operates on only one type of computer.

Contrast wi th machine-independent program. machine element Any standard mechanical part tln.t is used in constructing a machine, such as a bearing, fastener, cam, gear, lever, link, pin, or spring. machine error A deviation from correctness in computer data as a result of equipment failure. machine-independent Pertaining to proce­ dures or programs that are created without regard for the actual devices that will be used to express them. machine-independent program A program that operates on a variety of different com­ puters. Contrast with machine-dependent pro­

gram. machine instruction An instruction that a machine can recognize and execute. machine language Instructions that are writ­ ten in binary form that a computer can exe­ cute directly. Also called machine code, object code, and object language. machine-language code Same as computer code and contrasted with symbolic code.

machine-language programming Program­ ming that uses machine language. See machine-language code and computer code. machine operator The person who manipu­ lates the computer controls, places informa­ tion media into the input devices, removes the output, and performs other related func­ tions. machine-oriented language 1. A language that is designed to be interpreted and used by a machine ,,:itho~t translation. 2. A sys­ tem for expressing information that is intelli­ gible to a specific machine, for example, a computer or class of computers. Such a lan­ guage may include instructions that define and direct machine operations as well as information to be recorded by or acted upon by these machine operations. 3. The set of instructions that are expressed in the number system basic to a computer together with the symbolic operation codes that have absolute addresses, relative addresses, or symbolic addresses. Synonymous with machine lan­ guage. Clarified by language. Related to object language and contrasted with problem-oriented

language (POL). machine program 1. A program that is to be loaded in a computer and executed by it. 2.

In numerical control, an ordered set of instructions that are in automatic control lan­ guage and format and are based on the part program. These instructions are also

recorded on appropriate input media and are

sufficiently complete to effect the direct oper­

ation of an automatic control.

machine readable Data that will be accepted by a computer through an input device. machine-readable medium A medium that can convey data to a given sensing device. machinery One or a group of machines. An apparatus or system that is constructed of machines. machine vision Computer perception of visually based sensory output, which is used to produce a concise description of an image. machine vision system A system that, with­ out human intervention, inspects devices by capturing images and making decisions based on comparisons of the image~' features ':f, to expected features. machine word A unit of informatiGh that has a standard number of bits or characters that a machine regularly handles in each transfer.

For example, a machine may regularly han­ dle numbers or instructions in units of 36 binary digits. machining center A versatile machine tool used in computer numerical control (CNC)

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Mach number / magnetic core

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that has multi-axis control and, usually, automatic tool loading. These machining centers are designed to carry out a range of operations Mach number The ratio of the fluid velocity to the velocity of sound in the fluid, at the same temperature and pressure. macro In software, directions for expanding abbreviated text. A macro is a piece of boilerplate that generates a known set of instructions, data, or symbols. A macro is used to eliminate the need to write a set of instructions that are used repeatedly. For example, an assembly-language macro instruction enables the programmer to request that the assembler generate a predefined set of machine instructions. macro-assembler An assembler that allows the use of macros ana converts them into machine code. macro instruction The more powerful instructions that allow a programmer to refer to several instructions as though they were a single instruction. When a programmer uses the name of a macro instruction, all of the instructions are inserted at that point in his or her coding by the macroprocessor. macroloss Excess loss in fiber-optic links as a result of fiber bends. macro modeling The representation of a component or device in terms of a net-list description of an equivalent circuit. Standard components, such as resistors or capacitors, are typically employed in such modeling. macroprocessor 1. A program that translates a single symbolic statement into one or more assembly language statements. 2. A phase of an assembler that has the ability to translate selected mnemonic or symbolic instructions into multiple machine-language instructions. macro-program A program that contains macros. macroprogramming Programming that has macro instructions. macroscopic stress Load per unit area distributed over an entire structure or over a visible region of the structure. macrostructure The features of a polycrystalline metal, which are revealed by etching and are visible at magnifications of 10 diameters or less.

MACT Maximum Achievable Control Technology. Usually used to refer to a response to EPA (U.s.) regulations. magenta A color hue that transmits only blue and red light, with no green, from the video screen view. Magenta reflects only red and

blue light and absorbs green light on paper tha t uses four-color process inks. magnetically actuated extensions A device attached to a meter body that contains an electrical switch and is magnetically actuated by the metering float extension in order to signal a high or low flow. The switch is adjustable with respect to the float position over a range that is equal to the travel of the metering float. Standard switch ratings are usually 0.3 arnp.eres for. a 110 volt, 60 cycle AC supply (five amperes or more if relays are used). magnetic amplifier An" electronic amplification or control device that functions by using saturable reactors, either alone or in combi- .

-.{lation with other circuit elements. • magnetic bearing The angle between the line of sight to an object and the direction from the observer to magnetic north, as measured in a plane parallel to the earth's surface. magnetic biasing The conditioning of a magnetic recording medium by simultaneously superimposing a second magnetic field on the magnetic signal being recorded. magnetic blowout switch A special type of switch that is designed to switch high DC loads. A small permanent magnet that is contained in the switch housing deflects the arc to quench it when the contacts open. magnetic bubble memory A high-density information storage device that is composed of a magnetic film only a few micrometers thick. The film is deposited on a garnet substrate. Information is stored in small, magnetized regions (bubbles) whose magnetic polarity is opposite that of the surrounding region. magnetic card A card that has a magnetic surface on which data can be stored by selectively magnetizing portions of the flat surface. magnetic compass Any of several devices for indicating the direction of the horizontal component of a magnetic field, but especially for indicating magnetic north in the earth's magnetic field. magnetic contactor A device for opening and closing one or more sets of el~trical contacts.

It is actuated by either energl'Zing or deenergizing an electromagnet within the device. magnetic core 1. A configuration of magnetic material that is, or is intended to be, placed in a spatial relationship to current-carrying conductors and whose magnetic properties are essential to its use. The magnetic core may be used to concentrate an induced magnetic field, as in transformer, induction coil,

304

magnetic damping I magnetic printing

)

I

or armature, so as to retain a magnetic polar­ ization for the purpose of storing data. Or it may be used for its nonlinear properties as in a logic element. It may be made of such material as iron, iron oxide, or ferrite and in such shapes as wires, tapes, toroids, or thin film. 2. A storage device in which binary data is represented by the direction of magnetiza­ tion in each unit of an array of magnetic material. The material is usually in the shape of toroi<;lal rings, but may also take forms such as the wraps on bobbins. Synonymous with core. magnetic damping The progressive reduc­ tion of oscillation amplitude brought about by the current induced in electrical conduc­ tors as a result of changes in magnetic flux. magnetic disk A flat, circular plate with a magnetic surface on which data can be stored by selectively magnetizing portions of the flat surface. magnetic drum A right circular cylinder with a magnetic surface on which computer data can be stored by selectively magnetizing por­ tions of the curved surface. magnetic extensions A device that provides an indication of flow rate by means of a mag­ netic coupling lying between the extension of the metering float and an external indicator follower that surrounds the extension tube. magnetic field interference A form of inter­ ference that is induced in the circuits of a device as a result of the presence of a mag­ netic field. It may appear as common-mode or normal-mode interference in the measur­ ing circuits. See also interference, electromag­ netic. magnetic float gauge Any of several designs of liquid-level indicator that use a magnetic float to position a pointer or change the ori­ entation of bicolor wafers. magnetic float switch A device for operating a mercury switch by repositioning a mag­ netic piston with respect to a small perma­ nent magnet that is attached to the pivoting mercury switch capsule. In the usual config­ uration, a float attached to the piston posi­ tions the piston near the small magnet when liquid level is high. The float drops the pis­ ton out of proximity when the level is low, which allows a light spring to retract the magnet and pivot the mercury capsule. magnetic flowmeter A device for measuring volumetric flow rate across a fluid stream by setting up a magnetic field perpendicular to the direction of flow. A flowing conductive fluid then generates a voltage proportional to fluid speed.

VARIABLE FLOW RATE (fVs)

r-

0

......-::ml==::;".--- PROCESS PIPE (INNER DIAMETER, 0 ) MAGNETIC FIELD B E (ELECTRIC FIELD)

E

ttt CONDUCTIVE PROCESS FLUID IN

Maglletic Flowmeter magnetic focusing Causing an electron beam to diverge or converge so as to position an image or beam on an object-usually a CRT screen-by interacting with a magnetic or electromagnetic field. magnetic hardness comparator A device for determining the hardness of a steel part by comparing its response to electromagnetic induction with the response of a similar part of known hardness. magnetic head A transducer for converting electrical signals into magnetic signals that are suitable for storing on magnetic record­ ing media, for converting stored magnetic signals into electrical output signals, or for erasing stored magnetic signals. magnetic ink An ink that contains magnetic particles. Characters that are printed in mag­ netic ink can be read both by humans and by machines that are designed to read the mag­ netic pattern. magnetic lens Electric coils electromagnets or permanent magnets that are assembled into a configuration that can accomplish magnetic focusing. magnetic medium Any data storage medium and related technology, such as core, drum, film, tape, and disk, in which difff.rent pat­ terns of magnetization representpit values. magnetic printing Permanently transferring a recorded signal from one magnetic record­ ing medium to another magnetic recording medium (or to another portion of the same medium) by bringing the two sections into close proximity.

305

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magnetic proximity sensor / mainframe magnetic proximity sensor Any of several devices that are activated when a magnetized or ferromagnetic object passes within a defined distance of the active element. There are four types: variable-reluctance sensors, hermetically sealed dry-reed switches, Hall-effect switches, and Weigand-effect sensors. magnetic recorder A device for producing a stored record of a variable electrical signal as a variable magnetic field in a ferromagnetic recording medium. magnetic separator A machine that uses strong magnetic fields to remove pieces of magnetic material from a mixture of magnetic material and nonmagnetic or less strongly magnetic material. magnetic shield A metal shield that insulates the contents from external magnetic fields.

Such shields are often used with photomultiplier tubes. magnetic storage A device or devices that utilize the magnetic properties of materials so as to store information. magnetic tape L A tape that has a magnetic surface on which computer data can be stored by selectively polarizing portions of the surface. 2. A tape of a magnetic material that is used as the constituent in some forms of magnetic cores. magnetic tape encoder An electronic device that will accept data from a keyboard and write it to magnetic tape. magnetic test coil A coil that is used in conjunction with a suitable indicating or recording instrument to measure variations in magnetic flux when the coil is linked with a magnetic field. magnetic variometer An instrument for measuring variations in magnetic field strength with respect to space or time. magnet meter An instrument for measuring the magnetic flux of a permanent magnet under specified conditions. It usually incorporates a torque coil or a moving-magnet magnetometer that has a unique arrangement of pole pieces. magnetometer An instrument for measuring the magnitude of a magnetic field and sometimes also for determining its direction. magnetoresistive (MR) Involving changes in the electrical resistance in materials that are composed of metallic elements or in magnetic metals used in memory storage devices. magnetostriction A characteristic of some ferromagnetic materials whereby their physical dimensions vary with the intensity of an applied magnetic or electromagnetic field.

VARIABLE FLOW RATE (It/s)

r-

0

.......-::~;::::::::J>I.---- PROCESS PIPE (INNER DIAMETER, D)

MAGNETIC FIELD B

E (ELECTRIC FIELD)

E

'ttt CONDUCTIVE PROCESS FLUID IN

Magnetic Flowmeter magnetostrictive effect An inherent property of some ferromagnetic materials to deform elastically. This deformation generates mechanical force, when the materials are subjected to a magnetic field. magnetostrictive resonato A ferromagnetic rod that is constructed so that an alternating magnetic field can excite it into resonance at one or more frequencies. magnification 1. The ratio of output to input signal magnitudes. 2. Attaining a change in magnitude without a change in power. 3.

Producing an enlarged visual image. 4. The ra tio of a specific dimension on a virtual image to the corresponding dimension on the physical object being viewed. magnitude In digital signal processing (DSP), the square root of the sum of the squares of the real and imaginary parts of a complex signal. magnitude ratio The ratio of output signal magnitude to input signal magnitude. [ISA26-1968] See also gail!. magnitude signal The peak-to-peak value of a signal. [ISA-26-1968] mag tape In computer systems, the nine-track (in some cases, seven-track), 1/2-inch medium on which data can be stored and transferred to other computers'.i maillist In e-mail systems, a (ust~ally automated) method that allows a message to be sent to only one address, where it is then routed to specific other addresses. mainframe A large-scale computer system that is provided with a large number of peripherals and comprehensive software.

306 _.-l

main-line class / maintenance engineer

main-line class A term that is used to specify the pressure and temperature ratings (of a pipe), the material from which it is con­ structed, and the appropriate code, such as ANSI B31.1. [ANSI/ISA-67.02.01-1999] main memory The set of storage locations that are connected directly to the central pro­ cessir:g unit. Also called (generically) core

memor.y:­ main program The module of a computer program that contains the instructions by . which the prograrfihegins to execute. Nor­ mally, the main program exercises primary control over the operations that are per­ formed and calls subroutines or subpro­ grams to perform specific functions. mains The electricity supply that is available to the consumer from the distribution system or systems for which the equipment in ques­ tion is deSigned. [ANSI/ISA-82.02.02-1996 (lEC 61010-2-031)]. The British equivalent of what in United States is called "line power./I See line power. main storage 1. Usually, the fastest storage device on a computer and the one from which instructions are executed. Contrast with auxiliary storage. [ISA-RP55.1-1975 (R1983)] 2. The fastest general-purpose stor­ age of a computer. maintain 1. To keep in continuance or in a certain state, as of repair. 2. To preserve or keep in a given existing condition, as of effi­ ciency or repair. maintainability 1. The relative ability of a device or system to remain in operation such that it requires only routine scheduled main­ tenance and occasional unscheduled mainte­ nance, without extensive periods of downtime for major repairs. 2. The probabil­ ity that a device will be restored to operating condition within a specified period when maintenance is done with prescribed resources and procedures. 3. The inherent characteristic of a design or installation that determines the ease, economy, safety, and accuracy with which maintenance actions can be performed on it. 4. The ability to restore a product to service or to perform preventive maintenance within required lim­ its. maintained 1. An alarm that returns to nor­ mal after it is acknowledged. 2. Term used to describe a device that remains maintained after pressure or signal are removed. maintained alarm See alarm. maintenance 1. Any act that either prevents the failure or malfunction of equipment or restores its operating capability after a failure

or malfunction. 2. Any activity that is intended to eliminate faults or to keep com­ puter hardware or programs in satisfactory working condition. These include tests, mea­ surements, replacements, adjustments, and repairs. maintenance, corrective Any maintenance activity that is not normal to the operation of equipment and requires gaining access to the equ.ipmept's interior. Such activities must be performed by a q':lalifted person and typi­ cally include locatirig the causes of faulty performance, replacing defective compo­ nents, adjusting internal controls, and the like. [ISA-12.01.01-1999] maintenance, operational Any maintenance activity, excluding corrective maintenance, that the operator is intended to perform and that is required if the equipment is to serve its intended purpose. Such activities typi­ cally include correcting zero on a panel instrument, changing charts, record keeping, adding ink, and the like. [ISA-12.01.01-1999] maintenance conditions The conditions under which maintenance is performed. maintenance engineer A trained profes­ sional who assists maintenance supervisors, technicians, and mechanics in maintaining the facilities or systems by providing in-depth engineering assistance on high­ maintenance equipment. Maintenance engi­ neers help design and project engineers dur­ ing plant start-ups, retrofits, and modifica­ tions to ensure that the design is engineered for maintenance. They ensure standardiza­ tion of equipment and systems and helps determine the frequency of preventive main­ tenance. Such engineers determine the ser­ vice life of equipment by evaluating the cost of repair and the frequency of repair. They ensure that the equipment continues to con­ form to the technical specifications and that equipment is kept in calibration. Mainte­ nance engineers work with management to ensure that customers, production personnel, and maintenance staff are cooperating by providing systems and equipment so the end item meets all specifications and production schedules. They ensure that new systems are designed to be maintainable and ti{at the proper documentation is proVided; They suggest and provide training when required to ensure that maintenance personnel have the knowledge to maintain the equipment or system. They also help determine if in-house maintenance or contract maintenance is more feasible and ensure that operational maintenance is being performed. Mainte-

307

I

maintenance engineering / Management Information System

I

nance engineers ensure that maintenance mechanics, technicians, technologists, and engineers are involved in a project from the very beginning and that instruments, wiring, and equipment is standardized, staff is trained in new equipment, equipment is tested, and equipment is calibrated. maintenance engineering The process of developing concepts, criteria, and technical requirements for maintenance during the conceptual and acquisition phases of a project. Involves providing policy guidance for maintenance activities and exercising technical and management direction and review of maintenance programs.

Maintenance Management System A part of the Management Information System (MIS) that is useful for maintaining a company's equipment. It accesses equipment informa­ tion, the availability and location of spare parts, order systems for maintenance work, preventive maintenance systems, the qualifi­ cations of maintenance personnel, the history of equipment maintenance, and any other information that will help the maintenance engineer, supervisor, technician, or mechanic be more proficient. See Management Injomza­ tion System (MIS). maintenance time The time that is used for equipment maintenance. It includes preven­ tive maintenance time and corrective mainte­ nance time. major diameter The largest diameter of a screw thread. It is measured at the crest of an external thread and at the root of an internal thread. major frame With reference to telemetry for­ mats, the time period during which all data of a multiplex are sampled at least once. It includes one or more minor frames. Major frame length is determined as (N)(Z) words, where N = the number of words per minor (prime) frame and Z = the number of words in the longest submultiple frame. major graduations The intermediate gradua­ tion marks on a scale. They are heavier or longer than other graduation marks but are not index graduations. majority A logic operator that is true if more than half its inputs are true, false if half or less than half of its inputs are true. major time In telemetry computer systems, two sixteen-bit words: minutes/seconds and hours/days. makelbreak component Components that have contacts that can interrupt a circuit (even if the interruption is transient in nature). Examples of make/break compo­

nents are relays, circuit breakers, servo potentiometers, adjustable resistors, switches, connectors, and motor brushes.

[ANSI/lSA-12.01.01-1999; ANSI/ISA­ 12.12.01-2000] make-to-order Products that are manufac­ tured to a specific customer's order configu­ ration and delivery time specifications. make-to-stock Products that are manufac­ tured to be stored in finished-goods storage before the·customer's order arrives. makeup . Thewa'ter that is added to boil~r

feed to compensate for the water lost

through exhaust, blowdown, leakage, and

the like.

male branch tee (MBT) In the tubing to a pipe con.nector, the tee that allows two tubes to be joined to a pipe. The male pipe thread connection is perpendicular to the axis that is shared by the two tubing connections. male conn~dor (Me) A type of t';1bing.to '. pipe conneCtor. The male pipe threaded con­ nection is on one end, and the tubing connec­ tion is on the other. male elbow (!"IE) In the tubing to pipe con­ nector, a 90 change in direction in which there is a male pipe thread connection on one end and a tubing connection on the other. male fitting An element of a connection in pipe, tubing, electrical conductors or mechanical assemblies that fits into the mat­ ing (female) element. For example, the exter­ nally threaded end of a pipe fitting is termed "male." male run tee (MRT) In tubing to a pipe con­ nector, the tee that allows two tubes to be joined to a pipe. The male pipe thread con­ nection and one of the tubing connectors share a common axis. malfunction The effect of a fault. malfunction routine Same as diagnostic rou­ tine. malleable iron A somewhat ductile form of cast iron that is made by heat-treating white cast iron in order to convert the carbon-con­ taining phase from iron carbide into nodular graphite.

MAN Metropolitan Area Network. A "stretched" LAN that provid~s digital data communications over a distaice of about 50 km. Generally associated wifh the IEEE 802.6 MAN standard.

Management Information System (MIS) A computerized system that uses a large data­ base that contains information on customers, equipment, supplies, spare parts, personnel, processes, sales forecasts, history, costs, prof­ its, and the like. Selected information is

308

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manager, control systems and "

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available to decision-makers in the organiza­ tion. manager, control systems and instrumentation This manager is responsi­ ble for all departmental or sectional activi­ ties, including: (a) defining and reporting activities and needs to management; (b) maintaining liaisons with other departments or sections so as to coordinate work assign­ ments; (c) providing administrative and technical support to other departments or sections; (d) assigning projects to personnel and handling manpower scheduling, recruit­ ment, evaluation, and salary reviews; (e) managing the development of training pro­ grams; (f) making decisions on cruciClI or complex project activities; (g) supervising all departmental or sectional personnel; (h) pre­ paring departmental or s~ctional budgets, forecasts, and goals; and (i) promoting safety.

Manchester encoding 1. The means by which separate data and clock signals can be com­ bined into a single self-synchronizing data stream that is suitable for transmission on a serial channel. [ANSI/ISA-50.02, Part 2-1992] 2. A digital-encoding technique (specified for IEEE 802.3, Ethernet) in which each bit is divided into two complementary halves. A negative-to-positive (voltage) transition in the middle of the bit period designates binary"}," while a positive-to-negative tran­ sition represents "0." The Manchester encod­ ing technique also allows the receiving device to recover the transmitted clock from the incoming data stream (self-clocking). manhead A boiler drum or other pressure vessel head that has a manhole. manhole The opening in a pressure vessel that is sufficiently large in size to permit a man to enter. manifold 1. A pipe or header from which a fluid can be collected or to which a fluid can be distributed to a number of pipes or tubes.

2. A branch pipe that distributes intake or exhaust fluids to a series of valve ports, as in a multicylinder engine such as an automo­ bile engine. manifold equalizing line The conduit within a manifold that connects the high and low differential-pressure impulse lines. manifold (instrumentation) Any configura­ tion of valves that can be manipulated to cre­ ate zero differential pressure at the measuring instrument. manifold pressure The fluid pressure in the intake manifold of an internal combustion engine.

000

/

manual loading station

manifold variable A quantity or condition that is varied in order to change the value of the controlled variable, manipulated variable (MV) 1. In a process that is intended to regulate some condition, a quantity or a condition that the control alters in order to initiate a change in the value of the regulated condition. 2. The part of the process that is adjusted in order to close the gap between the set point and the controlled variable. See also variable, manipulated. manipulative variable In a control loop, the variable that is used by the controller to reg­ ulate the controlled variable. manipulators Mechanical devices for remotely handling hazardous materials.

They are usually hand operated, often from behind a shield, and mayor may not be power assisted. manometer A gauge for measuring pressure or a pressure difference between two fluid chambers. A U-tube manometer consists of two legs, each of which contains a liquid of known specific gravity. manometric equivalent The length of a verti­ cal column of a given liquid at standard room temperature. It indicates a pressure dif­ ferential that is equal to the differential that is indicated by a I-mm-long column of mer­ curv at o°e. mantissa See floating point. manual backup An alternate method of pro­ cess control in which control is effectuated by manually adjusting final control elements when the computer system fails. manual control The operation of a process by adjusting final control elements manually. manual controller A control device whose output signals, power, or motions are all var­ ied by hand. manual data-entry module A device that monitors a number of manual input devices from one or more operator consoles and/ or remote data-entry devices and transmits information from them to the computer. manual input 1. The entry of data by hand into a device at the time the data is pro­ cessed. 2. The data that is entered as described in definition 1. " manual loading station A device11r function whose output is manually adjust~ble that is used to actuate one or more remote devices.

The station does not provide for switching between the manual and automatic control modes of a control loop (See controller and control station). The station may have integral indicators, lights, or other features and is also known as a "manual station" or a "man-

309

I

manual operation / margin

II

ualloader." See manual station. [ANSI/ISA­ 5.1-1984 (RI992)] manual operation The processing of data in a system by using direct manual techniques. manual override See hand jack and lor hand­ wheel. [ANSI/lSA-75.05.01-2000] manual reset See reset. manual reset switch A switch in a limit con­ troller that manually resets the controller after the limit has been exceeded. manuals A compilation of electrical and mechanical specifications, parts lists, operat­ ing or service instructions, calibration proce­ dures, test logs, performance requirements, and pertinent technical data that is required for the specific project at hand. [ISA-RP60.4­ 1990] manual station 1. Synonymous with manual loading station. 2. A single-loop, hard manual control for operating the final control devices in case the control system fails. 3. Makes it possible for normal controller operation to be bypassed so an analog output signal in a con­ troller can be varied manually. A manual sta­ tion is used primarily in emergencies or possibly during a maintenance shutdown of the controller. manufactured gas Fuel gas that is manufac­

tured from coal, oil, and the like, as differen­

tiated from natural gas.

manufacturer software A complex program package that develops the user's application and organizes computer procedures so as to obtain efficient response from the application program. Often this software is referred to as an operating system. See operating system. manufacturer's recommended cavitation limit An operational limit that is expressed as a cavitation coefficient smr. This smr is supplied by the valve manufacturer for a given valve type, size, opening, and refer­ ence upstream pressure. Applying the limit may require scale effect and influence factors if the service conditions and valve size are different than for the reference pressure and size. [ISA-RP75.23-1995] Manufacturing Automation Protocol (MAP) A specification for a suite of com­ munication standards to be used in manufac­ turing automation. Developed under the auspices of General Motors Corporation, the further development of this specification is being taken over by the MAP ITOP Users Group under the auspices of Computer and Automated Systems Association of the Soci­ ety of Manufacturing Engineers. (CASAl SME).

manufacturing defects analyzer (MDA) A device that checks loaded printed-circuit boards for assembly faults.

Manufacturing Message Specification (MMS) An ISO standard 9506, OSI applica­ tion-layer protocol for messaging within and between industrial automation systems.

Manufacturing Messaging Format Standard (MMFS) One of the application protocols specified by MAP. See Manufacturing Auto­

'mation Protocol (M:4 P).

manufacturing operations and control domain (MO&C domain) This domain includes all the activities in level 3 as well as information flows to and from levels 0, I, and 2 across the boundary to level 4. (These levels are defined in ANSI/ISA-88.01-1995.)

[ANSI/ISA-95.00.01-2000] MAP Manufacturing Automation Protocol.

Based on th.e IEEE 802.4, a networking proto­ col originated at General Motors that follows the seven-layer OSI model. Note: A device described as MAP-compliant conforms to specifications and will talk with other devices over the system; MAP-compatible means only that it will not interfere (physical and data link layers only) with "foreign" devices, but will only talk with like devices while sharing the timing with those foreign devices). map 1. To establish a correspondence or rela­ tionship between the members of two sets and to perform a transformation from one set to another. An example of creating such a map is to form a set of truth tables from a set of Boolean expressions. Information should not be lost or added when transforming the map from one to another. 2. See memory map. mapped system A system that uses the mem­ ory management unit of computer hardware to relocate virtual memory addresses. mapping 1. A set of objects that have a defined correspondence with the quantities or objects of another set. [ISA-TR50.02, Part 9-2000] 2. The logical association of one set of values, such as the addresses on one net­ work, with the quantities or values of another set, such as the devices on another network (that is, a name-address internet work route or protocol-to-pr~colmap­ ping)"h margin In the process of determining a set point, an allowance that is added to the uncertainty of the instrument channel. Mar­ gin moves the set point farther away from the analytical limit. [ANSI/ISA 67.04.02­ 2000]

310

marginal check / mass flow rate

•t

marginal check A preventive-maintenance procedure in which certain operating condi­ tions are varied about their normal values in order to detect and locate incipient defective units. For example, varying supply voltage or frequency would be marginal checks. Syn­ onymous with "marginal test" and "high-low bias test." Related to check. marginal test Same as marginal check. margin of safety The ratio between maxi­ mum ~ervice load (allowable design load) for a structure and the load that would cause the structure to deform, collapse, or break. margins In the typographical composition of video screen displays and printing, the white space that surrounds the text area on a page. marine engineering A branch of engineering that deals with the design, construction, and operation of shipboard propulsion systems and associated auxiliary machinery. mark A sign or symbol that is used to signify or indicate an event in time or space. Exam­ ples include an end-of-word or -message mark, a file mark, a drum mark, or an end-of­ tape mark. mark-hold The normal no-traffic line condi­ tion when a steady mark is transmitted. See mark. marking pointer An adjustable stationary pointer, usually one whose color is different from that of the indicating pointer, that can be positioned opposite any location on the scale that is of interest to the user. markings Information shown on the trans­ ducer itself. It will normally include the man­ ufacturer, model number, and serial number.

[ISA-RP37.2-1982 (R1995)] Markov chain A probabilistic model of events in which the probability of an event is dependent only on the event that precedes it. mark-sense To mark a position on a punch card with an electrically conductive pencil so it can later be converted to machine punch­ ing. See sensing, mark. mark-sense device An electronic machine that will read mark-sensed forms. See mark­ sense and sensing, mark. mark sensing See sensing, mark. marshaling cabinet A cabinet, sometimes located outside the control or rack rooms, that houses terminal boards for plant or pro­ cess field wiring. In it, the wiring coming from or going to divergent locations is rear­ ranged appropriately to control system I/O requirements, often with signal-condition­ ing equipment, such as is needed for various transmitters and sensors. The term comes

from the British term for railroad switch yards: marshaling yards.

Marx generators A high-voltage electrical pulse generator in which capacitors are charged in parallel and then discharged in series so as to generate a voltage that is much higher than the charging voltage. mask 1. A protective face covering that usu­ ally provides for the filtration of breathing air or can be attached to an external supply of breathing air. 2. A frame or similar device that is used to pre\':ent certain areas of a workpiece surface from being coated, as with paint. 3. A frame that conceals the edges of a cathode-ray tube, such as a television screen.

4. A machine word or register that specifies which parts of another machine word or reg­ ister are to be operated on. m.isking 1. The process of extracting a non­ word group or a field of characters from a word or a string of words. 2. The process of setting internal program controls in order to prevent transfers that otherwise would occur when internal machine latches are set. mask-programmed memory Computer memory that is dedicated to the storage of a particular set of data. A mask that contains a particular pattern of bits is used in the manu­ facture of the memorv. mass The amount of ~atter an object con­

tains.

mass feed water flow rate The mass flow rate of all water delivered to the boiler. It is derived either from direct process measure­ ments and/ or from calculations from other parameters. When measurement techniques for volumetric feedwater flow rate are employed and the feedwater temperature at the flow-measuring element varies lOO°F (37.8°C), the measured (indicated) flow must be compensated for flowing feedwater den­ sity in order to determine the true mass feed­ water flow rate. [ANSI/ISA-77.42.01-1999] mass flow The amount of fluid, measured in mass units, that passes a given location or reference plane per unit time. mass-flow bin A bin with steep, smooth sides, which allow its contents to flow, with­ out stagnant regions, whenever some of the "~ contents are withdrawn. mass flowmeter An instrument for~measur­ ing the rate of flow in a pipe, duct, or channel in terms of mass per unit time. mass flow rate The mass of fluid that moves through a pipe or channel within a given period of time.

!

I

311

I

mass number / material lot

DIRECT MASS MEASURE VOLUME

AND DENSITY

MEASURE VOLUME AND INFER

DENSITY BY MEASURING

TEMPERATURE AND PRESSURE

W=Qp =Qp(P,T)

Ma:;s Flowmeter

I I

I I ,!

mass number The sum of the number of pro­ tons and neutrons in the nucleus of a specific nuclide. mass spectrograph A mass spectroscope that records intensity distributions on a photo­ graphic plate. , mass spectrometer A mass spectroscope that uses an electronic instrument to indicate the distribution of intensity in the separated ion beam. mass spectroscope An instrument for deter­ mining the masses of atoms or molecules or the mass distribution of an ion mixture. The atoms, molecules, or ion mixture are deflected with a combination of electric and magnetic fields, which act on the particles according to their relative masses. mass spectrum In a mixture of ions, the sta­ tistical distribution by mass or by mass-to-charge ratio. mass steam flow rate The mass flow rate of steam from the boiler, which is derived either from direct process measurements and j or calculations from other parameters. If volu­ metric steam flow-rate measuring techniques are employed, the measured (indicated) flow must be compensated for flowing steam den­ sity in order to determine the true mass steam flow rate. [A SI/lSA-77.42.01-1999] mass storage A digital device like a disk or magnetic tape that can store large amounts of data, which are readily accessible to the cen­ tral processing unit. mass velocity Mass flow per unit of cross-sectional area. master 1. A device that controls other devices in a system. 2. A precise pattern for making replicate workpieces, as in certain types of casting processes. master clock A device that functions as the primary source of timing signals. master file directory The system-maintained file on a volume that contains the names and addresses of all the files stored on the vol­ ume.

master flowmeter A flowmeter that is used as an interlaboratory standard in correlation checks of calibration systems. [ISA-RP31.1­ 1997] master fuel trip (MFT) See fuel trip. An event that results in the rapid shutoff of all fuel.

[A SI/ISA-77.44.01-2000; ANSljISA­ 77.44.02-2001] master gauge A device that has fixed loca­ tions for positioning parts or holes in three dimensions. mast~r recipe'" A't);pe of process recipe that takes in~o accounf equipment capabilities and may include information that is process cell-specific. [ANSI/ISA-88.01-1995] master reference A signal point that is tl1e signal reference point for an entire system.

Usually, a ground rod or grid. All local refer­ ences are tied back to the master reference point.

Qlaster station A unit that has control of all other stations on a li:1e. master-slave A mode of operation in which one data station (the master) controls the net­ work access of one or more data stations (the slaves). master/slave manipulator A remote manipu­ lator that mechanically, hydromechanically, or electromechanically reproduces the hand or arm motions of an operator. material balance 1. The procedure of accounting for the mass of material that goes into a process versus the mass that leaves the process. 2. The balance that relates the mate­ rial in and material out of a distillation col­ umn. Material-balance manipulative variables are "overhead flow," "bottoms flow," "sidestreams flow," and "feed flow." material balance control (control, material balance) A calculation for inventorying material inputs versus outputs in a process system. material class A means for describing a grouping of materials with similar character­ istics for the purposes of scheduling and planning. [A SI/ISA-95.00.01-2000] material definition A definition of the prop­ erties and characteristics of a substance.

[A SI/ISA-95.00.01-2000] , material dispersion The bro~ening of light pulse as a result of the differ~ntial delay of various wavelengths of light in a waveguide material. This group delay is aggravated by broad bandwidth light sources. material lot A uniquely identifiable amount of a material. Lot describes the actual total quantity or amount of material that is avail­

312

materials handling / maximum external capacitance

'! i

I I

t

able, its current state, and its specific prop­ erty values. [ANSI/ISA-95.00.01-2000] materials handling Transporting or convey­ ing ma terials, parts, or assemblies. This includes all aspects of loading, unloading, moving, storing, and shipping them, both within a facilitv and between facilities. materials scienc~ The study of materials that are used in research, construction, and man­ ufacturing. Includes the fields of metallurgy, ceramics, plastics, rubber, and composites. material sublot A uniquely identifiable sub­ set of a material lot, containing quantity and location. It may be a single item. [ANSI/ISA­ 95.00.01-2000] mathematical check A check that uses math­ ematical identities or other properties, occa­ sionally with some degree of discrepancy considered acceptable. An example would be checking multiplication by verifying that A x B = B x A. Synonymous with "arithmetic check." mathematical logic Same as symbolic logic. mathematical model The general character­ ization of a process, object, or concept in terms of mathematics. The mathematical model enables the relatively simple manipu­ lation of variables to be accomplished in order to determine how the process, object, or concept would behave in different situa­ tions. mathematical programming In operations research, a procedure for locating the maxi­ mum or minimum of a function, subject to constraints. Contrast with convex program­

ming, dynamic programming, integer program­ ming, linear programming, nonlinear programming, and quadratic programmillg. matrix 1. In mathematics, an n-dimensional rectangular array of quantities. Matrices are manipulated in accordance with the rules of matrix algebra. 2. In computers, a matrix is a logic network that takes the form of an array of input leads and output leads, in which logic elements are connected at some of their intersections. 3. The principal microstruc­ tural constituent of an alloy. 4. The binding agent in a composite or agglomerated mass. matrix control strategies (MCS) In process control, strategies that regulate the process from several inputs and usually involve unit ~everities and product compositions. Also called "multivariable predictive control strat­ egies." See multivariable control. matrix printer A type of computer device that forms letters and symbols by printing a pattern of dots.

matte 1. A smooth but relatively nonreflec­ tive surface finish. 2. An intermediate prod­ uct in the refining of sulfide ores by smelting. devices).

MAU Multistation access unit; media attach­ ment unit. A multistation access unit is a wir­ ing concentrator used in local area networks.

A media attachment unit is also known as a transceiver and should not to be confused with a token ring MAU (media access unit).

It is an Ethern~t devite·for transmitting and receiving data that often provides data­ packet collision detection as well. It can either be an internal' or a external feature of a network device such as a network interface card, repeater, hub, or concentrator. A multi­ port MAU, or transceiver, allows a number of computers or workstations to be attached to a single connection on Ethernet bus, and each port performs standard transceiver . functions. maximum allowable working pressure The highest gauge pressure that can safely be applied to an internally pressurized system under normal operating conditions. It is usu­ ally well below the system's design-bursting pressure and hydrostatic test pressure, and is the pressure at which relief valves are set to lift. maximum continuous load The maximum load that can be maintained for a specified period. maximum elongation In strain gauges for making force or pressure measurements, a strain value in which a deviation of more than ±5 percent occurs with respect to mean characteristic (resistance change versus strain). maximum, error See error, maxil/lum (data pro­

cessing). maximum excitation The maximum value of excitation voltage or current that can be applied to some device at ambient conditions without causing damage or degrading per­ formance beyond specified tolerances. maximum experimental safe gap (MESG) The maximum. clearance between two parallel metal surfaces that under speci­ fied test conditions has been found to pre­ vent an explosion in a test chamr'r from propagating to a secondary chamber that contains the same gas or vapor at the same concentration. [ANSI/ISA-12.01.01-1999; ANSl/ISA-12.22.01-1998 (IEC 60079-1 Mod)] maximum external capacitance ( Co or C a ) The maximum capacitance in an intrin­ sically safe circuit that can be connected to

313

I

maximum external inductance / maximum pointer

I

the connection facilities of the apparatus.

[ISA 12.02.01-1999 (IEC 60079-11 Mod)] maximum external inductance ( Lo or La> The maximum value of inductance in an intrinsically safe circuit that can be con­ nected to the connection facilities of the appara tus. [ISA 12.02.01-1999 (IEC 60079-11 Mod)] maximum external inductance to resistance ratio (L o IR o ) The ratio of inductance (L o ) to resistance (R a ) of any external ci"rcuit that can be connected to the connection facilities of the electrical apparatus without invalidat­ ing intrinsic safety. [ISA 12.02.01-1999 (IEC 60079-11 Mod)] maximum input current ( I i or I max ) The maximum current (peak AC or DC) that can be applied to the connection facilities of the intrinsically safe apparatus. [ISA 12.02.01­ 1999 (IEC 60079-11 Mod)] maximum input power ( Pi) The maximum power in an external, intrinsically safe circuit that can be applied to the connection facili­ ties of the apparatus. [ISA 12.02.01-1999 (IEC 60079-11 Mod)] maximum input voltage (V i or Vmax) The maximum voltage (peak AC or DC) that can be applied to the connection facilities of the intrinsically safe apparatus without invali­ dating the type of protection. [ISA 12.02.01­ 1999 (IEC 60079-11 Mod)] maximum instantaneous demand The sud­ den load demand on a boiler beyond which an unbalanced condition may be established in the boiler's internal flow pattern and/ or surface release conditions. maximum internal capacitance ( C i) The total equivalent internal capacitance of the apparatus that appears across the connection facilities of the apparatus. [ISA 12.02.01-1999 (IEC 60079-11 Mod)] maximum internal inductance ( L i) The total equivalent internal inductance of the apparatus that appears at the connection facilities of the apparatus. [ISA 12.02.01-1999 (IEC 60079-11 Mod)] maximum-internal-inductance-to-resistance ratio (L i IR i) The ratio of inductance (L i) to resistance (R i ) that appears at the external connection facilities of the electrical appara­ tus. [ISA 12.02.01-1999 (lEC 60079-11 Mod)] maximum (minimum) ambient temperature The value of the highest (or lowest) ambient temperature that a trans­ ducer can be exposed to, regardless of excita­ tion applied, without being damaged or later showing performance degradation beyond specified tolerances. [ISA-37.1-1975 (R1982)]

maximum (minimum) fluid temperature The value of the highest (or lowest) measured-fluid temperature that a transducer can be exposed to, regardless of excitation applied, without being damaged or later showing performance degradation beyond specified tolerances. Note: When a maximum or minimum fluid temperature is not separately specified it should be the same as any specified maximum or minimum .. ambient temp'er~t~re. [ISA-37.1-1975 (R1982)]" .. maximum operating'conditions The maxi­ mum environmental"conditions in which a device or system can operate safely. These conditions may, however, still limit the life span of that device or system compared to operating in specified normal conditions. maximum operating pressure The maximum internal pressure that is permitted for an enclosure. [ISA-RP12.4-1996] maximum output current ( 10 or I sc ) The maximum current (peak AC or DC) in an intrinsically safe circuit that can be taken from the connection facilities of the appara­ tus. [ISA-.12.02.01-1999 (lEC 60079-11 Mod)] maximum output current - multiple channel apparatus (It) The maximum DC or peak AC current that can be extracted from any combination of terminals of a multiple-chan­ nel associated apparatus. [ISA-12.02.01-1999 (IEC 60079-11 Mod)] maximum output voltage ( V o or Voc ) The maximum output voltage (peak AC or DC) in an intrinsically safe circuit that can appear under open-circuit conditions at the connec­ tion facilities of the apparatus at any applied voltage up to the maximum voltage, includ­ ing U m and U i' Note: Where there is more than one applied voltage, the maximum out­ put voltage is the one that occurs under the most onerous combination of applied volt­ ages. [ISA-12.02.01-1999 (IEC 60079-11 Mod)] maximum permissible protective liquid level The maximum level that the protec­ tive liquid can attain in normal service. This level takes into account the effects of expan­ sion from the worst-case filling condition specified by the manufacturer.to the condi­ tion of full load at maximum-imbient tem­ perature for which the apparfltus is designed. [ANSIIISA-12.26.01-1998] maximum pointer A movable pointer that is repositioned as the indicating pointer of an instrument moves upscale. However, it remains stationary at the highest point reached when the indicating pointer moves downscale.

314

maximum service temperature / mean-time-between-failures

1 I

maximum service temperature 1. The high­ est value of the service temperatures. Note: Each apparatus may reach different service temperatures in different parts. [ISA­ 12.00.01-1999 (IEC 60079-0 Mod)] 2. When referring to electrical instruments in hazard­ ous locations, maximum surface temperature is the highest temperature attained by a sur­ face that is accessible to flammable gases, vapors, or combustible dusts under operat­ ing conditions within the ratings of the appa­ .' TfltU5 (including recognized overloads and abnormal and defined fault conditions).

[ANSI/ISA-12.01.01-1999] 3. The highest temperature capable of igniting the explosive atmosphere that surrounds any part or sur­ face of an electrical apparatus in service under the most adverse conditions (but within the recognized tolerances). Note 1: The manufacturer will prescribe the product standard. Also, in the manufacturer's partic­ ular design it should take into account the following other conditions: fault conditions specified in the standard for the type of pro­ tection involved; all operating conditions that are specified in any other standard spec­ ified by the manufacturer, including recog­ nized overloads; any other operating condition specified by the manufacturer.

Note 2: The relevant surface temperature may be internal or external, depending upon the type of protection involved. [ISA­ 12.00.01-1999 (IEC 60079-0 Mod)] maximum thermometer A thermometer that indicates the maximum temperature that is reached during a given time interval. A clini­ cal thermometer used to determine a patient's body temperature is one type of maximum thermometer. maximum vibration cavitation The level of cavitation that is associated with peak vibra­ tion measurements. It is determined from a cavitation level plot at the peak that sepa­ rates Regime III and Regime IV. The test con­ ditions at this point define the conditions for calculating the valve cavitation coefficient smv' [ISA-RP75.23-1995] maximum working pressure See pressure, maximum working (MWP).

Maxwell The CC;S unit of magnetic flux.

Maxwell bridge A type of AC bridge circuit in which the impedance of an unknown inductor is measured in terms of an adjust­ able resistor and an adjustable inductor.

Since the latter may be difficult to obtain, an alternative bridge arrangement uses an adjustable resistor and capacitor in parallel with the unknown inductor.

Maxwellian distribution The velocity distri­ bution of the moving molecules of a gas in thermal equilibrium. It is determined by applying the kinetic theory of gases.

MCAA Measurement and Control Automa­ tion Association. Develops standards for industrial process instrumentation and con­ trol. Formerly, the Scientific Apparatus Mak­ ers Association (SAMA).

McLeod vacuum gauge A common type of mercury-filled press"ure gauge whose design is a special cil~e of a "liquid manometer used as a pressure amplifier. The design enables a manometer-type instrument to be used for measuring vacuum on the order of 10-6 torr instead of the 10-2 torr that is usually achieved with precision manometers.

MCS Matrix control strategies. In process control, strategies that regulate the process from several inputs, usually involving unit severities and product compositions. Also called 111ultivariable pretiictive control strategies. mean Arithmetic average value. mean accuracy See accuracy, mean (data pro­ cessing). mean effective pressure The average net pressure difference across a piston in a posi­ tive displacement machine such as a com­ pressor, engine, or pump. It is commonly used to evaluate the performance of such a machine. mean error (E) In data processing, the mean error is defined as the deviation between the mean value of a statistically significant num­ ber of output readings and the true value of the input signal. The mean error is expressed as a percentage of the full range (F.R.). [ISA­ RP55.1-1975] mean free path In a gas, liquid, or colloid, the average distance that is traveled by an indi­ vidual atom, molecule, or particle between successive collisions with other particles. mean output curve The curve through the mean values of output during anyone cali­ bration cycle or a different specified number of calibration cycles. [ISA-37.l-1975 (R1982)] mean-square-error criterion The evaluation of the performance of a control system by calculating the square root of the a~rage, over time, of the square of the dif~ence between the actual output and thetlesired output. This is the most commonly used measure of control performance. mean-time-between-failures (MTBF) The limit of the ratio of the equipment's operat­ ing time to the number of observed failures as that number approaches infinity. The total operating time divided by the quantity (n +

315

II

mean-ume-to-failure / mechanical atomizing oil burner

I

1), where n is the number of failures during the time considered. mean-time-to-failure (MTTF) The average or mean time between the initial operation of a device and the first occurrence of a failure or malfunction, as the number of measurements of such time on many pieces of identical equipment approaches infinity. measurand A physical quantity, property, or condition that is measured. Note: The term measurand is preferred to "input," "parame­ ter to be measured," "physical phenome­ non," "stimulus," and "variable." [ISA-37.1­ 1975 (R1982)] See also variable, measured. measure In the typographical composition of screen displays and printing, the width of type, usually expressed in picas. measured accuracy See accuracy, measured. measured fluid The fluid that comes into contact with the sensing element. Note: The chemical and/or physical properties of this fluid may be specified to ensure that the transducer operates properly. [ISA-37.1-1975 (R1982)] measured signal See signal, measured. measured value The numerical quantity that results from the information that is obtained by a measuring device, at the instant under consideration. measured value of an analog DC current signal The measured value of an analog DC current signal is its specified mean value during the stated duration. measured value of a pneumatic transmission signal The indicated value during a stated duration. measured variable See variable, measured and measural1d. measurement 1. The determination of the existence or of the magnitude of a variable.

[ANSI/ISA-5.1-1984 (R1992]2. A data point that is or can be converted into a suitable sig­ nal for telemetry transmission. measurement component A general term that indicates the components or subassem­ blies in a specific device that together deter­ mine the value of a quantity and produce the indicated or recorded output. measurement device A self-contained assem­ bly that is comprised of all the components needed to perform one or more measuring operations. measurement energy The energy that is required to operate a measurement device or system. It is usually obtained from the mea­ surand or the primary detector. measurement equipment A general term that is used to describe the components,

devices, assemblies, or systems that are capa­ ble of performing measuring operations. measurement mechanism A mechanical

device that performs one or more operations

in a measuring sequence.

measurement range The portion of the total

response range of an instrument over which

specific standards of accuracy are met.

measurement system Any set of intercon­

nected components, including one or more

measurement dli'vices, that perform a com­

plete measuring function, from initial detec­

tion to final indicati~n, recording, or

control-signal output

measuring-circuit voltage The voltage

between two terminals of a measuring circuit

or between one of these terminals and

ground. [ANSI/ISA-82.02.01-1999 (IEC

61010-1 Mod)]

measuring instrument See instrument, mea­ suring.

measuring junction The electrical connection

between the two legs of a thermocouple that

is attached to the body or immersed in the

medium whose temperature is to be mea­

sured. Also referred to as the hot junction.

measuring means The components of an

automatic controller that determine the value

of a controlled variable and communicate

that value to the controlling means.

measuring modulator A component in a

measuring system that modulates a DC or

low-frequency AC input signal so as to pro­

duce an AC output signal whose amplitude

is related to the measured value. Such a mod­

ulator is usually used as a preliminary step

to producing an amplified output signal.

measuring range The extreme values of the

measured variable within which measure­

ments can be made within the specified accu­

racy. The difference between these extreme

values is called "span." See span.

measuring vessel The container in which the liquid that is metered by the turbine flowme­ ter during the calibration interval is collected and measured. In a direct-gravimetric cali­ bra tion system, this is a tank on a weigh scale, and the exact dimensions are not sig­ nificant. In indirect-gravimetri~systems and in volumetric systems the cro.!f>-sectional area or actual volume, respectively, must be known to a precision that is compatible with I the desired accuracy of calibration. [ISA­ I RP31.1-1977] mechanical Referring to tools or machinery. mechanical atomizing oil burner A burner that uses the pressure of the oil for atomiza­ tion.

I

316

1 1

mechanical chart drive / media attachment unit

mechanical chart drive A spring-driven clock mechanism that feeds continuous chart paper past a recorder head at a predeter­ mined speed. mechanical classification Any of several methods for separating mixtures of particles or aggregates according to size or density.

These methods usually involve the action of a stream of water. mechanical compliance The displacement of a mechanical element per unit of force.

Mechanical compliance is the mechanical equivalent of capacitance in an electrical cir­ cuit. mechanical damping Attenuating a vibra­ tional amplitude b.y absorbing mechanical energy. mechanical draft The negative pressure that is created by mechanical means. mechanical efficiency The ratio of power output to power input. mechanical engineering A branch of engi­ neering that deals with the generation and use of thermal and mechanical energy as well as with the design, manufacture, and use of tools and machinery. mechanical hygrometer A hygrometer that uses an organic material, such as a bundle of human hair, to sense changes in humidity. In operation, the organic material expands and contracts with changes in moisture content in the air. The change in length alters the posi­ tion of a pointer through a spring-loaded mechanical linkage. mechanical impedance 1. An apparent oppo­ sition to the transfer of vibration amplitude that is frequency dependent. 2. The complex quotient of alternating force applied to a sys­ tem divided by the resulting alternating lin­ ear velocity in the direction of the force at its point of application. mechanical isolation of transduction element The internal construction of a transducer that allows forces (particularly bending forces and external pressures) to be applied to the transducer case with negligi­ ble resulting forces on the transducer ele­ ment. [ISA-RP37.2-1982 (R199S)] mechanical limit stop A mechanical device for limiting the travel of the valve stem.

[ANSI/ISA-7S.0S.01-2000] mechanical linkage A set of rigid bars or links that are joined together at pivot points and used to transmit motion. Frequently, they are used in a mechanism along with a crank and slide to convert rotary motion into linear motion.

mechanical properties The properties of a material that can be determined through the application of a force and by measuring the material's response. mechanical reactance The imaginary compo­ nent of mechanical impedance. mechanical register A mechanical or electro­ mechanical recording or indicating counter. mechanical resistance The real component of mechanical impedance. mechanical scale .~ '\lv~ighing device in which objects are balanced through a system of levers against a counterweight or counter­ poise. mechanical shock The momentary applica­ tion of an acceleration force to a device. Note: Mechanical shock is usually expressed in units of acceleration of gravity (g). [ANSI! ISA-S1.1-1979 (R~993)1 mechanical transmission An assembly of mechanical <;:omponents that is suitable for transmitting m~chanical power and motion. mechanism 1. Generally, an arrangement of two or more mechanical parts in which the motion of one part compels the motion of the others. 2. Specifically, in an indicating instru­ ment the arrangement of parts that control the motion of the pointer or other indicating means. Excluded are those parts that form the enclosure, scale, or support structure or that adapt the instrument to the quantity being measured. 3. In a recording instru­ ment, the arrangement of parts that control the motion of the marking device, the mark­ ing device itself, the device for driving the chart, and the parts that carry the chart. mechanized dew point meter See dew point

recorder. media 1. The physical interconnection between devices attached to the local area network (LAN). Typical LAN media are twisted pair, baseband coax, broadband coax, and fiber optics. 2. The plural of medium. 3. A name for the various materials that are used to hold or store electronic data, such as printer paper, disks, magnetic tape, or punched cards. media access control (MAC) The lower sub­ layer of the data link layer (Layer 2) that is unique to each type of IEEE 8021q1'al area network. MAC provides a mechamsm that enables users access to share the network. media attachment unit (MAD) Also known as a transceiver and not to be confused with a token ring MAU (multistation access unit).

A media attachment unit is an Ethernet device for transmitting and receiving data that often provides data-packet collision

317

I

median I memory protect

II

detection as well. A media attachment can either be an internal or external feature of a network device such as a network interface card, repeater, hub, or concentrator. A multi­ port MAU, or transceiver, allows a number of computers or workstations to be attached to a single connection on the Ethernet bus.

Each port performs standard transceiver functions. median The middle value in a sample of rank-ordered data or measurements. There are as many values in this sample that are larger than a median as there are values that are smaller. medium [Comm] 1. Cable, optical fiber, or other means by which communication sig­ nals are transmitted between two or more points. Note: In this part of ANSI/ISA­ 550.02, Part 2-1992, the term media is used only as the plural of medium. [ANSI/ISA­ 50.02, Part 2-1992] 2. Any material substance that is used to propagate or transmit signals, usually in the form of electrons, light, modu­ lated radio, or acoustic waves such as optical fiber, metal wire, dielectric slab, air, water, free space, and so on. [Cont]3. In data pro­ cessing, the material on which data is recorded and stored. medium-carbon steel An alloy of iron and carbon that contains about 0.25 percent to 0.6 percent C, and up to about 0.7 percent Mn. medium-dependent interface (MDI) In data communications, a mechanical and electrical interface between a network segment and a media attachment unit (MAD). medium-scale integration (MSI) The fabrica­ tion of integrated circuits that contain 100 to 1,000 transistors. mega- A prefix denoting 1,000,000.

megabit One million bits.

megabyte (Mbyte) A unit of computer mem­

ory size. One million bytes. megaflops One million floating-point opera­ tions per second. megahertz One million hertz or cycles per second. melting point The temperature at which a solid substance becomes liquid. For pure substances and some mixtures, melting point is a single unique temperature. For impure substances, solutions, and most mixtures it is a temperature range. membrane 1. A thin tissue that covers organs, lines cavities, and forms canal walls in the bod y of an animal. 2. A thin sheet of metal, rubber, or treated fabric that is used to line cavities or ducts or to act as a semirigid separator betvveen two fluid chambers.

memory Any form of computer data storage, including main memory and mass storage, in which data can be read and written. In its strictest sense, memory refers to "main mem­ orv." me~ory, logic (flip-flop) If 5 represents set memory and R represents reset memory, logic output C exists as soon as logic input A exists. C continues to exist, regardless of the subsequent state of A, until the memory is reset, thaI: is, ten;.ninated by logic input B existing. C rema.ins terminated regardless of the subsequent state of B until A causes the memory to be set. Logic output 0, if used, exists when C does not exist, and 0 does not exist when C exists. [ANSI/ISA-5.2-1976 (R1992)] memory access time See access time. memory address The address in computer

memory of the location that contains an

instruction or operand.

memory addressability A measure of capa­ bility and ease of programming that is used in evaluating computers. The maximum number of locations that is specifiable by a nonindexed instruction using the instruc­ tion's minimum execution time. memory bus The computer bus (or buses)

that interconnects the processor, memory,

and peripherals on a high-speed data pro­

cessing highway.

memory capacity Same as storage capacity. memory chip An electronic device that accepts data for computer use or for storage. memory cycle time The minimum time between two successive data accesses from a memory. memory dump A listing of the contents of a storage device or selected parts of it. memory image A replication of the contents of a portion of memory. memory latency time See latency. memory management A feature that allows a computer to operate as if its maim memory were larger. See virtual mernory. memory map The graphic representation of the general functional assignments of vari­ ous areas in memory. These areas are defined by ranges of addresses. , memory mapping 1. A map tl'tit shows the usable and unusable (or proteded) areas of memory. 2. The duplication of all or part of the data in one memory location to the mem­ ory in another location or device. memory protect A technique for protecting the contents of sections of memory from being altered. The execution of any memory modification instruction is inhibited as soon

318 - - - - - . . . . : .• j

memory protection / message switching

as the presence of a guard bit associated with the accessed memory location is detected.

Memory modification instructions that access protected memory are usually exe­ cuted as a no-operation, and a memory pro­ tect violation program interrupt is generated. memory protection A scheme for preventing

read and/ or write access to certain areas of

memory.

memory resident A program that remains in

RAM memory even when other programs

are operating. It is called up by interrupting

the currently running program.

MEMS Microelectro mechanical systems.

Micromachined integrated systems, usually

on silicon chips, that perform some intelli­

gent sensing function as well as containing

micromoving sensing diaphragms and

beams and actuating devices such as valves,

motors, linear motors, cantilevers, switches,

and gear trains.

meniscus The concave or convex surface,

caused by surface tension, at the top of a liq­

uid column, as in a manometer tube.

meniscus lens A lens that has one concave

surface and one convex surface.

menu A list of alternative functions from

which the use makes a selection through a

mouse, key or sequence of keys, touch-screen

hot spots, and so on, rather than through the

command language of the computer pro­ , gram. mercury meter A differential-pressure mea­

suring device that utilizes mercury as the

seal between the high and low chambers.

mercury switch A type of switch that consists

of two wires that are sealed into the end of a

glass capsule containing a bead of mercury. If

the capsule is tipped one way, the mercury

covers the exposed ends of the wires and

completes the circuit. If it is tipped the other

way, the mercury exposes the wires and

breaks the circuit.

mercury vapor lamp A type of ion-discharge

lamp that is widely used in ultraviolet ana­

lyzers because it emits several strong mono­

chromatic lines with characteristic wave­

lengths such as 254, 3D, 360, 405, and the

like. Lamp emission can be made almost

completely monochromatic by using special

filters.

mercury-vapor tube A gas tube in which the

active gas is mercury vapor.

mercury-wetted relap A device that uses

mercury as the relay contact closure sub­

stance.

merge In data processing, to combine two or

more groups of records into a single file.

319

merge sort In data processing, an operation in which data is combined and then sorted in some prescribed manner. meridian plane Any plane that contains the optical axis.

MES Manufacturing Execution System. Soft­ ware packages for such functions as plant management, supervisory control and moni­ tering, plant engi\leer.ing, and quality man­ agement. The model concept was developed

by Advanced Ma.nufac~ring Research (AMR), Boston, in the'late 1980s with the intention of describing a system that, rather than focusing on measurements of material usage or process control, "centers on product itself as it moves through plant on way to customer./I MES is intended to bridge the real-time information gap between planning (MIS) and controls (peS) so as to link opera­ tors and managers with the current views of all processing resources.

MESFET Metalized semiconductor field effect transistor. An FET in which a Schottky barrier is used for the gate. mesh 1. A measure of screen size that is equal to the number of openings per inch along the principal direction of the weave. 2. The size classification of particles that pass through a sieve of the stated screen size. 3. The engage­ ment of a gear with its mating pinion or rack.

4. A closed path through ductwork in a ven­ tilation survey. message An arbitrary amount of information whose beginning and end are defined or implied. message box In workstation screen views, a special dialog box within the application window that displays the information needed at some appropriate point of activity within that application. For example, a mes­ sage box may alert the user when informa­ tion is needed or display diagnostics when some error has occurred. message exchange A device that is placed between a communication line and a com­ puter in order to take care of certain commu­ nication functions and thereby free the computer for other work. message routing The function, uSl!flly per­ formed at a central message proc~sor, of selecting the route, or alternate route if required, by which a message will proceed to the next point toward its destination. message switching A method for handling messages over communications networks.

The entire message is transmitted to an inter­ mediate point (such as a switching com­ puter), stored for a (perhaps very short) time,

I)

messaging I mhol

! i

j

I

·1

I I I

I I

II

•

then transmitted toward its destination (indi­ cated by an address integral to the message).

See also cirCllit switching and packet switching. messaging In object-oriented programming (OOP), objects that communicate according to defined rules. messaging application programming inter­ face (MAPI) A system built into Microsoft Windows that enables different e-mail appli­ cations to work together for mail distribu­ tion. As long as both applications are MAPI­ enabled, they can share mail messages with each other. Confusion over MAPI occurs because there are two very different kinds.

First, there is the MAPI of Microsoft Mail (MS Mail), which was a C-language API (application program interface) that allowed programmable access to those features. It is now called "Simple MAPL" Second, there is the "new MAPI," a COM/OLE-based set of complex interfaces, sometimes called "Extended MAPI" or XMAPL It includes Simple MAPI for compatibility with older software as well as including OLE Messag­ ing, which is a set of OLE automation inter­ faces for messaging for use in Visual Basic, and the like. metal A chemical element that is crystalline in the solid state, exhibits relatively high thermal and electrical conductivity, and has a generally lustrous or reflective surface appearance. metallic Exhibiting the characteristics of a metal. See mctal. metallic coating A thin layer of metal applied that is to an optical surface to enhance reflec­ tivity. metallic glass See glassy alloy. metallography The study of the structure of metals. The most common techniques are optical microscopy, electron microscopy, and X-ray diffraction analysis. metal-nitride-oxide semiconductor One type of computer semiconductor memory that is used in EAROMs (electrically alter­ able read-only memory). metal piston type seal In a butterfly valve, a self-expandable metal seal ring is installed in a groove on the disk circumference in order to block the clearance between the disk's outer diameter and the liner bore with the disk in closed position. [ANSI/ISA-7S.0S.01­ 2000] metal units Concentration units that are defined as the number of gm-moles per 1,000 gm of solvent.

meteorograph A recording instrument for measuring meteorological data, such as tem­ perature, barometric pressure, and humidity. meteorological instrumentation Equipment for measuring weather data. meter 1. A device for measuring and indicat­ ing the value of an observed quantity. 2. An international metric standard for measuring length. It is equivalent to approximately 39.37 in. in the U.s. customary system of ilnits. Spel1~g:'ruetre"in the International Standard of Units (SI). meter factor 1. A constant that is used to mul­ tiply the actual reading on a scale or chart in order to produce the measured value in actual units. 2. A correction factor that is applied to a meter's indicated value in order to compensate for variations in ambient con­ ditions, such as a temperature correction applied to a pressure indication. metering 1. Regulating the flow of a fluid so that only a measured amount is permitted to flow past 3 given point in the system. 2. Mea­ suring any variable (flow rate, electrical power, etc.). metering pump A plunger-type pump that is designed to control small-scale fluid-flow rates accurately. It is used to inject small quantities of materials into continuous-flow liquid streams. Also known as a proportioning

pump. meter prover A device for checking the accu­ racy of a gas meter. meter proving tank See calibrating tank. meter run A flowmeter that is installed and calibrated in a section of pipe that has ade­ quate upstream and downstream length so as to satisfy standards of flowmeter installa­ tion. See also orifice run. meter sensitivity The accuracy with which a meter can measure a value. It is usually expressed as a percentage of the meter's full­ scale reading.

MeV Mega-electron-volts. A unit of energy that is equivalent to the kinetic energy of a single electron accelerated through an elec­ tric potential of 1 million volts.

MFD Mode field diameter. The diameter of optical energy in single-mode optical fiber.

Because it is greater than cor/diameter, MFD replaces core diameter as a p.ractical parame­ ter.

MFP Multifunction printer. A printer that will also scan, fax, and copy. mhol A customary unit of conductance and admittance that is generally defined as the reciprocal of one ohm or the conductance of

320

micro- / microscopic stress

an element whose resistance is one ohm. The equivalent SI unit, a Siemen, is preferred. micro- A common prefix meaning "very smal!." microbalance A small analytical balance for weighing masses of 0.1 g or less to the near­ est ig. microbar A unit of pressure that is equal to one dyne per square centimeter. microchannel plate A glass device that has many tiny, parallel holes passing through it.

With suitable biasing, it is used as an electron amplifier, primarily in imaging detectors. micro code 1. Software that exercises bit-level control of hardware. 2. A system of coding that makes use of suboperations that are not ordinarily accessible in programming, for example, coding that makes use of parts of multiplication or division operations. 3. A list of small program steps. Combinations of these steps, performed automatically in a prescribed sequence from a macro-operation like multiply, divide, and square root. See

micrometer (m) 1. A metric measure that has a value of 10-6 meters or 0.000001 meter (pre­ viously referred to as "micron"). [ANSI/ISA­ 7.0.01-1996] 2. Any device that incorporates a screw thread for precisely measuring dis­ tances or angles, such as is sometimes attached to a telescope or microscope. 3. A type of calipers that incorporates a precision screw thread and is capable of measuring the distance between two opposing surfaces to the nearest 0.001 .or 0.00G1 in. microphone An el!~ctro-acoustic transducer that transmits an electrical output signal that is directly related to the loudness and fre­ quency distribution of sound waves that strike the active element. microphonis 1. In an electron tube, a modu­ lation of one or more electrode currents as a direct result of mechanical vibrations of a tube element. 2. An undesirable electrical output signal in response to mechanical or acoustic vibration of an electronic or electri­ cal device. microprocessor (p.P) 1. A usually monolithic, large-scale-integrated (LSI) central process­ ing unit (CPU) on a single chip of semicon­ ductor materia!. Memory, input/output circuits, power supply, and the like are needed to turn a microprocessor into a microcomputer. 2. A large-scale integrated circuit that has all the functions of a com­ puter, except memory and input/ output sys­

tems. The microprocessor thus includes the

instruction set, arithmetic logic unit (ALU),

registers, and control functions.

microprogramming A method of operating the control unit of a computer, wherein each instruction initiates or calls for the execution of a sequence of more elementary instruc­ tions. The microprogram is generally a per­ manently stored section of nonvolatile storClge. The instruction repertory of the microprogrammed system can thus be changed by replacing the microprogrammed section of storage without otherwise affect­ ing the construction of the computer. microradiography The production of a mag­ nified radiographic image. microradiometer A device for det~cting radi­ ant power. It consists of a thermO;ile that is supported on and directly conne"(;.ted to the moving coil of a galvanometer. microscopic stress Load per unit area over a very short distance, on the order of the diam­ eter of a metal grain or smaller. The term is usually reserved for characterizing residual stress patterns.

multiprocessor. microcomputer 1. A computer that is based on the use of a microprocessor-integrated cir­ cuit. The entire computer often fits on a small printed circuit board and works with a data word of 4,8, or 16 bits. 2. A complete com­ puter in which the CPU is a microprocessor. microcontroller, p.C A microprocessor in which timers, counters, RAM, and ROM are included. microcurie A unit of radioactivity that is equal to one millionth (10-6) curie. microdensitometer A device for measuring the density of photographic films or plates on a microscopic scale. The small scale ver­ sion of a densitometer. microfaradmeter A capacitance meter that is calibrated in microfarads. micro-floppy disks Three-and-a-half-inch disks that have greater storage capacity than a 5-1/4-inch floppy disk. microinstruction Controls the operations of the various primitive resources of a com­ puter: the main and local store registers (both general and special-purpose), the arithmetic and logic units (ALUs), data paths, and so on. Microinstructions are stored as words in a control store that is traditionally (but not necessarily) separate from the main storage. micromanipulator A positioning device for making small adjustments to the position of an optical component or other device. micron One millionth of a meter, or 0.000039 in. The diameter of dust particles is often expressed in microns. '.

321

I

microwave / minimum explosion concentration

microwave Electromagnetic radiation that

has a wavelength of 1 to 300 mm.

microwave amplification by the stimulated

emission of radiation (MASER) The

microwave equivalent and the predecessor

of the laser. It produces coherent micro­

waves. See laser.

microwave spectrum The portion of the elec­ tromagnetic spectrum of frequencies that lies between infrared waves and radio waves. middleware Loosely defined as software for interconnecting application software manu­ factured by separate vendors and that involve different plant functions.

MIDI Musical Instrument Digital Interface.

An industry standard connection for the computer control of musical instruments and devices. migration The movement of ions from an area of the same charge to an area of opposite . -charge. mil 1. A unit of linear measurement that is equal to 0.001 in. 2. A unit of angular mea­ surement that is commonly used in the mili­ tary for setting artillery elevations. mile A British and U.s. unit of length that is commonly used to specify distances betvveen widely separated points on the earth's sur­ face. A statute mile, used for distances over land, is defined as 5,280 ft. A nautical mile, used for distances over ocean surfaces, is defined as one minute of arc measured along the equator, which equals 6,080.27 ft or 1.1516 statute miles. milestones Identified events for indicating the progression of a project. millimeter Also spelled "millimetre." 1. A unit of length that is equal to 0.001 meter. 2.

A millimeter of mercury (abbreviated mm Hg) is a unit of pressure that is equivalent to the pressure that is exerted by a column of pure liquid mercury one mm high at O°C under a standard gravity of 980.665 cm/ S2. It is roughly equivalent to 1/760th of standard atmospheric pressure.

MIL-STD-1533 The military standard that defines the serial data communications pro­ tocol on modern military vehicles, especially aircraft.

MIMD Multiple instruction multiple data stream (pronounced "mimdee"). A type of computing, in which at every instant each processor applies its own unique set of instructions on the data in its own local memory. miniature boiled Fired pressure vessels tha t do not exceed the following limits: 16 in. inside the diameter of the shell; 42 in. for the

overall length to the outside of the heads at center; 20 sq ft for the water heating surface; or 100 psi for the maximum allowable work­ ing pressure. miniaturization The deSign and production of a scaled-down version of a device or mechanism that is capable of performing all of the same functions as the larger-sized original. miniqlmputer A medium-size computer that is designed for: more dedicated applications than mainframe computers. It generally has a larger instruction set, a wider range of lan­ guages, and better support than microcom­ puters.

MINI-MAP A subset of the Manufacturing Automation Protocol (MAP) protocols that has beeo extended to provide higher perfor­ mance for applications whose communica­ tions are limited to a single local area network (LAN). A MINI-MAP node contains only the lower two layers (physical and link) of the MAP protocols. It can only communi­ cate directly with the MAP /EPA or MINI-MAP nodes on the same segment.

Using MINI-MAP, a device that has a token can request a response from an address device. Unlike the standard MAP protocol, the addressed device need not wait for the token to respond. See Manufacturing Automa­

tion Protocol (MAP). mmI-micro In data processing, a very small microcomputer that contains a CPU, mem­ ory, and I/O interfaces. It is used for data ex~hange and for timing circuits to control the flow of data. minimum bend radius The smallest radius around which a piece of sheet metal, wire, bar stock, or tubing can be bent without frac­ ture or, in the case of tubing, without col­ lapse. minimum cloud ignition temperature The minimum temperature at which a combusti­ ble dust atmosphere will autoignite and propagate an explosion. [ANSI/ISA­ 12.01.01-1999] minimum dust-layer ignition temperature The minimum temperature of a surface that will ignite a dust on that surf~ce after a long time (theoretically, until infirlty). In most dusts, free moisture has been-:vaporized before ignition. [ANSI/ ISA-12.01.01-1999] minimum explosion concentration The min­ imum concentration of a dust cloud that, when ignited, will propagate flame away from the source of ignition. Note: The mea­ surable combustible properties of dusts depend not only on the chemical structure of

322

minimum explosive (dust) concentration / mixer

.

,i

'\

the dust, but on test conditions, the size of the dust particles, weight, density, and other particle characteristics. minimum explosive (dust) concentration The minimum concentration of a dust cloud that, when ignited, will propagate a flame away from the source of ignition. [ANSI! ISA-12.01.01-1999] minimum igniting current (MIC) The mini­ mum current in resistive or inductive circuits that cause~ the explosive test mixture in the spark-test apparatus to ignite. [ISA-12.02.01­ 1999 (lEC 60079-11 Mod)] minimum igniting current ratio (MIC Ratio) The ratio that is derived by dividing (a) the minimum current required from an inductive spark discharge to ignite the most easily ignitable mixture of a gas or vapor by (b) the minimum current required from an inductive spark discharge to ignite methane under the same test conditions. Note: For additional information, refer to IEC 60079.

[ISA-12.01.01-1999] minimum igniting voltage The minimum voltage of capacitive circuits that causes the explosive test mixture in the spark-test appa­ ratus to ignite. [ISA-12.02.01-1999 (IEC 60079-11 Mod)] minimum ignition energy (MIE) The small­ est amount of energy that can ignite the most easily ignitable mixture of a specific gas or vapor-in-air or dust-in-air mixture. [ANSI! ISA-12.01.01-1999] minimum permissible protective liquid level The minimum level that the protec­ tive liquid can attain in normal service. This take into account the effects of contraction from the worst-case filling condition to the condition of de-energization at minimum ambient temperature. [ANSI!ISA-12.26.01­ 1998 (IEC 60079-6 Mod)] minimum reflux The quantity of reflux that is required in order to perform a specified separation in a column that has an unlimited number of trays. At minimum reflux, no products are withdrawn. minimum thermometer A thermometer that indicates the lowest temperature reached during a given interval of time. mining engineering A branch of engineering that deals with the discovery, extraction, and initial processing of minerals, usually metals such as ores or coal found in the earth's crust. minor frame The period between frame syn­ chronization words that includes one com­ plete cycle of a commutator that has the highest rate. Minor frame normally does not

exceed 8,192 bit internals. Synonymous with "prime frame." minor graduations The shortest or lightest division marks on a graduated scale. These marks indicate subdivisions that lie between successive major graduations or between an index graduation and an adjacent major graduation. minus leading In the typographical composi­ tion of screen displays and printing, leading in which til.e baseline space is less than the point size (or less than. solid leading). See

leading. minute 1. A measure of angle that is equal to 1/60th of one degree. 2. A measure of time that is equal to 60 s. mirroring In workstation screen displays, a display or the creation of some graphic that portrays an image in the exact reverse orien­ tation it originally had. This is done by flip­ ping that graphic on its x-axis or y-axis. mirror scale An instrument scale and a mir­ ror that are so arranged that the indicating pointer and its reflection are aligned when the observer's eye is in the correct position to read the instrument without parallax error. misalignment loss In fiber optics, a loss of power resulting from angular misalignment, lateral displacement, and end separation. mismatch Lateral offset between two halves of a casting mold or forging die. This pro­ duces distortion in shape across the parting line.

MISO Multiple input single output. Systems that require advanced control methods, such as fuzzy logic and neural networks. See 5150, MIMO, IITO. miter valve A valve in which the disk is at an angle of approximately 45° to the axis of the valve body. mixed level A simulation system that com­ bines both low-level transistor and gate cir­ cuit descriptions with high-level, behavioral circuit representations. mixed mode See mixed signal. mixed radix Pertaining to a numeration sys­ tem that uses more than one radix, such as the biquinary system. mixed signal A simulation system;,that com­ bines both analog and digital cirqfiit repre­ sentations. "" mixer In sound recording or reproduction equipment, a device that is capable of com­ bining two or more input signals into a sin­ gle linearly proportioned output signal.

Usually, this includes the additional capabil­ ity of adjusting the levels of any of the inputs.

323

I

mixing valve / model basin

mixing valve A valve that has more than one inlet but only one outlet port. It is used to blend two or more fluids in order to yield a mixture that has a predetermined composi­ tion.

MKS Meter-kilogram-second. A system of absolute units for length, mass, and time.

Now the basis of Sl units.

MMCD MultiMedia Compact Disk. Made by Sony / Phillips. Now called DVD (see DVD).

MMS (Manufacturing Message Specification) ISO/IEC 69506 A set of international stan­ dards that were developed to facilitate the interconnection of information processing systems. The first part of these standards is to define the service provided by the MMS. The second part specifies the protocol that supports the MMS. mnemonic Assisting, or intending to assist, human memory. Thus, in language, a mne­ monic term, usually an abbreviation, is one that is easy to remember, for example, MPY for "multiply" and ACC for "accumulator." mnemonic operation code An operation code in which the names of operations are abbreviated and expressed mnemonically in order to help people remember the opera­ tions they represent. A mnemonic code nor­ mally needs to be converted into an actual operation code by an assembler before the computer executes it. Examples of mnemonic codes are ADD for "addition," CLR for "clear storage," and SQR for "square root." mnemonics An assembly language instruc­ tion, defined by a symbol, that has some resemblance to the operations being carried out. Mnemonics are easier to remember and use than the equivalent Hex code or machine code.

MNOS Metal-nitride-oxide semiconductor.

One type of computer semiconductor mem­ ory that is used in EAROMs. mobile See mobile instrument. mobile instrument A continuous-monitoring instrument that is mounted on a vehicle, such as a mining machine or industrial truck, among others. See ANSI/ISA and ISA 92 series standards and recommended practices (RP's). [ANSl/ISA 12.13.01 2000] mobile telemetering Any arrangement for transmitting instrument readings from a movable data acquisition station to a remote stationary or movable indicating or record­ ing station without using interconnecting wire. mobility 1. The average drift velocity of a charged particle that is induced by a unit electrical potential gradient. 2. In gases, liq­

uids, solids, or colloids, the relative ease with which atoms, molecules, or particles can move from one location to another without external stimulus. mockup A model (frequently full size) of a piece of equipment or a system that is used for experiments, performance testing, or training. modal analysis The study of mode shapes in order to find the locations of maximum deflection where s.tiffeners can be applied. modal dispersion Dispersion that results from different transit lengths of different propagating modes in multimode optical fiber. mode [Comp] 1. A computer system of data representation, for example, the binary mode. [ISA-RP55.1-1975 (R1983)] 2. A selected ~ethod of computer operation.

[ISA-RP55.1-1975 (R1983)]3. A single com­ ponent in a computer network. 4. In science, a real or complex (number system). S. A sta­ ble condition of oscillation in a laser. A laser can operate in one mode (single-mode) or in many modes (multimode). 6. The most fre­ quently occurring value in a sample. [Cont] 7. An output form or a type of action. For example, PID algorithms can operate in sev­ eral modes: AUTO, CASCADE, MANUAL, and so on. 8. The manner in which sequential functions are transitioned to within a proce­ dural element or the readiness with which the states of equipment entities can be manipulated manually or by other types of control. [ANSI/ISA-88.01-1995] mode changer A device for changing the characteristics of a guided wave from one mode of propagation to another. mode filter In a waveguide circuit, an arrangement of waveguide elements that pass waves that are being propagated in cer­ tain mode(s) and exclude waves being prop­ agated in others. model A representation of an entity. [ISA­ TR50.02, Part 9-2000] model-based predictive control A method of process control that goes beyond the abilities of the traditional PID type. Similar to the way humans learn, model-based predictive control correlates training (o~perating image [internal model]), targ~t (or reference trajectory), action (computation of the struc­ tured manipulated variable), and compari­ son of the actual versus the expected (modeling error compensator). model basin A large tank of water for design experiments and performance studies of ship

324

model dispersion / modulation

hulls using scale models. Also known as a "model tank" and a "towing tank." model dispersion That component of pulse spreading that is caused by differential opti­ cal path lengths in a multimode fiber. modeling The re-creation of an event or object in a controlled environment so as to predict results from that event or object.

Mathematically characterizing a process so that variables may be manipulated to deter­ mine their behavior in different situations. model reference adaptive control A method of self-adaptive control that compares real process parameters with a reference model. model reference system An ideal system whose response is agreed to be optimum. A computer simulation in which both the model system and the actual system are sub­ jected to the same stimulus, and the parame­ ters of the actual system are adjusted to minimize the difference between the outputs of the model and the actual system. modem A contraction of the term "modula­ tor-demodulator." 1. A device used in data transmission. The term may be used in two different contexts: (a) the modulator and the demodulator of a modem are associated at the same end of a circuit, or (b) the modula­ tor and the demodulator of a modem are associated at the opposite ends to form a channel. [ISA-RP55.1-1975 (RI9S3)] 2. A device that performs both the combining . (modulation) and separation (demodulation) of data. Modems are typically used to con­ nect a node to a broadband network. See also transceiver. 3. An electronic device for the serial transmission of digital data in the audio frequency spectrum over a voice-grade telephone line. 4. A device that converts signals in one form to another form that is compatible with another kind of equipment. In particular, a circuit board that changes digital data being transmitted within a particular device into a form that is suitable for transmission over a data high­ way and vice versa. modem eliminator A usually passive device that serves as a modem between a local ter­ minal that requires a modem and a computer system. moderation Reducing the kinetic energy of neutrons, usually by means of successive col­ lisions with hydrogen, carbon, or other light atoms. mode shape The shape that a part takes in oscillating at a specific frequency. mode (submode) A particular operating con­ dition of a control system, such as manual,

automatic, remote, or coordinated. [ANSI/ ISA-77.13.01-1999] modified frequency modulation (MFM) A technique for storing and encoding data on media. modified parabolic characteristic An inher­ ent flow characteristic that provides an equal-percentage characteristic at the travel of a lOyY-closure member and approximately a linear characteristic for upper portions of closure member travel. [ANSVISA-75.05.01­ 2000] .

Modula-2 "Modular language-2." A com­ puter language designed by Niklaus Wirth to enhance Pascal. A multiprocessing language

with co-routines that may be executed simul­

taneously.

modular automatic test equipment (MATE) Automatic test equipment for mil­ itary users that consists of compatible mod­ ules and is .configured to test a particular weapon system. modularity The degree to which a system of programs is developed in relatively indepen­ dent components. A design that will allow some modules to be eliminated if a reduced version of the program is acceptable. modularization Designing a series of compo­ nents, subassemblies, or devices for inter­ changeability of their physicallocaticn. This makes it possible for different assemblies to be easily constructed on a standard frame or mounted in standard enclosures. modular programming Programming in which tasks are programmed in distinct sec­ tions or subsections. This makes it possible to modify one section without reference to other sections. modulated wave A radio-frequency wave in which amplitude, phase, or frequency are varied in accordance with the waveform of a mod ula ting signal. modulating The actions to keep a quantity or quality in proper measure or proportion.

Also known as "throttling." [ANSI/ISA­ 75.05.01-2000] modulating control To vary an output signal based upon some variation of input (as opposed to on/off control). . modulation 1. The process or the res~t of the process by which some characterist~of one wave is varied in accordance with some characteristic of another wave. [A 'SI/ISA­ 51.1-1979 (RI993)] 2. The process of impress­ ing information on a carrier for the purpose of transmission (AM--amplitude modula­ tion; PM--phase modulation; FM--frequency modulation). 3. The regulation of the fuel-air

325

I

modulation analyzer / Moll thermopile

·

,

II

mixture to a burner in response to fluctua­ tions of load on a boiler. 4. The action of a control valve in regulating fluid flow by varying the position of the closure member.

[ANSI/ISA-75.05.01-2000] 5. The mixing of two signals, which causes variation in ampli­ tude or frequency. The higher frequency is usually called the "carrier," and its ampli­ tude or frequency is changed by another periodic event. In vibration, this means that two vibrations arrive at the transducer loca­ tion. When separated into discrete frequen­ cies by the fast-Fourier transform (FFT) process, the result is a component at the car­ rier frequency and adjacent components, or sidebands, that is spaced at the frequency of the modulating signal. Modulation implies that the two vibrations are related physically. modulation analyzer A receiver that is tuned to a desired frequency and designed to pass the entire modulation envelope in order to measure carrier frequency, power, and phase modulation characteristics. modulation factor The ratio of the peak vari­ ation actually used in a given type of modu­ lation to the maximum design variation possible. modulation index In frequency modulation with a sinusoidal waveform, the modulation index is the ratio of the peak (not peak-to-peak) frequency deviation to the fre­ quency of the modulating wave. modulation meter An instrument for mea­ suring the modulation factor of a wave train, usually expressed as a percentage. modulation noise The noise in an electronic or acoustic circuit that is caused by the pres­ ence of a signal, but not including the wave­ form of the signal itself. module 1. In engineering, an assembly of interconnected components that constitutes an identifiable device, instrument, or piece of equipment. A module can be disconnected, removed as a unit, and replaced with a spare.

It has definable performance characteristics that permit it to be tested as a unit. A module could be a card or other subassembly of a larger device, provided it meets the require­ ments of the definition in IEEE Standard 60.

[ISA-RP 67.04.02-2000; ANSI/ISA-51.1-1979 (RI993)] 2. In computing, a program lmit that is discrete and identifiable with respect to compiling. It can be combined with other units and, for example, can load the input to or the output from an assembler, compiler, linkage editor, or executive routine.

modulo A mathematical operation that yields the remainder function of division.

Thus, 39 modulo 6 equals 3. modulo N check 1. A check that makes use of a check number that is equal to the remain­ der of the desired number when divided by n. For example, in a modulo 4 check, the check number will be 0, 1, 2, or 3. Moreover, the remainder of the desired number when divided by 4 must equal the reported check number, othli'rwi~~.~n equipment malfunc~ tion has occurred. 2. A method of verification by congruences, for example, casting out nines. modulus of elasticity In any solid, the slope of the stress-strain curve within the elastic region. For most materials, the value is nearly constant up to some limiting value of stress, which is known as the elastic limit.

The modulus of elasticity can be measured in tension, compression, torsion, or shear. The tension modulus is often referred to as "Young's modulus." moisture Water in the liquid or vapor phase. moisture barrier A material or coating that retards the passage of moisture through a wall that is made of more permeable materi­ als. moisture-free See bone dry. moisture in steam Particles of water that are carried in steam. Usually expressed as the percentage of particles by weight. moisture loss The loss that represents the dif­ ference in the heat content of the moisture in the exit gases versus the heat content at the temperature of the ambient air. mol See mole. molar units Concentration units that are defined as the number of gm-moles of the component per liter of solution. molecular attrition See fretting. molecular beam A unidirectional beam of neutral-charge molecules that passes through a vacuum. molecular flow The gas flow in a tube at a pressure that is low enough that the mean free path of the molecules is greater than the inside diameter of the tube. molecule The smallest divisio~of a unique chemical substance that maint«ins its lmique chemical identity. t~ moles Number of molecular weights. This is the weight of the component divided by its molecular weight.

Moll thermopile A type of thermopile that is used in some radiation-measuring instru­ ments. It consists of multiple mangan-con­ stantan thermocouples connected in series.

326

moment / most significant bit

.,

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Alternate junctions are embedded in a shielded nonconductive plate of large heat capacity. The remaining junctions are black­ ened and exposed directly to the radiation.

The voltage across the thermopile is directly proportional to the intensity of radiation. moment 1. Of force, its effectiveness in pro­ ducing rotation about an axis. Moment equals the product of (a) the radius perpen­ dicular to the axis of rotation that passes throngh the point at which force is apphed and (b) the tangential component of force that is perpendicular to the plane defined by the radius and axis of rotation. 2. Of inertia, the resistance of a body at rest or in motion to changes in its angular velocity. momentary An alarm that returns to normal before being acknowledged. It returns to nor­ mal state when pressure or signal is removed. momentary alarm See alann. momentary digital output A contact closure, operated by a computer, that holds its condi­ tion (set or reset) for only a short time. See

latching digital outpllt. momentary switch A spring-loaded switch whose contacts complete a circuit only while an actuating force is applied. For a typical momentary push button, electric current flows through the switch only while the operator has a finger on the button. momentum The product of a body's mass and its linear velocity.

Monel A series of high-nickel, high-copper alloys manufactured by International Nickel Co. that are used for their corrosion-resistant properties in certain conditions. monitor [Cont] 1. A general term for an instrument or instrument system that is used to measure or sense the status or magnitude of one or more variables for the purpose of deriving useful information. The term "moni­ tor" is very unspecific. In different contexts it can mean analyzer, indicator, or alarm. Moni­ tor can also be used as a verb. [ANSI/ISA­ 5.1-1984 (R1992)] 2. To measure a quantity continuously or at regular intervals so that corrections to a process or condition may be made without delay if the quantity varies outside of prescribed limits. [Comp] 3. Soft­ ware or hardware that observes, supervises, controls, or verifies the operations of a sys­ tem. 4. In data processing, a high-resolution viewing screen. monitor command An instruction that a user issues directly to a monitor. monitor console The system control termi­ nal.

monitored burn-in The use of high-voltage stress tests and functional pattern tests dur­ ing dynamic bum-in. See burn-in. monitor light See pilot light. monitor routine See executive program. monitor software That portion of the opera­ tional software that controls on-line and off-line events, develops new on-line appli­ cations, and helps to debug them. This soft­ ware is also known as a "batch monitor." monitor system. Same as operating system. monochromatic A single wavelength or fre­ quency. In reality, light cannot be purely monochromatic and actually extends over a range of wavelengths. The breadth of this range determines how monochromatic the light is. monochromatic radiation Any electromag­ netic radiation that has an essentially single wavelength o~ in which the photons all have essentially the same energy. monochromator An optical device that uses a prism or diffraction grating to spread out the spectrum and then passes a narrow portion of that spectrum thfOugh a slit. A monochro­ mator generates monochromatic light from a non-monochromatic source. monolithic An integrated circuit all of whose components have been formed on a single piece of semiconductor material. monostable Pertaining to a device that has one stable state. monotonic A quantity is monotonic if it increases (or never decreases) as a function of some other quantity.

Monte Carlo method A technique that uses statistical sampling techniques to obtain a probabilistic approximation to the solution of a problem. Often used when a great num­ ber of variables are present and their interre­ lationships are so extremely complex as to forestall straightforward analytical handling.

MOSFET Metal oxide semiconductor field­ effect transistor. A field-effect transistor that has a gate which is insulated from the semi­ conductor substrate by a thin layer of silicon dioxide. Formerly known as "insulated-gate field-effect trclnsistor."

Mosaic In computer networks, us~r interface software for navigating, browsin~~ and accessing files across a network !uch as the Internet). Developed at the National Center for Supercomputing Applications (NCSA) at the University of Illinois. most significant bit (MSB) The bit in a digi­ tal sequence that defines the largest value. It is usually at the extreme left.

327

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most significant digit I moving-iron instrument

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ianificant digit (MSD) The leftmost 0 ., flzero digit. nOherboard The printed circuit board of a mot puter, which contains bus lines and edge CO[!1f1eetors so as to accommodate other Cofl rds in the system. In a microcomputer, a bO<1tperboard often contains the microproces­ rnO afld expansion boards. so: j1 balance instrument An instrument modUO' vn technique that utilizes the motion of eSlo .

I . .. [!1easunng e ement agamst a spnng m th~er to reach a balance of forces that repre­ or ts the magnitude of the measured vari­ sen

moS t S

a~le~ control The application of moving moUo s in m . d ustna . I settmgs, . . I u d'mg me t lpomt-to-pomt ' .

P ~ \encing, spee d contro, seq~rol, and incremental motion. cO,n 11 conversion mechanism 1. A device moUoded on some, but not all, assemblies to ne~\.ert linear action into rotary-valve opera­ cO fl. 2. A mechanism between the valve and tlO ower unit of the actuator to convert th~Zeen linear and rotary motion. The con­ be sion can be from linear-actuator action to . or f rom rotary-actua­ ver ry-va 1ve operation rot<1aetion to linear-valve operation. [ANSI! tO~_75.05.01-2000]

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IS, 11 JPEG In video development, any of mO~~eral proprietary implementations of s tiO n video compression based on the ~~G standard. This standard produces out­ J ding quality video when the degree or stan \1l 0 f compresslOn . .IS not over d one.

1t af\l~J1leter A type of integrating meter. It moto ~ists of a rotor, one or more stators, a eO~'rding device that :nakes the speed of th~ re r directly proportIOnal to the mtegral ot r~~Oqllantity measured (usually power or t I ,.·ic current), and a counter or set of dials e ee,· that indicates the number of rotor revolu­ tions. operator The electric or hydraulic motor.er mec h ' ' . amsm th at receives a contro 1slg. .

P O~\and reposItions nal a va 1ve or ot h er f'ma I con-

I element. tro t1' Oa effects The effects (errors) that are mouO 0 . oduced into transducer performance dur­ ~ntrinstallation. They are caused during the tngtening of the unit or its mounting hard­ fas e or by irregularities in the surface on w~~ch the transducer is mounted. [ISA-37.12­ ~82 (R1995); ISA-37.6-1982 (R1995)] 1 tjog error The error that results from moul1h~nical deformation of the transducer. It me C ' . callsed by the process of mounting the IS sdllcer and making all the measurand traI1

and electrical connections. [ISA-37.1-1975 (R1982)] mounting position 1. The position of a device relative to its physical surroundings.

[ANSI/ISA-51.1-1979 (R1993)] 2. The loca­ tion and orientation of an actuator or auxil­ iary component relative to the control valve.

This term can apply to the control valve itself relative to the piping. [ANSI/ISA-75.0S.01­ 2000] mounting strain error See error, mounting

strain.

.'

mouse A hand-operated device developed

by Doug Englebart of the Stanford Research Institute in 1964. Moving it along a flat sur­ face drives and positions a cursor on a work­ station screen so the user can direct the views or inputs.

MOV Metal oxide varistor; motor-operated valve. A device whose impedance changes appreciably in response to applied voltage.

MOYs are used to limit the maximum volt­ age across an output device and to protect vulnerable cin;uit components against tran­ sients by clamping the circuit to safe levels. moving-coil instrument An instrument whose output is related to the reaction between the magnetic field that is set up by current flow in one or more movable coils and the magnetic field of a fixed-position permanent magnet. Also known as a "per­ manent magnet moving-coil instrument." moving-dial indicator A type of indicator in which a flat, circular scale (dial) is attached to the moving element. The instrument scale is continually repositioned with respect to a fixed pointer so as to indicate the changing values of a measured variable. Compare with moving-drum indicator and moving-scale indi­

cator. moving-drum indicator A type of indicator in which a circular member (drum) with a scale along its periphery revolves in relation to a fixed pointer so as to indicate the chang­ ing values of a measured variable. Compare with moving-dial indicator and mO'uing-seale

indicator. moving element Of an instrument, the parts that move as a direct result of.j variation in the quantity being measuredj, , moving-iron instrument An l1i.strument whose output indication or signal is pro­ duced by the reaction between (a) one or more pieces of magnetically soft material, at least one of which moves, and (b) the mag­ netic field that is set up by electric current flmving in one or more fixed coils.

328

moving-magnet instrument I multi-element control system

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moving-magnet instrument An instrument whose output indication or signal is pro­ duced by the reaction between (a) a movable permanent magnet that aligns itself with the field produced by (b) another permanent magnet that interacts with one or more cur­ rent-carrying coils or by two or more coils interacting with each other. moving-scale indicator Any of several designs of instrument indicator in which the scale moves in relation to a fixed pointer to indicate the changing values of a measured variable. See moving-dial indicator and 1110V­

Msrrp Master-slave/token-passing. A data link protocol of BACnet that provides the same services to the network layer as ISO 8802-2 (IEEE 802.2) LLC. MTBF Mean time between failures (since 1962); mean time before failure (until 1962).

In the definition of US. military specifica­ tions, MTBF is calculated to be MTTF + MTTR. The stated or published period of time for which the user may expect a device or system to operat~;before failure occurs (a computed aritnmetic mean of the time, not a tested value).

M synchronization A type cif link between a camera shutter and a flash unit that gives a 15- millisecond delay so the metal-foil flash lamp reaches peak brightness before the shutter actually trips. muffle The insulated enclosure of a furnace. multi-access A multiprogramming system that permits a number of users to simulta­ neously make online program changes. multi-address Same as multiple address. multi-bus Intel's proprietary link between single-board systems used for industrial sys­ tems. multicast A message that is addressed to a group of stations connected to a local area network (LAN). multichannel spectral analyzer A measure­ ment system that sorts signals into a number of different channels, then counts and ana­ lyzes the signals channel by channel. multicoupler A device for coupling several receivers or transmitters to one antenna. It also enables the proper impedance match to be made between them. multicraft 1. Maintenance personnel who are proficient in more than one craft, such as instrument technicians, electricians, and instrument mechanics. 2. Pertaining to a pro­ fessional who is responsible for maintaining a variety of equipment used in control sys­ tems.

MULTICS The time-sharing system devel­ oped at Project MAC ("Man and Computer") at M.LT. See task, definition 3. multidrop In fieldbus, the connection of mul­ tiple field devices to one pair of wires. They are usually "tee-connected.".l, multi-element control system A tvntrol sys­ tem that utilizes input signals derived from two or more process variables for the pur­ pose of jointly affecting the action of the con­ trol system. Examples include input signals from pressure and temperature or from speed and flow and the like. See also multi-

ing-drum indicator.

MPC Multivariable predictive control. In process control, strategies that regulate a pro­ cess from several inputs, usually by using unit severities and product compositions.

Also called "matrix control strategies."

MPEG' Motion Picture Experts Group. A standards committee under the auspices of the ISO that is working on algorithm stan­ dards that will allow the digital compression, storage, and transmission of moving image information such as motion video, CD-qual­ ity audio, and control data at CD-ROM band­ width. The MPEG algorithm makes possible the interframe compression of video images and can have an effective compression rate of 100:1 to 200:1.

IVIPP Massively parallel processing. A type of computer architecture that uses a matrix of separate CPUs. Each CPU controls its own block of main memory and is linked in some way so as they can communicate very quickly with each other.

MPR Maximum power rating. The maximum power in watts at which a device can safely operate.

MRAC Model Reference Adaptive Control.

A method of self-adaptive control that com­ pares real process parameters with a refer­ ence model.

MRP (MRP II) Material Requirements Plan­ ning (Manufacturing Resource Planning II).

A computerized method for planning a plant's use of resources, including raw rna terials, financial, vendors, prod uction equipment, and processes.

MS Manual station. Sends the process control signal directly to the final element.

MS-DOS Microsoft disk operating system.

Developed for the IBM PC, MS-DOS became a de facto standard. Sometimes called "PC­ DOS," it was designed to control and man­ age I/O devices and memory for personal computers (PCs).

329

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multitiber cable I multiplexing variable control and control system, multiele­ ment (multivariable).

II

multifiber cable A fiber-optic cable that con­ tains many fibers that transmit signals inde­ pendently and are housed in separate substructures within the cable. multifuel burner A burner by means of which more than one fuel (such as pulver­ ized fuel, oil, or gas) can be burned, either separately or simultaneously. multifunction multiloop controller A type of microprocessor-based controller that com­ bines the process control functions of a dedi­ cated loop controller with many of the logic functions of a programmable logic controller in order to provide the control strategy of an entire unit operation. multilayer A type of printed circuit board that has several layers of circuit etch or pat­ tern, one over the other and each intercon­ nected by electroplated holes. Since these holes can also receive component leads, a given component lead can connect to several circuit points. This reduces the required dimensions of a printed circuit board. multilayer coating Optical coatings in which several layers of varying materials of differ­ ent thicknesses are applied to an optical sur­ face. Interference affects the light passing through the layers. Reflection and transmis­ sion are influenced differently at different angles of incidence and at different wave­ lengths. multilevel address See indirect address. multimeter See volt-ohm-milliammeter. multimode fiber An optical fiber that is capable of carrying more than one mode of light in its core. multiple action A control system action that is a composite of the actions of two or more individual controllers. multiple address A type of instruction that specifies the addresses of two or more items.

These addresses may be the addresses of the locations of the calculating unit's inputs or outputs or the addresses of the locations for the control unit's instructions. The term nllll­ tiple-address is also used in characterizing computers, for example, two-, three-, or four-address machines. Synonymous with "multi-address." multiple input See reflash (multiple input). multiple linear regression A technique for determining the linear relationship between one dependent variable and two or more independent variables. multiple orifice A style of valve trim in which the flow passes through a multiple of

orifices that are in parallel or in series.

[ANSI/ISA-75.05.01-2000] multiple-output system A system that manipulates a plurality of variables so as to achieve control of a single variable. multiple-purpose meter See volt-ohm-mil­

liammeter. multiple sampling A type of statistical qual­ ity control (SQc) in which several samples, each of which consists of a specified number of items, are witlidrawn from a lot and inspected. The tot'is accepted, rejected, or resampled depending on how many unac­ ceptable items are found,.' " multiplex To interleave or simultaneously transmit two or more messages on a single channel. multiplexer 1. A device that interleaves or simultaneously transmits two or more mes­ sages or signals on a single channel. [ISA­ RP55.1-1975 (R1983)] Optical multiplexers combine signals at different wavelengths.

Electronic multiplexers combine signals elec­ tronically before they are converted into opti­ cal form. 2. A device for combining two or more signals (as for multiplex) or for creating the composite color video signal from its components in color television. 3. A device that samples input and/or output channels and interleaves the signals in frequency or time. 4. A device that allows one of many input channels of analog data to be selected under computer control. The device is often an integral part of a data acquisition system (DAS). 5. A device that mixes several mea­ surements for transmission and/ or tape recording: time-division (pulse amplitude modulation [PAM] or pulse code modulation [peM]) or frequency-division (FM). 6. A device or circuit that samples many data lines in a time- ordered sequence one at a time, and puts all sampled data onto a single bus. (A demultiplexer does the reverse job.) multiplexer channel 1. An input/output channel that serves several input/ output units. 2. A single path that is capable of transferring data from multiple sources or to multiple destinations by using time multi­ plexing. multiplexing 1. The simultan~us transmis­ sion of a number of different rt\essages over a single circuit. 2. Utilizing a single device for several similar purposes or using several devices for the same purpose, for example, a duplexed communications channel that car­ ries two messages simultaneously. 3. A tech­ nique for selecting from many inputs in order to provide a specified output. Multi­

330

multiplier tube / MV plexing allows a single ADC to serve several voltage sources by selecting them one at a time. multiplier tube A phototube in which the secondary emission from auxiliary electrodes produces an internally amplified output signal. Also known as "multiplier phototube" and "photomultiplier tube." multipoint (multidrop) line A single communications line or circuit that interconnects several stations. It usually requires some kind of polling mechanism so each connected terminal can be addressed with a unique address code. multi port burner A burner that has a number of nozzles from which fuel and air are discharged. multiposition action A type of controller action in which the final control element is positioned in one of three or more preset configurations. Each configuration corresponds to a definite range of values for the controlled variable. multiposition controller See controller, lIlulti-

raises the pressure above the outlet pressure of the previous stage. multitasking The facility that allows the programmer to make use of the multiprogramming capability of a computer system. multivariable control A control system that involves several measured and controlled variables and in which the interdependences are considered when calculating the output \'ariables. multivariable co"nlrol S:9'stem See control sys-

tem, multi-element (ntliltivariable).

position. multiprocessing 1. Pertaining to the simultaneous execution of two or more programs or sequences of instructions by a computer or computer network. 2. Loosely, parallel processing. multiprocessor A machine that has multiple arithmetic and logic units to be used simultaneously. multiprocessors A group of a number of independent central processing units that each has access to a common memory. One unit is usually an information interchange controller while the others carry out distinct, defined parts of a task. multiprogramming A computer processing method in which more than one task is in an executable state at anyone time. multirange Having two or more specific ranges of values over which an instrument or control device can be used. Changing from one range to another usually involves simply repositioning a switch. No internal parts need to be removed or replaced. multiskilled Maintenance personnel who are skilled in more than one craft. multispeed floating controlled See control-

ler, multiple-speed floating. multistage Occurring in a sequence of separate steps. In a multistage pump or compressor, for instance, pressure is raised by passing the working fluid through a series of impellers or pistons. Each impeller or piston

331

MUMS Multiuser Management Systems. The modern term for the role of SCADA systems, which give key decision makers the ability to analyze system operation so they can make it more efficient by providing access to spreadsheets, RDBMS, and the like.

MUX Multiplexer. An I/O device that routes data from several sources to a common destination.

MV Measured variable; manipulated variable. In process control, that variable of a process that is monitored by a sensor so as to provide a signal to the controller. In process control, the quality or condition that is altered by a control action so as to change the value of the regulated condition.

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