Emcwb21 by American Technical Publishers

Tech-Chek Name ______________________________________________________ Date ________________

Section 21-1: Thermistors �� 1. A thermistor is a(n) ___-sensitive resistor. A. airflow C. temperature B. sound D. light �� 2. The operation of a thermistor is based on the ___-hole theory. A. electron C. neutron B. proton D. positron �� 3. ___ heated thermistors are used for precision temperature measurement and temperature compensation. A. Directly C. Chemically B. Indirectly D. Mechanically �� 4. With a(n) ___ thermistor, an increase in temperature causes the resistance of the thermistor to decrease. A. NTC C. NPN B. PTC D. PNP �� 5. Cold resistance is measured at ___°C. A. 5 C. 25 B. 15 D. 35

Section 21-2: Photoconductive Cells �� 1. A photoconductive cell (photocell) is a device that conducts current when energized by ___. A. temperature C. sound B. humidity D. light �� 2. A photocell is, in effect, a variable ___. A. amplifier C. transistor B. resistor D. transformer �� 3. ___ and contamination are the primary causes of photocell failure. A. Humidity C. Voltage swells B. Overheating D. Transient voltages

265

266 ELECTRICAL MOTOR CONTROLS for Integrated Systems WORKBOOK

Section 21-3: Photoconductive Diodes �� 1. The primary difference between a photodiode and a regular diode is that a photodiode has an addition of a ___ in its housing for focusing light on the PN junction. A. prism C. lens B. condenser D. mirror �� 2. Without light, the ___ of the photodiode is high. A. power C. voltage B. current D. resistance �� 3. The ___ flowing through a photodiode increases as the resistance decreases. A. capacitance C. voltage B. current D. frequency

Section 21-4: Pressure Sensors �� 1. A voltage-output pressure sensor typically outputs 0 VDC to ___ VDC proportional to the rating of the pressure sensor. A. 5 C. 15 B. 10 D. 20 �� 2. A current-output pressure sensor typically outputs 4 mA to ___ mA proportional to the rating of the pressure sensor. A. 10 C. 30 B. 20 D. 40 �� 3. Pressure sensors are suited for a wide variety of pressure measurements on ___, pumps, and other similar equipment. A. transformers C. AC motors B. DC motors D. compressors

Section 21-5: Flow Detection Sensors �� 1. A flow detection sensor is a sensor that detects the movement (flow) of liquid or gas using a(n) ___. A. amplifier C. solid-state device B. flow switch D. flapper �� 2. A flow detection sensor operates on the principle of ___ conductivity. A. thermal C. fluid B. magnetic D. variable

Chapter 21 — Semiconductor Input Devices 267

�� 3. Because there is a small delay (usually less than 30 sec) before a flow detection sensor heats enough to signal no flow, the sensor acts like a ___, which allows for a short time delay to pass before signaling a problem. A. transistor C. surge protection device B. GFCI D. motor starter overload

Section 21-6: Hall Effect Sensors �� 1. A(n) ___ sensor detects the proximity of a magnetic field. A. ultrasonic C. inductive proximity B. Hall effect D. pressure �� 2. Hall voltage varies depending on how close the magnet is to the Hall generator, which acts as a(n) ___ signal. A. magnetic C. digital B. thermal D. analog �� 3. Typical Hall effect sensor package configurations include cylinder, proximity, vane, and ___. A. plunger C. delay B. float D. dual-level �� 4. ___ actuation is an active method of Hall effect sensor activation in which a magnet is oriented perpendicular to the surface of the sensor and is usually centered over the point of maximum sensitivity. A. Cylinder C. Head-on B. Slide-by D. Electromagnetic �� 5. Hall effect sensors are also used to replace mechanical ___ switches in applications that require the detection of an object’s position. A. limit C. level B. flow D. selector

Section 21-7: Proximity Sensors �� 1. A proximity sensor (proximity switch) is a solid-state sensor that detects the presence of an object by means of a(n) ___ sensing field. A. thermal C. magnetic B. electronic D. physical �� 2. A(n) ___ proximity sensor is a sensor that detects only conductive substances. A. inductive C. electromagnetic B. resistive D. capacitive �� 3. Inductive proximity sensors operate on the ___ principle. A. electromagnetic C. eddy current killed oscillator B. dielectric D. radio frequency © 2014 American Technical Publishers, Inc. All rights reserved

268 ELECTRICAL MOTOR CONTROLS for Integrated Systems WORKBOOK

�� 4. ___ sensors can detect materials such as plastic, glass, water, moist wood, etc. A. Variable C. Inductive B. Conductive D. Capacitive �� 5. Generally, any material with a ___ constant greater than 1.2 may be detected. A. magnetic C. dielectric B. resistance D. dual-field

Section 21-8: Ultrasonic Sensors �� 1. The high-frequency sound waves of an ultrasonic sensor are typically in the ___ kHz range. A. 100 C. 300 B. 200 D. 400 �� 2. Materials such as foam, fabric, and ___ are difficult for ultrasonic sensors to detect and are better detected by photoelectric or proximity sensors. A. plastic C. glass B. metal D. rubber �� 3. ___ mode is a method of ultrasonic sensor operation in which the emitter and receiver are placed opposite each other so that the sound waves from the emitter are received directly by the receiver. A. Direct C. Diffused B. Indirect D. Tuning

269 ELECTRICAL MOTOR CONTROLS for Integrated Systems WORKBOOK

Worksheets Name ______________________________________________________ Date ________________

Section 21-1: Thermistors In a thermistor application, a fan motor is controlled by an NTC thermistor through an SSR. The fan motor turns off at a set lowering temperature and on at a set rising temperature. Complete the following circuit. 1. Design a circuit using a timer so that the fan does not turn on until the thermistor has reached the highest set point and 30 sec has passed, eliminating false turn-on. Also, add a second timer that keeps the fan motor turned on 2 min after the thermistor has reopened the SSR contacts, allowing the fan to clear any heat away. L1

L2 115 VAC

76°F (LOW RESISTANCE SSR ON)

FAN MOTOR

NTC 72°F (HIGH RESISTANCE SSR OFF)

SOLID-STATE RELAY FAN MOTOR TURNS ON AUTOMATICALLY AT HIGH TEMPERATURE

THERMISTOR APPLICATION DC

SSR

L1 L1

115 VAC

269

270 ELECTRICAL MOTOR CONTROLS for Integrated Systems WORKBOOK

Worksheets Worksheets Name ______________________________________________________ Date ________________

Section 21-2: Photoconductive Cells A photoconductive cell can be used to detect the presence of a pilot flame before a gas valve is opened. Complete the following circuit. 1. Design a circuit so that the heating valve cannot be energized unless a photoconductive cell detects a pilot flame. An SSR is used as the interface between the photoconductive cell and the gas valve. This is required because the photoconductive cell cannot carry the higher current of the gas valve. The SSR coil is rated for a few milliamperes (mA), but the SSR contacts can switch several amperes (A).

ELECTRONIC ROOM THERMOSTAT 24 VAC IN

74°

18 VDC OUT

Thermostat

DC POWER SUPPLY

ELECTRONIC HEATING VALVE

ELECTRONIC COOLING VALVE

TO THERMOSTAT

ELECTRONIC HEATING VALVE

– 18 VDC CUT OFF POWER SUPPLY

270

271 ELECTRICAL MOTOR CONTROLS for Integrated Systems WORKBOOK

Worksheets Name ______________________________________________________ Date ________________

Section 21-3: Photoconductive Diodes Photodiodes are used for light detection because they have a fast response time to variations in light levels. Photodiodes, unlike regular diodes, are connected into the circuit in reverse bias mode. In this mode, the amount of current flowing through the diode increases with an increase in light level. Complete the following circuits. 1. Connect circuit 1 adding a photodiode so that the load turns on when the diode has light on it. CIRCUIT 1

– LOAD

2. Connect circuit 2 adding two photodiodes so that the load turns on any time either diode has light on it. CIRCUIT 2

– LOAD

3. Connect circuit 3 adding two photodiodes so that the load turns on any time both diodes have light on them. CIRCUIT 3

– LOAD

271

272 ELECTRICAL MOTOR CONTROLS for Integrated Systems WORKBOOK

Worksheets Worksheets Name ______________________________________________________ Date ________________

Section 21-4: Pressure Sensors Pressure sensors can be used to automatically control a compressor motor. 1. Complete the following diagram so that the ON/OFF switch determines if the compressor motor can start through a pressure sensor or cannot be on at any time. The pressure sensors output automatically controls the compressor motor. A yellow lamp is ON any time the ON/OFF switch is in the ON position regardless of if the compressor motor is ON or OFF. A red lamp is ON anytime the compressor motor is ON.

PRESSURE SENSOR

272

273 ELECTRICAL MOTOR CONTROLS for Integrated Systems WORKBOOK

Worksheets Name ______________________________________________________ Date ________________

Section 21-5: Flow Detection Sensors Flow detection sensors are used to detect flow in a system. The flow can be a liquid or gas (water, air, etc.). The sensors are used to shut down pumps when little or no liquid flow is moving through the pump/pipe. They are also used to indicate little or no air flow in exhaust systems. Complete the following control circuit. 1. Design a control circuit with a GREEN lamp that turns on any time the selector switch is placed in the ON position; a YELLOW lamp that turns on any time the switch detects a flow; and a second relay (CR-2) that latches the alarm on until a RESET pushbutton turns the alarm off. This circuit will allow the alarm to remain on if flow is restored, so the problem must still be acknowledged until an operator resets the alarm. L1

SYSTEM ON

OFF

(2)

FLOW DETECTION SENSOR (SWITCH) CLOSED WHEN FLOW DETECTED 2

(3)

TR CR

3 TR

ALARM

273

274 ELECTRICAL MOTOR CONTROLS for Integrated Systems WORKBOOK

Worksheets Worksheets Name ______________________________________________________ Date ________________

Section 21-6: Hall Effect Sensors A DMM can be used to test Hall effect sensor operation. Complete the following steps to test a Hall effect sensor. 1. Draw in the required position of the DMM selector switch for testing a Hall effect sensor. Connect the DMM test leads to the meter. Connect the test leads to the correct pins to measure the output (+) of the Hall effect sensor.

CURRENT FLOW

WIRE COIL HALL EFFECT SENSOR

274

–

275 ELECTRICAL MOTOR CONTROLS for Integrated Systems WORKBOOK

Worksheets Name ______________________________________________________ Date ________________

Section 21-7: Proximity Sensors Steel Cutting Operation. Use Data Sheet K on page 399 to complete the line diagram. Use standard lettering, numbering, and coding information. Mark all manufacturers’ numbers (1–11) on the line diagram. 1. Design a circuit with a proximity switch that is used to automatically stop a motor from supplying steel to a cutting press. A start pushbutton is used to start the steel infeed, and a proximity switch or stop pushbutton is used to stop the steel infeed. PROXIMITY SWITCH (NORMALLY OPEN ONLY)

CUTTING PRESS

SUPPLY SPOOL

115 VAC

275

276 ELECTRICAL MOTOR CONTROLS for Integrated Systems WORKBOOK

Piston Control. Use Data Sheet K on page 399 to complete the line diagram. Use standard lettering, numbering, and coding information. Mark all manufacturers’ numbers (1–11) on the line diagram. 2. Design a circuit in which two proximity switches are used to cycle the piston in a cylinder back and forth automatically. A standard start/stop pushbutton station with memory is used to start and stop the automatic cycling. The piston is controlled by a double-solenoid fluid power valve. One solenoid controls the piston out function and the other controls the piston in function. Power must be maintained on the solenoids to keep the piston moving.

CYLINDER

PROXIMITY SWITCH 1 (IN)

PROXIMITY SWITCH 2 (OUT)

115 VAC

Bottle Detection. Four capacitive proximity sensors may be used to detect bottles through a carton. Capacitive proximity sensors can detect plastic, glass, or metal containers inside the carton. Complete the following control circuit. 3. Design a control circuit using four PNP capacitive proximity sensors and four DC-to-AC solid-state relays. In the DC circuit, each capacitive proximity sensor energizes one light and one solid-state relay when a bottle is present. In the AC circuit, the four solid-state relay contacts energize an operate delay relay. The relay is set for 5 sec and controls the conveyor motor starter. When all four sensors detect a bottle, the conveyor motor runs for 5 sec and automatically advances each carton after it is filled. If the conveyor does not advance, an operator checks the lights to see which bottles have not dropped. If the carton advances, the circuit is automatically reset when the carton passes the four sensors. Mark the color of each wire used on the sensor. © 2014 American Technical Publishers, Inc. All rights reserved

Chapter 21 — Semiconductor Input Devices 277

SSR

SOLID-STATE RELAY COIL

PROXIMITY SENSOR

SOLID-STATE RELAY CONTACTS

SYMBOLS R

W BL

BL R

PNP TRANSISTOR OUTPUT (CURRENT SOURCE)

NPN TRANSISTOR OUTPUT (CURRENT SINK) L1

–

278 ELECTRICAL MOTOR CONTROLS for Integrated Systems WORKBOOK

Glass Panel Detection. A capacitive proximity sensor may be used to detect the presence of glass panels moving along a production line. Complete the following control circuit. 4. Draw a control circuit using a PNP capacitive proximity sensor and two DC-to-AC solid-state relays. In the DC circuit, the proximity sensor energizes two solid-state relays when the glass panels are present. In the AC circuit, a three-position selector switch controls a two-speed conveyor motor that moves the glass panels along the production line. When the selector switch is in the low position, the low-speed starter is energized. When the low-speed starter is energized, glass panels move along the production line at 15 sec intervals. When the selector switch is in the high position, the high-speed starter is energized. When the high-speed starter is energized, glass panels move along the production line at 10 sec intervals. When the selector switch is in the OFF position, no starter is energized. Design the circuit so an alarm sounds when the proximity sensor does not detect a glass panel every 15 sec in low speed. An alarm also should sound when the proximity sensor does not detect a glass panel every 10 sec in high speed. Use the NPN Transistor Output and PNP Transistor Output diagrams on the previous page. Mark the color of each wire used on the proximity sensor.

GLASS PANELS

CAPACITIVE PROXIMITY SENSOR

CONVEYOR MOTOR

Chapter 21 — Semiconductor Input Devices 279

AC H

OL LL LOW HIGH

L H

– DC

280 ELECTRICAL MOTOR CONTROLS for Integrated Systems WORKBOOK

PLR Wiring. A PLR that requires an external DC power supply to provide power to its input section and input switches is normally designed for a positive (PNP) input or a negative (NPN) input. Complete the following circuits. 5. Wire the PNP proximity switch and DC power supply to the PLR for proper operation. Connect the proximity switch to input 1. – +

DC PROXIMITY SENSOR

PNP SWITCH

PNP INPUTS +

–

I1 I2 I3 I4 I5 I6 INPUT 6 × DC

+ –

24 VDC

EXTERNAL DC POWER SUPPLY

DEL

SEL

ESC

OUTPUT 4 × RELAY / 8A

6. Wire the NPN proximity switch and DC power supply to the PLR for proper operation. Connect the proximity switch to input 1. + –

DC PROXIMITY SENSOR

NPN SWITCH

NPN INPUTS +

–

I1 I2 I3 I4 I5 I6 INPUT 6 × DC

+ –

DEL

SEL

ESC

24 VDC

EXTERNAL DC POWER SUPPLY

OUTPUT 4 × RELAY / 8A

281 ELECTRICAL MOTOR CONTROLS for Integrated Systems WORKBOOK

Worksheets Name ______________________________________________________ Date ________________

Section 21-8: Ultrasonic Sensors Ultrasonic sensors are available with a switch type (open/closed) output. The switch output is usually a PNP or NPN transistor. Switch type output can be used to detect the presence (closed switch) or absence (open switch) of an object. Ultrasonic sensors are also available with an analog output. The analog output is usually a 0 VDC to 10 VDC or 4 mA to 20 mA output. The analog output is linear to the distance the object is from the target. Complete the following steps.

HIGH FREQUENCY SOUND WAVES

ULTRASONIC SENSOR

SUPPLY VOLTAGE

1 2 + –

4-20 mA OUT

0-10 VDC OUT

1. Set DMM 1 to the appropriate setting and connect the test leads and power supply to test the function of Switch 1, an ultrasonic sensor with an analog voltage output. SWITCH 1

–

DMM 1

281

282 ELECTRICAL MOTOR CONTROLS for Integrated Systems WORKBOOK

2. Set DMM 2 to the appropriate setting and connect the test leads and power supply to test the function of Switch 2, an ultrasonic sensor with an analog current output.

SWITCH 2

DMM 2

–