An Introduction to Testo Compressed Air Flowmeters -
6440 and 6446/6447 series
What / why / how ? What is a flowmeter ? : Simply a device that can monitor and measure the actual amount of ‘product’ being sent through it. Typically flowmeters in industry are used for monitoring use of water, chemicals, ingredients, etc. Some flowmeters have a basic ‘indicator’ built in to show value, more sophisticated will have ‘outputs’ that can be fed into measurement & control systems.
Why use a flowmeter ? : To accurately determine how much of ‘something’ is being used for cost/performance reasons. Often they are used as part of a overall process plant control system.
How does a flowmeter work ? : There are many technologies used depending upon the product to be monitored and its physical variables, common types for airflow would be insertion pitot, turbine/vane, variable area, venturi, etc. All technologies have good/bad points – it is usually a case of matching the best technology to the required application.
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Testo compressed air flowmeters – basic info We have a range of flowmeters marketed for use within the compressed air industry – these have been designed around specific requirements found within compressed air systems, however with a ‘correction factor’ applied they can be used for nitrogen (N2), carbon dioxide (CO2), and argon (Ar). Why use a flowmeter to monitor compressed air ? : Unlike all other ‘utilities’ used in a factory or production line, compressed air is usually NOT metered, so usage is unknown. The compressed air comes from having a compressor somewhere in the facility, and this compressor is using electricity. Also you may have leakage within the air system. Compressor systems typically represent between 5%-40% of total facility energy consumption.
Surveys have found that on average 20% of the compressed air produced on a system is wasted through leakage. At 7 bar (100psi) : 3mm hole = 12 l/s = £3,260 per annum.
6mm hole = 47 l/s = £12,770 per annum. A 2 l/s leak is to small to hear but would still cost £590 annually.
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Typical compressed air system Diagram below shows a basic schematic for a typical industrial compressed air system. The flowmeter must be placed after the dryer so that the air flowing through is as dry and as clean as possible.
Note the amount of condensate drains in a typical system – this is due to the fact that when ambient air is compressed there is a huge amount of moisture generated. This needs to be removed by a dryer system otherwise this ‘wet’ air will destroy downstream equipment. – Testo also make specialised sensors for measuring trace humidity in compressed air systems. Testo Limited
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Testo compressed air flowmeters – basic info What can we offer : 2 main versions of product. 6441 – 6444 suitable for most small bore pipework. 6446/6447 for larger plant pipework and also special feature of replacement ‘sensor’ whilst system is under pressure.
Common process conditions for both series are : 0 to 60°C 16 bar max (PN16) <90% RH Air quality ISO 8573 Rec. classes 1-4-1 Testo Limited
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Testo flowmeters â&#x20AC;&#x201C; principle of operation The optimal method for measuring airflow within gases is â&#x20AC;&#x2DC;thermal mass flowâ&#x20AC;&#x2122; measurement
Only this technique is independent of temperature and pressure changes within the process, and also has the added benefit of minimal back pressure within the system.
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Testo flowmeters – principle of operation Conversion of ‘mass’ flow to volumetric flow :
For consumers of the air, normalised volume flow is the most important function. The Testo 6440 divides the ‘mass’ flow value by the normalised density value (according to ISO 2533) to give a value of normalised volumetric flow which is also independent of temperature and pressure.
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6441 / 6444 - overview Supplied as pre-formed flow tube, with precise internal dimensions, and threaded process connections.
Uses ‘calorimetric’ thermal mass flow measurement principle for high accuracy, independent of temperature and pressure fluctuations, and almost zero backpressure (approx 1mbar).
Compact electronics module has built-in digital display to allow for programming and operation of unit. (Display can be turned through 180° to suit flow direction).
24VDC supply configured in 4-wire format.
Output options include 4..20mA analogue output proportional to flowrate, PNP alarm outputs for Hi/low flow warning, pulse output for use with flow totalisers. Max of 2 outputs possible.
Unit can be configured to display units of Nm³/h, Nl/min, m³, °C.
High accuracy : for class 1-4-1 air, ±3% of reading & ±0.3% of final value.
Can measure bi-directional flow within compressed air ring main.
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6446 / 6447 - overview Supplied as pre-formed flow tube, with precise internal dimensions, and DN flanged connection (DN65…DN250)
Uses ‘calorimetric’ thermal mass flow measurement principle for high accuracy, independent of temperature and pressure fluctuations, and almost zero backpressure.
6446 has fixed sensor and electronics module, 6447 version allows removal of sensor unit whilst system is under pressure (also called ‘hot-swap’)
Compact electronics module has built-in digital display to allow for programming and operation of unit.
24VDC supply configured in 4-wire format.
Output options include 4..20mA analogue output proportional to flowrate, PNP alarm outputs for Hi/low flow warning, pulse output for use with flow totalizers. Max of 2 outputs possible.
Unit can be configured to display units of Nm³/h, Nl/min, m³, °C
High accuracy : for class 1-4-1 air, ±3% of reading & ±0.3% of final value.
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Technical issues Technology used is tried and tested, so no issues there. Robust construction with precision dimensions of flowtube, give good accuracy compared to other technologies (clamp-on meters, etc) Watch out for mounting position guidelines, and also the required inflow / outflow conditions recommended within our installation manual.
Also if oil is used, then the unit must be placed in front of the lubricator to remove possibility of contamination of sensors.
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Applications Why use a compressed air flowmeter ? Cost transparency – clear information on usage overall and to individual machines/areas. Leakage detection – installed on supply to individual machines the 6440 will detect the smallest amount of compressed air volume flow. If the machine is switched off but flow is continuing then a leak or leaks are occurring (costs money). Machine usage – also the flowmeter can be used as part of maintenance regime by monitoring flow when system is new, against gradual increase in flow rate as leakage starts to occur over time. Peak load management – allows production systems to be balanced to make sure maximum air usage is within compressors range. Protection – Hi/Low switch outputs can protect expensive plant against under/over supply of air. Precise dosing of air quantity – filling of container, etc.
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Applications Typical applications / customers include :
Any processing or manufacturing site using compressed air. Packaging lines, beverage, plastics moulding, production lines, etc
Manufacturers of machinery which uses compressed air.
Any company involved in compressed air systems installation/maintenance/upgrades.
Compressor manufacturers/suppliers.
Companies involved in energy audits within compressed air systems.
Suppliers of components/parts for compressed air/pneumatic systems.
Potential for use on special welding systems with Argon purge.
Manufacturers of nitrogen gas generators.
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