Flow meter installation checklist

There can be many reasons why a flow meter does show a value which is lower or higher than expected. Here is a little checklist you may want to follow before blaming it all on the flow meter!

Stepwise checklist:

1. Check the 4..20 mA scaling settings. Is it bi-directional? Then 12 mA is the zero. Make sure also that the scaling of your PLC input is identical to the flowmeter output.
2. Latency: Receivers can influence the readings dramatically. A flow meter upstream of the receiver can show a totally different value compared to a flow meter downstream. This may average the signals over a longer period of time.
3. Check process conditions: Is the temperature within specified limits? Beware of heat-regenerated desiccant driers when using thermal flow sensors. If temperature limits are exceeded, the flow may go to a very low value, high value or zero. Cool the sensor down, place it in a colder spot. And get your desiccant drier repaired.
4. Up-downstream length. If the length between an elbow or another object and the flow meter is too short, it can affect the readings. And these influences can be dependent on the flow rate. Always respect the installation table as shown in the user manual.
5. Wrong drilling of the insertion point. We have seen it many times: the insertion point drilled too small. Probe not in the pipe: Flow to zero or nearly zero.
6. Wrong power supply or bargaining on your cables. An undersized power supply or a long cable with too thin copper wires inside (wrong wire gauge, to save some costs, great idea!) can cause the sensor to turn off/ on/ off when flow starts to exceed a certain limit.
7. RS485 daisy chains: See also point 6. A too long cable can cause too much voltage drop. Result: sensor turns off initially, or when the flow is higher and more power is taken from the line.
8. Fouling. This comes in many forms. Oil. Desiccant powder, water, some kind of aerosol. Keep the sensor clean! If fouled, gently wash with warm water and some dishwasher hand soap (non aggressive, aluminum friendly please). Then shake the sensor dry in air, or blow it dry. Gently. Do not use toothpicks, metal brushes or high pressure compressed air to blow off the sensor, as this may damage it.
9. Leakages in the system. Sometimes there is a leak between two sensors, causing deviation. Check your drains (if any) and get them fixed if broken.
10. Measurement uncertainties: An air compressor -even when it is brand new- is NOT a reference flow meter. Best case, your compressor is generating a flow with 5% uncertainty (as per CAGI or ISO 1217), but don't put bet on it. Output flow can be influenced by many external factors. And let's suppose it is 5% accurate: According to the metrology laws, this "reference" can be used to check a real flow meter with 15% uncertainty (factor of 3!). The master meter/ reference needs to be at least three times better than the sensor you are checking. In other words: compressors should never be used as a flow "reference". So what about other flow meters? This can also be tricky as their uncertainty can be equal to the device you want to compare. If you want the real deal, you need to have a laboratory grade test stand, which is rare find in a compressor room.

Need more help? Not to worry, we can assist you at all times Call or e-mail us at [email protected] for assistance with your flow measurement needs.

We also have some useful check lists on our website, for example this e-book with 10 installation tips.