I am troubleshooting an Annubar Flow Meter on a 8" line. It is measuring discharge air flow from a scrubber. When VFD for blower motor gets below 60% (325 SCF/M) the measurement drops off to 0. Does anyone have any suggestions on how to read lower flows in this situation? Thanks.

 

Re-range or replace the DP transmitter with one that has higher sensitivity at low ΔP. Consider using a smart DP transmitter with a lower turndown ratio or an auto-ranging feature.

 

You may find that the range of the annubar isn't able to measure the flow at the lower rates due to the not so great turn down these primary elements inherently exhibit. Ask the manufacturers what the lowest accurate measurement is for the Annubar.

 

DP might have a high value for Low Flow Cutoff.

 

1. Check/re-range your DP transmitter to a lower span for better sensitivity
2. Verify impulse lines aren't blocked with moisture from the scrubber
3. Confirm proper zero calibration of the transmitter
4. Consider a thermal mass flow meter for reliable low-flow measurement in air applications