Thermal mass flow meter in-situ validation attempt
In an earlier post I discussed the advantages of having an onsite calibration method to verify the accuracy of thermal mass flow meters. Recently I shared how the largest flowmeter manufacturer handles in-situ verification, and here I discuss another manufacturer’s in-situ validation attempt.
A popular thermal mass flow meter manufacturer claims to have a feature that “validates the flow meter’s calibration accuracy by testing the functionality of the sensor and associated signal processing circuitry.” This manufacturer suggests that the operator can validate flow meter calibration while the meter is still in in the pipe at operating conditions by simply pushing a button. The company claims that in three to four minutes the operator will receive a pass or fail message and the data is stored in the meter.
While the meter is being “validated,” an integrated circuit within the meter regulates the signal to the sensor. Data is collected and compared to the original factory calibration records. If the data matches within a customary range of tolerance, the meter is apparently validated. A validation certification, can even be produced if a software tool is used to activate the process.
While this company claims the meter’s accuracy is validated by testing the sensor functionality, the only thing that is verified is that the flow meter is working properly, not that it’s accurate. Without having a way of testing at a known flow point, there is no way to confirm if the meter is truly in calibration. In contrast, Sage uses “no flow” (0 SCFM) as a known, dependable and repeatable flow point – and with our digital circuitry, any known flow point, even 0 SCFM is an indicator of the absolute calibration curve. The other drawback for this company’s method is that you cannot verify if the sensor is clean or dirty. When the sensor is dirty the meter continues to measure flow producing inaccurate data, and the operator never knows.
In the Sage Metering In-Situ Calibration method, a “no flow” condition is easily created with the use of an isolation valve assembly, and if the sensor is dirty the meter will not pass the calibration check. This gives the technician a chance to inspect and clean the sensor, and recheck the calibration.
On another point, the Sage Metering thermal mass flowmeter is less expensive. In fact, when comparing the Sage Prime with this model, the customer could save $825-$1,175 depending on which options are selected.
While this manufacturer’s attempt is certainly simpler than the last method I discussed, it is not a true calibration check, and another indicator that Sage Metering still leads the way in in-situ calibration.
In my next post, I share the steps needed to perform the Sage Metering In-Situ Calibrations Check.