The differential pressure transmitter was linearly calibrated, but it was found to not exhibit linearity during testing
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I would appreciate some expert advice: For two sets of linear calibration values, the testing is fine for one set, but in the other set, the low-pressure side does not exhibit linearity during pressure testing. The range is -50mmH2O to 50mmH2O. The pressure testing at the high-pressure end shows a linear pattern, but it is not linear during testing at the low-pressure end. For example, when a pressure of around 40 mmH2O is applied, the differential pressure transmitter displays around -9 mmH2O. As more pressure is applied, the readings from the differential pressure transmitter increase gradually, showing values of -8 mmH2O, -7 mmH2O, -6 mmH2O… up to 3 mmH2O and 4 mmH2O. But it works normally when another set of linear calibration values is used. Please ask an expert to help analyze it
It took me three readings to understand that what was being said was: calibrating the range of the negative pressure range by applying a positive pressure signal from the negative pressure side. 1. The diaphragm chamber of a differential pressure transmitter is theoretically not designed to accept signals where the negative pressure side has a higher value than the positive pressure side (although in practice, many such transmitters can handle this) ； 2. The differential measurement of negative pressure is obtained by shifting after the positive pressure calibration range, to cover the negative pressure measurement section ； Therefore, the range of -50mmH2O to 50mmH2O should be calibrated within the 0–100mmH2O range and then applied to the actual measurement range. If there are linearity issues during calibration in the 0–100mmH2O range, it indicates a fault with the gauge
Differential pressure measurement range: -50mm to 50mmH2O. The correct way to apply pressure is to expose the low-pressure side (L) of the differential pressure gauge to the atmospheric pressure, while applying a pressure within the range of -50mm to 50mmH2O to the high-pressure side (H). The output current signal value, or display value, of the differential pressure gauge at each specified pressure should then be observed and recorded. ——Only by applying such pressure can the differential pressure gauge accurately output a current signal. . Measurement, right? It involves quantification, and first of all rules need to be established. Without rules, there can be no precision, no linearity, and it’s impossible to talk about any other aspects related to measurement. .
Calibration is always performed from the high-voltage side. The calibrated range is 0~100 mmH2O. After calibration, change the range setting to -50~50mmH2O. I also think that the issue arises due to problems with the calibration linearity for 0–100 mmH2O, but after recalibrating, the tests showed normal results.