Zero drift issue in differential pressure flow meters
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There is currently an orifice plate flow meter; a differential pressure transmitter is used for measuring flow, with a range of 0-16 kPa, and the signal is processed via DCS square root function. There is now a zero drift; with positive and negative pressures of 0.1 kPa relative to vacuum, zero calibration is performed. One method is to perform a direct zero adjustment while keeping the range setting unchanged. Another approach is to set the lower limit to 0.1 and the upper limit to 16.1. This approach is not feasible. Why? 0.1 corresponds to 4mA, 16.1 corresponds to 20mA
The pressure transmitter measures pressure; it has an isolation fluid tank, with a range of 0-20 kPa. If the isolation fluid fills the tank and there is no pressure present, the reading will be 5 kPa, at which point zero calibration can be performed. One method is to set the lower range limit to 5 and the upper limit to 25; another method is to leave the isolation tank empty and perform zero adjustment directly. Can both of these be used? What is the general approach?
Either is fine; the only drawback of range migration is that when the gauge display shows 0, flow is actually present, which can lead to misleading readings when looking at the gauge. The usual practice is to set the air conditioner to zero.
Yes, this approach is called zero-point migration