How to calibrate flow with a handheld controller
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A double-flange pressure transmitter was used on-site to measure flow, and with the handheld operator connected, the differential pressure was -6.86 while the range was 27.86. I’ve seen other methods for measuring liquid level: simply use the current differential pressure as the zero point and add the range to it, which gives the measurement range of this gauge. If what is being measured is flow rate, then using -6.86 as the zero point would mean negative migration – can flow rate actually migrate? How to check flow rate using a hand controller?
The hand controller can be used to view or modify the range, but it cannot be used as a testing tool. For on-site inspection: check whether the operating conditions permit the isolation of that transmitter. If possible, perform a small balance test to see whether the flow rate can return to zero (that is, by closing the transmitter’s secondary valve or isolation valve and opening the balance valve, the instrument’s differential pressure reading should be 0)
A handheld controller is, in essence, an analog signal generator, right?
The handheld controller is merely a tool for querying and setting transmitter parameters; it cannot be used to calibrate transmitters or flowmeters
The flow rate should be zero and the differential pressure should also be zero; your setting is negative, which is incorrect. It would be better to have an installation diagram available for more accurate assessment. The statement about using HART for flow verification isn’t entirely wrong either; some flowmeters require zero-point calibration, and it is feasible to use HART for this purpose.
There is a standard device for measuring flow rate; water is used as a reference for liquids, while air is used as a reference for gases. Such a device comes at a high cost, and these days few users still invest in equipment for flow rate calibration. No matter what communication protocol is used, the handheld device can only adjust the zero point of the transmitter; the entire flow measurement system cannot be calibrated. Moreover, negative values will not appear either. The liquid level can experience negative migration; it is necessary to calculate the height, convert it into a differential pressure, and set the transmitter’s range and zero point.