Why does a differential pressure transmitter still need to have its zero point calibrated?
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For example, a double-flange transmitter is used to measure liquid level; the lower pressure value and the corresponding liquid level are zero (the lowest level), with an output current of 4 milliamps； The upper pressure limit corresponds to a liquid level of 10 meters (the highest level), with an output current of 20 milliamps. When the valve is closed and the flange is loosened (with its position unchanged), its output should be 4 milliamps; then why is zero calibration still necessary? If the output is not 4 milliamps at this point, then is there a problem with the circuit part of the transmitter? What is the principle behind zeroing using a manual controller at this time? I’m asking experts to answer.
Using the zero calibration helps to determine whether the transmitter is functioning properly. If the transmitter’s zero-point output is not 4mA, it may be due to zero-point drift; in such cases, recalibration is sufficient. There could also be circuit issues that require a replacement of the circuit board, or it might be a problem with the sensing elements, in which case the transmitter needs to be replaced.
In the case of double-flange types, the differential pressure of the silicone oil will certainly vary depending on the installation height, and it needs to be corrected. For ordinary differential pressure types, we won’t calibrate them even if we start over. Unless you buy one of their refurbished models from upstairs, which drifts every day, it of course needs to be calibrated.
It is caused by the installation accuracy and the stress deformation of the flanges; zero drift is a real problem
Zeroing is primarily used to adjust the electrical device’s zero point; sometimes, due to interference over time, it may deviate from the initial zero point of the device
“When the valve is closed and the flange is loosened (with its position unchanged), its output should be 4 milliamps. ” If the device is in operation at this time and the gas phase is under pressure (for example, 1 KG), then the gas phase pressures in the positive and negative diaphragm boxes of the double flange design will be different; the pressure difference at this point is not the amount of migration. @jiaguoyun
During use, there are times when doubts arise regarding the accuracy of the instrument; one approach is to verify whether the process conditions have changed； Second, check whether the zero point and range of the instrument have changed to determine the source of the problem.
Since the transmitter can operate on non-standard ranges, the working range can be shifted by setting the zero and full-scale values. Similarly, it can be migrated artificially, which can also lead to natural zero-point drift.
Going back to the 10th floor: what I meant is that once the differential pressure transmitter has its upper and lower limits set, those limits constitute its operating range. Moreover, the lower limit corresponds to an output of 4 milliamps – so why is it still necessary to perform zero calibration? Excuse me, on the 7th floor – what does it mean to adjust the zero point of electrical appliances? What is the difference between him and setting the upper and lower limits of the range?
Factory zeroing refers to the zero point at which the two flanges are at the same height; when there is a difference in height between the two flanges after installation, it is necessary to perform zeroing.