Operation method for checking the zero point of the differential pressure transmitter during operation
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During the operation of the device, it is usual to check the zero point of the differential pressure transmitter. For differential pressure transmitters that do not have a zero-offset function, the standard three-valve method involves closing the negative pressure valve, opening the balance valve, and closing the positive pressure valve, in order to check whether the zero point is at zero. For intelligent differential pressure transmitters with migration function, close the negative pressure valve, open the balance valve, close the positive pressure valve, and use the operator to check whether the zero point is at the zero setting value. Such an approach sometimes overlooks the issues: 1. Typically, transmitter calibration is carried out by applying pressure on the positive pressure side only, while the negative pressure side is ignored ； 2. No hydrostatic test will be conducted ； 3. During the actual relocation of the instruments, there are also few issues such as static pressure, which makes it difficult to detect problems like poor static pressure characteristics or deformation of the diaphragm boxes. If the operating method is changed: close the negative pressure valve and open the balance valve, then check whether the zero point is at zero. It would be more appropriate to check the static pressure at the same time; please share your opinions.
I don’t think it’s necessary to shut off the negative-pressure side; after opening the balance valve, the same static pressure is applied to both the positive- and negative-pressure chambers. The component that is under pressure is the sealing diaphragm inside the pressure chamber, but what is truly relevant for detection is the deformation of this diaphragm under pressure； If the pressures on both sides of the sealing diaphragm are equal, theoretically the force acting on the load-bearing diaphragm is two forces of equal magnitude but opposite direction; as a result, the diaphragm does not deform, which is what we refer to as the zero point ； So, applying pressure only from the positive-pressure chamber is equivalent to adding a static pressure as well, though that static pressure is just atmospheric pressure; therefore, it can still meet the testing requirements ； If the diaphragm deforms due to mechanical fatigue or overpressure, etc., and even shifts, the linearity and accuracy of measurements will be affected, in which case the transmitter must be replaced