For a pressure difference in DCS, the maximum value that can be displayed in the control room is 0.8 MPa; however, the field transmitter can show a value greater than 0.8 MPa
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There is a pressure difference in the DCS system; in the control room, the maximum pressure difference that can be displayed is 0.8 MPa, yet the field transmitter can show a value greater than 0.8 MPa. Why is this?
The range displayed and output on-site has nothing to do with it
Is it the output current that determines the maximum amount of output? It’s still set by the instrument; I’m not quite sure
Is it caused by a discrepancy between the values shown on-site and those in the control room?
It might be that the ranges for indoor and outdoor use are not standardized – the indoor value should be the same as the outdoor value. If it’s not a problem with the ranges for indoor and outdoor use, then check the output current of the transmitter and calculate an approximate value to see if it matches the value indicated on-site. If it does, then there could be a problem with the transmitter’s output module
The display bit count and range settings of the central DCS system do not match those at the site.
So should this be considered as an improper calibration of the instruments before driving?
The most likely reason is a different range setting; it is best to calibrate both the transmitter and the DCS display using a standard gauge.
You can set the transmitter’s output range to be higher than the value displayed on-site, and then adjust the DCS range to match the transmitter’s output range. This way, it will display consistently.
The ranges displayed on the two devices are not consistent; the output current of the differential pressure sensor is measured, and an accurate value is calculated based on that range, which is then used to set both devices to the same value.