How are the range and calibration limits of pressure transmitters and temperature transmitters determined?
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The methods for determining local pressure gauges and local thermometers can be found in the design specifications; however, there are no clear regulations regarding the measurement ranges of remote-transmitted instruments. How should the range and calibration limits of pressure transmitters and temperature transmitters be chosen? What are everyone’s opinions?
When selecting a design, it’s best for online instruments to have the HART protocol, as this makes calibration much easier later on; it’s possible to set initial values that are similar to those at the surface level
. As for how to determine the calibration range for pressure transmitters and temperature transmitters, it depends on the requirements of the process; there is no fixed rule – as long as the requirements of the process are met, that’s sufficient. First, you need to know the approximate value of the parameter that is to be measured. For example, if the actual temperature at the measurement point is above 100°C, it’s not possible to set the measurement range to 0-50°C; you should set it to at least 0-150°C or 0-200°C. In short, it’s important to know the approximate values related to the process.
The range setting is determined based on the normal and maximum values provided by the process. The normal range is generally between 1/3 and 2/3 of the full scale, with the maximum value falling within that full scale range. An excessively large range can affect measurement accuracy.
The instrument series provided by the manufacturer determines the selection of the measurement range for the remote transmitter; as long as the range you use falls within the limits of the manufacturer’s transmitter, that’s fine – of course, the closer it is to those limits, the better. First, it is necessary to determine the range of each remote transmitter based on the requirements of the production process, and then select the transmitters according to these ranges as well as the ranges provided by the manufacturers. Generally, there are low, medium, and high ranges; differential pressure transmitters, for example, operate from a negative value to a positive value, which facilitates negative offset adjustment.
The range of pressure transmitters and temperature transmitters should also be determined based on the process parameters; it is advisable to have the normal values fall within the range of 1/2 to 2/3 of the transmitter’s measurement range.