How to determine the temperature measurement range
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If the operating temperature is 100°C, how should the temperature range displayed on the thermocouple instrument be determined? The operating pressure is 0.25 MPa; how is the display range determined in the configuration?
SHT 3005-2016 Specifications for the Selection and Design of Automation Instruments in the Petrochemical Industry 5.1.3 The operating temperature for temperature instruments: for local thermometers, it should be 30%~70% of the scale/range; for temperature transmitters, it should be 10%~90% of the range. For the selection of the range for pressure instruments, see the requirements in Section 6.1.
For non-intelligent temperature and pressure measuring instruments, the rated range at the time of manufacture is fixed; the instrument users cannot change it. Intelligent temperature and pressure measuring instruments, on the other hand, usually allow users to set the operating range, that is, to determine the temperature range or pressure range corresponding to a 4–20mA signal. The operating range must be set within the rated range. It generally should not be lower than 1:5.
Generally speaking, just input the instrument’s rated range into the signal receiving device – that’s it. There’s no need to worry about the operating temperature or pressure; whatever value they have is fine. As long as the instrument operates within its rated range and can function safely and without any risks, that’s sufficient.