How Do You Calibrate A Fieldbus Instrument?

1.	How Do You Calibrate A Fieldbus Instrument?
Answer» This is really no different to any other smart transmitter, except that now, you don’t have to worry about the 4-to-20mA analogue signal! You just need to read out the measurement over the bus with a suitable HOST device. You need a source of the process variable: PRESSURE, temperature (or ohms or millivolts), pH, or whatever. Typically, when you connect a known process value to the sensor, you can send a special MESSAGE to the device, INCLUDING the value you read, and what it should be. The field device will then adjust a stored parameter to make it so. Two values, near the ends of the instrument’s working range, are usually enough, though some devices may USE a more complex multi-point calibration in the factory to adjust linearity corrections, or even a temperature cycle to adjust temperature correction. Automatic calibrators will step through this process with only minimal user involvement.

Answer»

This is really no different to any other smart transmitter, except that now, you don’t have to worry about the 4-to-20mA analogue signal! You just need to read out the measurement over the bus with a suitable HOST device.
You need a source of the process variable: PRESSURE, temperature (or ohms or millivolts), pH, or whatever. Typically, when you connect a known process value to the sensor, you can send a special MESSAGE to the device, INCLUDING the value you read, and what it should be. The field device will then adjust a stored parameter to make it so. Two values, near the ends of the instrument’s working range, are usually enough, though some devices may USE a more complex multi-point calibration in the factory to adjust linearity corrections, or even a temperature cycle to adjust temperature correction.
Automatic calibrators will step through this process with only minimal user involvement.

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