Thermocouple and RTD testing using a calibrator
Thermocouples and RTDs are the most common sensors used to measure process temperature.
Simulating a processing sensor signal to a processing instrument or control system input enables a technician to check whether the device is responding correctly to the temperature measured by the device. There are many different ways to simulate these sensors for experimental purposes. To simulate thermocouples with a resistance box and temperature following the table to search for RTDs you can use a mV dc source and a mV vs. temperature.
However, this method is obsolete with modern temperature calibrations that perform the conversion for the user. Using modern calibrations, simply select the type of sensor to simulate, the input temperature to the source, and connect it to the devices being tested.
To perform the test:
Use a thermocouple simulator to test a device with a thermocouple input:
- Disconnect the process measurement sensor and connect the test connection wires in place (left figure).
- Connect the short circuit from the test wires to the TC calibrator connection.
- Connect the DMM or other measuring instrument to the mA output of the test device.
- Confirm device range or device length. Apply 0 با with the simulator and confirm with DMM that the value of mA or output voltage is as expected.
- Repeat the test, using temperature signals of 50% and 100%.
- If the measured output of the device is limited, the test is complete. Otherwise, set the device to zero (0% compensation) and aperture (100% increase).
- Repeat steps 4 and 5 and confirm for the correct answer.
To use an RTD simulator to test a device with RTD input
- Connect the calibrator to the input of the device as shown in the figure.
- Connect the output of the calibrator with the appropriate combination to match the configuration of the device ( 2, 3 or 4 wires ).
- Use the test step on the left to test the thermocouple, starting with step 3.
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