Thermocouple and RTD Simulation and Testing

In the world of process automation at power plants and process facilities, precise temperature measurement is crucial. Thermocouples (TCs) and Resistance Temperature Detectors (RTDs) are the most used sensors for this purpose. To ensure that the instruments and control systems are responding accurately to the temperatures being measured, simulating these sensors is a reliable method of verification. This blog will explore how to simulate thermocouples and RTDs for testing and calibration purposes.

Simulating Thermocouples and RTDs for Testing

Simulating a sensor signal into a process instrument allows technicians to verify whether the device’s input is functioning correctly. Historically, this has been done using a millivolt (mV) DC source for thermocouples, paired with a lookup table that converted the mV signal to temperature. Similarly, a resistance decade box and a resistance vs. temperature table were used for RTDs.

However, modern calibrators have simplified this process by performing these conversions automatically. With these advanced tools, all that is required is to select the sensor type, input the temperature, and connect the calibrator to the device under test. A high-level and typical step-by-step process for simulating thermocouples and RTDs using modern calibrators is provided below, but the steps vary slightly from manufacturer to manufacturer.

How to Perform Thermocouple Simulation:

1. Begin by disconnecting the thermocouple from the process measurement device.
2. Attach the test connection wires where the process sensor was connected, then link the mini connector to the thermocouple source connection on the calibrator.
3. Connect a Digital Multimeter (DMM) or another measurement tool to the output (mA or voltage) of the device you’re testing.
4. Check the device’s specified range. Apply the 0% temperature signal using the simulator and confirm the output reading with the DMM.
5. Repeat the process at 50% and 100% of the device’s range to verify the correct response.
6. If the readings aren’t as expected, calibrate the device by adjusting the offset (0%) and span (100%) settings.
7. After adjustment, reapply the 0%, 50%, and 100% signals to ensure the device outputs correctly.

How to Perform an RTD Simulation:

1. Attach the calibrator to the RTD input on the device.
2. Ensure the calibrator is connected using the appropriate wiring configuration (2, 3, or 4-wire, as applicable).
3. Starting from step 3 in the above thermocouple procedure, simulate the temperature values and confirm the device’s response.

Temperature simulation testing is essential for ensuring reliable process control at power plants and process facilities. With modern temperature calibrators and simple Ethernet testers, the process is streamlined, helping technicians perform accurate verifications with ease. Whether you’re calibrating an instrument or troubleshooting a network, following these guidelines will help ensure your systems are functioning correctly and efficiently. For more information, training, and/or maintenance procedures surrounding thermocouple and RTD simulation and testing, contact FCS.