How To Calculate Thermocouple Sensitivity

In scientific and manufacturing settings, temperature is one of the most frequently measured parameters. According to Bob Lefort and Bob Ries, electronic experts with Analog Devices, the thermocouple is the most widely used temperature sensor for instrumentation purposes. Its distinctive qualities include inherent accuracy, wide temperature range, fast thermal response, durability, affordability and versatility of applications. The factors used to distinguish between the most commonly used thermocouples are sensitivity and operating temperature range.

Step 1

Calibrate the equipment. For example, if you are using a thermocouple from Analog Devices, you would remove the thermocouple and input an AC signal to pins 1 and 14 of 10mV p-p, 100 HZ, according to Lefort and Ries. Adjust the Rgain for a p-p output of 3.481V (device AS594) or 4.451V (device AD595). Reconnect a thermocouple which is in an ice bath or ice point cell at 0 degree Celsius to pins 1 and 14, then adjust R offset until the output reads 320mV.

Step 2

Determine the direct, mean temperature. Measure the temperature directly using your device, then summarize the output and divide by the number of measurements in Celsius. For example, if a circuit output equaled (T1 + T2 + T3)/3 (in Celsius degrees).

Step 3

Calculate the thermocouple sensitivity. According to Lefort and Ries, determine the desired output sensitivity, in mV/C. Then decide on a temperature range T1 to T2 and calculate the average thermocouple sensitivity over that range. For example, this is calculated as (VT1 – VT2)/ (T1 – T2), dividing the desired sensitivity by the average thermocouple sensitivity.