How do you calibrate a thermocouple?

Answer 1

Usually, you don't have to calibrate a thermocouple. You just use the conversion equation, based on the type of thermocouple (eg B, J, K, etc), to convert the output voltage to a temperature. In my experience, this is quite accurate. My temperature usually only fluctuates 0.1 C or so.

If I had to calibrate a thermocouple, I would build a calibration model with the voltage on the Y axis and temperature on the X axis. Measurements can be made using a heated water bath and an accurate thermometer. Also, you could measure a the boiling and/or freezing point of a series of pure solvents where those temperatures are well known at STP.

Thermocouples & Kiln Control Offset Features

The above information is sound; however, I'd like to add to it.

If you have a computer-controlled kiln, e.g., as is used for pottery making, it is helpful to know how to offset the reading the controller registers from the thermocouple ("output voltage to a temperature").

See the related link listed below titled:

"Computer-Controlled Thermocouple Calibration"

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A thermocouple does not measure temperature, but measures temperature difference between two points. The points are sometimes called the "hot" or measurement junction and "cold" or reference junction. If the reference junction is not at 0 degrees C, you have to measure the temperature of the reference junction and convert that to an offset voltage, which is added to the sensed voltage. Both equations: temperature to voltage and voltage to temperature are non-linear high order polynomials and depend on the type of thermocouple being used. Instead of an equation, pre-computed tables can be used.

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Thermocouple calibration procedure.

The thermocouple validation procedure is widely used for all furnaces and also in heating equipment. Thermocouples are non-adjustable measuring devices, so we cannot calibrate them. However, we can validate functioning for a range of temperature through using a thermocouple calibration bath.

Thermocouple Calibration Procedure

Generally we use a temperature controller or SCADA to indicate thermocouple temperature. To validate thermocouple temperature on the display, we measure mV at the thermocouple end and by using standard ASTM E230-03 (Standard Specification and Temperature-Electromotive Force (EMF) Tables for Standardized Thermocouples”) we can obtain Temperature in degrees Centrigrade at a particular furnace location. We want to ensure that the same temperature will be displayed on SCADA or indicator and deviation, if any, will be recorded accordingly.

Thermocouple calibration and validation procedure article: click here http://www.brighthub.com/engineering/electrical/articles/122510.aspx