Temperature Measurement · Glossary

What is Cold Junction Compensation?

Symbol: CJCreference junction correctionTemperature Measurement

Cold junction compensation corrects a thermocouple reading for the temperature of the terminals where the thermocouple wires end.

Cold Junction Compensation Explained

A thermocouple measures the difference between hot and cold junction. The transmitter measures its terminal temperature, converts it to an equivalent voltage, and adds it before converting to temperature.

Errors appear when the terminal sensor does not see the true terminal temperature, for example in sun or near heat sources.

Cold Junction Compensation Formula

E(T_hot) = E_measured + E(T_cj)

E_measured	voltage at the terminals
E(T_cj)	table voltage at the cold junction temperature

Example: Type K: 3.096 mV measured at 25 °C terminals; add 1.000 mV to get 4.096 mV, which is 100 °C.

Calculators for Cold Junction Compensation

CalculatorThermocouple CalculatorFree online calculator with formula and worked example.CalculatorThermocouple TableFree online calculator with formula and worked example.

Free Downloads

Free downloadRTD and Thermocouple Calibration SOPFree step by step procedure, Word and PDF.Free downloadTemperature Transmitter Calibration SOPFree step by step procedure, Word and PDF.

Frequently Asked Questions

What is Cold Junction Compensation?

Cold junction compensation corrects a thermocouple reading for the temperature of the terminals where the thermocouple wires end.

Can I add the cold junction temperature in °C instead?

Only approximately; add voltages, not temperatures, because the curve is not linear.

How do I test CJC?

Inject the table mV with a calibrator set to the same type with its own CJC, or with copper leads and manual compensation.

Learn more on the blog

Thermocouple calibration: 7 proven steps

A practical guide on instrumentationblog.in with more detail on cold junction compensation and how it is applied on real plants.

Read Full Article

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