Thermocouple calibrations – everything you need to know

Questions about thermocouple calibrations? You’ve come to the right place! Our thermocouple calibration expert, Tom Bates, answers the industry’s commonly asked questions;

What is a thermocouple?

A thermocouple is a type of electrical thermometer which is capable of taking temperature measurements over a wide range of temperatures.

Thanks to their versatility, thermocouples are used in a wide range of applications. Their durability and high temperature limits make them a popular choice for temperature measurement across nearly all industrial markets. While their relatively low cost sees them used within utilities and many domestic appliances.

How does a thermocouple work?

Inside a typical thermocouple you will find two wires made of different metals. These metals are connected together at a measuring point (or junction), which is where the temperature is measured.

When the temperature at the measuring point rises or falls this creates a voltage which is then converted into a temperature reading.

Are there different types of thermocouple available?

Yes, there are many types of thermocouples on the market made with different combinations of metals;

‘Base Metal’ thermocouples (also known as Type J, K, T, N and E) are the most common type of thermocouple. Within this group, K Type thermocouples (often referred to as ‘general purpose thermocouples’) are the most commonly used due to their low cost and wide temperature range which spans -200ᵒC to +1372ᵒC.

‘Noble Metal’ thermocouples (also known as Types R, S and C) can provide accurate readings in high temperature applications. However, these are more expensive than base metal thermocouples as the internal wires are made from higher quality metals.

Why should thermocouples be calibrated?

A thermocouple calculates a temperature reading by measuring the voltage generated along both wires within the device. Crucially, the voltage which is used to determine the temperature is generated along the entire length of each wire, meaning the measurement voltage will only be accurate if each wire is uniform and has a consistent composition.

In many industrial settings thermocouple wires will lose their consistency over time because of the conditions they are exposed to, causing the thermocouple circuit to generate a different voltage and impact the temperature reading.

As the wires are internal, there is no way of knowing if a wire has been compromised without calibrating the thermocouple.

Is it true a thermocouple can’t fall out of calibration?

We’re often asked this by our customers, but actually it’s a common misconception. Although they are very durable, improper or harsh use can impact the accuracy of a thermocouple and the only way to maintain this is through regular calibration.

How often should a thermocouple be calibrated?

We recommend that thermocouples are calibrated once every 12 months to ensure they maintain accurate, repeatable and high-quality temperature measurements.

What happens during a thermocouple calibration?

Thermocouple calibrations take place in a laboratory under carefully controlled and maintained conditions. Most calibration laboratories will use a dry well or water bath to perform thermocouple calibrations as these can be set to mimic the various temperatures the thermocouple under test would usually be subject to.

The thermocouple under test is placed in the dry well or water bath with a reference thermocouple belonging to the calibration laboratory. A temperature reading is taken from both thermocouples at various test points and the results are compared to highlight any discrepancies.

After the calibration is complete, the thermocouple is returned with a calibration certificate which details the test performed and the results.

Who offers thermocouple calibrations?

We offer calibrations on a range of temperature equipment, including thermocouples. All calibrations are performed at our calibration laboratory in Birmingham.

Are there any questions we’ve not answered?

We hope that’s answered any questions you have about thermocouple calibrations. If there’s something we’ve not covered, leave a question in the box below and Tom will get back to you.