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Thursday 20 September 2018
Posted in Calibrator Information by Pyrosales

Why is it necessary to calibrate a thermocouple?

A thermocouple is a temperature sensor device, used for measuring a broad range of temperatures in a variety of scientific, industrial and even household settings. To effectively use thermocouples to collect accurate data, it is important to calibrate it regularly. Pyrosales offer calibration services including NATA Certification and NATA Traceable certification. Contact us or call 1300 737 976 to organise calibration of your instruments.

What is calibration and why is it important?

In general, regardless of the measuring device you are using, calibration is crucial for ensuring specific and accurate measurements. Calibration defines the quality of your measurements used by particular devices, because over time results can change slightly as the devices age or are affected by a variety of environmental factors.

In order to uphold a high level of confidence, you need to have an ongoing process of regular maintenance and calibration for your equipment and devices. Otherwise you risk slight (or eventually significant) fluctuations in the accuracy of the data being collected, which can have extensive practical implications that you want to actively avoid.

Why should you calibrate your thermocouple?

Made from a pair of wires – made of specific but different metals, thermocouples employ the “Seebeck” or thermoelectric effect to determine temperature differences resulting from voltage measurements between these two electrical conductors. At one end is the “hot / measuring junction” which is connected to the substance needing its temperature measured. The other ends are connected to a “cold / reference junction”, which is a substance with a known and easily measured reference temperature, and here the wires are also connected to copper wires which lead to a meter/display.

The voltage (millivolt/mV) which is used to determine the temperature differences is not actually generated where the metals join, but instead, the voltage is generated along the entire length of the wires between the hot and cold junctions. The measurement voltage is only accurate if each wire is entirely homogeneous, meaning it has a uniform and consistent composition.

In many industrial settings, thermocouple wires tend to lose homogeneity over time, as a result of a variety of factors including chemical exposure or mechanical damage (such as a bent wire). Some types of thermocouple metals are also affected by exposure to temperatures in excess of 200ºC, while others are less easily altered. This is important to note because if a section of the thermocouple circuit is not homogeneous, it can result in a different voltage being generated leading to an overall error in measurement. Consequently, thermocouples require calibration to ensure accurate temperatures are derived.

For thermocouples, calibration specifically refers to the approach of comparing one particular device to another with a known accuracy. By determining your device’s error margin, you then know how to properly calculate temperatures from the voltages being measured. Generally calibration takes place in a lab under carefully controlled and maintained conditions, however, field calibration can also be a quick and effective way of checking the quality of your measurements.

It is essential to check your thermocouples regularly and periodically, to ensure they are appropriately and accurately calibrated to maintain correct, repeatable and high-quality temperature measurements. Pyrosales recommends calibration every 12 months.

 

For more information or if you have any questions, contact us or call 1300 737 976.