Whatever their field of application, temperature measurement devices need to be calibrated in order to offer good precision. There Thermocouple probe is useful for raising the temperature on large measurement ranges in industry, food or transport. The calibration of the thermocouple measurement devices is carried out by following different stages in order to ensure the concordance between the emitted signal and the measured temperature.
What is the calibration of a thermocouple?
To tackle the question of calibration, it is necessary to recall The operation of the thermocouple. This type of temperature sensor contains Two conductive metals wires of dissimilar natures. One of their ends is connected, generally thanks to a weld. When the hot spot is exposed to a temperature variation, A tension is created within the wires. The other end, the cold point, is connected to a measurement instrument that will allow Calculate the temperature. Thermocouples are very useful in industry thanks to their reasonable price and the wide range of temperature they cover.
The calibration of a measurement apparatus is to ensure that it gives precise indications and correcting the errors raised. Many factors related to the environment cause wear. Oxidizing or pressurized environments can decalibrate the thermocouple. The verification of the probe also involves a Measuring device test. Finally, it is sometimes possible that the connection cables alter the measurement values. Test all the constituent elements of the probe Thermocouple as well as the quality of their connection is a recommendation.
When to calibrate a thermocouple?
Thermocouples are calibrated The first time by the manufacturer. The calibration of the instruments is then necessary:
- When the temperature probe is assigned to a new environment to be measured;
- When change of assignment measurement probe;
- In case of suspicion of inaccurate results ;
- Regularly, at a frequency which depends on the wear induced by its environment.
How to calibrate a thermocouple sensor?
The calibration procedure for a thermocouple is done By exposing the hot junction of the sensor to a known temperature. If the temperatures noted are not correct, it will be necessary to adjust the temperature calculation by adding a corrective coefficient.
To calibrate the thermocouple, you must first Make sure the probe is not damaged or soiled. It is also necessary to have adequate equipment. Calibration can be carried out internally or entrusted to a provider. It may be financially advantageous to equip yourself with calibration equipment.
Two main techniques Allow a thermocouple probe to calibrate: comparison calibration and calibration in fixed points.
Comparison calibration
This technique is widely used in the industry. Comparison calibration consists in placing the probe to calibrate and another standard probe in an environment where the temperature is stable and homogeneous. The type of probe chosen as a standard must offer greater precision. The heated medium is usually a dry well, a bath or a tube oven.
Fixed points calibration
The technique in fixed points consists in exposing the hot welding of thermocouple to an environment whose temperature is known with certainty. The principle used is that of triple point According to the international temperature scale of 1990. The triple point of water is 0.01 ° C and allows a very precise measurement.
Interpretation of calibration data
The ASTM (American Society for Testing and Materials) has issued recommendations to standardize the control measure. It is necessary Calculate the errors from the output voltage Thermocouples thanks to standard tables. Calibration is a long process since it is necessary Test the probe on its entire measurement range.
Go further on thermocouples
To deepen the subject, discover other articles on:
- The different types of thermocouples
- How do we measure the temperature by thermocouple?
- Thermocouples response time
- The thermocouples curves
- How to test a thermocouple?
- Thermocouples measurement range
- Thermocouples conversion table
- The operation of the thermocouple
