Thermocouple is a very widespread temperature sensor in the industry, with its versatility, its short response time and its advantageous cost. Manufacturers recommend performing tests throughout the life of the sensor, to ensure its good calibration. This operation involves a good understanding of the mechanisms of thermocouple. How does a thermocouple work? When should you test a thermocouple and in what way? We answer your questions in this detailed guide.
The operation of the thermocouple
What is the Seebeck effect?
The thermoelectric effect Seebeck is The appearance of a slight electric current. This happens in the event of a temperature variation Within an open circuit formed by two different nature metals connected at one point. This magnetic phenomenon, discovered by the German physicist Thomas Johann Seebeck in 1821, is at the source of several applications. The Seebeck effect has led to the creation of temperature measurement tools, but also, more marginal, electricity generators by thermoelectric effect.
What is the constitution of a thermocouple?
Thermocouple East A type of sensor which contains two wires of conductive metal alloys. It has two types of welds. Hot welding, or hot spot, connects the two sons between them at one end. This is this point in contact with the environment whose temperature is measured. The second type of welding, the cold point, is the one that connects each wire to the measuring device. For practical reasons, it is possible to place connection cables in order to create an extension between these junctions and the display via an element called connector.
How does a thermocouple sensor work?
When the hot spot is exposed to a different temperature of the cold point, an electrical voltage is created in the thermocouple. This electro-motor force (FEM) expressed in Ohms depends on the temperature. The conversion between the FEM and the temperature is done thanks to conversion tables also presented in the form of Thermocouple curves depending on the type. It is the nature of metals or metal alloys used for manufacturing that defines the Thermocouple type, taking into account their own conductivity. These tables use the principle that the cold point is 0 ° C. When at room temperature, a differential calculation must be made to calculate the real tension to convert.
Where do we use thermocouples?
There Thermocouple probe is a temperature measurement instrument. It is very useful For scientific and industrial applications. Companies in these areas also use probes to resistance sensor and in the infrared thermometer according to their needs. The highlight of thermocouple is its low cost for the most common models. This type of probe allows you to perform Measures ranging from very low to very high temperatures. As it works via a potential difference, it is possible to measure the temperature automatically. It is then possible to program a temperature measurement at regular intervals without human intervention thanks to a recorder.
What you need to know to test a thermocouple
What is a thermocouple test?
Testing a thermocouple temperature sensor is the First stage of the probe calibration of measurement. This type of test is to check the correlation between the electric current noted by the measurement device at a given temperature and the theoretical correspondence appearing in the Thermocouples conversion table.
Test and test proceduresThermocouples calibration are the subject of recommendations issued by the ASTM (American Society for Testing and Materials), a world recognized organization. By following their advice, it is not enough to measure a single temperature unit during the test. It's necessary Repeat the operation at different temperatures. Indeed, each type of thermocouple is planned to measure the temperature on a specific temperature range.
When to test a thermocouple?
As we have just seen, the Thermocouple test accompanies calibration. The latter is done in several cases :
- After its manufacture and before its sale.
- If in doubt about the accuracy of the measures.
- When changing the temperature probe.
- Regularly, throughout the life of the probe, at a frequency depending on the wear caused by the environment to which it is exposed.
Once the test is done on different points within the thermocouple measurement range, the results can highlight a temperature difference compared to the conversion tables. Then added a corrective coefficient When calculating conversion voltage/temperature.
What are the techniques to test a thermocouple?
To test a thermocouple, we use two main methods, the test by comparison and the fixed point test. The first is to Compare the temperature indicated by the thermocouple sensor to that obtained by another temperature sensor placed in the same environment which serves as a controller. It is then recommended to use another more precise type of sensor. The environment where these sensors are located must have a stable and homogeneous temperature.
During the fixed points test, The hot thermocouple sensor welding is exposed to a known temperature safe and precise. By following the international temperature scale of 1990, the generally used principle is the triple point of water. It is a temperature of 0.01 ° C. To which water is equal to its three states: liquid, sparkling and solid.
At Thermometre.fr, The quality of our products and services is one of our priorities. During the order process, after having determined your needs and created prototypes. We make sure to provide you with the messes that allow the sensors to be tested on your equipment. We benefit Quality certifications ISO 9001 since 2013 and ISO 14001 since 2023.
Go further on thermocouples:
- Category of thermocouples probes
- What are the different types of thermocouples
- Calibration of a thermocouple
- How do we measure the temperature by thermocouple?
- Thermocouples response time by type
- The thermocouples curves by type
- Thermocouples measurement range
- Thermocouples conversion table
- How does a thermocouple work?
- Thermocouples
