THE thermocouples are very widespread temperature sensors in the industry. They are robust, offer a quick response and can measure high temperatures. THE Thermocouple temperature sensor is a measurement system that comes into contact with the environment, unlike the infrared thermometer. It can be immersed in a liquid or gas and connected to a temperature recorder. To understand its functioning, you must first be interested in its composition and the thermal measurement method used.
The Thermocouple probe uses electro-motor strength
THE Thermocouple temperature sensor contains two metal sons connected to one end, called hot welding. The other end is connected to the measurement box via the cold junction.
When the hot welding undergoes a temperature change, a low electric current is generated. This electro-motor force (FEM) is proportional to the temperature of the measurement point. We use Thermocouples conversion tables To establish the correspondence between the measured current and the temperature.
How to choose the materials that constitute a thermocouple probe?
There temperature measurement range varies according to the metals used. This difference depends on the conductivity of the alloys of the couple's threads, classified according to their Thermocouple type.
Of the connection cables are used between the threads of the thermocouple and the measuring devices without distorting the results, thanks to the Intermediate metal law. This principle guarantees that the fem does not change, even with the addition of a third homogeneous driver.
How to ensure the temperature measurement accuracy of the thermocouple?
Two elements are essential: compensation for the cold welding and thecalibration regular probe.
Cold welding compensation
The measured electric current depends on the temperature difference between the hot welding and the cold welding. Several methods exist:
- Maintain it Cold welding at 0 ° C By placing it in an ice water bath.
- Use a calibration oven which maintains a stable temperature.
- Leave it Cold weld at room temperature and perform a differential calculus To determine the exact temperature.
Measuring instruments can directly compensate.
Calibrate the thermocouple probe
THE Thermocouple calibration is done after manufacture and each change of use. It is also recommended in case of dysfunction.
Two main methods exist:
- Comparison calibration : comparison with another reference probe.
- Fixed points calibration : exposure to a specific temperature like 0.01 ° C (triple point of water).
Thermal measurement in industry
In the industry, many processes require a temperature sensor. THE thermocouple is widely used for his quick response time, its affordable cost and its ability to measure high temperatures.
THE Thermistor sensors are also common and measure the temperature as a function of the Material resistance. Finally, the gas or liquid dilation thermometers offer great precision, but a more limited measurement range.
