THE Thermocouples sensors come into the composition of temperature probes used in many professional sectors. It is a technology that is both easy to use and economical. It also offers a short response Thermal variations. The different Types of thermocouples cover more or less extensive temperature beaches with variable precision.
To identify the thermocouple Best to your field of application and your budget, it is essential to understand how it works and distinguish its typologies.
What is a thermocouple?
THE thermocouple is one of the two main types of temperature sensors The most widespread.
- THE thermocouple allows the temperature to be measured by calculating a tension difference Between two points, based on a thermoelectric principle.
- The second category, the Temperature sensor with thermistor, uses a thermoreistive principle, based on resistance variation Materials.
The operation of the thermocouple
A thermocouple, or thermoelectric torque, consists of two wires in conductive metals Different connected by two types of welds: The hot spot and the cold point. A electrical voltage is created when the hot junction undergoes a temperature change. This is called The thermoelectric effect Seebeck.
A voltmeter Allows to measure the potential difference Between hot welding and cold welding. Then a temperature transmitter converts this data into Celsius degrees thanks to a reference table, which depends on Thermocouple type used.
Maintaining the temperature of the reference junction
So that the Thermocouple probe provides precise information, the cold welding must be at a stable temperature. Several compensation methods exist, in particular the icy water bath and the use of a Second measurement instrument To adjust the temperature.
If there distance between the measurement point and the device is important, a extension cable or a compensation cable may be necessary.
The types of normalized thermocouples
THE thermocouples are made with various metals, but 8 main types are standardized according to the CEI standard 60584.1.
The most used thermocouples types
- The type K (Nickel-chrome / nickel-aluminum) is the most widespread in the industry, measuring -200 to 1200 ° C.
- Type J (Iron / Constantan) is useful in a reducing environment, operating from -40 to 750 ° C.
- Type T (Copper / Constantan) is stable and adapted to low temperatures (-185 to 300 ° C).
- The type E (Nickel-Chrome / Constantan) is recommended for vacuum and inert gas environments.
The types of thermocouples for high temperatures
- Type n (Nickel-Chrome-Silicon / Nickel-Silicium) supports temperatures above 1280 ° C.
- The type S and R (Rhodied / platinum plate) are used to measure beyond 1000 ° C.
- Type B (Rhodied platinum 30 % / Rhodié platinum 6 %) can measure up to 1700 ° C.
