What is a thermocouple temperature sensor?

Thermocouple temperature sensor measurement is the most widely used in many temperature measurement methods. Because it has a wide range of measurements, between 180°C ~ 2800°C, the accuracy and sensitivity are high, and it is convenient for long distance measurement, especially in the range of high temperature. Therefore, the international practical temperature standard stipulates that the thermocouple is used as the reference instrument for the reappearance of thermodynamic temperature standard in the range of 630. 74°C and 1064. 43°C.

(1) Basic principles

Two kinds of different conductors, A and B end fusion welding, are called the hot end (or the temperature measuring end), the other end is connected with a sensitive voltmeter, and the end of the voltmeter is called the cold end (or the reference end). When the temperature of the hot end and the cold end is different, the electric potential will be generated in the loop. The direction and size of the electric potential are taken from the type of material of the two conductor and the temperature difference between the hot end and the cold end (the difference between T and TD), which is not related to the thickness and length of the two conductor, which is called the thermoelectric effect of the object.

In order to accurately measure the temperature of the hot end, the temperature at the cold end must be determined. At present, the temperature of the cold end is Tp=0°C. However, it is not convenient to maintain the cold end at 0 °C when the actual test is carried out. The cold end compensation is needed for the group to measure at room temperature. The thermoelectric potential generated by thermocouple is very small.It usually needs amplification by amplifier.

The electromotive force generated by the thermocouple is amplified by the amplifier A1 with a certain sensitivity ( mV / °C ), and the temperature of the cold end is detected by the PN junction temperature sensor and the measuring bridge, the output of the bridge is amplified by amplifier A2 and has the same sensitivity as the thermocouple. When the amplified signal voltage is re-fed to a differential amplifier circuit with a gain of 1, the error caused by the temperature change at the cold end can be automatically compensated. At 0°C, adjust the Rp, so that the A2 output is 0V; adjust RF2, so that the sensitivity of A2 output can be the same as A1. Generally, the compensation accuracy is better than 0.5°C in the range of 0°C ~ 50°C. Among these thermocouples, the CK type thermocouple is the most widely used. This is because the thermal potential is high, the characteristic is approximately linear, the performance is stable, the price is cheap ( no noble metal platinum and rhodium ), and the temperature measuring range is suitable for most industrial temperature range .

( 2 ) Structure of thermocouple

1)Hot electrode.

 It's the two wires that make up the thermocouple. The diameter of the hot electrode is from 0.3 to 3.2 mm and the length is 350 mm ~ 2m, depending on the type of metal and the conditions of action. It should be noted that the hot electrode is also made of non-metallic materials.

2)Insulating tube.

It is used to prevent short circuit of two hot electrodes. The insulating tube can be made into a single hole, a double hole and a four-hole form, or can be made into a filling form ( such as a cable thermocouple ).

3)Protection tube.

In order to make the thermocouple have a longer life and ensure the measuring accuracy, the hot electrode ( together with the insulating tube ) is usually installed in the protection tube, which can not only reduce various harmful the direct erosion of gases and harmful substances can also avoid the direct impact of flame and air flow.

4)Junction box is selected according to the temperature range of the heating zone and the environment atmosphere.

The junction box is used for connecting thermocouples and compensation wires, and is mostly made of aluminum and gold. In order to prevent harmful gas from entering thermocouple, the outlet and cover of the junction box should be sealed as far as possible (-like rubber, asbestos gasket, gasket and refractory mud, etc. ) . The hot electrode in the junction box and the compensating conductor are fastened on the connection board to ensure good contact. There are positive and negative markings at the junction for checking and wiring.

If you want to know more, our website has product specifications for the sensors, you can go to ALLICDATA ELECTRONICS LIMITED to get more information