Classification of armored thermocouples

Open armoured thermocouple: short thermal response time; Suitable for measuring engine exhaust, etc., requiring fast response temperature measurement; The mechanical strength is low.
Shell-connected armored thermocouple: short thermal response time; high nominal pressure (up to 34MPa); Not suitable for occasions with electromagnetic interference.
Insulated armored thermocouple: Thermal response time is longer than the previous two types, and the service life is long; Anti-electromagnetic interference; This form is often used in occasions where there is no special requirement for thermal response time.
Separate armored thermocouple:  Double branch, avoid signal interference, its characteristics are the same as the insulation type.

Armoured thermocouple structure

The armored thermocouple is mainly composed of junction box, terminal and armored thermocouple components, etc., and is equipped with various installation and fixing devices. The installation fixed type fixing device is for the user to use when installing. Armoured thermocouples have five structural types: no fixed device, fixed ferrule type, movable ferrule type, fixed flange type, and movable flange type. The fixed ferrule type is only for one-time fixed use, and the movable ferrule type can be used for multiple fixed uses.

The working principle of armored thermocouple

Galvanic couples are welded together with two conductors of different compositions. When the two ends have different temperatures, thermoelectric potential will be generated in the loop. Therefore, the electric couple is a kind of temperature sensing element that measures the temperature by measuring the thermoelectric potential. It is a kind of converter, which can convert the temperature signal into an electric signal and then display it by the display instrument.

The basic principle of thermocouple temperature measurement is the thermoelectric effect, which connects two metal conductors of different components end to end into a closed loop. If the temperature of the two junctions is not equal, the thermoelectromotive force will be generated in the loop to form a thermoelectric current, which is the thermoelectric effect. The thermocouple is made by welding one end of two different metal materials. The welded end is called the measurement end, and the unsoldered end is called the reference end. The reference end is usually constant at a certain temperature (such as 00C) during use. When the measurement end is heated, a thermoelectric potential is generated at the junction. If the temperature of the reference terminal is constant, the magnitude and direction of the thermoelectric potential are only related to the characteristics of the two metal materials and the temperature of the measuring terminal, but not to the fineness and length of the potentiometer. When the temperature of the measuring terminal changes, the electric potential also changes, and there is a fixed functional relationship between the temperature and the thermoelectric potential, and the temperature can be measured by using this relationship.

Armoured thermocouple electrodes are conductors of two different components, and the two ends are welded to form a loop. The direct temperature measurement terminal is called the working terminal, and the terminal is called the cold terminal, also called the reference terminal. When there is a temperature difference between the working end and the reference end, a thermal current will be generated in the loop. Connect the display meter, the meter will indicate the corresponding temperature value of the thermoelectromotive force generated by the thermocouple. The thermoelectromotive force of the sheathed thermocouple will increase as the temperature of the measuring terminal increases. The magnitude of the thermoelectromotive force is only related to the material of the thermocouple conductor and the temperature difference between the two ends, and has nothing to do with the length and diameter of the thermoelectrode. The structural principle of the armored thermocouple is that it is made of a conductor, a high-insulation magnesium oxide, and a stainless steel protective tube with an outer jacket, which are drawn as one piece for many times. Armored thermocouple products are mainly composed of junction box, terminal block and armored thermocouple. With various mounting fixtures and components.

Main features of armored thermocouple

Armored thermocouple is the most widely used temperature device in temperature measurement. Its main characteristics are wide temperature measurement range, relatively stable performance, simple structure, good dynamic response, and the ability to transmit 4-20mA electrical signals remotely, which is convenient for automatic control and centralized control. In addition, the thermal response time is short, reducing dynamic errors; Can be bent for installation and use; Large measuring range; High mechanical strength and good pressure resistance are the advantages of armored thermocouples.