Temperature sensors Thermocouples are one of the most commonly used temperature sensing devices in the industry. The advantages are:
① high measurement accuracy. Because the temperature sensor thermocouple directly contact with the measured object, not subject to the impact of intermediate media.
② measuring a wide range. Commonly used temperature sensor thermocouple from -50 ~ + 1600 ℃ can be continued measurement, some special temperature sensor thermocouple can be measured to a minimum of -269 ℃ (such as gold and iron nickel-chromium), up to +2800 ℃ (such as tungsten - rhenium ).
③ simple structure, easy to use. Temperature Sensor Thermocouple is usually composed of two different metal wire, and not subject to the size and the beginning of the restrictions, outside the protective sleeve, with very convenient.

1. Temperature sensor thermocouple temperature measurement basic principle
Two different materials of the conductor or semiconductor A and B welded together to form a closed loop, as shown in Figure 2-1-1. When there is a temperature difference between the two attachment points 1 and 2 of the conductors A and B, an electromotive force is generated therebetween, thereby forming a current of a large magnitude in the circuit. This phenomenon is called a thermoelectric effect. Temperature Sensor Thermocouple is the use of this effect to work.

2. Type of Temperature Sensor Thermocouple and Structure Forming

(1) Temperature sensor The type of thermocouple
Commonly used temperature sensor Thermocouple can be divided into standard temperature sensor thermocouple and non-standard temperature sensor thermocouple two categories. Called standard temperature sensor Thermocouple is the national standard provides the relationship between the thermoelectric power and temperature, allowing the error, and a unified standard temperature sensor table thermocouple, which has its supporting display instrument available. Non-standardized temperature sensor thermocouple in the use of the scope or magnitude are less than the standardization of temperature sensor thermocouple, generally there is no uniform indexing table, mainly for some special occasions. Standardized temperature sensor thermocouple China from January 1, 1988 onwards, the temperature sensor thermocouple and temperature sensor thermal resistance all according to IEC international standards of production, and specify the S, B, E, K, R, J, T seven standardized temperature Sensor thermocouple for our unified design temperature sensor thermocouple.

(2) temperature sensor thermocouple structure In order to ensure that the temperature sensor thermocouple reliable and stable work, its structural requirements are as follows:
① composition of the temperature sensor thermocouple of the two hot electrodes welding must be strong;
② two hot electrodes should be well insulated from each other to prevent short circuit;
③ compensation wire and the temperature sensor thermocouple free end of the connection to be convenient and reliable;
④ protective sleeve should be able to ensure adequate separation of the hot electrode and harmful media.

3. Temperature Compensation of Temperature Sensor Thermocouple Cold End
As the temperature sensor thermocouple materials are generally more valuable (especially when using precious metals), and the temperature measurement point to the instrument are far away, in order to save the thermocouple materials, reduce costs, usually using the compensation wire to the temperature sensor thermocouple The cold end (free end) extends into the temperature-controlled control room and is connected to the meter terminals. It must be pointed out that the role of the thermocouple compensation wire of the temperature sensor only serves to extend the hot electrode so that the cold end of the thermocouple of the temperature sensor is moved to the meter terminal of the control room, which itself can not eliminate the effect of the temperature change of the cold end on the temperature measurement. From the compensation effect. Therefore, the need to use other correction methods to compensate for the cold side temperature t0 ≠ 0 ℃ on the temperature measurement.
In the use of temperature sensor thermocouple compensation wire must pay attention to the model match, the polarity can not take the wrong, compensation wire and temperature sensor thermocouple junction temperature can not exceed 100 ℃.

Second, the temperature sensor thermal resistance of the application principle

Temperature sensor Thermal resistance is the most commonly used in the low temperature zone of a temperature detector. Its main characteristic is the measurement accuracy is high, the performance is stable. Platinum heat resistance is the highest measurement accuracy, which is widely used not only in industrial temperature measurement, and was made into a standard benchmark.

1. Principle and Material of Thermal Resistance Temperature Measurement of Temperature Sensor
Temperature sensor thermal resistance temperature measurement is based on the metal conductor resistance increases with the temperature of this feature to increase the temperature measurement. Temperature sensor thermal resistance mostly from pure metal materials, is currently the most widely used platinum and copper, in addition, has now begun to use Austin, nickel, manganese and rhodium materials such as temperature sensor thermal resistance.

2. Structure of thermal resistance of temperature sensor

(1) proficient temperature sensor thermal resistance industrial commonly used temperature sensor thermal resistance temperature components (resistance) structure and characteristics of the table 2-1-11. From the temperature sensor thermistor temperature measurement principle, we can see that the measured temperature change is directly through the temperature sensor thermal resistance changes to measure, therefore, the temperature sensor thermal resistance of the lead wire and other wire resistance changes will give Temperature measurement. In order to eliminate the influence of the lead resistance, the same applies to the three-wire system or four-wire system, the specific content of the third chapter of this chapter,

(2) armored temperature sensor thermal resistance armored temperature sensor thermal resistance by the temperature sensing element (resistor body), lead, insulation, stainless steel casing made of a combination of solid body, as shown in Figure 2-1-7, Its diameter is generally φ2 ~ φ8mm, the smallest up to φmm.
It has the following advantages compared with the common type thermal sensor thermal resistance: ① small volume, no internal air gap, thermal inertia, small measurement hysteresis; ② good mechanical performance, resistance to vibration and shock; ③ bending, easy to install ④ use long life.

(3) End face temperature sensor Thermal resistance end face temperature sensor Thermal resistance temperature sensing element is made of specially processed resistance wire material, which is close to the end face of the thermometer. Its structure is shown in Figure 2-1-8. Compared with the general thermal resistance of the axial temperature sensor, it can more accurately and quickly reflect the actual temperature of the measured end, suitable for measuring the bearing and other parts of the end surface temperature.

(4) flameproof temperature sensor thermal resistance flameproof temperature sensor thermal resistance through the special structure of the junction box, the explosive gas mixture within the shell due to the impact of sparks or arc explosion limited to the junction box, the production site is not Will lead to super-explosion. Flameproof temperature sensor thermal resistance can be used for Bla ~ B3c-class region with explosive temperature of the temperature measurement.

3. The Composition of Thermal Resistance Temperature Measurement System of Temperature Sensor

Temperature sensor Thermal resistance temperature measurement system generally consists of temperature sensor thermal resistance, connecting wires and display instruments and other components. Must pay attention to the following two points:

① temperature sensor thermal resistance and display the sub-degree number must be consistent

(2) In order to eliminate the influence of the change of resistance of the connecting wire, the three-wire connection method must be adopted. See the third chapter of this chapter.

(2) armored temperature sensor thermal resistance armored temperature sensor thermal resistance by the temperature sensing element (resistor body), lead, insulation, stainless steel casing made of a combination of solid body, as shown in Figure 2-1-7, Its diameter is generally φ2 ~ φ8mm, the smallest up to φmm. It has the following advantages: ① small size, no internal air gap, thermal inertia, the measurement of small hysteresis; ② good mechanical properties, resistance to vibration, impact, ③ bending, easy to install ④ use long life.

(3) End face temperature sensor Thermal resistance end face temperature sensor Thermal resistance temperature sensing element is made of specially processed resistance wire material, which is close to the end face of the thermometer. Its structure is shown in Figure 2-1-8. Compared with the general thermal resistance of the axial temperature sensor, it can more accurately and quickly reflect the actual temperature of the measured end, suitable for measuring the bearing and other parts of the end surface temperature.

(4) flameproof temperature sensor thermal resistance flameproof temperature sensor thermal resistance through the special structure of the junction box, the explosive gas mixture inside the shell due to the spark or arc and other resistors of the broken circuit repair must change the length of the resistance wire Affect the resistance value, for the replacement of the new resistor as well, if the use of welding repair, after welding to check the qualified before use