The working principle and classification of temperature sensors

temperature sensorWorking principle and classification of

1The application principle of temperature sensors, thermocouples, and thermocouples

Temperature sensor Temperature sensor Thermocouple is one of the most commonly used temperature detection components in industry.

Its advantages are:

① High measurement accuracy. Due to the direct contact between the temperature sensor thermocouple and the measured object, it is not affected by the intermediate medium;
② Wide measurement range. The commonly used temperature sensor thermocouples can measure continuously from -50 to+1600 ℃, while some special temperature sensor thermocouples can measure as low as -269 ℃ (such as gold iron nickel chromium) and as high as+2800 ℃ (such as tungsten rhenium);

③ Simple construction and convenient use. Temperature sensor thermocouples are usually composed of two different types of metal wires, and are not limited by size or beginning. They have protective sleeves outside, making them very convenient to use;

1. Basic principle of temperature sensor thermocouple temperature measurement

Soldering two different materials of conductors or semiconductors A and B together forms a closed circuit. When there is a temperature difference between the two attachment points 1 and 2 of conductors A and B, an electromotive force is generated between them, resulting in a current of a certain magnitude in the circuit. This phenomenon is called the thermoelectric effect. The temperature sensor thermocouple utilizes this effect to operate. 2. Types and structure formation of temperature sensor thermocouples

(1) Types of temperature sensor thermocouples

Commonly used temperature sensor thermocouples can be divided into two categories: standard temperature sensor thermocouples and non-standard temperature sensor thermocouples. The so-called standard temperature sensor thermocouple refers to a temperature sensor thermocouple that has a national standard that specifies the relationship between its thermal potential and temperature, allowable errors, and a unified standard graduation table. It has a matching display instrument for selection. Non standardized temperature sensor thermocouples are not as good as standardized temperature sensor thermocouples in terms of usage range or order of magnitude, and generally do not have a unified graduation table. They are mainly used for measurement in certain special occasions. Starting from January 1, 1988, standardized temperature sensor thermocouples and temperature sensor thermal resistors have been produced in accordance with IEC international standards in China. Seven standardized temperature sensor thermocouples, S, B, E, K, R, J, and T, have been designated as temperature sensor thermocouples with unified design in China.

(2) In order to ensure the reliable and stable operation of temperature sensor thermocouples, the structural requirements for temperature sensor thermocouples are as follows:

① The welding of the two thermoelectric electrodes that make up the temperature sensor thermocouple must be firm;

② The two thermoelectric electrodes should be well insulated from each other to prevent short circuits;

③ The connection between the compensation wire and the free end of the temperature sensor thermocouple should be convenient and reliable;

④ The protective sleeve should ensure sufficient isolation between the thermoelectric electrode and harmful media;

3. Temperature compensation for the cold end of temperature sensors and thermocouples

Due to the fact that the materials of temperature sensor thermocouples are generally relatively expensive (especially when using precious metals), and the distance from the temperature measurement point to the instrument is very far, in order to save thermocouple materials and reduce costs, compensation wires are usually used to extend the cold end (free end) of the temperature sensor thermocouple to a control room with relatively stable temperature and connect it to the instrument terminals. It must be pointed out that the function of the temperature sensor thermocouple compensation wire is only to extend the thermoelectric electrode, causing the cold end of the temperature sensor thermocouple to move to the instrument terminal in the control room. It itself cannot eliminate the impact of temperature changes at the cold end on temperature measurement and does not have a compensation effect. Therefore, other correction methods need to be used to compensate for the cold end temperature t0& Ne; The impact on temperature measurement at 0 ℃. When using temperature sensor thermocouple compensation wires, it is necessary to pay attention to the model matching, polarity cannot be connected incorrectly, and the temperature between the compensation wire and the temperature sensor thermocouple connection end cannot exceed 100 ℃.

1、 The application principle of temperature sensor thermocouples

Temperature sensor thermocouple is one of the most commonly used temperature detection components in industry. Its advantages are: ① High measurement accuracy. Due to the direct contact between the temperature sensor thermocouple and the measured object, it is not affected by the intermediate medium. ② Wide measurement range. The commonly used temperature sensor thermocouples can measure continuously from -50 to+1600 ℃, while some special temperature sensor thermocouples can measure up to -269 ℃ (such as gold iron nickel chromium) and up to+2800 ℃ (such as tungsten rhenium).

③ Simple construction and convenient use. Temperature sensor thermocouples are usually composed of two different types of metal wires, and are not limited by size or beginning. They have a protective sleeve outside, making them very convenient to use.

1. Basic principle of temperature sensor thermocouple temperature measurement

Soldering two different materials of conductors or semiconductors A and B together forms a closed circuit. When there is a temperature difference between the two attachment points 1 and 2 of conductors A and B, an electromotive force is generated between them, resulting in a current of a certain magnitude in the circuit. This phenomenon is called the thermoelectric effect. The temperature sensor thermocouple utilizes this effect to operate. 2. Types and structure formation of temperature sensor thermocouples

(1) Types of temperature sensor thermocouples

Commonly used temperature sensor thermocouples can be divided into two categories: standard temperature sensor thermocouples and non-standard temperature sensor thermocouples. The so-called standard temperature sensor thermocouple refers to a temperature sensor thermocouple that has a national standard that specifies the relationship between its thermal potential and temperature, allowable errors, and a unified standard graduation table. It has a matching display instrument for selection. Non standardized temperature sensor thermocouples are not as good as standardized temperature sensor thermocouples in terms of usage range or order of magnitude, and generally do not have a unified graduation table. They are mainly used for measurement in certain special occasions. Since January 1, 1988, standardized temperature sensor thermocouples and temperature sensor thermal resistors have been produced in accordance with IEC international standards in China. Seven standardized temperature sensor thermocouples, S, B, E, K, R, J, and T, have been designated as temperature sensor thermocouples with unified design in China.

(2) Structure form of temperature sensor thermocouple

In order to ensure the reliable and stable operation of the temperature sensor thermocouple, the structural requirements are as follows:

① The welding of the two thermoelectric electrodes that make up the temperature sensor thermocouple must be firm;

② The two thermoelectric electrodes should be well insulated from each other to prevent short circuits;

③ The connection between the compensation wire and the free end of the temperature sensor thermocouple should be convenient and reliable;

④ The protective sleeve should ensure sufficient isolation between the thermoelectric electrode and harmful media;

3. Temperature compensation for the cold end of temperature sensors and thermocouples

Due to the fact that the materials of temperature sensor thermocouples are generally relatively expensive (especially when using precious metals), and the distance from the temperature measurement point to the instrument is very far, in order to save thermocouple materials and reduce costs, compensation wires are usually used to extend the cold end (free end) of the temperature sensor thermocouple to a control room with relatively stable temperature and connect it to the instrument terminals. It must be pointed out that the function of the temperature sensor thermocouple compensation wire is only to extend the thermoelectric electrode, causing the cold end of the temperature sensor thermocouple to move to the instrument terminal in the control room. It itself cannot eliminate the impact of temperature changes at the cold end on temperature measurement and does not have a compensation effect. Therefore, other correction methods need to be used to compensate for the cold end temperature t0& Ne; The impact on temperature measurement at 0 ℃. When using temperature sensor thermocouple compensation wires, it is necessary to pay attention to the model matching, polarity cannot be connected incorrectly, and the temperature between the compensation wire and the temperature sensor thermocouple connection end cannot exceed 100 ℃.

2、 The application principle of temperature sensor thermal resistance

Temperature sensor thermal resistance is the most commonly used temperature detector in the medium to low temperature region. Its main characteristics are high measurement accuracy and stable performance. The measurement accuracy of platinum thermistor is the highest among them. It is not only widely used in industrial temperature measurement, but also made into a standard reference instrument.

1. Principle and Materials of Temperature Sensor Thermal Resistance Temperature Measurement

Temperature sensor thermal resistance temperature measurement is based on the characteristic that the resistance value of a metal conductor increases with the increase of temperature for temperature measurement. Most temperature sensor thermistors are made of pure metal materials, with platinum and copper being the most commonly used. In addition, materials such as platinum, nickel, manganese, and rhodium have now been used to manufacture temperature sensor thermistors. For example, Omega's PT100 temperature sensor includes a 100 ohm platinum resistance temperature probe.

2. Structure of temperature sensor thermal resistance

(1) Proficient temperature sensor thermal resistance

The commonly used temperature sensor thermoelectric resistance temperature sensing element (resistor body) in industry. From the temperature measurement principle of temperature sensor thermoelectric resistance, it can be known that the change in the measured temperature is directly measured through the change in the thermoelectric resistance value of the temperature sensor. Therefore, the change in the resistance of various wires such as the lead wire of the thermoelectric resistance of the temperature sensor will have an impact on temperature measurement. To eliminate the influence of lead resistance, a three wire or four wire system is generally used.

(2) Armored temperature sensor thermal resistance

Armored temperature sensor thermal resistance is a solid body composed of temperature sensing elements (resistors), leads, insulation materials, and stainless steel sleeves. Its outer diameter is generally& Phi; 2~& Phi; 8mm, minimum up to& Phi; Mm. Compared with ordinary temperature sensors, it has the following advantages:

① Small volume, no internal air gap, thermal inertia, and small measurement lag;

② Good mechanical performance, vibration resistance, and impact resistance;

③ Capable of bending and easy installation ④ Long service life;

(3) The end face temperature sensor thermoelectric resistance end face temperature sensor thermoelectric resistance temperature sensing element is wrapped with specially treated resistance wire and tightly adheres to the end face of the thermometer. Compared with general axial temperature sensors, it can more accurately and quickly reflect the actual temperature of the measured end face, and is suitable for measuring the end face temperature of bearing shells and other machinery components.

(4) Flameproof temperature sensor thermal resistance Flameproof temperature sensor thermal resistance uses a special structure of the junction box to limit the explosion of explosive mixed gases inside its casing caused by sparks or arcs to the junction box, and the production site will not cause excessive explosion. The explosion-proof temperature sensor thermal resistance can be used for temperature measurement in explosive hazardous areas within the Bla~B3c level zone.

3. The composition of temperature sensor thermal resistance temperature measurement system is generally composed of temperature sensor thermal resistance, connecting wires, and display instruments. The following two points must be noted:
① The temperature sensor thermal resistance and the graduation number of the display instrument must be consistent;

② In order to eliminate the influence of changes in the resistance of connecting wires, the three-wire connection method must be adopted;