Product Name: wzpm-201 thermal resistance wzpm-201 thermal resistance




Product No.: 153443-226
Product model: wzpm-201
Updated on: June 25, 2009
Manufacturer: thermocouple, thermal resistance, bimetal thermometer, polytetrafluoroethylene, PTFE gasket -- Shanghai Feilong instrument and Electrical Co., Ltd
Ordering notice: temperature probe and compensation wire can be customized according to the needs of customers
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Product details
Working principle of thermal resistance
Thermal resistance is the most commonly used temperature detector in the middle and low temperature region. Its main characteristics are high measurement accuracy and stable performance. Among them, the measurement accuracy of platinum thermal resistance is the highest. It is not only widely used in industrial temperature measurement, but also made into a standard reference instrument.
Different from the temperature measurement principle of thermocouple, the thermal resistance measures the temperature based on the thermal effect of resistance, that is, the resistance value of resistance body changes with the change of temperature. Therefore, the temperature can be measured as long as the resistance change of the thermal resistance is measured. At present, there are mainly two types: metal thermistor and semiconductor thermistor.
The resistance value and temperature of metal thermal resistance can be expressed by the following approximate relation, namely
Rt=Rt0[1+α（t-t0）]
Where RT is the resistance at temperature T, RT0 is the corresponding resistance at temperature t0 (usually t0 = 0 ℃), and α is the temperature coefficient.
The relationship between resistance and temperature of semiconductor thermistor is
Rt=AeB/t
Where RT is the resistance at temperature T; a and B depend on the constant of the structure of the semiconductor material.
In comparison, the temperature coefficient of thermistor is larger, and the resistance value at room temperature is higher (usually more than thousands of ohms), but the interchangeability is poor and the nonlinearity is serious. The temperature measurement range is only about - 50 ~ 300 ℃, which is widely used in temperature detection and control of home appliances and automobiles. Metal thermal resistance is generally suitable for temperature measurement in the range of - 200 ~ 500 ℃, which is characterized by accurate measurement, good stability and reliable performance, and is widely used in process control.
Thermal resistance material
Thermal resistance temperature measurement is based on the characteristic that the resistance value of metal conductor increases with the increase of temperature. At present, platinum and copper are the most widely used materials. In addition, nickel, manganese and rhodium have been used to make thermal resistance.
Type of thermal resistance
(1) Precision thermistor: the structure and characteristics of industrial common thermistor temperature sensing elements (resistors). It can be seen from the temperature measurement principle of thermal resistance that the change of measured temperature is directly measured by the change of the value of thermal resistance. Therefore, the change of the resistance of various wires such as the outgoing line of thermal resistance body will affect the temperature measurement. In order to eliminate the influence of lead resistance, three wire system or four wire system are generally used.
(2) Armored thermal resistance: armored thermal resistance is a solid body composed of temperature sensing element (resistance body), lead wire, insulating material and stainless steel sleeve. Its outer diameter is generally φ 2 ~ φ 8mm, and the minimum can be φ mm. Compared with the ordinary thermistor, it has the following advantages:
① Small volume, no air gap inside, small measurement lag in thermal inertia;
② Good mechanical properties, vibration resistance, impact resistance;
③ Able to bend, easy to install;
④ Long service life.
(3) End thermal resistance: the end thermal resistance and temperature sensing element is wound with specially treated resistance wire and is close to the end surface of the thermometer. Compared with the general axial thermal resistance, it can more accurately and quickly reflect the actual temperature of the measured end face, which is suitable for measuring the end face temperature of bearing shells and other parts.
(4) Explosion proof thermal resistance: the explosion-proof thermal resistance is limited in the junction box through the junction box with special structure, and the explosion of explosive gas mixture inside the shell due to the influence of sparks or electric arc will not lead to super explosion at the production site. The flame-proof thermal resistance can be used to measure the temperature in the area of BLA ~ B3c with explosion risk.




Metal thermistor commonly used in industry
From the change of resistance with temperature, most of the metal conductors have this property, but not all of them can be used as thermoelectric resistance. As a general requirement of the metal materials for thermoelectric resistance, they should be as large and stable as possible in temperature coefficient, resistivity should be large (reduce the size of the sensor under the same sensitivity), have stable chemical and physical properties within the temperature range of use, material Good reproducibility, the resistance value with the temperature change to have a value function relationship (preferably linear relationship).

　　At present, the most widely used thermal resistance materials are platinum and copper: platinum resistance has high accuracy, is suitable for neutral and oxidizing media, has good stability, has certain nonlinearity, the higher the temperature, the smaller the resistance change rate; copper resistance in the temperature range has a linear relationship with the temperature, and has a large number of temperature lines, which is suitable for non corrosive media, more than 150 is easy to be oxidized. The most commonly used ones in China are R0 = 10 Ω, R0 = 100 Ω and R0 = 1000 Ω. Their graduation numbers are pt10, PT100 and PT1000 respectively. The copper resistances are R0 = 50 Ω and R0 = 100 Ω, and their graduation numbers are cu50 and cu100. PT100 and cu50 are widely used.
Signal connection mode of thermal resistance
Thermal resistance is a primary element that converts temperature change into resistance change. It is usually necessary to transmit resistance signal to computer control device or other primary instrument through lead wire. There is a certain distance between the industrial thermistor and the control room when it is installed in the production site, so the lead of the thermistor will have a great influence on the measurement results.




At present, there are three main ways to lead the thermal resistance
Two wire system: two wire system refers to the method of connecting a wire at both ends of the thermal resistance to lead out the resistance signal: this lead method is very simple, but there must be a lead resistance R in the connecting wire. The size of R is related to the material and length of the wire, so this lead method is only applicable to the occasions with low measurement accuracy
Three wire system: the method of connecting one lead wire at one end of the root of the thermal resistance and two leads at the other end is called three wire system. This method is usually used together with the bridge, which can better eliminate the influence of the lead wire resistance. It is the most commonly used lead wire resistance in industrial process control.
Four wire system: the method of connecting two wires at both ends of the root of the thermal resistance is called four wire system. Two wires provide a constant current I for the thermal resistance, convert r into a voltage signal U, and then lead u to the secondary instrument through the other two wires. It can be seen that this kind of lead mode can completely eliminate the influence of lead resistance and is mainly used for high-precision temperature detection.




The thermal resistance is connected by three wire system. The three wire system is used to eliminate the measurement error caused by the resistance of connecting wires. This is because the circuit for measuring the thermal resistance is generally an unbalanced bridge. As a bridge arm resistance of the bridge, its connecting wire (from the thermal resistance to the central control room) also becomes a part of the bridge arm resistance, which is unknown and changes with the ambient temperature, resulting in measurement errors. With the three wire system, one wire is connected to the power supply end of the bridge, and the other two wires are connected to the bridge arm where the thermal resistance is located and the adjacent bridge arm, so as to eliminate the measurement error caused by the wire line resistance. Generally, three wire system is adopted in industry. Thermocouples produce millivolt signals, and there is no such problem.
Composition of thermal resistance temperature measurement system
(1) Thermal resistance temperature measurement system is generally composed of thermal resistance, connecting wire and display instrument. The following two points must be noted:
① The graduation number of thermal resistance and display instrument must be the same
② In order to eliminate the influence of the change of the resistance of the connecting wire, the three wire connection method must be adopted. Please refer to Chapter 3 for details.
(2) Armored thermal resistance armored thermal resistance is a solid body composed of temperature sensing element (resistance body), lead wire, insulating material and stainless steel sleeve. Its outer diameter is generally φ 2 ~ φ 8mm, and the minimum can be φ mm. Compared with the ordinary thermistor, it has the following advantages:
① Small volume, no air gap inside, small measurement lag in thermal inertia;
② Good mechanical properties, vibration resistance, impact resistance;
③ Can be bent, easy to install
④ Long service life.
(3) The end surface thermal resistance end surface thermal resistance temperature sensing element is made of specially treated resistance wire and is closely attached to the end surface of the thermometer. Compared with the general axial thermal resistance, it can more accurately and quickly reflect the actual temperature of the measured end face, which is suitable for measuring the end face temperature of bearing shells and other parts.
(4) Through the special junction box, the explosion-proof type thermal resistance will change the length of the resistance wire and affect the resistance value due to the open circuit repair of the explosive gas mixture inside the shell due to the spark or arc shadow resistance body. Therefore, it is better to replace the new resistance body. If the welding repair is adopted, it can be used only after the verification is qualified.
The difference between thermocouple and thermal resistance
Both thermocouple and thermal resistance belong to the contact temperature measurement in temperature measurement. Although their functions are the same as measuring the temperature of objects, their principles and characteristics are different

　　At present, the most widely used thermal resistance materials are platinum and copper: platinum resistance has high accuracy, is suitable for neutral and oxidizing media, has good stability, has certain nonlinearity, the higher the temperature, the smaller the resistance change rate; copper resistance in the temperature range has a linear relationship with the temperature, and has a large number of temperature lines, which is suitable for non corrosive media, more than 150 is easy to be oxidized. The most commonly used ones in China are R0 = 10 Ω, R0 = 100 Ω and R0 = 1000 Ω. Their graduation numbers are pt10, PT100 and PT1000 respectively. The copper resistances are R0 = 50 Ω and R0 = 100 Ω, and their graduation numbers are cu50 and cu100. PT100 and cu50 are widely used.
Signal connection mode of thermal resistance
Thermal resistance is a primary element that converts temperature change into resistance change. It is usually necessary to transmit resistance signal to computer control device or other primary instrument through lead wire. There is a certain distance between the industrial thermistor and the control room when it is installed in the production site, so the lead of the thermistor will have a great influence on the measurement results.




At present, there are three main ways to lead the thermal resistance
Two wire system: two wire system refers to the method of connecting a wire at both ends of the thermal resistance to lead out the resistance signal: this lead method is very simple, but there must be a lead resistance R in the connecting wire. The size of R is related to the material and length of the wire, so this lead method is only applicable to the occasions with low measurement accuracy
Three wire system: the method of connecting one lead wire at one end of the root of the thermal resistance and two leads at the other end is called three wire system. This method is usually used together with the bridge, which can better eliminate the influence of the lead wire resistance. It is the most commonly used lead wire resistance in industrial process control.
Four wire system: the method of connecting two wires at both ends of the root of the thermal resistance is called four wire system. Two wires provide a constant current I for the thermal resistance, convert r into a voltage signal U, and then lead u to the secondary instrument through the other two wires. It can be seen that this kind of lead mode can completely eliminate the influence of lead resistance and is mainly used for high-precision temperature detection.




The thermal resistance is connected by three wire system. The three wire system is used to eliminate the measurement error caused by the resistance of connecting wires. This is because the circuit for measuring the thermal resistance is generally an unbalanced bridge. As a bridge arm resistance of the bridge, its connecting wire (from the thermal resistance to the central control room) also becomes a part of the bridge arm resistance, which is unknown and changes with the ambient temperature, resulting in measurement errors. With the three wire system, one wire is connected to the power supply end of the bridge, and the other two wires are connected to the bridge arm where the thermal resistance is located and the adjacent bridge arm, so as to eliminate the measurement error caused by the wire line resistance. Generally, three wire system is adopted in industry. Thermocouples produce millivolt signals, and there is no such problem.
Composition of thermal resistance temperature measurement system
(1) Thermal resistance temperature measurement system is generally composed of thermal resistance, connecting wire and display instrument. The following two points must be noted:
① The graduation number of thermal resistance and display instrument must be the same
② In order to eliminate the influence of the change of the resistance of the connecting wire, the three wire connection method must be adopted. Please refer to Chapter 3 for details.
(2) Armored thermal resistance armored thermal resistance is a solid body composed of temperature sensing element (resistance body), lead wire, insulating material and stainless steel sleeve. Its outer diameter is generally φ 2 ~ φ 8mm, and the minimum can be φ mm. Compared with the ordinary thermistor, it has the following advantages:
① Small volume, no air gap inside, small measurement lag in thermal inertia;
② Good mechanical properties, vibration resistance, impact resistance;
③ Can be bent, easy to install
④ Long service life.
(3) The end surface thermal resistance end surface thermal resistance temperature sensing element is made of specially treated resistance wire and is closely attached to the end surface of the thermometer. Compared with the general axial thermal resistance, it can more accurately and quickly reflect the actual temperature of the measured end face, which is suitable for measuring the end face temperature of bearing shells and other parts.
(4) Through the special junction box, the explosion-proof type thermal resistance will change the length of the resistance wire and affect the resistance value due to the open circuit repair of the explosive gas mixture inside the shell due to the spark or arc shadow resistance body. Therefore, it is better to replace the new resistance body. If the welding repair is adopted, it can be used only after the verification is qualified.
The difference between thermocouple and thermal resistance
Both thermocouple and thermal resistance belong to the contact temperature measurement in temperature measurement. Although their functions are the same as measuring the temperature of objects, their principles and characteristics are different