Working principle, classification and application of thermal resistors、。

The temperature sensing elements of metal thermal resistors include quartz tube cross skeleton structure, twist skeleton structure, rod structure, etc. There are many types of temperature sensing materials commonly used in metal thermal resistors, and the most commonly used is platinum wire. In addition to platinum wire, metal thermal resistor materials for industrial measurement include copper, nickel, iron, iron-nickel, UE thermal resistor tungsten, silver, etc. Thin film thermal resistors are manufactured by electron cathode sputtering, which can be industrialized and mass-produced. Among them, the skeleton is made of ceramic and the lead wire is made of platinum-palladium alloy.
Raw materials of thermal resistors
Thermal resistor resistance materials Thermal resistor temperature measurement is based on the characteristic that the resistance value of metal conductors increases with the increase of temperature to measure temperature. Most thermal resistors are made of pure metal materials. Currently, platinum and copper are the most widely used. In addition, nickel, manganese and rhodium are now used to manufacture thermal resistors.
Main features of thermal resistors
· Pressure thermal resistor spring-type temperature sensing element, good vibration resistance;
· High temperature measurement accuracy;
· High mechanical strength, good high temperature and pressure resistance;
· Imported thin film resistor elements, reliable and stable performance.
Working principle of thermal resistor
The temperature measurement principle of thermal resistor is based on the property that the resistance value of conductor or semiconductor changes with the change of temperature. Most thermal resistors are made of pure metal materials. Platinum and copper are the most widely used. Now, materials such as nickel, manganese and rhodium have begun to be used to manufacture thermal resistors. Thermal resistors usually need to transmit the resistance signal to the computer control device or other secondary instruments through the lead wire.
Types of thermal resistors
Ordinary thermal resistors
From the temperature measurement principle of thermoelectric thermal resistors, it can be seen that the change of the measured temperature is directly measured by the change of the resistance value of the thermal resistor. Therefore, the change of the resistance of various wires such as the lead wire of the thermal resistor body will affect the temperature measurement.
Armored thermal resistor
The armored thermal resistor is a solid body composed of a temperature sensing element (resistor body), lead wire, insulating material, and stainless steel casing. Its outer diameter is generally φ2--φ8mm, and the minimum can reach φmm. Compared with ordinary thermal resistors, it has the following advantages: ① small size, 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.
End face thermal resistor
The thermal resistor temperature sensing element is wound with specially treated resistance wire and is close to the end face of the thermometer. Compared with general axial thermal resistors, 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 bearings and other parts.
Flameproof thermal resistor
The explosion of the explosive mixed gas inside its shell due to sparks or arcs is confined to the junction box through a specially structured junction box, and the production site will not cause an explosion. Flameproof thermal resistors can be used for temperature measurement in explosion-hazardous places in Bla--B3c zones. The temperature measurement principle of thermal resistors is different from that of thermocouples in that thermal resistors measure temperature based on the thermal effect of the resistor, that is, the resistance value of the resistor changes with temperature. Therefore, as long as the resistance change of the temperature-sensitive thermistor is measured, the temperature can be measured. At present, there are mainly two types of metal thermistors and semiconductor thermistors.
The resistance value and temperature of metal thermistors can generally be expressed by the following approximate relationship, namely
Rt=Rt0[1+α(t-t0)]
Wherein, Rt is the resistance value at temperature t; Rt0 is the corresponding resistance value at temperature t0 (usually t0=0℃); α is the temperature coefficient.
The relationship between the resistance value and temperature of semiconductor thermistors is
Rt=AeB/t
Wherein, Rt is the resistance value at temperature t; A and B depend on the constants of the structure of the semiconductor material.
In comparison, the temperature coefficient of thermistors is larger, and the resistance value at room temperature is higher (usually above several thousand ohms), but the interchangeability is poor, the nonlinearity is serious, and the temperature measurement range is only about -50~300℃. It is widely used in temperature detection and control of household appliances and automobiles. Metal thermal resistors are generally suitable for temperature measurement in the range of -200~500℃. They are characterized by accurate measurement, good stability, and reliable performance, and are widely used in process control.