What is the performance of WRNM-201 end face thermistor (even)?

The end face thermistor temperature sensing element is made of specially processed resistance wire wound tightly against the end face of the thermometer. Compared with general axial resistance thermometers, 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 components.

Principle of Temperature Measurement
The temperature measurement principle of thermal resistance is different from that of thermocouple. Thermal resistance is based on the thermal effect of resistance for temperature measurement, that is, the characteristic of the resistance value of the resistor changing with temperature. Therefore, as long as the resistance change of the thermistor is measured, the temperature can be measured. At present, there are mainly

Wiring method
Thermistor is a primary component that converts temperature changes into changes in resistance values. Thermistors typically need to transmit resistance signals to computer control devices or other primary instruments through leads. Industrial thermal resistors are installed on the production site and there is a certain distance between them and the control room, so the leads of the thermal resistors will have a significant impact on the measurement results.

At present, there are three main ways to lead thermal resistors:

Two wire system: The method of connecting a wire at each end of a thermal resistor to extract a resistance signal is called a two wire system: This lead method is simple, but due to the inevitable lead resistance r of the connecting wire, the size of r is related to the material and length of the wire, so this lead method is only suitable for situations with low measurement accuracy

Three wire system: The method of connecting one end of the root of a thermal resistor to a lead and the other end to two leads is called the three wire system. This method is usually used in conjunction with an electric bridge to effectively eliminate the influence of lead resistance and is commonly used in industrial process control.

Four wire system: The method of connecting two wires at each end of the root of a thermistor is called a four wire system, in which two leads provide a constant current I to the thermistor, convert R into a voltage signal U, and then lead U to the secondary instrument through the other two leads. It can be seen that this lead method can completely eliminate the influence of lead resistance and is mainly used for high-precision temperature detection.

The thermal resistor adopts a three wire connection method. The use of a three wire system is to eliminate measurement errors caused by the resistance of connecting wires. This is because the circuit for measuring thermal resistance is usually an unbalanced bridge. As a bridge arm resistor of the electric bridge, the thermal resistor's connecting wire (from the thermal resistor to the central control room) also becomes a part of the bridge arm resistor. This part of the resistor is unknown and varies with the ambient temperature, causing measurement errors. Adopting a three wire system, one wire is connected to the power terminal of the bridge, and the other two wires are respectively connected to the bridge arm where the thermal resistance is located and the adjacent bridge arm, thus eliminating measurement errors caused by the resistance of the wire line.

Installation requirements

Attention should be paid to the installation of thermistor, which is conducive to accurate temperature measurement, safe and reliable, easy maintenance, and does not affect equipment operation and production operation. To meet the above requirements, the following points should be noted when selecting the installation location and insertion depth of the thermistor:

1. In order to ensure sufficient heat exchange between the measuring end of the thermistor and the measured medium, the position of the measuring point should be selected reasonably, and the installation of the thermistor near the dead corners of valves, elbows, pipelines, and equipment should be avoided as much as possible.

2. Thermistors with protective sleeves suffer from heat transfer and dissipation losses. To reduce measurement errors, thermocouples and thermistors should have sufficient insertion depth:

1) For measuring the temperature of the fluid at the center of the pipeline, the measuring end of the thermistor should generally be inserted into the center of the pipeline (vertically or obliquely installed). If the diameter of the tested fluid pipeline is 200 millimeters, the insertion depth of the thermistor should be selected as 100 millimeters;

2) For temperature measurement of high temperature, high pressure, and high-speed fluids (such as main steam temperature), in order to reduce the resistance of the protective sleeve to the fluid and prevent the protective sleeve from breaking under the action of the fluid, shallow insertion of the protective tube or the use of a hot sleeve thermistor can be adopted. The shallow insertion type thermal resistance protective sleeve should be inserted into the main steam pipeline to a depth of not less than 75mm; The standard insertion depth for hot sleeve thermal resistors is 100mm.

3) If it is necessary to measure the temperature of the flue gas inside the flue, even though the diameter of the flue is 4m, the insertion depth of the thermistor is 1m.

4) When the insertion depth of the measuring element exceeds 1m, it should be installed vertically as much as possible, or support frames and protective sleeves should be added.