Ms. took a call from a friend today and asked about the difference between the thermocouple, thermistor and the thermistor. It should be said that Ms. is familiar with these things, but when asked so coldly, it takes a lot of trouble to explain, and in the end it still feels a little bit unfinished. Although it is a common temperature measurement protection component of the motor, it is still difficult to say clearly in a few words.

In general terms, thermocouples, RTDs, and thermistors are all measurement components related to temperature measurement, but there is still a big difference in fine separation.

The thermocouple temperature measurement must be composed of three parts: thermocouple, connecting wire and display instrument. It is often used as the temperature measuring component of high-voltage motor sliding bearing; the temperature sensor of motor insulating paint drying equipment is usually also thermocouple. The thermal resistance is a platinum thermal resistance such as PT100 or PT1000, which is a change in the resistance of the metal conductor or semiconductor when the temperature changes. Thermistors are temperature sensitive components, and small temperature changes can exhibit proportional large resistance changes.

Thermocouple

Thermocouples are used to solder conductors or semiconductors A and B of two different materials to form a closed loop. When there is a temperature difference between the two attachment points of the conductors A and B, an electromotive force is generated between the two, thereby forming a current in the loop, which is called a thermoelectric effect. Thermocouples use this effect to work. Thermocouples are widely used in the kiln equipment for motor manufacturing. The temperature indication displayed on the equipment is conducted by thermoelectric conduction.

Thermal resistance

Thermal resistance is the most commonly used temperature detector in the mid-low temperature zone. Its main features are high measurement accuracy and stable performance. Among them, platinum thermal resistance has the highest measurement accuracy, and it is not only widely used in industrial temperature measurement, but also made into a standard reference instrument.

Thermistor temperature measurement is based on the fact that the resistance value of a metal conductor increases as the temperature increases. Most of the thermal resistance is made of pure metal materials. At present, platinum and copper are the most widely used. In addition, thermal resistances such as nickel and manganese have been used.

The biggest difference between the choice of thermal resistance and thermocouple is the choice of temperature range. The thermal resistance is the temperature sensor for measuring low temperature. The general measurement temperature is -200~800 °C, and the thermocouple is the temperature sensor for measuring medium and high temperature. Generally, the temperature is measured. 400~1800°C, if the measurement temperature is about 200°C, the thermal resistance measurement should be selected. If the measurement temperature is 600°C, the K-type thermocouple should be selected. If the measurement temperature is 1200~1600°C, the S-type should be selected. Type B thermocouple.

Thermal resistance compared to thermocouples

● The output signal is large at the same temperature, easy to measure; ● The resistance must be applied by means of an external power supply; ● The temperature of the thermal resistance is larger, and the working end of the thermocouple is a small solder joint, so the reaction speed of the thermal resistance is measured. Slower than thermocouples; ● The thermal resistance of similar materials is not as high as the upper limit of thermocouple temperature measurement.

Thermistor

The thermistor changes its own resistance value depending on the temperature. It is mainly used on temperature sensors, such as electronic thermometers and motor temperature sensors. Thermistors include positive temperature coefficient (PTC) and negative temperature coefficient (NTC) thermistors. The main features of the thermistor are:

● High sensitivity, the temperature coefficient of resistance is 10~100 times larger than metal;

● Wide operating temperature range, normal temperature device is suitable for -55 ° C ~ 315 ° C, high temperature device is suitable for temperature higher than 315 ° C (currently up to 2000 ° C) low temperature device is suitable for -273 ° C ~ 55 ° C;

● Small size, able to measure the temperature of the voids, cavities and blood vessels in the body that other thermometers cannot measure;

● Easy to use, the resistance value can be arbitrarily selected between 0.1~100kΩ;

● Easy to process into complex shapes for mass production;

● Good stability and strong overload capability. Due to the unique performance of the semiconductor thermistor, it can be used not only as a measuring component (such as measuring temperature, flow, liquid level, etc.) but also as a control component (such as thermal Switch, current limiter) and circuit compensation components.