What are the working principles of thermocouples and thermal resistors?

1. Thermocouple

When two different conductors or semiconductors A and B form a circuit, and their two ends are connected to each other, as long as the temperature at the two nodes is different, with one end having a temperature of T, it is called the working end or hot end, and the other end having a temperature of T0, it is called the free end (also known as the reference end) or cold end, an electromotive force will be generated in the circuit, and the direction and magnitude of this electromotive force are related to the material of the conductor and the temperature of the two nodes.

This phenomenon is called the "thermoelectric effect", and the circuit composed of two conductors is called a "thermocouple". These two conductors are called "thermoelectric poles", and the generated electromotive force is called the "thermoelectric potential".

2. Thermal resistance

The temperature measurement principle of thermal resistance is based on the characteristic that the resistance value of a conductor or semiconductor changes with temperature to measure temperature and temperature related parameters. Thermistors are mostly made of pure metal materials, with platinum and copper being widely used. Currently, materials such as nickel, manganese, and rhodium have been adopted to manufacture thermistors. Thermistors typically require the transmission of resistance signals through leads to computer control devices or other secondary instruments.

Additional Information:

The difference between thermocouples and thermal resistors:

1, On site judgment in work

Thermocouples have positive and negative poles, and compensation wires also have positive and negative poles. First, ensure proper connection and configuration In operation. Common ones include short circuit, open circuit, poor contact (judged by a multimeter), and deterioration (identified by surface color).

When checking, the thermocouple should be separated from the secondary meter. Use a tool to short-circuit the compensation wire on the secondary meter. The meter should indicate the room temperature, and then short-circuit the thermocouple wiring terminal. The meter should indicate the ambient temperature where the thermocouple is located (if not, the compensation wire is faulty). Use a multimeter to roughly estimate the thermoelectric potential of the thermocouple (if normal, please check the process).

A multimeter can be used to detect short circuits and open circuits in thermal resistors. In operation, if a short circuit is suspected, simply remove a wire end from the resistor end and check the display instrument. If it reaches a large value, the thermal resistor will short-circuit back to low, the wire will short-circuit, and when ensuring normal connection and configuration, the meter value will display low or unstable, indicating that the protective tube may have been flooded and the display will be very large. The thermal blocking circuit will display a very small short circuit.

2, From a material perspective, thermal resistance is a type of metal material that is sensitive to temperature changes. Thermocouples are bimetallic materials, where two different metals generate a potential difference at the ends of two different metal wires due to temperature changes.

3, The temperature ranges detected by the two sensors are different. Thermal resistance generally detects temperatures in the range of 0-150 degrees (although negative temperatures can be detected), while thermocouples can detect temperatures in the range of 0-1000 degrees (or even higher). Therefore, the former is for low-temperature detection, while the latter is for high-temperature detection.