Working principle of thermal resistor

Thermistors (RTRs) are the most commonly used temperature sensors in the medium and low temperature range. Their main features are high measurement accuracy and stable performance. Platinum RTDs offer the highest measurement accuracy and are not only widely used in industrial temperature measurement but also used in standard temperature measuring instruments.

Unlike thermocouples, which measure temperature based on the thermal effect of resistance, RTDs measure temperature based on the thermal effect of resistance-the property that the resistance of a resistor changes with temperature. Therefore, by measuring the change in the resistance of a temperature-sensing RTD, the temperature can be measured.

Currently, there are two main types of RTDs: RTDs and semiconductor thermistors. The resistance and temperature of a RTD can generally be expressed using the following approximate relationship: Rt = Rt0[1+α(t-t0)], where Rt is the resistance at temperature t; Rt0 is the resistance at temperature t0 (usually t0 = 0°C); and α is the temperature coefficient. The resistance and temperature relationship of a semiconductor thermistor is Rt = AeB/t, where Rt is the resistance at temperature t; A and B are constants determined by the structure of the semiconductor material. In comparison, thermistors have a larger temperature coefficient and higher resistance values ​​at room temperature (often exceeding several thousand ohms). However, they have poor interchangeability and severe nonlinearity, and their temperature measurement range is limited to approximately -50°C to 300°C. They are widely used in temperature detection and control in household appliances and automobiles. RTDs are generally suitable for temperature measurement in the -200°C to 500°C range. They are characterized by accurate measurement, good stability, and reliable performance, making them extremely widely used in process control.

The temperature measurement principle of RTDs is based on the property that the resistance of a conductor or semiconductor changes with temperature. They have many advantages, including the ability to transmit electrical signals remotely, high sensitivity, strong stability, and good interchangeability and accuracy. However, they require power excitation and cannot measure instantaneous temperature changes. Industrial RTDs typically use Pt100, Pt10, Cu50, and Cu100. Platinum RTDs typically measure temperatures from -200°C to 800°C, while copper RTDs measure from -40°C to 140°C. Thermal resistors are of the same type as thermocouples, but they do not require compensation wires and are cheaper than thermocouples.