What is the difference between temperature sensors and thermocouples?

Thermistors and thermocouples are the most commonly used temperature sensing components in temperature sensors. The working principle of a thermocouple temperature sensor is that two different metal contact surfaces generate different weak voltages at different temperatures, and the temperature is measured through an amplification circuit. It is mainly used for measuring high temperatures. The working principle of a thermistor temperature sensor is that the resistance value changes with temperature, mainly used to measure small temperature changes. How should we choose these two temperature sensors when we want to measure temperature?
First, look at the temperature measurement range. Thermistors and thermocouples each have suitable temperature measurement ranges, and sensors should be selected according to the actual temperature and temperature gradient distribution at the measurement points. High temperature measurement usually chooses hot spot thermocouple, while for medium and low temperatures, thermal resistance is chosen.
Secondly, considering the on-site environmental conditions, especially the electromagnetic compatibility performance, various clutter, harmonics, differential mode, and common mode interference signals. When using a thermocouple temperature sensor, measurement errors are introduced due to the weak electrical signal of temperature difference and thermoelectric potential, which is easily interfered with. On the other hand, a thermal resistance temperature sensor is less susceptible to interference due to its current signal and can further reduce measurement system errors due to its three wire and four wire systems. Therefore, thermal resistance has the advantage of strong anti-interference performance while meeting the measurement range, There is no trouble with the cold end compensation of thermocouples yet. In addition, at the temperature measurement point on site, the thermal resistance temperature sensor is usually connected to the transmitter and then output to the secondary instrument. It is not afraid of signal attenuation caused by a long circuit, and there is no need to use expensive compensation wires. Thermocouple temperature sensors require compensation wires, which are suitable for use in these situations. Of course, the non-linear variation of the resistance value of a thermal resistor with temperature can introduce system errors, and the thermal inertia of a thermal resistor is slightly larger, making it difficult to track rapid and significant temperature changes effectively. To avoid excessive system errors, the resolution of the connected secondary instrument should not be too large.
Once again, due to the simple calibration of the thermistor temperature sensor, its calibration points only correspond to the resistance values at zero and 100 degrees, and the calibration equipment is simple, with a short calibration time. The calibration of thermocouple temperature sensors, due to the slow heating and cooling process, not only takes a long time and the equipment is complex, but also has strict environmental requirements. Therefore, when measuring the temperature of the medium that meets the usage conditions of a thermistor, a thermistor temperature sensor should be used first.