The difference between temperature sensor thermistor and thermocouple

The difference between thermocouples and thermal resistors
1. The properties of signals are different:
Thermal resistance itself is a resistor, and a thermal resistance thermometer works based on the principle that the resistance of a metal wire changes with temperature; And thermocouple: It is a closed circuit formed by welding wires or semiconductors of two different materials together. When there is a temperature difference between the two contacts of the wires, an electromotive force is generated between them, thus forming a certain amount of current in the circuit. This phenomenon is called thermoelectric effect. Thermocouples work by utilizing this effect.
2. The temperature ranges detected by the two sensors are different:
Thermal resistance is generally detected in the temperature range of 0-150 degrees, with a maximum measurement range of around 600 degrees, while thermocouples can detect temperatures in the range of 0-1000 degrees (or even higher).
3. Different materials:
Thermistor is a metal material that is sensitive to temperature changes. Thermistor is a resistance signal that outputs a resistance value (Ω) without positive or negative poles. Commonly used ones include PT100 cu50.. And thermal coupling is a bimetallic material, where two different metal materials generate a potential difference at the two ends of two different metal wires due to temperature changes. It can be divided into k, s, e, r, t, and n-type equal scale numbers, which can be used in different measuring media and temperature measurement ranges. Thermocouples are voltage signals that output millivolts (mv) and have positive and negative poles. There are some that are more expensive than resistors, and some that are cheaper than resistors, but including compensation wires, the overall cost of thermocouples is higher.
4. The relationship with PLC is different:
The input modules for thermal resistors and thermocouples corresponding to PLCs are also different. This statement is not a problem, but generally PLCs are directly connected to 4-20mA signals, while thermal resistors and thermocouples are usually connected to PLCs with transmitters. If connected to DCS, there is no need to use a transmitter. Thermistor is an RTD signal, thermocouple is a TC signal! PLC also has thermal resistance module and thermocouple module, which can directly input resistance and thermocouple signals.
The difference between the temperature measurement principle of a thermistor and a thermocouple is that a thermistor measures temperature based on the thermal effect of resistance, 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 two types of thermistors: metal thermistors and semiconductor thermistors.
The resistance value and temperature of a metal thermistor can generally be approximated by the following equation: Rt=Rt0 [1+α (t-t0)]
In the formula, Rt is the resistance value at temperature t; Rt0 is the corresponding resistance value at temperature t0 (usually t0=0 ℃); α is the temperature coefficient. The relationship between the resistance value of a semiconductor thermistor and temperature is Rt=AeB/t, where Rt is the resistance value at temperature t; A. B depends on the constant of the structure of the semiconductor material.
Compared to others, thermistors have a larger temperature coefficient and higher resistance values at room temperature (usually above several thousand ohms), but they have poor interchangeability, severe nonlinearity, and a temperature measurement range of only -50~300 ℃. They are widely used for temperature detection and control in household appliances and automobiles. Metal thermistors are generally suitable for temperature measurement in the range of -200~500 ℃, characterized by accurate measurement, good stability, and reliable performance. They are widely used in process control.
From the perspective of the change in resistance with temperature, most metal conductors in industry commonly use metal thermistors, but not all can be used as thermometers. As a metal material for thermistors, it is generally required to have a large and stable temperature coefficient, a high resistivity (reducing the size of the sensor at the same sensitivity), stable chemical and physical properties within the temperature range of use, good material reproducibility, and a linear relationship between the resistance value and temperature change