Thermal resistance and thermocouple are the most commonly used temperature sensing components for temperature sensors. The working principle of the thermocouple temperature sensor is that two different metal contact surfaces generate different micro-voltages at different temperatures. The temperature is measured by an amplifier circuit, which is mainly used to measure high temperatures. The working principle of the thermal resistance temperature sensor is that the resistance changes with the temperature, and it is mainly used to measure small temperature changes. When we want to measure temperature, how should we choose these two temperature sensors?
First look at the temperature measurement range. The thermal resistance and thermocouple each have a suitable temperature measurement range, and the sensor should be selected according to the temperature of the actual temperature measurement point and the temperature gradient distribution. Thermocouple is usually selected for high temperature measurement, and thermal resistance is selected for medium and low temperature. To
Secondly, consider the on-site environmental conditions, especially the on-site electromagnetic compatibility performance, various clutter, harmonics, differential mode and common mode interference signals. When using a thermocouple temperature sensor, because the temperature difference thermoelectric potential is a weak electrical signal, it is susceptible to interference and introduces measurement errors. The thermal resistance temperature sensor is not susceptible to interference because it is a current signal, and because it has a three-wire system, a four-wire system, etc. The measurement system error can be further reduced, so the thermal resistance also has the advantage of strong anti-interference performance under the premise of meeting the measurement range. There is no cold junction compensation problem of the thermocouple. In addition, the temperature measurement point is generally heated at the site. The resistance temperature sensor is connected to the transmitter and then output to the secondary instrument. It is not afraid of signal attenuation caused by the long line, and it is not necessary to use a more expensive compensation wire, while the thermocouple temperature sensor needs to use a compensation wire, which is suitable for use in these cases Thermal resistance. Of course, the non-linear change of the resistance value with temperature will introduce system error, and the thermal inertia of the thermal resistance is slightly larger, and it cannot better track the rapid and large changes in temperature. In order to avoid the system difference being too large, the resolution of the connected secondary meter should not be too large.
Again, because the calibration of the thermal resistance temperature sensor is simple, the calibration points are only the zero point and the corresponding resistance value at 100 degrees, the calibration equipment is simple, the calibration time is very short, and the calibration of the thermocouple temperature sensor is due to the slowness of heating and cooling. The calibration of the thermocouple is not only a long time, the equipment is complicated, and the environmental requirements are also very strict. Therefore, when the temperature of the measuring medium meets the use conditions of the thermal resistance, the thermal resistance temperature sensor should be used first.
If you encounter any questions about the selection of thermocouple temperature sensors and thermal resistance temperature sensors, please feel free to contact us.