How to determine the type of temperature sensor

First, the temperature sensor must select the sensor structure so that the sensitive component can reach the measured fluid or the measured surface temperature within the measurement time. The temperature sensor output is only sensitive to the component temperature. In fact, it is often difficult to ensure that the sensor indicates the temperature, ie the temperature of the object being measured.

The temperature of the fluid in the vessel is measured by a thermocouple or RTD probe, but when the life of the whole system is much longer than the expected life of the probe, or the probe is expected to be removed quite frequently to calibrate or repair the container, the container wall Install a permanent thermowell on the top. The use of thermowells significantly increases the measurement time constant. When the temperature changes very slowly and the thermal conductivity error is small, the thermowell will affect the measurement accuracy. However, if the temperature changes rapidly and the temperature of the sensitive component changes rapidly, and the thermal error increases, the measurement accuracy will be affected. Therefore, we must weigh the two factors of maintenance and measurement accuracy.

All materials of the thermocouple or RTD probe should be compatible with the fluid they are in contact with. When using a bare component probe, the suitability of the material of each component (sensitive components, connecting leads, supports, partial protective covers, etc.) must be considered in contact with the fluid being measured. When using a thermowell, only the casing material needs to be considered.

When the resistive thermal element is immersed in the liquid level transmitter body and most gases, it is usually sealed, at least coated, and the exposed resistive element can be immersed in conductive or contaminated fluid. When it needs to respond quickly, use it for dry air and Limited to several gases and some liquid level transmitter bodies. Resistive elements, such as those used in stagnant or slow-flowing fluids, typically require some kind of housing to cover for mechanical protection.

When the tube, conduit or container can open or prohibit the opening, the probe or thermowell can be used to measure and measure by means of an external wall clamp or a fixed surface temperature sensor. To ensure reasonable measurement accuracy, the sensor must be thermally isolated from the ambient atmosphere and isolated from the source of thermal radiation, and must be properly designed and installed by the sensor to achieve optimal heat transfer from the wall to the sensitive component.

Selecting a temperature sensor requires more consideration than selecting another type of sensor. First, the sensor structure must be selected so that the sensitive component is within the measurement time to reach the measured fluid or the temperature of the surface being measured. The temperature sensor output is only sensitive to the component temperature. In fact, it is often difficult to ensure that the sensor indicates the temperature, ie the temperature of the object being measured.

In most cases, for temperature sensors, consider the following:

(1) Whether the temperature of the object to be tested needs to be recorded, alarmed and automatically controlled, whether remote measurement and transmission are required.

(2) Temperature measurement range size and accuracy requirements.

(3) The size of the temperature measuring component is appropriate.

(4) If the temperature of the measured object changes with time, the temperature component lag can adapt to the temperature measurement requirements.

(5) Whether the environmental conditions of the measured object damage the temperature measuring element.

(6) If the price is guaranteed, it is convenient to use.