The choice of 4 20ma temperature sensor is mainly based on the measurement range. When the measurement range is expected to be within the total range, a platinum resistance sensor can be selected. The narrower range usually requires the sensor to have a fairly high basic resistance in order to obtain a sufficiently large resistance change. The large enough resistance variation provided by thermistors makes these sensors ideal for narrow measurement ranges.

Choosing a temperature sensor should pay attention to the following aspects:

(1) Whether the temperature of the measured object needs to be recorded, alarm and automatic control, whether it needs to be measured and transmitted remotely;

(2) the size and accuracy requirements of the temperature measurement range;

(3) Whether the size of the temperature measuring element is appropriate;

(4) In the case that the temperature of the measured object changes with time, whether the hysteresis of the temperature measuring element can meet the temperature measuring requirements;

(5) Whether the environmental conditions of the tested object have damage to the temperature measuring element.

The choice of temperature sensor transmitter is mainly based on the measurement range. When the measurement range is expected to be within the total range, a platinum resistance sensor can be selected. The narrower range usually requires the sensor to have a fairly high basic resistance in order to obtain a sufficiently large resistance change. The large enough resistance variation provided by thermistors makes these sensors ideal for narrow measurement ranges. If the measurement range is quite large, thermocouples are more suitable. It is best to include the freezing point in this range, because the index meter of the thermocouple is based on this temperature. Sensor linearity within a known range can also be used as an additional condition for selecting a sensor.

Response time is usually expressed as a time constant, which is another basic basis for selecting a sensor. The time constant is less important when monitoring the temperature in the tank.However, when the temperature in the vibration tube must be measured during use, the time constant becomes the determining factor in selecting the sensor.