Common temperature sensors and temperature transmitters are divided into expansion type, working pressure type, thermal resistance type and thermocouple type according to the conversion principle. The first three types are mainly used in intelligent building systems:

1. The temperature sensor is made based on the principle of thermal expansion and contraction of objects. According to the shape of the chemical substance, it is divided into solid and liquid types. Mercury thermometer uses the thermal expansion and contraction characteristics of liquid mercury to measure temperature, which belongs to the liquid expansion type thermometer. The wear-resistant steel tube thermometer belongs to the solid expansion type thermometer. The temperature measurement element of the wear-resistant steel tube thermometer is made of two different metal composite materials with very different expansion coefficients wound together and welded together. Because the wire expansion coefficients of the two copper sheets are different, when the temperature rises, the resistance belt will bend to the side with a smaller expansion coefficient, and the higher the temperature rises, the greater the bend.

The principle diagram of the wear-resistant steel pipe thermometer is that it uses the positive correlation between the size of the deformation of the resistance strip and the temperature change. The needle is pushed by the lever to indicate the temperature value. At the same time, the recording needle (pen) is pushed by the lever to automatically record the measured temperature on the moving recording paper. The wear-resistant steel pipe thermometer has a simple structure, high impact toughness, high quality and low price, but its precision is low, and the measurement range and application scope are relatively limited.

2. The working pressure temperature sensor uses the property that the working pressure of the temperature sensor material changes with the change of temperature to measure the temperature. This is the basic temperature measurement principle of the working pressure temperature sensor.

3. Thermal resistor temperature sensor Thermal resistor temperature sensors are divided into two categories: metal material thermal resistors and semiconductor material temperature sensors. The resistance of most metal thermal resistors increases with increasing temperature, which is called a positive temperature coefficient; while the resistance of semiconductor temperature sensors generally decreases with increasing temperature, which is called a negative temperature coefficient. Since the resistance of conductors and semiconductors changes with temperature, the corresponding temperature can be measured by accurately measuring their resistance. The characteristic of copper thermistor is that its resistance is linearly related to temperature, the resistor temperature coefficient is relatively large, and the material is easy to purify and the price is relatively cheap. However, its resistance is low, the precision is not high, it is easy to oxidize at high temperature, and the chemical stability is poor. Therefore, copper thermistor can be used when the temperature is not high and there is no special restriction on the sensor volume.