A temperature sensor is a sensor that senses temperature and converts it into an available output signal. The temperature sensor is the core part of the temperature measuring instrument, which has many kinds. According to the measurement method, it can be divided into contact type and non-contact type. According to the sensor material and electronic component characteristics, it can be divided into two types: thermal resistance and thermocouple.

1. Classification of temperature sensor

Contact type

The detection part of contact temperature sensor has good contact with the tested object, also known as thermometer.

The thermometer achieves heat balance through conduction or convection, so that the temperature of the measured object can be directly indicated by the thermometer.

Generally, the measurement accuracy is high. In a certain range of temperature measurement, the thermometer can also measure the temperature distribution inside the object. However, for moving objects, small targets or objects with small heat capacity, there will be large measurement errors. Commonly used thermometers include bimetal thermometers, glass liquid thermometers, pressure thermometers, resistance thermometers, thermistors and thermocouple. They are widely used in industry, agriculture, commerce and other sectors. These thermometers are often used in daily life. With the wide application of low temperature technology in national defense engineering, space technology, metallurgy, electronics, food, medicine, petrochemical and other sectors and the research of superconducting technology, low temperature thermometers for measuring temperatures below 120K have been developed, such as low temperature gas thermometers, steam pressure thermometers, acoustic thermometers, paramagnetic salt thermometers, quantum thermometers, low temperature thermal resistance and low temperature thermocouple And so on. Low temperature thermometer requires small volume, high accuracy, good reproducibility and stability of temperature sensing element. The thermal resistance of carburized glass made of porous high silica glass is a kind of temperature sensing element of low temperature thermometer, which can be used to measure the temperature in the range of 1.6-300k.

② contactless

Its sensitive elements are not in contact with the measured object, also known as non-contact temperature measuring instrument. This instrument can be used to measure the surface temperature of moving objects, small targets and objects with small heat capacity or rapid temperature change (transient), and also can be used to measure the temperature distribution of the temperature field.

Based on the basic law of blackbody radiation, the commonly used non-contact thermometers are called radiation thermometers.

Advantages of non-contact temperature measurement: the upper limit of measurement is not limited by the degree of temperature resistance of the temperature sensing element, so there is no limit to the very high measurable temperature in principle. For high temperature above 1800 ℃, non-contact temperature measurement method is mainly used. With the development of infrared technology, the radiation temperature measurement gradually expands from visible light to infrared, and has been used up to 700 ℃ and normal temperature, with high resolution.

2. Working principle

(1) working according to the principle that the resistance of the wire changes with the temperature.

(2) thermocouple: if two kinds of conductors are in contact with each other, there will be a stable one at the junction; if the temperature of two ends of the same conductor is different, there will be a certain size between the two ends.

(3) liquid thermometer: it works on the principle of thermal expansion of temperature sensing liquid.