What is a temperature sensor

Temperature sensor is a sensor that can sense the temperature and convert it into a usable output signal. Temperature sensor is the core part of temperature measuring instrument. According to the measurement method, it can be divided into contact type and non-contact type, and according to the characteristics of sensor materials and electronic components, it can be divided into thermal resistance and thermocouple.

Contact type

The detection part of the contact temperature sensor has good contact with the measured object, also known as the thermometer.
Thermometers achieve thermal balance by conduction or convection, so that the value of the thermometer can directly represent the temperature of the measured object. Generally, the measurement accuracy is higher. A thermometer can also measure the temperature distribution inside an object within a certain temperature range. But for the moving body, small target or small thermal capacity of the object will produce a large measurement error, commonly used thermometer bimetal thermometer, glass liquid thermometer, pressure thermometer, resistance thermometer, thermistor and thermocouple. They are widely used in industry, agriculture, commerce and other sectors. People often use these thermometers in their daily life. With the wide application of cryogenic technology in national defense engineering, space technology, metallurgy, electronics, food, medicine, petrochemical and other sectors and the research of superconductivity technology, the cryogenic thermometer for measuring temperatures below 120K has been developed. Such as low temperature gas thermometer, vapor pressure thermometer, acoustic thermometer, paramagnetic salt thermometer, quantum thermometer, low temperature thermal resistance and low temperature thermocouple. Low temperature thermometer requires small size of temperature sensing element, high accuracy, good recurrence and stability. The carburized glass resistance made of porous high silica glass carburizing sintering 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.

Non-contact type
Its sensitive element and the measured object do not contact, also known as non-contact thermometer table. The 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). It can also be used to measure the temperature distribution of a temperature field.

The most commonly used non-contact thermometers are based on the fundamental laws of blackbody radiation and are called radiometric thermometers. Radiation thermometry includes luminance method (see optical pyrometer), radiation method (see radiation pyrometer), and colorimetric method (see colorimetric thermometer). All kinds of radiation temperature measurement methods can only measure the corresponding luminosity temperature, radiation temperature or colorimetric temperature.

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