Temperature transducer refers to a sensor that can sense temperature and convert it into a usable output signal. The temperature sensor is the core part of the temperature measuring instrument, and there are many varieties. According to the measurement method, it can be divided into two categories: contact type and non-contact type. According to the characteristics of sensor materials and electronic components, it can be divided into two types: thermal resistance and thermocouple.

Contact type The detection part of the contact temperature sensor is in good contact with the measured object, also known as a thermometer. The thermometer achieves thermal equilibrium through conduction or convection, so that the value of the thermometer can directly indicate the temperature of the measured object. Generally, the measurement accuracy is high. Within a certain temperature measurement range, the thermometer can also measure the temperature distribution inside the object. But for moving objects, small targets or objects with small heat capacity, large measurement errors will occur. Commonly used thermometers include bimetallic thermometers, glass liquid thermometers, pressure thermometers, resistance thermometers, thermistors, and thermocouples. They are widely used in industries, agriculture, commerce and other sectors. People often use these thermometers in 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 superconducting technology, cryogenic thermometers measuring temperatures below 120K have been developed, such as cryogenic gas thermometers, steam Pressure thermometer, acoustic thermometer, paramagnetic salt thermometer, quantum thermometer, low temperature thermal resistance and low temperature thermocouple, etc. Low temperature thermometers require small size, high accuracy, good reproducibility and stability. The carburized glass thermal resistance made of porous high silica glass carburized and sintered is a kind of temperature sensing element of the low temperature thermometer, which can be used to measure the temperature in the range of 1.6 to 300K.

Non-contact type Its sensitive components and the measured object do not touch each other, also known as non-contact temperature measuring instrument. This kind of instrument can be used to measure the surface temperature of moving objects, small targets and objects with small heat capacity or rapid temperature changes (transient), and can also be used to measure the temperature distribution of the temperature field. The most commonly used non-contact temperature measuring instrument is based on the basic law of black body radiation and is called a radiation temperature measuring instrument. . All kinds of radiation temperature measurement methods can only measure the corresponding luminosity temperature, radiation temperature or colorimetric temperature. Only the temperature measured for a black body (an object that absorbs all radiation and does not reflect light) is the true temperature. If you want to determine the true temperature of an object, you must correct the surface emissivity of the material. The surface emissivity of the material not only depends on the temperature and wavelength, but also on the surface state, coating film and microstructure, so it is difficult to accurately measure. In automated production, it is often necessary to use radiation temperature measurement to measure or control the surface temperature of certain objects, such as the steel strip rolling temperature, roll temperature, forging temperature in metallurgy, and the temperature of various molten metals in smelting furnaces or crucibles. . Under these specific circumstances, the measurement of the surface emissivity of an object is quite difficult. For the automatic measurement and control of the solid surface temperature, an additional mirror can be used to form a black body cavity together with the measured surface. The influence of additional radiation can increase the effective radiation and effective emission coefficient of the measured surface. Use the effective emission coefficient to correct the measured temperature through the meter, and finally get the true temperature of the measured surface. The most typical additional mirror is a hemispherical mirror. The diffuse radiation energy of the measured surface near the center of the sphere is reflected back to the surface by the hemispherical mirror to form additional radiation, thereby increasing the effective emission coefficient, where ε is the surface emissivity of the material, and ρ is the reflectivity of the mirror. As for the radiation measurement of the true temperature of gas and liquid media, the method of inserting a heat-resistant material tube to a certain depth to form a black body cavity can be used. The effective emission coefficient of the cylindrical cavity after reaching thermal equilibrium with the medium is calculated by calculation. In automatic measurement and control, this value can be used to correct the measured cavity bottom temperature (that is, the temperature of the medium) to obtain the true temperature of the medium. Advantages of non-contact temperature measurement: The upper limit of measurement is not limited by the temperature resistance of the temperature sensing element, so there is no limit to the maximum measurable temperature in principle. For high temperatures above 1800°C, non-contact temperature measurement methods are mainly used. With the development of infrared technology, radiation temperature measurement has gradually expanded from visible light to infrared. It has been adopted from below 700°C to room temperature, and the resolution is very high.