Temperature Sensor

The detection part of the contact type temperature sensor has good contact with the measured object, which is also called a thermometer.

The thermometer achieves thermal equilibrium through conduction or convection so that the indication of the thermometer can directly represent the temperature of the measured object.

Temperature sensor (Figure 2)

The general measurement accuracy is high. Within a certain temperature range, the thermometer can also measure the temperature distribution inside the object. However, for sports objects, small objects or objects with small heat capacity, large measurement errors will occur. Commonly used thermometers include bimetal thermometers, glass liquid thermometers, pressure thermometers, resistance thermometers, thermistors, and thermocouples. They are widely used in industrial, agricultural, commercial and other sectors. People often use these thermometers in everyday life. With the wide application of cryogenic technology in defense engineering, space technology, metallurgy, electronics, food, medicine, and petrochemicals, and the study of superconducting technology, cryogenic thermometers measuring temperatures below 120K have been developed, such as cryogenic gas thermometers, steam Pressure thermometers, acoustic thermometers, paramagnetic salt thermometers, quantum thermometers, low-temperature thermal resistance, and low-temperature thermocouples. Cryogenic thermometers require that the temperature sensing element be small, accurate, reproducible, and stable. The carburizing glass thermal resistance formed by carburizing sintered porous high-silica glass is a temperature sensing element of a low-temperature thermometer and can be used to measure temperatures in the range of 1.6 to 300K.

Its sensitive components and the measured object do not contact each other, also known as non-contact temperature measuring instrument. This instrument can be used to measure the surface temperature of moving objects, small objects and objects with small heat or rapid temperature changes (transients). It can also be used to measure the temperature distribution of a temperature field.

The most commonly used non-contact temperature measurement instrument is based on the basic law of blackbody radiation and is called a radiation thermometer.

Temperature sensor (Figure 3)

Radiation thermometry includes the brightness method (see optical pyrometer), radiation method (see radiation pyrometer) and colorimetry (see colorimeter). All kinds of radiation temperature measurement methods can only measure the corresponding photometric temperature, radiation temperature or colorimetric temperature. Only the temperature measured for a black body (a body that absorbs all radiation and does not reflect light) is the true temperature. To determine the true temperature of the object, the material surface emissivity must be corrected. The surface emissivity of the material depends not only on the temperature and wavelength, but also on the surface state, coating film, and microstructure, and it is difficult to measure accurately. In automated production it is often necessary to use radiation thermometry to measure or control the surface temperature of certain objects, such as steel strip rolling temperature in metallurgy, roll temperature, forging temperature, and the temperature of various molten metals in the smelting furnace or crucible . In these specific cases, the measurement of the surface emissivity of the object is quite difficult. For the automatic measurement and control of the solid surface temperature, additional mirrors can be used to make the black body cavity together with the measured surface. The effect of additional radiation can increase the effective radiation and effective emission coefficient of the measured surface. The actual measured temperature is corrected by the instrument using the effective emission coefficient, and the true temperature of the measured surface can be finally obtained. The most typical additional mirror is a hemispherical mirror. The diffuse radiant 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. ε is the material surface emissivity, and ρ is the reflectivity of the mirror.

Temperature sensor (Figure 4)

For radiometric measurements of the true temperature of gas and liquid media, a method of inserting a tube of a heat-resistant material to a depth to form a black body cavity may be used. The calculation of the effective emission coefficient of the cylindrical cavity after thermal equilibrium with the medium is calculated. In automatic measurement and control, this value can be used to correct the temperature of the measured cavity bottom (ie the medium temperature) to obtain the real temperature of the medium.

Non-contact temperature measurement Advantages: 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 temperatures above 1800°C, non-contact temperature measurement methods are used. With the development of infrared technology, the radiation temperature measurement gradually expands from visible light to infrared light, and temperatures below 700° C. have been used up to room temperature, and the resolution is very high.

Metal expansion principle designed sensor

The metal will have a corresponding extension after the ambient temperature changes, so the sensor can signal this reaction in different ways.

Bimetal sensor

The bimetal consists of two sheets of metal with different coefficients of expansion. As the temperature changes, the material A swells more than the other metal, causing the sheet to bend. The curvature of curvature can be converted into an output signal.

Bimetal rod and metal tube sensor

As the temperature rises, the length of the metal tube (Material A)