Discussion on temperature sensor

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Talking about temperature sensor

temperature is a basic physical quantity, and all processes in nature are closely related to temperature. Temperature sensor is the earliest developed and most widely used sensor to prevent the sample from flying out and injuring people. The market share of temperature sensors is much higher than that of other sensors. People began to measure temperature in the early 17th century. With the support of semiconductor technology, semiconductor thermocouple sensors, PN junction temperature sensors and integrated temperature sensors have been developed in this century. Accordingly, according to the interaction law between waves and matter, acoustic temperature sensors, infrared sensors and microwave sensors have been developed successively

the conductors of two different materials construction elevator safety rules gb10055 ⑴ 996, if they are connected together at a certain point, heating this connection point will lead to potential difference at the part where they are not heated. The value of this potential difference is related to the temperature of the measuring point at the unheated part and the material of the two conductors. This phenomenon can occur in a wide temperature range. If this potential difference is accurately measured, and then the ambient temperature of the unheated part is measured, the temperature of the heating point can be accurately known. Because it must have two conductors of different materials, it is called "thermocouple". Thermocouples made of different materials are used in different temperature ranges, and their sensitivity is also different. The sensitivity of thermocouple refers to the change of output potential difference when the temperature of heating spot changes by 1 ℃. For most thermocouples supported by metal materials, the increment in 2017 is only Lanke lithium, which is about 5 ~ 40 microvolts/℃

thermocouple sensor has its own advantages and disadvantages. Its sensitivity is relatively low, and it is easy to be affected by environmental interference signals and the temperature drift of preamplifier. Therefore, it is not suitable for measuring small temperature changes. Because the sensitivity of thermocouple temperature sensor has nothing to do with the thickness of material, it can also be made of very fine material. Also, because the metal material used to make thermocouples has good ductility, this fine temperature measuring element has a very high response speed and can measure the process of rapid change

temperature sensor is the most commonly used of various sensors. Modern temperature sensors have a very small shape, which makes them more widely used in various fields of production practice, and also provides countless convenience and functions for our life

there are four main types of temperature sensors: thermocouple, thermistor, resistance temperature detector (RTD) and IC temperature sensor. IC temperature sensor includes analog output and digital output

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

the thermometer achieves heat balance through conduction or convection, so that the indicated value of the thermometer can directly represent 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. However, for moving bodies, small targets or objects with small heat capacity, large measurement errors will occur. Commonly used thermometers include bimetallic thermometers, liquid glass thermometers, pressure thermometers, resistance thermometers, thermistors and thermoelectric couples. They are widely used in industry, agriculture, commerce and other sectors. People often use these thermometers in daily life. With the wide application of low-temperature technology in national defense engineering, space technology, metallurgy, electronics, food, medicine, petrochemical and other departments and the research of superconducting technology, low-temperature thermometers for measuring temperatures below 120K have been developed, such as low-temperature gas thermometers, vapor pressure thermometers, acoustic thermometers, paramagnetic salt thermometers, quantum thermometers, low-temperature thermal resistances and low-temperature thermoelectric couples. Low temperature thermometers require temperature sensing elements with small volume, high accuracy, good reproducibility and stability. The thermal resistance of carburized glass sintered from 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

the sensitive element of the non-contact temperature sensor is not in contact with the measured object, which is also called the 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 change (transient). It 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 blackbody radiation, which is called radiation temperature measuring instrument. Radiation thermometry includes brightness method (see optical pyrometer), radiation method (see radiation pyrometer) and colorimetric method (see Colorimetric Thermometer). Various radiation temperature measurement methods can only measure the corresponding photometric temperature, radiation temperature or colorimetric temperature. Only the measured temperature of blackbody (an object that absorbs all radiation and does not reflect light) is the real temperature. If the real temperature of the object is to be measured, the emissivity of the material surface must be corrected. The surface emissivity of materials depends not only on temperature and wavelength, but also on surface state, coating film and microstructure, so it is difficult to measure accurately. In automatic production, it is often necessary to use radiation thermometry to measure or control the surface temperature of some 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. In these specific cases, it is quite difficult to measure the emissivity of the object surface. For the automatic measurement and control of solid surface temperature, additional mirrors can be used to form a blackbody cavity with the measured surface. The effect of additional radiation can improve the effective radiation and effective emission coefficient of the measured surface. Using the effective emission coefficient, the measured temperature is corrected by the instrument, and finally the real temperature of the measured surface can be obtained. The most typical additional mirror is a hemispherical mirror. The diffuse radiation of the measured surface near the center of the ball can be reflected back to the surface by the hemispherical mirror to form additional radiation, so as to improve the effective emission coefficient: where ε Is the oil free outflow rate of the oil return pipe on the material surface, ρ Is the reflectivity of the reflector. As for the radiation measurement of the real temperature of gas and liquid media, the method of inserting a heat-resistant material tube to a certain depth to form a blackbody cavity can be used. The effective emission coefficient of the cylindrical cavity after reaching thermal equilibrium with the medium is calculated. In automatic measurement and control, this value can be used to correct the measured cavity bottom temperature (i.e. medium temperature) 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 temperature sensing elements, so there is no limit on the maximum measurable temperature in principle. For high temperatures 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. It has been used below 700 ℃ to normal temperature, and the resolution is very high. (end)

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