A temperature sensor refers to a sensor that can sense temperature and convert it into a usable output signal. Temperature sensors are the core part of temperature measuring instruments, with a wide variety of types. According to measurement methods, 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 categories: thermistor and thermocouple.
A temperature sensor refers to a sensor that can sense temperature and convert it into a usable output signal. Temperature sensors are the core part of temperature measurement instruments, with a wide variety of types that can be divided into contact and non-contact based on measurement methods. They can be divided into two categories based on sensor materials and electronic component characteristics: thermistors and thermocouples. There are four main types of temperature sensors: thermocouples, thermistors, resistance temperature detectors (RTDs), and IC temperature sensors. IC temperature sensors include two types of contact type:
analog output and digital output
The detection part of a contact temperature sensor has good contact with the measured object, also known as a thermometer. Thermometers achieve thermal equilibrium through conduction or convection, allowing their readings to directly represent the temperature of the object being measured. Generally, the measurement accuracy is relatively high. Within a certain temperature measurement range, a thermometer can also measure the temperature distribution inside an object. However, for moving objects, small targets, or objects with very small thermal capacity, significant measurement errors can occur. Commonly used thermometers include bimetallic thermometers, liquid in glass thermometers, pressure thermometers, electropositive thermometers, thermistors, and thermocouple thermometers. They are widely used in industry, agriculture, commerce, and so on. In daily life, people often use these thermometers to measure temperatures below 120K. Low temperature thermometers have been developed, such as low-temperature gas thermometers, vapor pressure thermometers, acoustic thermometers, paramagnetic salt thermometers, quantum thermometers, low-temperature thermistors, and low-temperature thermoelectric couples. Low temperature thermometers require temperature sensing elements with small volume, high accuracy, good reproducibility and stability. The carburized glass thermistor made by sintering porous high silica glass is a temperature sensing element for low-temperature thermometers, which can be used to measure temperatures in the range of 1.6-300K.
Non-contact
Its sensitive components are not in contact with the measured object, also known as non-contact temperature measuring instruments. This type of instrument can be used to measure the surface temperature of moving objects, small targets, and objects with small thermal capacity or rapid temperature changes (transient), as well as to measure the temperature distribution of the temperature field.
The commonly used non-contact temperature measuring instruments are based on the basic law of blackbody radiation and are called radiation temperature measuring instruments. Radiation temperature measurement methods include 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 temperature measured for a blackbody (an object that absorbs all radiation but does not reflect light) is the true temperature. If you want to determine the true temperature of an object, correct the surface emissivity of the material. The surface emissivity of materials not only depends on temperature and wavelength, but also on surface condition, coating, and microstructure. In automation, it is often necessary to use radiation thermometry to measure or control the surface temperature of certain objects, such as the rolling temperature of steel strips, rolling roller temperature, forging temperature, and the temperature of various molten metals in smelting furnaces or crucibles in metallurgy. In these specific situations, measuring the surface emissivity of an object is quite difficult. For automatic measurement and control of solid surface temperature, an additional reflector can be used to form a blackbody cavity together with the measured surface. The influence of additional radiation can increase the effective radiation and effective emission coefficient of the measured surface. By using the effective emission coefficient and adjusting the measured temperature through an instrument, the true temperature of the measured surface can be obtained. A typical additional reflector is a hemispherical reflector. The diffuse radiation near the center of the ball on the measured surface can be reflected back to the surface by the hemispherical mirror, forming additional radiation, thereby improving the effective emission coefficient is the surface emissivity of the material, and p is the reflectivity of the reflector. As for the radiation measurement of the true temperature of gas and liquid media, the method of inserting heat-resistant material tubes to a certain depth to form blackbody cavities can be used. Calculate the effective emission coefficient of the cylindrical cavity after reaching thermal equilibrium with the medium. In automatic measurement and control, this value can be used to correct the measured bottom temperature (i.e. medium temperature) and 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 limitation on the measurable temperature in principle. For high temperatures above 18009C, the main method used is non contact pufferfish mixing measurement. With the development of infrared technology, radiation temperature measurement has gradually expanded from visible light to infrared, and has been adopted from below 7009 ℃ to room temperature with high visual resolution.
