The temperature measurement principle of thermal resistors
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This post was last edited by qinweijun on 2012-4-19 08:36. A thermistor thermometer measures temperature by taking advantage of the fact that the resistance value of a metal conductor changes as the temperature changes. The relationship between the resistance value of a thermistor and temperature is given by the following formula: http://www.zhanjiao.com/up/201110251826361101.jpg As can be seen from this formula, temperature causes changes in the resistance of a conductor. Experiments have shown that for every 1°C increase in temperature, the resistance value of most metals increases by 0.4% to 0.6%. Therefore, by measuring the change in resistance value using instruments, it is possible to determine the corresponding temperature, thus achieving the purpose of temperature measurement. :$
This post was last edited by qinweijun on 2012-4-19 08:38. Let’s learn together! Types of thermal resistors: 1) Ordinary thermal resistors. As can be understood from the principle of temperature measurement using thermal resistors, changes in the temperature being measured are detected directly through changes in the resistance value of the thermal resistor. Therefore, changes in the resistance of various wires, such as those connecting the thermal resistor element, can affect the temperature measurement. 2) Encased thermoresistors: Encased thermoresistors are solid devices composed of a temperature-sensing element (resistive body), leads, insulating material, and a stainless steel sleeve. Their outer diameter is generally between φ2–φ8 mm, with the minimum value reaching φ mm. Compared to ordinary thermal resistors, it has the following advantages: ① Small size, no air gaps inside, resulting in low thermal inertia and minimal measurement lag ； ②Good mechanical properties, vibration resistance, and impact resistance ； ③It can bend, making installation easier. ④ It has a long service life. 3) Face thermoresistor: The temperature-sensing element of the face thermoresistor is made of specially treated resistive wire material, which is wound tightly against the surface of the thermometer. Compared with ordinary axial thermoresistors, it can reflect the actual temperature of the measured end face more accurately and quickly, and is suitable for measuring the end face temperatures of bearing shells and other mechanical components. 4) Flameproof thermal resistors: Flameproof thermal resistors utilize a specially designed junction box to contain any explosions that may occur due to explosive gases inside their enclosure as a result of sparks or arcs; this prevents explosions from occurring at the production site. Flameproof thermoresistors can be used for temperature measurement in areas with explosion hazards classified as Bla--B3c. Common materials: platinum thermoresistors, copper thermoresistors, nickel thermoresistors, and semiconductor thermistors.