Detailed introduction to the principle of various thermometers

Bimetal thermometer 

Working principle: Use thermocouple to connect the two ends of two different metal conductors to form a closed circuit. One end is heated and the other end is cooled. Then the two contact points will generate electromotive force due to the difference in temperature. There will be current. Because this thermoelectromotive force is a function of the temperature difference between the two contact points, a thermometer is made using this feature.

Working characteristics: According to the difference of two metal materials, the measuring range of the thermometer is also different. For example, the temperature measurement range of the thermocouple composed of copper and constantan is between 200～400℃; iron and constantan are used at 200～1000 Between ℃; The thermocouple made of platinum and platinum-rhodium alloy (10% rhodium) can measure the temperature above 1,000 degrees Celsius; iridium and iridium rhodium (rhodium 50%) can be used at 2300℃; if tungsten and molybdenum (molybdenum 25%) are used It can be as high as 2600°C.

 

 

Pointer thermometer

Working principle: It works based on the principle that two different metals expand at different degrees when the temperature changes. The main element is a multilayer metal sheet composed of two or more metal sheets laminated together. In order to improve the sensitivity of temperature measurement, the metal sheet is usually made into a spiral shape. When the temperature of the multi-layer metal sheet changes, the amount of expansion or contraction of each layer of metal varies, causing the spiral coil to roll up or loosen. Because one end of the spiral coil is fixed and the other end is connected with a pointer that can rotate freely, when the bimetallic piece feels the temperature change, the pointer can indicate the temperature on a circular graduation scale.

Working characteristics: temperature display is intuitive and convenient; safe and reliable, long service life; a variety of structural forms, which can meet different requirements; can directly measure the temperature of liquid, steam and gas media in the range of -80℃～500℃ in various production processes.