The working principle of the thermometer

Laboratory thermometer: The principle of mercury thermometer is very simple-it is because mercury expands and contracts with heat, so why not use water, because when water is 4 degrees, it expands with heat and cold, and the expansion coefficient of mercury is relatively large and changes. Obviously there are alcohols in it, the red alcohol thermometer is suitable for measuring low temperature (about -78~+110 degrees), mercury thermometer is suitable for higher temperature laboratory thermometers: the principle of mercury thermometer is very simple- It is because of the thermal expansion and contraction of mercury. As for why you should not use water, because when the water is 4 degrees, it expands with heat and cold, and the expansion coefficient of mercury is relatively large, and the change is obvious. There are also alcohols inside, which are red and red. This kind of alcohol thermometer is suitable for measuring low temperature (about -78~+110 degrees), and the mercury thermometer is suitable for higher temperature (about 15~300 degrees). There are also kerosene thermometers. There are also some industrial thermometers: pressure thermometers The principle of ——According to the law of liquid expansion, that is, for a certain mass of liquid, under the condition of constant volume, the pressure and temperature of the liquid are linear. The pressure and temperature of gas and steam also have a certain functional relationship, so the scale of the pressure thermometer should be evenly divided. The pressure thermometer is composed of a temperature bulb filled with a temperature sensing medium, a pressure transmission element (capillary tube) and a pressure sensitive element (spring tube). The principle of infrared thermometer-any object will have infrared radiation, it shows the temperature of the object. The higher the temperature, the greater the radiation. Use the infrared receiver as the sensor, after digital filtering and amplification, and then function calculation, the number is displayed. Infrared thermometer is composed of optical system, photodetector, signal amplifier and signal processing. Display output and other parts. The optical system condenses the infrared radiation energy of the target in its field of view. The infrared energy is focused on the photodetector and converted into a corresponding electrical signal, which is converted into the temperature value of the measured target. The principle of thermocouple thermometer- －－-The principle of the thermocouple thermometer is to connect the 'galvanometer-copper wire-iron wire-copper wire' in series into a loop. At this time, the two ends of the iron wire and the copper wire will form two 'joints' ( junction), if the temperature of the two junctions is different, a voltage will be generated between them, and the weak current flowing through the iron wire and the copper wire can be measured in the microammeter. To use a thermocouple as a thermometer, the following calibration must be done first. Put one joint into ice water and put the other joint into boiling water, and write down the current intensity at this time. This is the current value when the temperature difference is 100°C. For two known metal wires, the current value is proportional to the temperature difference between the two junctions, and the measurement range is large, that is, from -200°C to 1700°C, and the sensitivity is very high.