Introduction to the main temperature measurement methods of the thermometer
There are two types of temperature measurement methods: contact and non-contact.
1. The sensor is placed in the same thermal equilibrium state as the object, and the temperature measurement method that keeps the sensor and the object at the same temperature is the contact temperature measurement method. For example, mercury thermometers, pressure thermometers, and bimetallic thermometers that use the principle of thermal expansion of the medium. There is also the use of the characteristics of the electrical parameters of the object changing with the temperature to detect the temperature. Such as thermal resistance, thermistor, electronic temperature sensor and thermocouple etc.
Contact temperature measuring instrument The temperature measuring instrument is relatively simple, reliable, and has high measurement accuracy; but because the temperature measuring element and the measured medium need to conduct sufficient heat exchange, it takes a certain amount of time to reach thermal equilibrium, so there is a delay in temperature measurement. At the same time, due to the limitation of high temperature resistant materials, it cannot be applied to high temperature measurement.
2. Non-contact instrument temperature measurement measures temperature through the principle of heat radiation, and the temperature measurement element does not need to be in contact with the measured medium. To achieve this temperature measurement method, the temperature can be detected by using the relationship between the surface thermal radiation intensity of the object and the temperature. There are full radiation method, partial radiation method, brightness method of single wavelength radiation power and colorimetric method of comparing two wavelength radiation power, etc. Non-contact instrument temperature measurement has a wide range of temperature measurement, is not limited by the upper limit of temperature measurement, and will not destroy the temperature field of the measured object. The reaction speed is generally faster; but it is affected by the emissivity of the object, measurement distance, smoke and Influenced by external factors such as water vapor, the measurement error is relatively large.
standard requirement
Basically all CSA and UL electrical product standards require temperature rise testing, and will require detailed test conditions, such as product input power, load requirements, and test environment, etc.; test methods, such as installation location and use of temperature measurement methods, etc.; Test time; Judgment criteria, maximum temperature rise and incidental tests, etc. In the test method, the method of temperature measurement will be stipulated. Usually, the thermocouple must be 30AWG (0.51 square centimeters), iron-constantan (gradation number J) or copper-constantan (gradation number T ) and matching recording instruments.
Thermocouple temperature measurement principle, method and scope of application
Weld two conductors (or semiconductors) A and B of different materials to form a closed circuit, as shown in the figure. When there is a temperature difference between the two junctions T1 and T2 of the conductor and the conductor, an electromotive force is generated between the two, thus forming a current in the circuit. This phenomenon is called the thermoelectric effect. Thermocouples use this effect to work.
