Temperature measuring instruments can be divided into contact type and non - contact type. Generally speaking, the contact thermometer is relatively simple, reliable and of high measuring accuracy. However, due to the fact that the temperature measuring element and the medium under test need sufficient heat exchange, it takes a certain amount of time to achieve the thermal balance, so there is a delay phenomenon of temperature measurement, and due to the limitation of high-temperature resistant materials, it cannot be applied to very high temperature measurement. Non-contact instrument temperature measurement is through the principle of thermal radiation to measure the temperature, temperature measuring components do not need to contact with the measured medium, the temperature range is wide, is not subject to the limit of the temperature measurement limit, will not destroy the temperature field of the measured object, the reaction speed is generally faster; However, due to the influence of external factors such as the emissivity of the object, measuring distance, smoke and vapor, the measurement error is large.
