The temperature measuring instrument can be divided into two categories: contact and non-contact. General contact temperature measuring instrument for temperature measurement instrument is simple, reliable, high measurement precision; but because of the temperature element and the measured medium need sufficient heat to help Kong needs time to reach thermal equilibrium, so the delay phenomenon of temperature, and high temperature resistant material limit, cannot be applied to temperature measurement is high. Non contact temperature measurement instrument is used to measure the temperature by thermal radiation principle, measuring element need not contacted with measured medium, wide temperature range, the temperature will not damage the upper limit of the temperature field of the measured object, the response rate is relatively fast; but by the object emissivity, distance measurement, the dust and water vapor and other external factors, the measurement error is big.