ear thermometer is composed of optical system, photoelectric detector, signal amplifier, signal processing, display output and other parts. The optical system collects the target infrared radiation energy in its field of view, and the size of the field of view is determined by the optical parts and position of the thermometer. The infrared radiated by the measured object first enters the optical system of the thermometer, and then the incident infrared is collected by the optical system to make the energy more concentrated; the collected infrared is input into the photoelectric detector, and the key component of the detector is the infrared sensor. Its task is to convert the optical signal into an electrical signal; the electrical signal output from the photodetector is converted into the temperature value of the measured target after being corrected by the amplifier and the signal processing circuit according to the internal algorithm of the instrument and the target emissivity.