There are many kinds of photoelectric sensors with photoelectric elements as sensitive elements, which are widely used. According to the output characteristics of photoelectric sensors, they can be divided into two categories: (1) photoelectric measuring instruments made by converting the measured photocurrent into a continuously changing photocurrent can be used to measure the intensity and physical quantities of light, such as temperature, light transmission capacity, object displacement and surface state. For example: illuminance meter, photoelectric pyrometer, photoelectric colorimeter and turbidity meter for measuring light intensity, photoelectric alarm for fire prevention, automatic detection device and instrument for checking the diameter, length, Ovality and surface roughness of machined parts. Their sensitive elements are photoelectric elements. Semiconductor optoelectronic components are not only widely used in civil industry, but also play an important role in military. For example, lead sulfide photoresist can be used to make infrared night vision instrument, infrared camera and infrared navigation system; (2) The measured value is converted into a continuously varying photocurrent. Various photoelectric automatic devices are made by using the "yes" or "no" electrical signal output characteristics of photoelectric elements when exposed to light or no light. The photoelectric element is used as a switching photoelectric conversion element. Such as photoelectric input device of electronic computer, switch temperature regulating device, digital photoelectric tachometer for speed measurement, etc.