Cold metal detectors are mainly used in metallurgical production lines. They detect the position of the workpiece and output a switch control signal (contact or level signal) to participate in automatic control. Cold metal detectors can be divided into two types according to the light source: visible red light type cold metal detectors and infrared light type cold metal detectors. Cold metal detectors can be divided into feedback reflection type (R), through-beam type (T), and direct reflection type (D) according to the detection form.