The metal separator uses the principle of electromagnetic inductance to detect metals. All metals, including iron and non iron, have high detection sensitivity. The entry of ferromagnetic metal into the detection area will affect the distribution of magnetic field in the detection region, and thus affect the fixed range of flux. Non-ferromagnetic metal entering the detection area will produce eddy effect, but also will make the detection area of the magnetic field distribution changes, usually metal separator consists of two parts, namely metal separator and automatic culling device, in which the detector is the core part. Detector internal distribution of three sets of coils, that is, the central and two equivalent receiving coils, through the middle of the transmission coil connected to the oscillator to produce high-frequency variable magnetic field, the idle state when the two sides receive the coil induction voltage before the magnetic field is not interfered with each other to achieve a balanced state. Once the metal impurities enter the magnetic field, the magnetic field is disturbed, the balance is broken, two of the receiving coil of the induction voltage can not be offset, not offset by the control system to enlarge the induction voltage processing, and generate alarm signal (detection of metal impurities). The system can use the alarm signal to drive the automatic culling device, etc., so as to exclude the metal impurity from the production line.