The transistor proximity switch XS612B1MAL2 is now widely used as a contactless switch composed of transistor oscillation as the core. This type of switch generates eddy currents inside the ferromagnetic material when it approaches (without touching) the spatial magnetic field of its transistor oscillator, dissipating oscillation energy and weakening oscillation until it stops; After the ferromagnet leaves, the transistor oscillator resumes oscillation, which depends on whether the oscillator oscillates or whether the antiferromagnetic stopper is close to the switch. The proximity switch has quick response, accurate positioning, long service life, and no mechanical collision. Currently, it has been applied in stroke control, positioning control, and various protection controls. The following diagram shows a circuit that is close to a switch, consisting of an LC oscillation circuit, a switch circuit, and an emitter output. The oscillator is composed of v1, where l2 and c2 form a frequency selection circuit. l1 is the feedback coil, l3 is the output coil, and these three coils are wound on the same magnetic core, as shown in Figure a. When the ferromagnet is not close to the induction head of the switch, the oscillation circuit maintains oscillation, and there is AC output on l3. After rectification by diode vd1, v2 obtains sufficient bias current and works in a saturated conduction state. At this time, u2≈ 0, v3 cut-off, no output from the emitter output, and the relay ka connected to the output end is not powered on. When the ferromagnet approaches the sensing head, it induces eddy currents. Due to the demagnetization effect of the eddy currents, the coupling between l1 and l2 is weakened, making the feedback insufficient to maintain oscillation. As a result, the oscillator is forced to stop oscillating, with no AC output on l3 and v2 cut off. If r7>& gt;r5， At this point, u2≈ ucc， The output of the emitter output is also close to the ucc, causing the relay ka to be energized and activated. Figure C shows the symbol of the proximity switch moving contact. V3 uses emitter output to improve load capacity. RF is a positive feedback resistor. When the circuit stops oscillating, it feeds back a portion of the collector voltage of v2 to the emitter of v1, raising the emitter potential to quickly and reliably stop the oscillating circuit. When the circuit starts oscillating, u2≈ 0 has no feedback voltage, allowing the oscillating circuit to quickly resume oscillation and make the switch action more rapid and accurate< Transistor proximity switch XS612B1MAL2& nbsp;