Resistance spin material level switch using principle is very simple, resistance spin material level meter is usually installed in a bunker at the top, middle or bottom of the silo wall, in the material level under the condition of normal (no material level signal), synchronous motor rotor blades at the speed of IRPM: when the blade is material block 2 cannot turn, synchronous motor will stop running, and drive the micro switch action, change the current state of instructions (indicating alarm or control)