The rotary paddle switches operating principle is simple. The unit is usually mounted through a bin wall at the top, middle or low-level point. During normal operation (no material present) a synchronous motor rotates the paddle at 1 RPM. When paddle rotation is impeded by material surrounding the paddle the motor will stall and cause the microswitch output to change state to signal an alarm or signal control.
There is two models of the rotary paddle switches. One made in plastic and the other in metal.