Abstract: A monitoring circuit for a door operating D.C. electric motor, the circuit comprises a first means for detecting a back EMF of the motor and producing a load signal indicative of the magnitude of the back EMF, a second means for detecting the time rate of change of the load signal and issuing an obstruction signal if the magnitude of the time rate of change of the load signal exceeds a predetermined value.

Abstract: A solenoid torquer system with flux rate feed-back. The system includes a torquer coil and an associated core, and a device adapted to drive a current through the coil having an amplitude proportional to the difference between a coil current command signal and the actual current in the coil. A flux rate servo loop includes a sensor coil coupled to the core to provide a signal representative of the flux rate in the core. This flux rate signal is compared with a flux rate command signal having a ternary width-modulated form. The resultant difference signal is used as the current command signal. The system network provides a precise flux level, or force.