SOLENOID CONTROL SYSTEM WITH CUSP DETECTOR

A solenoid control system wherein the duration of actuation of a solenoid is a function of the workload imposed thereon so that the current to the solenoid is always turned off as soon as the solenoid plunger or armature is seated. Solenoid control logic responds to an external demand for the energization of the solenoid and enables a solenoid drive circuit which supplies current to the solenoid coil. The level of current builds in the solenoid coil until the solenoid plunger or armature is pulled in. The current continues to build as the solenoid plunger or armature is drawn in until that point at which the reluctance of the magnetic circuit is changing faster than the current in the solenoid coil is able to build. From this point until the solenoid plunger is seated, the current drops. As soon as seating has occurred, the reluctance ceases to change and the current once again begins to build in the solenoid coil. The change in reluctance and the termination of that change is represented by a cusp in the waveform of the current through the solenoid coil. A broad band cusp detector senses the point at which this change in reluctance ceases (i.e., when the solenoid plunger or armature seats) and generates a pulse which is supplied to solenoid control logic causing it to disable the solenoid drive circuit and turn off or reduce the current to the solenoid coil. The solenoid control logic further insures that the solenoid drive circuit is disabled in the event that the cusp-indicative pulse does not occur within a predetermined interval of time so as to conserve energy and protect the solenoid and associated circuitry.