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An electrical actuator such as a direct current solenoid or motor is energized by a square wave voltage having an amplitude which applies full operating voltage to the actuator during each pulse. The duty cycle of the applied voltage is variable between predetermined minimum and maximum values, the

An electrical actuator such as a direct current solenoid or motor is energized by a square wave voltage having an amplitude which applies full operating voltage to the actuator during each pulse. The duty cycle of the applied voltage is variable between predetermined minimum and maximum values, the minimum value being sufficiently high to overcome the starting hysteresis of the actuator. The control apparatus has particular application to proportional control systems, such as in the selective operation of dual solenoid, hydraulic control valves. A hand controller is provided with a handle having a center off position and on positions in opposite directions corresponding to the two solenoids. As the handle is moved away from the off position in either direction through an initial, relatively small displacement, a switch is actuated to apply the square wave voltage to the appropriate solenoid. Additional movement by the operator causes the duty cycle to vary from minimum to maximum as desired. The resistance of a phototransistor determines the value of the duty cycle, and is varied by a cam-shaped shutter operated by the controller handle and which is interposed between the phototransistor and a light-emitting diode. The hand controller may be electrically isolated from the actuators through the use of fiber optic light guides to transmit control information. A fail-safe circuit is provided by a missing pulse detector that deenergizes the controlled actuator if a component failure causes a constant driving voltage to be produced.

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