Abstract: The present invention is a load sensor for use in an automatic portal operator such as an industrial gate operator. An induction motor is employed to move the gate. The power factor of the AC electric power supplied to the induction motor is monitored. A safety operation is triggered when the power factor indicates the motor load is greater than a predetermined amount, as when an obstruction is encountered by the gate.

Abstract: A control system for operating a bidirectional gate driven by a reversible electric motor includes an overload protection circuit to prevent motor current overload produced by gate obstructions and the like. The system includes control switches for operating gate opening and gate closing circuits which respectively energize the motor for rotation in opposite directions. The safety circuit includes a motor current sensing device and a first comparator which compares the level of sensed motor current with a temperature adjusted, selectable reference value and delivers a motor disabling signal to the opening and closing circuits if the sensed value exceeds the reference level. The safety circuit also includes a second comparator which compares the sensed current level with another reference value to produce the disabling signal in the event that the selected reference value of the first comparator is incorrect.