Abstract: A method and apparatus for detecting blockages in one or more vapor flow lines such as vapor recovery lines used in liquid gasoline dispensing systems. The method and apparatus operate by sensing pressure in vapor flow lines and determining whether the frequency of the variations in the filtered rate of change with time of the pressure signal exceeds a preset limit indicating vapor bubbling through a liquid blockage. The method and apparatus also operate to determine whether the pressure signal exceeds a preset limit indicating a blockage condition.

Abstract: A ramp and pedestal phase control circuit for controlling electrical energy supplied from an alternating current source to a load. The circuit has a controllable alternating current switching device, and bilateral threshold means is provided for enabling the switching device to conduct current from the source to the load when the magnitude of the voltage across the threshold means exceeds a predetermined value. A first circuit rapidly increases the voltage across the threshold means to a value less than the predetermined value, and a second circuit more slowly further increases the voltage across the threshold means to the predetermined value so as to enable the switching device. The first and second circuits are effective on successive half cycles of the alternating current source to reverse the polarity of the voltage across the threshold means.

Abstract: A circuit for controlling the application of power from a source thereof to a load. In this controlling circuit, a phase control circuit is provided for supplying current from the source to the load for varying voltage applied to the control node to maintain the effective voltage near a preferred value despite variations in the voltage of the source. An initializing circuit is also provided for preventing the application of excessive voltage to the load upon the initial energization of the controlling circuit.

Abstract: A control system for controlling a condition, such as temperature, to maintain that condition in a generally enclosed space near a selected condition value. The system has a condition responsive impedance in series with a selectable impedance across a regulated voltage source to provide a voltage divider network, the output of which reflects the instantaneous condition of the environmental space relative to a selected condition therefor. This output is supplied to a Schmitt trigger circuit having hysteresis characteristics sufficient to provide a stable operating mode for the control system, and the Schmitt trigger circuit output controls a means for changing the condition of the enclosed space. A manual mode selecting switch may be provided for inserting any of several different impedances in the series combination, and a timer may be provided to automatically switch between different impedances in the series combination as determined by elapsed time with respect to application of power to the circuit.

Abstract: A control for supplying not more than one complete cycle of an alternating current upon command. The circuit has a plurality of gate controlled switching devices and a command switch. An energy storage device has one of the switching devices connected in the circuit for conducting a short time after the beginning of each current excursion of a specific polarity, and another of the switching devices is connected in series between a power source and a load for supplying energy to the load when gated. A third switching device is adapted to conduct, when gated, for depleting energy from the storage device only when the command switch so indicates. Conduction of the third switching device gates the other switching device and occurs only during current excursions of the desired polarity when the one switching device is non-conducting.