Safety circuit for detecting asymmetry in thyristor load currents

Claim 1

A symmetry sensing safety circuit means controlling an alternating electrical current flow through a bidirectional triode thyristor having its main terminals serially connected to an electrical device and to a source of electrical energy, the symmetry sensing safety circuit means having sensors connected in series and control logic connected in parallel with the thyristor, comprising: a current sensing resistor device having a low resistance serially connected to thyristor and to the source of electrical energy sensing the alternating electrical current flow; differential amplifier circuit means operatively associated with said resistor device generating a signal which is indicative of the direction and proportional to the amplitude of the sensed electrical current flow; integrating circuit means operatively associated with said differential amplifier means generating a signal which is indicative of the direction and proportional to the amplitude of said signal generated by said differential amplifier circuit means integrated over a predetermined time interval, said time interval being variable by a user, said integrating circuit means having a time constant of at least 0.5 seconds; window comparator circuit means operatively associated with said integrating circuit means generating a signal indicating when said signal generated by said integrating circuit means is outside of a predetermined range of values, said range of values being user adjustable; relay control circuit means operatively associated with said window comparator circuit means generating a triggering signal whenever said window comparator circuit means generates said signal indicating said signal generated by said integrating circuit means is outside of said predetermined range of values; electromechanical relay means operatively associated with said electromechanical relay means latching, in a selectively releasable manner, said electromechanical relay means in said latched state switching off the alternating current flow to the thyristor.

Claim 20

A method of detecting and acknowledging asymmetry in a load current flow, comprising the steps of: sensing said load current flow; generating a first signal which is proportional to the amplitude and direction of said sensed load current flow; generating a second signal which is proportional to the amplitude and direction of said first signal integrated over a predetermined interval of time; comparing said second signal to a predetermined range of values and generating a trigger signal whenever said second signal is outside of said range of values; actuating an electromechanical relay means operatively associated with said load current flow by means of said trigger signal to disable said load current flow.

Claim 21

A method of detecting and acknowledging asymmetry in a load current flow, comprising the steps of: sensing said load current flow; generating a first signal which is proportional to the amplitude and direction of said sensed load current flow; generating a second signal which is proportional to the amplitude and direction of said first signal integrated over a predetermined interval of time; comparing said second signal to a predetermined range of values and generating a trigger signal whenever said second signal is outside of said range of values; actuating an electromechanical relay means operatively associated with said load current flow by means of said trigger signal to disable said load current flow.

Claim 22

A method of protecting a bidirectional triode thyristor from excessive asymmetrical flow of alternating load current therethrough, comprising the steps of: sensing the load current flow; generating a first signal indicative of the direction and amplitude of the sensed current flow; integrating said first signal over a predetermined interval of time corresponding to a predetermined number of current alterations so as to produce an integrated signal indicative of the asymmetry of the current flow during said predetermined interval of time; comparing said integrated signal to a predetermined range of values to produce a comparison signal; whenever said comparison signal indicates that said integrated signal is outside said predetermined range of values, producing a trigger signal; and, in response to the trigger signal, shutting off the flow of load current to the thyristor.

Claim 23

A method of protecting a bidirectional triode thyristor from excessive asymmetrical flow of alternating load current therethrough, comprising the steps of: sensing the load current flow; generating a first signal indicative of the direction and amplitude of the sensed current flow; integrating said first signal over a predetermined interval of time corresponding to a predetermined number of current alterations so as to produce an integrated signal indicative of the asymmetry of the current flow during said predetermined interval of time; comparing said integrated signal to a predetermined range of values to produce a comparison signal; whenever said comparison signal indicates that said integrated signal is outside said predetermined range of values, producing a trigger signal; and, in response to the trigger signal, shutting off the flow of load current to the thyristor.