Short circuit monitor for static inverters and the like

Claim 1

Apparatus for monitoring the output of an inverter utilized to generate a regulated a.c. signal of a predetermined frequency, said apparatus comprising: first and second input terminals for receiving signals respectively representing the value of line current and line voltage at the output of the inverter; first normally non-conductive means coupled to said first input terminal and being turned on when said line current reaches a first threshold level; second means coupled to said second input terminal for maintaining said first means in the non-conductive state when said line voltage is above a second predetermined threshold level, said second means being adapted to enable said first means to be turned on only when said line voltage falls below said second threshold level; a source of electrical energy; a timing circuit coupled to said energy source and adapted to charge toward a predetermined value; switch means coupled across said timing circuit for normally providing a by-pass path to prevent charging from said energy source to be applied to said timing circuit, said switch means having an input coupled to said first means for disabling said by-pass path and enabling charging of said timing circuit when said first means is turned on; means coupled to said timing circuit for generating an alarm signal when said timing circuit reaches a third predetermined threshold level whereby said alarm signal is generated only when circuit condition persists for a predetermined time interval.