Lamp failure indicator

Claim 1

In a system including first and second critical electrical circuit elements, a power supply, and first switch means for selectively connecting either of said first and second critical electrical circuit elements to said power supply, the improvement comprising: means for monitoring the operation of said critical electrical circuit elements and for intermittently substituting the nonselected circuit element for the selected circuit element in the event of a failure of the latter, said means comprising: an interrupter device connected in circuit with said critical electrical circuit elements and said power supply and said first switch means for monitoring the current from said power supply to either selected circuit element, said interrupter device being inhibited from functioning as an active interrupter by a normal current to said selected circuit element, said interrupter device being enabled to function as an active interrupter to produce an audible indication and to simultaneously and intermittently connect the nonselected circuit element to said power supply in the presence of a subnormal current to said selected circuit element, said interruPter device comprising: second switch means having an open circuit position and a closed circuit position connected between said first and second circuit elements; bias means operatively associated with said second switch means for biasing said second switch means in said closed position thereby connecting said nonselected circuit element to said power supply with said selected circuit element; and a single current sensing coil connected in circuit with said power supply and said first switch means for sensing the current flowing from said power supply to said first switch means and thence to either of said critical electrical circuit elements, said current sensing coil electromagnetically actuating said second switch means to said open position to disconnect said nonselected circuit element from said power supply when said current is above a predetermined value, said second switch means returning to said closed position to connect said nonselected circuit element to said power supply when said current through said selected circuit element is below said predetermined value, the current flowing from said power supply through said nonselected circuit element again actuating said second switch means to said open position until said second switch means again opens so that said second switch means vibrates producing an audible indication and simultaneously and intermittently substitutes said nonselected circuit element for said selected circuit element.