Current supervision circuit

Claim 1

In a circuit for supervising possible excursions of a signal having a value which normally lies intermediate predetermined upper and lower limits and which provides an alarm when said signal attains a value exceeding said upper limit and which is sustained during a predetermined time period, the combination comprising a power supply unit, an alarm unit, an actuation circuit interposed in the circuit connections between said power supply unit and alarm unit for controlling energization of said alarm unit, first and second threshold detectors connected to said actuation circuit for controlling the same, a gate normally enabled to apply said signal to said threshold detectors when the value of said signal lies between said upper and lower limits, said first threshold detector being responsive to a value of said signal exceeding said upper limit first to initiate a gateinfluencing cycle during which said gate is first disabled and again enabled following termination of said time period, and secondly to deliver a signal to said actuation circuit, and thirdly to change its own operational state such that renewed application of a signal at a value exceeding said upper limit will initiate said gate-influencing cycle only if said renewed application takes place following termination of a first predetermined delay, said actuation circuit being normally held by said second threshold detector in a first state where it is not influenced by said signal from said first threshold detector, said actuation circuit being changed over during said gateinfluencing cycle to a second state where it closes the circuit between said power supply unit and alarm unit when influenced by a signal from said first threshold detector, said second threshold detector being operative to reconvert said actuation circuit back to said first state following termination of said gate-influencing cycle only after termination of a second predetermined delay.