Counter controlled digital limit detector

Claim 1

In a digital alarm system, the improvement comprising: an alarm means for monitoring a digital apparatus, activating means for activating said alarm means when a digital quantity in said digital apparatus exceeds predetermined limits, said activating means comprising a main counter, an auxiliary counter, gating means controlled by said main counter for gating a signal to said alarm means when said digital quantity exceeds predetermined limits, means for incrementing and decrementing the count in said main counter, said decrementing means including said auxiliary counter, add signal input means for said incrementing means and a subtract signal input means for said decrementing means, means for inhibiting an alarm signal while an adD signal is present, means for inhibiting an alarm signal while said subtract signal is present, said decrementing means including a frequency generator, means for transmitting a pulse frequency from said frequency generator to said main counter and to said auxiliary counter to be counted therein, means for terminating the counting of said frequency when said auxiliary counter counts to a predetermined condition, means for presetting said auxiliary counter to a predetermined condition when said counting of said frequency is terminated, said add signal input means including a shaping multivibrator for shaping and transmitting said add signal to a first input of an add NOR gate, an add flip-flop connected to receive said add signal from said add NOR gate, said main counter being connected to receive said add signal from said add flip-flop, and inhibiting means connected to a second input of said add NOR circuit, whereby an add signal is inhibited when there is a subtract signal at said subtract signal input means.