Pulse detector for missing or extra pulses

Abstract

A missing pulse detector is disclosed in which the absence of a pulse in a variable frequency periodic pulse train is detected and distinguished from a reduction in the pulse repetition rate. Between successive pulse train pulses a first counter counts clock pulses at a first rate and develops a maximum count related to the time duration between successive pulses. This maximum count is maintained by a latch circuit during the next time duration between successive pulses and is compared with the count of a second pulse counter which counts clock pulses during successive pulse train pulses at a second rate normally less than the first incrementing rate. When the count of the second counter exceeds by a predetermined amount the latched count of the first counter, this indicates the occurrence of longer time duration and a count comparator and logic circuit provides an arming output signal. In response to the arming output signal, the incrementing rate of the second pulse counter is increased to a third rate which exceeds the first incrementing rate. If after the arming output signal the maximum count of the second counter between successive pulses is less than the maximum count achieved by the first counter between preceding successive pulses, then a missing pulse detection signal is produced.