Electrical apparatus for recognizing missing pulses in an otherwise

Abstract

Omission of a pulse in an otherwise regular pulse sequence, such as may be produced by omission of a tooth of a rotating gear that is used to generate a pulse sequence through a pick-up, is utilized after the manner of a special framing pulse, saving the complications of providing a framing pulse, especially in gasoline engine ignition timing. A counter is started with the beginning of every pulse of the sequence and is operated at a multiple of the sequence frequency. If the frequency varies, the count status when the next pulse arrives will vary slightly and this variation may be caused to change the initial condition for the beginning of each count cycle to keep the repetitive counting generally in step with the varying frequency. When a pulse of the sequence is skipped, however, the repetitive counter goes into a range of content states well beyond those produced by frequency variation and a decoding stage with an appropriate threshold value stored therein gives an indication that a pulse has been missed, which prepares a response to the next pulse which will produce a timing reference signal instead of a correction to the circuits following the frequency of the observed pulse sequence. The latter and also an engine load sensor address an ROM to provide the timing angle signal.