REMOTE ENGINE TACHOMETER

  • US 3,811,089 A
  • Filed: 07/14/1972
  • Issued: 05/14/1974
  • Est. Priority Date: 07/14/1972
  • Status: Expired due to Term
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First Claim
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1. A tachometer for an engine, said engine having an electric ignition system radiating bursts of electromagnetic signals at a rate proportional to the rate of engine rotation, the tachometer comprising, in combination:

  • means effective to receive electromaGnetic signals radiated by the engine;

    a bandpass filter connected to the output of the electromagnetic signal receiving means, the bandpass filter passing only signals having frequencies within a narrow band in the audio range;

    signal amplification means amplifying the output of the bandpass filter, the signal amplification means including an amplifier with a negative feedback loop, the negative feedback loop containing a variable resistor;

    a peak memory circuit responsive to the output of the signal amplification means and operative to generate a DC voltage proportional to the peak amplitude of the output of the signal amplification means;

    filter means connected to the output of the peak memory circuit to smooth the DC voltage output thereof;

    means responsive to the output of the filter means to vary the resistance of the variable resistor so as to stabilize the output of the signal amplification means;

    voltage attenuating means responsive to the output of the peak memory circuit and operative to attenuate this output by a fixed fraction;

    a comparator operative to compare the output of the signal amplification means with the output of the voltage attenuating means and generate an output signal when the former exceeds the latter; and

    means to generate a pulse of constant duration each time the comparator produces an output signal.

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