Two and four cycle digital tachometer

Electricity: measuring and testing – Electrical speed measuring – Including speed-related frequency generator

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G01P 354

Patent

active

046879919

ABSTRACT:
A digital tachometer (2) is provided for two and four cycle internal combustion engines. A transformer (14) senses ignition pulses on the primary lead (6) of the ignition coil (4) of the two cycle engine, and an electrical connector (64) senses ignition pulses at the primary lead post terminal (66) of the ignition coil (54) of the four cycle engine. First and second signal conditioning circuits (50 and 96) are provided for each ignition pulse sensor for polarity immunity, RFI suppression, and transient and overvoltage protection. A precision timer (166) responds to pulses from the signal conditioning circuitry and outputs an output pulse of given delay, and ignores other pulses from the signal conditioning circuitry during the given delay, to protect against transient false triggering, especially in breaker point ignition systems. A phase-locked loop (186) responds to the delay pulses and outputs a pulse train having a frequency which is a function of frequency of the delay pulses. A counter and display circuit (190) counts the pulses in the pulse train as a function of time and displays same to indicate revolutions of the engine per unit time. A battery saver circuit (112) generates a reference voltage from the battery (110) and compares it against the voltage from the signal conditioning circuitry for outputting a turn-on signal to a transistor (154) to connect the battery (110) to various circuit components only above a threshold engine speed.

REFERENCES:
patent: 3095536 (1963-06-01), Westberg
patent: 3134943 (1964-05-01), Evenson
patent: 3636451 (1972-01-01), Westberg
patent: 3781656 (1973-12-01), Glew
patent: 4010415 (1977-03-01), Reeves et al.
patent: 4059799 (1977-11-01), Faria
patent: 4243938 (1981-01-01), Bliven et al.
patent: 4251774 (1981-02-01), Knodler
"Design of Phase-Locked Loop Circuits", Howard M. Berlin, Howard W. Sams & Co., 4300 West 62, Indianapolis, IN, 1978, pp. 360-367 and FIGS. 7-22.

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