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

• Current Assignee: Anthony S. Strzelewicz
• Original Assignee: Anthony S. Strzelewicz
• Inventors: Strzelewicz, Anthony S.
• Primary Examiner(s): Lynch, Michael J.
• Application Number:
  US05/271,996
• Time in Patent Office: 669 Days
• Field of Search: 324/169,170,173,78I,78E,15-18
• US Class Current: 324/170
• CPC Class Codes: G01P 3/4807 by using circuits for the detection of the pulses delivered by the ignition system of an internal combustion engine

Abstract

A tachometer which does not require connection with the engine. A probe placed near the engine picks up electromagnetic radiation produced by the distributor points and coil in bursts timed with engine speed. A bandpass filter suppresses all frequencies except a narrow band which is amplified in a circuit with automatic gain control using optic elements in the feedback loop. A reference voltage whose level is a constant fraction less than the signal maximum is produced and compared with the signal in a comparator, the output of which triggers a one shot pulse generator to produce a train of pulses of constant width and amplitude at a frequency proportional to engine speed.

Claims

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.

2. A tachometer for indicating the rotational speed of an engine having an electrical ignition system radiating bursts of electromagnetic signals at a rate proportional to the rate of engine rotation, the tachometer comprising, in combination:

an electromagnetic signal sensing probe;

a bandpass filter connected to said probe, the bandpass filter being tuned to a frequency in the audio range;

a first capacitor having one end connected to the output of the bandpass filter;

a first operational amplifier having an output, a grounded non-inverting input and an inverting input connected through an input resistor to the other end of the first capacitor;

first and second resistors in parallel connecting the output and inverting input of the first operational amplifier, the first resistor having a resistance varying inversely with light intensity;

a third resistor having one end connected to the output of the first operational amplifier;

a first forward biased diode having an input connected to the other end of the third resistor;

a second capacitor and fourth resistor connected between the output of the first forward biased diode and ground;

a second operational amplifier having an output, an inverting input and a non-inverting input connected to the output of the first forward-biased diode;

a second forward-biased diode having an input connected to the output of the second operational amplifier and an output connected to the inverting input of the second operational amplifier;

a fifth resistor having one end connected to the output of the second operational amplifier;

a sixth resistor and third capacitor connected between the other end of the fifth resistor and ground, the sixth resistor having a variable resistance tap;

an NPN transistor having a base connected to the variable resistance tap of the sixth resistor, a collector and an emitter;

a constant voltage source connected to the collector of the NPN transistor;

a seventh resistor connecting the emitter and collector of the NPN transistor;

a lamp physically adjacent the first resistor, the lamp being connected between the emitter of the transistor and ground;

an eighth resistor connected between the output of the second operational amplifier and ground, the eighth resistor having a variable resistance tap;

a comparator having an output, an inverting input and a non-inverting input;

a third forward biased diode having an input connected to the variable tap of the eighth resistor and an output connected to the non-inverting input of the comparator;

niNth and tenth resistors connected in series between the constant voltage source and ground;

an eleventh resistor connecting the junction of the ninth and tenth resistors with the non-inverting input of the comparator;

a fourth forward-biased diode connecting the output of the first operational amplifier with the inverting input of the comparator;

a fourth capacitor having one end connected to the output of the comparator; and

a pulse generator having an input connected to the other end of the fourth capacitor and an output at which is produced a train of pulses at a frequency proportional to engine rotation.

3. The tachometer of claim 2 in which the bandpass filter is tuned to a frequency of 10.5 KHz.