PULSE OPERATED TACHOMETER WITH HIGHEST SPEED MEMORY

• US 3,818,342 A
• Filed: 11/13/1972
• Issued: 06/18/1974
• Est. Priority Date: 11/13/1972
• Status: Expired due to Term

• Current Assignee: Harmon Industries, Inc. (GE Aerospace)
• Original Assignee: Harry S. Stevens
• Inventors: Stevens, Harry S.
• Primary Examiner(s): Smith, Alfred E.
• Assistant Examiner(s): Hille, Rolf
• Application Number:
  US05/305,798
• Time in Patent Office: 582 Days
• Field of Search: 324/166,169,173 73/491 235/92CA,92HT 340/62
• US Class Current: 324/169
• CPC Class Codes: G01P 3/489 Digital circuits therefor
• CPC Class Codes: G01R 23/10 by converting frequency into a train of pulses, which are then counted , i.e. converting the signal into a square wave

Abstract

A tachometer employs decade counters responsive to electrical pulses having a repetition rate dependent upon the speed of rotation of a rotating device, such as the crankshaft of an internal combustion engine. The counters are operational during spaced counting intervals; at the end of each interval, a count is accumulated representing the speed of the device during that interval. This count information is stored in a register until the next succeeding count has been derived. An independent memory is also responsive to the count information and remembers the highest count derived by the counters during any previous counting interval. Normally, digital indicators display the speed of the device as continuously updated by the counters, but a manual selector switch is provided which, when actuated, causes the indicators to display the highest speed previously attained stored in the independent memory. A pulse shaping circuit is provided which adapts the tachometer for use with various types of ignition systems, including the Kettering ignition that employs breaker points from which input impulses are obtained for the tachometer logic.

Claims

1. A tachometer comprising:

means for generating electrical pulses having a repetition rate dependent upon the speed of rotation of a rotating device;

counter means coupled with said generating means for receiving said pulses therefrom;

timing means coupled with said counter means for rendering the latter operational at spaced intervals of predetermined length whereby, at the end of each interval, a count is accumulated representing the speed of the device during that interval;

a storage register responsive to each count from said counter means for storing each count until the next succeeding count has been derived;

memory means responsive to each count from said counter means for remembering the highest count derived by said counter means;

display means responsive to a count delivered thereto for indicating the speed of the device; and

selector means coupled with said register, said memory means, and said display means for permitting selective coupling of either said register or said memory means with said display means to render the display means responsive exclusively to the counts successively stored in said register, when said register is selected in order to provide continuous updating of the speed indication, or responsive exclusively to said highest count when said memory means is selected so that said display means will indicate the highest speed previously attained.

2. The tachometer as claimed in claim 1, wherein said memory means includes a second storage register receiving each count from said counter means, and comparator means receiving each count from said counter means and the count stored in said second register, said comparator means delivering an output when the count from the counter means is greater than the count stored in said second register, and wherein said second register stores a received count only in response to said output, whereby the count stored in said second register is said highest count.

3. The tachometer as claimed in claim 1, wherein said selector means has a normal operating condition in which it couples said register with said display means, and wherein said selector means includes manually operable switching means for causing the selector means to assume a second operating condition coupling said memory means with said display means.

4. The tachometer as claimed in claim 1, wherein said display means includes at least a pair of electrically responsive digital indicators for displaying significant digits of the indicated speed, and wherein said selector means includes a multiplexer for alternately exciting said indicators with count information from either said register or said memory means, said multiplexer having a first set of inputs receiving the count stored in said register and a second set of inputs receiving said highest count from said memory means.

5. The tachometer as claimed in claim 4, wherein said memory means includes a second storage register receiving each count from said counter means, and comparator means receiving each count from said counter means and the count stored in said second register, said comparator means delivering an output when the count from the counter means is greater than the count stored in said second register, and wherein said second register stores a received count only in response to said output, whereby the count stored in said second register is said highest count, there being circuit means connecting said second register with said second set of inputs of the multiplexer.

6. The tachometer as claimed in claim 4, wherein said multiplexer has a normal operating condition in which it is responsive exclusively to the count information at said first set of inputs, and wherein said selector means further includes manually operable switching means for rendering said multiplexer responsive exclusively to the count information at said second set of inputs.

7. The tachometer as claimed in claim 1, wherein said pulse generating means includes circuitry responsive to time-spaced oscillatory impulses occurring at said repetition rate, each having a relatively high initial frequency followed by significantly lower frequencies, for converting each impulse into a unidirectional pulse of limited maximum amplitude in which the lower frequencies are attenuated, and a one shot having a control input coupled with the output of said circuitry for receiving said unidirectional pulses.

8. The tachometer as claimed in claim 1, wherein said tachometer is for use in conjunction with internal combustion engines having different numbers of cylinders, and wherein said timing means includes programmable prescaling means for scaling the predetermined length of said intervals in accordance with the number of cylinders, said pulse generating means including a one shot having an output for delivering said pulses to said counter means, there being means interconnecting said timing means and said one shot for automatically controlling the duration of each of said pulses in accordance with the programming of said prescaling means.

9. In a tachometer employing apparatus which responds to discrete electrical pulses having a repetition rate dependent upon the speed of rotation of a rotating device, where said pulses are derived from time-spaced oscillatory impulses occurring at said repetition rate and each having a relatively high initial frequency followed by significantly lower frequencies, the improvement comprising:

a shaper responsive to each oscillatory impulse for attenuating the lower frequency portion thereof, and for converting each oscillatory impulse into a time-varying unidirectional pulse and limiting the maximum amplitude thereof; and

output means triggered by the initial excursions of the time-varying pulses from said shaper for delivering said discrete electrical pulses at said repetition rate to said apparatus, said shaper having a pair of output terminals at which said time-varying pulses are delivered, and including a resistor and a capacitor connected between an input connection and an output connection, said oscillatory impulses being applied to said input connection and developing voltages across said resistor and capacitor divided in accordance with the impedances thereof, a unidirectional current-carrying device coupled between said output connection and one of said output terminals, said output connection being coupled with the other of said output terminals, and a resistive shunt across said output terminals, said capacitor being selected to present a small impedance, relative to said resistor, to frequencies above said high initial frequency and said shunt being selected to effect rapid discharging of said capacitor at said lower frequencies, whereby to attenuate frequencies above and below said high initial frequency.

10. The improvement as claimed in claim 9, wherein said output means includes a one shot having a control input for receiving said time-varying pulses from said shaper.

11. The improvement as claimed in claim 9, wherein said output means includes a digital one shot provided with a control input for receiving said time-varying pulses from said shaper, said one shot having a counting period initiated by each pulse from said shaper and during which time said input is disabled.

12. The improvement as claimed in claim 9, wherein said unidirectional current-carrying device is a zener diode for effecting said limiting of the maximum amplitude of said time-varying pulses.