Acoustic tachometer
First Claim
1. Apparatus for measuring the operating speed of a device, said device producing sound waves having components at a number of frequencies, wherein the frequency at which the sound waves are of maximum amplitude is systematically related to said operating speed, said frequency of said maximum occurring in a frequency spectrum of interest which is systematically related to a predetermined range of operating speeds, said apparatus comprisingtransducer means responsive to said sound waves for producing systematically related electrical signals;
- a band-pass filter having a variable center frequency and a narrow pass band for selectively passing the components of said electrical signals having frequencies within said pass band, said variable center frequency corresponding to the amplitude of an applied control signal;
sweep means for applying said control signal to said filter with a varying amplitude for cyclically sweeping said center frequency of said filter through said frequency spectrum of interest;
peak detecting means for selectively detecting the maximum amplitude of the output of said filter during respective sweeping cycles; and
measuring means responsive to said peak detecting means and said sweep means for measuring the amplitude of said control signal when said peak detecting means detects said maximum amplitude, thereby providing an indication of said operating speed.
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Accused Products
Abstract
An acoustic tachometer for diesel engines includes a microphone which is responsive to the sounds generated by the engine combustion occurrences. The microphone signal is passed through a band-pass filter having a variable center frequency which is determined by a control signal from a sweep generator. The control signal has a known relationship to the operating speed of the engine. As the band-pass filter is swept through its frequency spectrum, a peak detector identifies the signals of maximum amplitude, which occur at the fundamental frequency of the combustion occurrences. The control signal voltage at the maximum amplitude and hence at the fundamental frequency is stored. At the end of each sweep, the stored control signal voltage is fed to an oscillator having a frequency which is dependent upon the stored control signal voltage, and is related to revolutions per minute (RPM). The output of the oscillator excites a counter-display circuit which displays the operating speed in RPM. In an alternate embodiment, the stored control signal voltage is connected to a second band-pass filter having a variable center frequency which is dependent upon the stored control signal voltage. The microphone signal is fed through the second filter, which passes only the fundamental frequency to a clipper and phase locked loop, from which is driven a counter and digital display showing RPM. Error detection circuitry alerts the operator if the sound to the microphone is inadequate or excessive for accurate measurement.
29 Citations
17 Claims
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1. Apparatus for measuring the operating speed of a device, said device producing sound waves having components at a number of frequencies, wherein the frequency at which the sound waves are of maximum amplitude is systematically related to said operating speed, said frequency of said maximum occurring in a frequency spectrum of interest which is systematically related to a predetermined range of operating speeds, said apparatus comprising
transducer means responsive to said sound waves for producing systematically related electrical signals; -
a band-pass filter having a variable center frequency and a narrow pass band for selectively passing the components of said electrical signals having frequencies within said pass band, said variable center frequency corresponding to the amplitude of an applied control signal; sweep means for applying said control signal to said filter with a varying amplitude for cyclically sweeping said center frequency of said filter through said frequency spectrum of interest; peak detecting means for selectively detecting the maximum amplitude of the output of said filter during respective sweeping cycles; and measuring means responsive to said peak detecting means and said sweep means for measuring the amplitude of said control signal when said peak detecting means detects said maximum amplitude, thereby providing an indication of said operating speed. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method for measuring the operating speed of a rotating member of a device, said device having a sound output which includes a single frequency at which the sound is of maximum amplitude, said frequency being functionally related to said operating speed and occurring in a frequency spectrum of interest which is functionally related to a predetermined range of operating speeds, comprising the steps of
producing electrical signals systematically related to said sound; -
applying said electrical signals to a band-pass filter having a variable center frequency and a narrow pass band; cyclically sweeping the center frequency of said filter through said frequency spectrum of interest by an independent control signal having a known relationship to said operating speed; detecting the signals of maximum amplitude from the output of said filter during respective sweeping cycles; and measuring said control signal producing said maximum amplitude as an indication of said operating speed. - View Dependent Claims (15, 16, 17)
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Specification