Indirectly sensed signal processing in active periodic acoustic noise cancellation
First Claim
1. The method of providing an indirectly sensed noise input signal for introduction at an active noise cancellation system input, comprising in combination the steps of:
- generating a signal representative of said noise, said signal having sequential pulses within repeating periods,dividing, an increment of said sequential pulses, out of the sequential pulses in each individual period,forming each said increment of said sequential pulses into a single, controlled width, converted pulse signal, per period,reducing the amplitude of each said converted pulse signal,A filtering from each said converted pulse signal all frequencies above a predetermined value, and, blocking any direct current from said input of said active noise cancellation system.
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Abstract
The system employing and the processing of, an indirectly sensed signal representative of a periodic noise acoustic wave into an input signal for a noise cancelling system where the indirectly sensed signal is converted into a pulse signal per period that carries fundamental and harmonic frequency information of the periodic noise. A tachometer type RPM signal is processed in a counter circuit controlled by a logic circuit to produce a signal of one pulse per revolution with a controlled duration, the pulse amplitude is adjusted, the pulses are low pass filtered and any D.C. is blocked from the noise cancelling system input.
50 Citations
17 Claims
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1. The method of providing an indirectly sensed noise input signal for introduction at an active noise cancellation system input, comprising in combination the steps of:
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generating a signal representative of said noise, said signal having sequential pulses within repeating periods, dividing, an increment of said sequential pulses, out of the sequential pulses in each individual period, forming each said increment of said sequential pulses into a single, controlled width, converted pulse signal, per period, reducing the amplitude of each said converted pulse signal, A filtering from each said converted pulse signal all frequencies above a predetermined value, and, blocking any direct current from said input of said active noise cancellation system. - View Dependent Claims (2, 3, 4, 5)
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6. The method of producing a signal representative of, and correlated with, an acoustic noise wave associated with a rotating machine, comprising in combination the steps of:
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providing signals each having sequential pulses within each revolution of said machine, forming a converted pulse signal for each said revolution of said machine each said converted pulse signal having a duration of an increment of said sequential pulses, said duration being 20% or less of the duration of each said revolution of said machine, reducing the amplitude of said converted pulse signals, filtering from said converted pulse signals all frequencies above a predetermined value, and providing capacitive coupling at an output. - View Dependent Claims (7, 8)
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9. A signal conversion circuit for converting a signal representative of noise, said signal having sequential pulses within repeating periods, into an analog signal coordinated with the fundamental and low frequency harmonic frequencies of said noise, comprising:
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a converted pulse with controlled width forming stage, where said width of said converted pulse is a selected portion of one of said repeating periods, said forming stage including a sequential pulse counter and a multiple input logic circuit, said sequential pulse counter being interruptable by the output signal of said multiple input logic circuit and the inputs of said multiple input logic circuit being connected into said sequential pulse counter at points determinative of said selected portion of one of said repeating periods, and, serially connected, following said forming stage, a converted pulse amplitude reducing stage, a low frequency passing filtering stage, and, a direct current blocking stage. - View Dependent Claims (10, 11, 12, 13)
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14. In a periodic acoustic noise sound cancellation system of the type wherein a cancelling acoustic wave is provided at a location, said cancelling wave being determined by iterative computations based on input signals representing said noise and feedback signals from monitoring at said location, an improved input signal comprising:
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a source of sequential pulses within a repeating period of said noise, signal generating means for forming, a single pulse per period of said repeating periods signals, said single pulse per period signals having a duration of 20% or less of said repeating period, and, signal adjusting means to deliver, as at least a portion of said input signals to said system, a signal containing the low frequency fundamental and harmonic component information of said single pulse per period signals. - View Dependent Claims (15, 16, 17)
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Specification