5311453 : Variable point sampling


We claim:
  • 1. In a digital, synchronous, noise cancellation system for canceling the frequency components, the method of maintaining the sampling rate and required processing resources within a small range while the fundamental noise cycle varies over a large range, said method comprising
    • determining the highest frequency to be processed,
    • determining the current noise cycle rate,
    • changing the number of sample points per noise cycle dependent upon the noise cycle rate and the highest frequency to be processed.
  • 2. A method as in claim 1, said method additionally including
    • checking the actual frequency of the component by multiplying its harmonic number by a measurement of the current fundamental noise cycle frequency so that if the harmonic is above the highest frequency, that harmonic is not processed.
  • 3. A method as in claim 2, said method wherein the number of sample points used to define the noise cycle of the algorithm varies based on the fundamental operating frequency of the system and the constraints placed on it by fhi and flo parameters.
  • 4. The method of claim 3 where the variation of the number of points used to represent the noise cycle is determined by halving the number whenever the condition
  • ((Ns /k)-1)*fnc >2*fhi is met, where
    • Ns is the number of points in the noise cycle
    • fnc is the current fundamental frequency of the noise
    • fhi is a predetermined high frequency cutoff
    • k is a constant greater than 2 to satisfy the Nyquist criteria or, inversely, doubling the number of points whenever
    ((Ns /k)+1)*fnc <2*fhi.