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Shadow zone fault detection

  • US 7,520,573 B2
  • Filed: 12/22/2005
  • Issued: 04/21/2009
  • Est. Priority Date: 12/22/2005
  • Status: Expired due to Fees
First Claim
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1. A method for monitoring an active wheel speed sensor comprising the steps of:

  • (a) providing an active wheel speed sensor that generates alternating high and low output signals;

    (b) sampling the high and low output signals of the wheel speed sensor within a sampling range that is dithered;

    (c) constructing high and low histograms corresponding to the high and low output signal samples obtained in step (b);

    (d) comparing the histogram values within each of the histograms to one another to determine whether a single histogram value for each of the histograms is dominate over the other values contained in that histogram;

    (e) comparing a voltage corresponding to the single dominant value of the high histogram to a threshold voltage value that is determined by the following formula;


    VTH=K*VL, whereVTH is the voltage threshold,VL is the voltage value associated with the dominate value of the low histogram, andK is a constant associated with the wheel speed sensor; and

    (f) setting an error flag upon the voltage corresponding to the single dominant value of the high histogram being less than the threshold voltage value.

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