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Method of and arrangement for accurately measuring low capacitances

  • US 4,849,686 A
  • Filed: 02/13/1987
  • Issued: 07/18/1989
  • Est. Priority Date: 02/13/1986
  • Status: Expired due to Term
First Claim
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1. A method of accurately measuring physical quantities using measurement impedances having low impedance values, comprising the steps of:

  • (a) selecting first and second stable reference impedance with impedance values respectively at lower and upper regions of an impedance measurement range;

    (b) selecting a third stable reference impedance with an impedance value at an intermediate region between the lower and upper regions of the measurement range;

    (c) determining an initial correction parameter by connecting each reference impedance, one at a time, to a measuring circuit during calibration mode, said initial correction parameter being a function of each reference impedance and of operating conditions of calibration environment;

    (d) storing the initial correction parameter;

    (e) providing a measuring circuit connectable in calibration and measurement modes of operation to each reference impedance and measurement impedance for measuring the impedance value of a selected measurement impedance, said measuring circuit having a variable response characteristic as a function of different operating conditions during the calibration and measurement modes;

    (f) determining an updated correction parameter by connecting each reference impedance, one at a time, to the measuring circuit during the measurement mode, said updated correction parameter being a function of each reference impedance;

    (g) comparing the updated correction parameter with the initial correction parameter, and storing a correction factor based on the difference between the updated and initial correction parameters;

    (h) measuring the impedance value of the measurement impedance by connecting the latter to the measuring circuit during the measurement mode; and

    (i) determining a corrected impedance value for the measurement impedance as a function of the impedance value measured in step (h) and the correction factor, thereby reducing measurement errors caused by the variable response characteristic due to the different operating conditions.

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