METHOD OF LINEAR MEASUREMENT OF A VARIATION IN CAPACITANCE AND CORRESPONDING DIGITAL-DISPLAY DEVICE

• US 3,805,149 A
• Filed: 06/20/1972
• Issued: 04/16/1974
• Est. Priority Date: 06/24/1971
• Status: Expired due to Term

• Current Assignee: Gilles Delapierre
• Original Assignee: Gilles Delapierre
• Inventors: Delapierre, Gilles
• Primary Examiner(s): Krawczewicz, Stanley T.
• Application Number:
  US05/264,508
• Time in Patent Office: 665 Days
• Field of Search: 324/6C,6R
• US Class Current: 324/681
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: H03M 1/00 Analogue/digital conversion; Digital/analogue conversion conversion of analogue values to or from differential modulation H03M3/00
• CPC Class Codes: H03M 1/60 with intermediate conversion to frequency of pulses

Abstract

A fixed or variable capacitor is inserted in the circuit of an oscillator having an operating frequency which is inversely proportional to the value of the capacitor. The method consists in counting a constant number of periods of the oscillator, the resultant counting time being accordingly a linear function of the value of the capacitor.

Claims

1. A method of measurement of a capacitance and/or of a variation in capacitance, in which a fixed and/or variable capacitor is inserted in the circuit of an electric oscillator, wherein said method comprises selecting an oscillator having an operating frequency which is inversely proportional to the value of said capacitor, and counting a constant number of periods of said oscillator wherein the resulting counting time is a linear function of the value of said capacitor.

2. A system for measuring compacitance comprising a reference oscillator having a first frequency, a measuring oscillator having a capacitor corresponding to the capacitance to be measured electrically connected thereto, said measuring oscillator having a second frequency which is inversely proportional to the capacitance, a first counting means for receiving and counting the output signals of the reference oscillator, second counting means for receiving and counting the output signals of the measuring oscillator, blocking circuit means responsive to a predetermined count N of signals of said measuring oscillator by said second counting means for providing a stop output signal to said first counting means for stopping the processing of the signals of said reference oscillator, and display means connected at the output of said first counting means for recording the count of said first counting means at the time of receipt of the stop signal by said first counting means.

3. A system according to claim 2, wherein said reference oscillator and said measuring oscillator are resistance-capacitance type of oscillators.

4. A system according to claim 2, wherein said first counting means includes an up/down counter having two inputs, a display control element means for controlling the presetting of a count in said up/down counter and an operational mode selector means having two inputs and two outputs, said selector means having a first input connected to an output of said blocking circuit means and a second input connected to said display control element means, said selector means having the two outputs thereof connected to the two inputs of said up/down counter.

5. A system according to claim 2, wherein said reference oscillator and said measuring oscillator include adjustable resistance means for eliminating temperature drift of said oscillators.

6. A system according to claim 2, wherein said blocking circuit means is provided with one input and four outputs, said blocking circuit means having the input thereof connected to the output of said second counting means and being responsive to said second counting means reaching said predetermined count N corresponding to a predetermined number of signals of the second frequency from said measuring oscillator for providing a stop signal to said first counting means at a first output thereof and providing a record and display signal to said display means at a second output thereof, said blocking circuit means also providing reset signals to said first and second counting means at third and fourth outputs thereof, respectively.