MOISTURE MONITOR HAVING A RESISTOR BETWEEN SENSING CAPACITOR AND OSCILLATOR TUNED INPUT TO IMPROVE OSCILLATOR RESPONSE

• US 3,793,585 A
• Filed: 02/02/1972
• Issued: 02/19/1974
• Est. Priority Date: 02/02/1972
• Status: Expired due to Term

• Current Assignee: Matti Gunnar Wilska
• Original Assignee: Matti Gunnar Wilska
• Inventors: Wilska, Matti Gunnar
• Primary Examiner(s): Krawczewicz, Stanley T.
• Application Number:
  US05/222,790
• Time in Patent Office: 748 Days
• Field of Search: 324/61QS 331/65
• US Class Current: 324/668
• CPC Class Codes: G01N 27/223 for determining moisture content, e.g. humidity rain detectors on vehicle windows B60S1/0825
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24

Abstract

An electrical circuit provides a measurement or control in accordance with the moisture content of a specimen or sample, and includes: a capacitive cell comprising two spaced and insulated metal plates between which the specimen or sample can be placed to act as a part of a dielectric between the two plates; an oscillatory circuit to which said capacitive cell is coupled in such a manner that variations in the capacitance of the cell produces variations in the state of loading of said oscillatory circuit; and output means providing a measurement and/or a control in accordance with the said state of loading of said oscillatory circuit.

Claims

1. An electrical circuit providing a measurement or control in accordance with the moisture content of a specimen or sample, and including:

a. a capacitive cell comprising two spaced and insulated metal plates between which the specimen or sample can be placed to act as a part of a dielectric between the two plates;

b. an oscillatory circuit to which said capacitive cell is coupled through a resistor so that variations in the capacitance of said cell produces variations in the resistive loading of said oscillatory circuit by said resistor; and

c. output means providing a measurement and/or a control in accordance with the said resistive loading of said oscillatory circuit.

2. An electrical circuit according to claim 1, and in which said output means is an electrical meter providing a visual indication of the said resistive loading.

3. An electrical circuit according to claim 1, and in which the oscillatory circuit is coupled to said capacitive cell through a resistor so that an increase in the capacitance of said cell provides an increased resistive loading of said oscillatory circuit by said resistor.

4. An electrical circuit according to claim 1, and in which variation of loading of said oscillatory circuit produced by variation in the capacitance of said cell is accompanied by corresponding change in the frequency of oscillation of said oscillatory circuit.

5. An electrical circuit according to claim 1, in which said oscillatory circuit operates with positive feedback to maintain it in oscillatory condition, and feedback elements providing said positive feedback are so selected that an output voltage across said oscillatory circuit decreases as the said resistive loading of said oscillatory circuit is increased.

6. An electrical circuit according to claim 1, in which the oscillatory circuit operates with positive feedback to maintain it in oscillatory condition, and feedback elements providing said feedback are so selected that upon incrEase of the capacitance of said capacitive cell past a predetermined value, the condition for oscillation is no longer fulfilled and the oscillation ceases.

7. An electrical circuit according to claim 3, and in which the value of said resistor lies in the range 0.5 to 1.0 thousand ohms.

8. An electrical circuit according to claim 1, and in which the oscillatory circuit includes a transistor and a feedback capacitor is connected between the emitter electrode and the collector electrode of that transistor.

9. An electrical circuit according to claim 1, and in which the oscillatory circuit is energised through a variable resistor, and calibration of the output means is obtainable by adjustment of said variable resistor.

10. An electrical circuit according to claim 1, and in which the oscillatory circuit includes an inductance and said capacitive cell, a resistor being connected in series with said capacitive cell and the series combination of the resistor and said cell being connected in parallel with said inductance.

11. An electrical circuit according to claim 10, and in which the output means is connected to a tapping on said inductance.

12. An electrical circuit according to claim 11, and in which the output means is a d.c. device and is connected to said tapping and includes a rectifying device which applies a rectified voltage to the output means derived from said tapping.

13. An electrical circuit as claimed in claim 1, and in which the capacitive cell includes outer and inner electrodes defining an annular space into which said specimen or sample is placed.