US4950998A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Continuous condition sensing system
Assignee: Drexelbrook Controls Inc
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Filing: 1988-07-21
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Granted: 1990-08-21
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Expires: 2008-07-21
Abstract
Abstract A probe developing an admittance with a material whose condition is to be continuously measured is capacitively coupled with a variable frequency oscillator, preferably one having a digital output stage, for generating a variable frequency signal having a period varying with the admittance developed at the probe. Both the oscillator input and output are capacitively coupled to the probe. In a preferred embodiment, a set point circuit including a plurality of resistors coupled in parallel with the oscillator output and a plurality of switches coupled in parallel with the probe conductor and each with a different one of the resistor, provides easy circuit adjustment for use of the system with a variety of materials. A preferred digital circuit employing a pair of flip flops, fixed timer and one shot generate a fixed period variable duration duty cycle digital voltage level signal for transmission, if desired, or for conversion into a variable current signal.
Inventors
- 👤 Jonathan L. Kramer
- 👤 Steven R. Petersen
- 👤 Herbert A. Shauger, Jr.
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 01:36
CPC Classifications
G; G01; G01R; G01R27/00; G01R27/02; G01R27/26; G01R27/2605
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
172 words
A system for continuous material condition monitoring comprising: probe means developing an admittance with a material to be monitored, the admittance varying with changes in a condition of the material; a R-C circuit operatively coupled to receive an admittance signal from the probe means and for providing a signal having a generally triangular waveform based upon the admittance; oscillator means having an input coupled to receive the signal from the R-C circuit for generating an oscillating digital signal having a period varying with the admittance at the probe means and having an output operatively coupled in feedback to the R-C circuit; and capacitor means disposed between said probe means and said oscillator means for capacitively isolating the probe means from the oscillator means, the capacitor means having a capacitance greater than any capacitance that is normally developed at the probe means so that the oscillator means operates over a linear range and preventing any substantial discharge of the R-C circuit in the event of substantial leakage to ground in the probe means.
Claim 2
Independent Claim
172 words
A system for continuous material condition monitoring comprising: probe means developing an admittance with a material to be monitored, the admittance varying with changes in a condition of the material; a R-C circuit operatively coupled to receive an admittance signal from the probe means and for providing a signal having a generally triangular waveform based upon the admittance; oscillator means having an input coupled to receive the signal from the R-C circuit for generating an oscillating digital signal having a period varying with the admittance at the probe means and having an output operatively coupled in feedback to the R-C circuit; and capacitor means disposed between said probe means and said oscillator means for capacitively isolating the probe means from the oscillator means, the capacitor means having a capacitance greater than any capacitance that is normally developed at the probe means so that the oscillator means operates over a linear range and preventing any substantial discharge of the R-C circuit in the event of substantial leakage to ground in the probe means.
Claim 3
Dependent Claim
20 words
The system of claim 1 further comprising: output means for providing a varying signalling current indicative of the monitored condition.
Claim 4
Dependent Claim
37 words
The system of claim 1 wherein the probe means comprises: an electrical conductor coupled with the capacitor means; and electrical insulator means covering the electrical conductor for shielding said electrical conductor from direct contact with said material.
Claim 5
Dependent Claim
26 words
The system of claim 1 wherein the probe means comprises an electrical conductor in combination with at least an essentially non-conductive material contacting the electrical conductor.
Claim 6
Dependent Claim
59 words
The system of claim 1 wherein the oscillator means comprises: reference means for generating a reference voltage signal; and comparison means operatively coupled with the probe means and the reference means for comparing a signal indicative of the probe admittance to the reference signal; multivibrator means responsive to the comparison means for generating a logic level voltage oscillating signal.
Claim 7
Dependent Claim
54 words
The system of claim 1 wherein the oscillator means comprises: reference means for generating a reference voltage signal; a comparator having one input operatively coupled with said probe means through said first circuit means and another input coupled with said reference means; and multivibrator means responsive to said comparator for generating said oscillating signal.
Claim 8
Dependent Claim
63 words
The system of claim 1 wherein the oscillator means comprises: a pair of comparators each operatively coupled with said probe means; and an RS flip-flop having a set input coupled with an output of one comparator and a reset input coupled with an output of the remaining comparator and generating said oscillating signal in response to the outputs of said pair of comparators.
Claim 9
Dependent Claim
70 words
The system of claim 1 further comprising: a plurality of resistors each having an end coupled to the output of said oscillator means; an equal plurality of switch means each having an end operatively coupled to the probe means and a remaining end coupled with a different one of each of said plurality of resistors for selectively and operatively coupling one or more of said resistors with said probe means.
Claim 10
Dependent Claim
32 words
The system of claim 8 further comprising: an equal plurality of capacitors each having an end coupled with a remaining end of a different one of each of said plurality of resistors.
Claim 11
Independent Claim
117 words
A method of continuously monitoring a condition of a material comprising the steps of: developing at a conductor an admittance related to the condition of the material; capacitively coupling, with a capacitance greater than any capacitance that is normally developed at the conductor, the conductor to an R-C circuit and generating a signal having a generally triangular waveform; conducting the signal to an input of an oscillator and feeding back an output of the oscillator to the R-C circuit, the capacitance preventing any substantive discharge of the R-C circuit in the event of substantial leakage to ground in the probe means; generating with the oscillator a variable frequency digital signal having a period varying with the admittance.
Claim 12
Independent Claim
117 words
A method of continuously monitoring a condition of a material comprising the steps of: developing at a conductor an admittance related to the condition of the material; capacitively coupling, with a capacitance greater than any capacitance that is normally developed at the conductor, the conductor to an R-C circuit and generating a signal having a generally triangular waveform; conducting the signal to an input of an oscillator and feeding back an output of the oscillator to the R-C circuit, the capacitance preventing any substantive discharge of the R-C circuit in the event of substantial leakage to ground in the probe means; generating with the oscillator a variable frequency digital signal having a period varying with the admittance.
Claim 13
Dependent Claim
20 words
The method of claim 10 wherein said generating step comprises generating a digital voltage level, square wave, variable frequency signal.
Claim 14
Dependent Claim
24 words
The method of claim 11 further comprising the step of: circuiting said variable frequency signal to said conductor through a resistance and a capacitor.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1993-08-20 | 1994-02-19 | 1994-08-21 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1997-08-20 | 1998-02-19 | 1998-08-21 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2001-08-20 | 2002-02-19 | 2002-08-21 | $7700.00 | Window Closed / Lapsed |