US3636444A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Apparatus for measuring small changes in condition-sensitive capacitance transducers
Assignee: Johnson Controls International Inc
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Filing: 1970-01-30
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Granted: 1972-01-18
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Expires: 1990-01-30
Abstract
Abstract A humidity-sensitive capacitance sensor or transducer is connected in one leg of a modified Maxwell commutated DC bridge with the other legs formed of resistors. The sensor continually senses the humidity condition and establishes a proportional output signal of the bridge in accordance with changes in capacitance over a small range on a suitable galvanometer. A crystal-controlled oscillator actuates a pair of transistors to alternately connect the condition-sensitive capacitance transducer in a discharging circuit and in a charging circuit in the bridge network. The capacitance transducer alternately charges and discharges with a null output at a given condition and a proportionate output in response to any deviation of the condition sensed by the capacitance sensor. A span adjustment and a charge reservoir capacitor are employed to facilitate the operation.
Inventors
- 👤 Charles F Strawn
- 👤 John C Donovan
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 11:20
CPC Classifications
G; G01; G01N; G01N27/00; G01N27/02; G01N27/22; G01N27/223; G01N27/225
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
138 words
Apparatus for continuously measuring and indicating the change in a capacitive element, comprising direct current input means, a condition-sensitive capacitive transducer having dielectric material, the electrical and dielectric characteristic of said transducer varying with said condition, a low impedanCe discharge path means, a switching means selectively connecting the transducer to the input means to establish a charging circuit and in said low impedance discharge path means to establish a discharging circuit, said dielectric material having an effective resistive component, said charging circuit of said capacitive transducer including compensating resistive elements essentially balancing and cancelling the effective resistive component effect on the charging current, and sensing means connected to said charging circuit for sensing changes in charging energy which are proportional to corresponding changes in capacitance with said transducer connected to said input means to thereby detect said condition.
Claim 2
Dependent Claim
138 words
Apparatus for continuously measuring and indicating the change in a capacitive element, comprising direct current input means, a condition-sensitive capacitive transducer having dielectric material, the electrical and dielectric characteristic of said transducer varying with said condition, a low impedanCe discharge path means, a switching means selectively connecting the transducer to the input means to establish a charging circuit and in said low impedance discharge path means to establish a discharging circuit, said dielectric material having an effective resistive component, said charging circuit of said capacitive transducer including compensating resistive elements essentially balancing and cancelling the effective resistive component effect on the charging current, and sensing means connected to said charging circuit for sensing changes in charging energy which are proportional to corresponding changes in capacitance with said transducer connected to said input means to thereby detect said condition.
Claim 3
Dependent Claim
60 words
The apparatus of claim 1, having a charge reservoir element connected to said input means in parallel with said condition-sensitive capacitive transducer and said switching means, said condition-sensitive capacitive transducer receiving electrical charges from said charge reservoir element in parallel with said input means with said switching means connecting said transducer to said input means to rapidly charge the transducer.
Claim 4
Dependent Claim
70 words
The apparatus of claim 2, wherein said switching device includes a pair of solid-state devices, a crystal-controlled electrical oscillating device connected to alternately turn on each of said pair of devices, one of said solid-state devices alternately connects and disconnects said condition-sensitive capacitive transducer from said input means and the other of said solid-state devices being connected in parallel with said transducer and defining said low impedance discharge path means.
Claim 5
Dependent Claim
30 words
The apparatus of claim 1, wherein said capacitive transducer forms a leg of a Maxwell commutated direct current bridge having three other legs of resistive elements including adjustable resistive elements.
Claim 6
Dependent Claim
101 words
The bridge apparatus of claim 4, having said sensing means connected across the output of the bridge for sensing proportional average cyclic charging current and resistive current, said resistive elements having a predetermined resistance to establish said charging and resistive currents equal upon a balanced condition, said charging and resistive currents being unequal for an unbalanced condition in accordance with a change in the capacitance of said condition-sensitive capacitive transducer, said sensing means establishing a null signal in response to said balanced condition and a proportional signal in accordance with a capacitance change as a result of the corresponding current changes.
Claim 7
Dependent Claim
50 words
The bridge apparatus of claim 5, wherein a span adjustment device is connected in electrical series with the sensing means, said span adjustment device comprising an adjustable resistive element, said adjustable resistive element limiting the amount of said charging and resistive currents permitted to be sensed by the sensing means.
Claim 8
Dependent Claim
49 words
The apparatus of claim 1, having a commutated direct bridge current including a plurality of bridge legs, said capacitive transducer being selectively connected in one leg of said commutated direct current bridge by said switching means, said bridge have three other legs of resistive elements including adjustable resistive elements.
Claim 9
Dependent Claim
105 words
The apparatus of claim 7, wherein said electrical and condition-sensitive capacitive transducer is a humidity-sensing device having an absorptive dielectric material with the electrical and dielectric characteristic varying with humidity, said switching means including a solid-state switching element connected in series with the transducer in said one leg and a second solid-state state switching element connected in parallel with said capacitive transducer, and alternating polarity power means connected to said switching elements to alternately turn said elements on and off at a selected frequency having said first element on for a sufficient period to fully charge the transducer for a selected maximum capacitance sensed condition.
Claim 10
Dependent Claim
50 words
The apparatus of claim 8, wherein said sensing means includes a current-sensitive metering means connected across the output of the bridge for sensing proportional average cyclic charging and resistive currents, a humidity controller connected to said metering means and having an output to control the humidity environment about said transducer.
Claim 11
Dependent Claim
93 words
The bridge apparatus of claim 8, wherein said sensing means includes a current-sensitive meter, a span adjustment resistor connected in electrical series with said meter across the output of the bridge, said adjustable resistive elements of said other legs limiting the amount of said charging and resistive currents permitted to be sensed by the sensing means. 11 The apparatus of claim 8, having a capacitor connected in parallel with said condition-sensitive capacitive transducer and first solid-state switching element and establishing an electrical charge source to rapidly charge the transducer within the charging period.
Claim 12
Dependent Claim
14 words
The apparatus of claim 8, wherein said power means includes a high-frequency crystal oscillator.
Claim 13
Dependent Claim
33 words
The apparatus of claim 8, wherein said switching elements are transistors alternately connecting and disconnecting said condition-sensitive capacitive transducer from said bridge apparatus, and said power means includes a high-frequency crystal-controlled electrical oscillator.
Claim 14
Dependent Claim
34 words
The apparatus of claim 1, wherein the transducer is connected in said charging circuit for a period essentially corresponding to the period to fully charge the transducer for a selected maximum condition established capacitance.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-01-17 | 1975-07-19 | 1976-01-18 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-01-17 | 1979-07-19 | 1980-01-18 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-01-17 | 1983-07-19 | 1984-01-18 | $7700.00 | Window Closed / Lapsed |