US4347709A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Demand defrost sensor
Assignee: Honeywell Inc
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Filing: 1981-01-19
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Granted: 1982-09-07
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Expires: 2001-01-19
Abstract
Abstract A demand defrost system in which a high resistive epoxy resin hermetically seals a capacitive sensor plate and a noise immune phase detector detects a phase shift caused by the build up of frost.
Inventors
- 👤 M. T. Wu
- 👤 Thomas Y. Chai
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 15:33
CPC Classifications
F; F25; F25D; F25D21/00; F25D21/02
Claims Analysis
Total Claims: 3
Claim 1
Independent Claim
146 words
A demand defrost sensor for sensing and controlling the frost build up on an evaporator surface, comprising in combination: a conductive plate disposed adjacent said surface, said plate and said surface forming a capacitor; a high resistive material encapsulating said plate; a first and second operational amplifier; means for coupling a source of AC reference signal to said first amplifier; means including said capacitor and coupling said source of AC reference signal to said second amplifier; means for comparing an output of said first and said second amplifier, said comparing means producing a series of output pulses whose width is a function of the phase shift caused by said capacitive coupling; means to integrate said pulses, said integrating means producing a DC signal whose magnitude is a function of said pulse width; and means responsive to said DC signal for initiating and terminating a defrost cycle.
Claim 2
Dependent Claim
146 words
A demand defrost sensor for sensing and controlling the frost build up on an evaporator surface, comprising in combination: a conductive plate disposed adjacent said surface, said plate and said surface forming a capacitor; a high resistive material encapsulating said plate; a first and second operational amplifier; means for coupling a source of AC reference signal to said first amplifier; means including said capacitor and coupling said source of AC reference signal to said second amplifier; means for comparing an output of said first and said second amplifier, said comparing means producing a series of output pulses whose width is a function of the phase shift caused by said capacitive coupling; means to integrate said pulses, said integrating means producing a DC signal whose magnitude is a function of said pulse width; and means responsive to said DC signal for initiating and terminating a defrost cycle.
Claim 3
Dependent Claim
30 words
A demand defrost sensor for sensing and controlling the frost build up on an evaporator surface as in claim 1 including a plurality of conductor plates disposed adjacent said surface.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1985-09-06 | 1986-03-08 | 1986-09-07 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1989-09-06 | 1990-03-08 | 1990-09-07 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1993-09-06 | 1994-03-08 | 1994-09-07 | $7700.00 | Window Closed / Lapsed |