US3748389A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Alarm detection system
Assignee: AT&T Inc
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Filing: 1971-12-13
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Granted: 1973-07-24
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Expires: 1991-12-13
Abstract
Abstract A telephone system which employs an alarm detection arrangement is disclosed. Each subscriber set of the telephone system includes a subscriber set switch connected between an associated pair of conductors and an alarm indicator which replaces the subscriber set switch in response to an alarm situation. A central office, which applies a first polarity of DC voltage between each pair of conductors, responds to the opening or closing of the subscriber set switch and the replacement of the subscriber set switch with the alarm indicator by reversing the voltage polarity between the conductors. When the scanner detects that the subscriber set indicated an open circuit in response to one DC voltage polarity and a closed circuit in response to the other DC voltage polarity, an alarm signal is generated.
Inventors
- 👤 R Casterline
- 👤 W Garraty
- 👤 J Scanlon
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-03 11:00
CPC Classifications
H; H04; H04M; H04M11/00; H04M11/04
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
168 words
In combination; a signaling means for selectively applying a voltage polarity independent low impedance between a pair of conductors to which a first polarity of DC voltage is applied or a voltage polarity independent high impedance between said pair of conductors; an alarm indicator exhibiting a low impedance in response to one DC voltage polarity and a high impedance in response to the other DC voltage polarity; means responsive to the occurrence of an alarm situation for replacing said signaling means between said conductors with said alarm indicator; means responsive to said signaling means for controlling said alarm indicator to provide an impedance between said Conductors in response to said first DC voltage polarity substantially opposite to the impedance provided by said signaling means at the time of said replacement; and circuitry responsive to changes in impedance between said conductors for applying a detection signal between said conductors to determine if said change in impedance was caused by the substitution of said alarm indicator for said signaling means.
Claim 2
Dependent Claim
168 words
In combination; a signaling means for selectively applying a voltage polarity independent low impedance between a pair of conductors to which a first polarity of DC voltage is applied or a voltage polarity independent high impedance between said pair of conductors; an alarm indicator exhibiting a low impedance in response to one DC voltage polarity and a high impedance in response to the other DC voltage polarity; means responsive to the occurrence of an alarm situation for replacing said signaling means between said conductors with said alarm indicator; means responsive to said signaling means for controlling said alarm indicator to provide an impedance between said Conductors in response to said first DC voltage polarity substantially opposite to the impedance provided by said signaling means at the time of said replacement; and circuitry responsive to changes in impedance between said conductors for applying a detection signal between said conductors to determine if said change in impedance was caused by the substitution of said alarm indicator for said signaling means.
Claim 3
Dependent Claim
44 words
The combination in accordance with claim 1 wherein said circuitry includes a means responsive to changes in impedance between said conductors for removing the first polarity of DC voltage applied between said conductors and applying a second polarity of DC voltage between said conductors.
Claim 4
Dependent Claim
47 words
The combination of claim 2 wherein said circuitry includes a means for generating an alarm signal each time the impedance between said conductors in response to said second polarity DC voltage is different than the impedance between said conductors in response to said first DC voltage polarity.
Claim 5
Dependent Claim
195 words
In combination; a plurality of signaling means for selectively applying a voltage polarity independent low impedance between an associated pair of conductors to which a first polarity DC voltage is applied or a voltage polarity independent high impedance between said associated pair of conductors; an alarm indicator associated with each of said signaling means exhibiting a low impedance in response to one polarity of DC voltage and a high impedance in response to the other polarity of DC voltage; means responsive to the occurrence of an alarm situation for replacing said signaling means between a predetermined pair of conductors with said associated alarm indicator; means responsive to each of said signaling means for controlling said associated alarm indicator to provide an impedance between said predetermined conductors in response to said first polarity of DC voltage substantially opposite to the impedance provided by said signaling means at the time of said replacement; and circuitry responsive to changes in impedance between said predetermined pair of conductors for applying a detection signal between said predetermined pair of conductors to determine if said change in impedance was caused by the substitution of said alarm indicator for said signaling means.
Claim 6
Dependent Claim
195 words
In combination; a plurality of signaling means for selectively applying a voltage polarity independent low impedance between an associated pair of conductors to which a first polarity DC voltage is applied or a voltage polarity independent high impedance between said associated pair of conductors; an alarm indicator associated with each of said signaling means exhibiting a low impedance in response to one polarity of DC voltage and a high impedance in response to the other polarity of DC voltage; means responsive to the occurrence of an alarm situation for replacing said signaling means between a predetermined pair of conductors with said associated alarm indicator; means responsive to each of said signaling means for controlling said associated alarm indicator to provide an impedance between said predetermined conductors in response to said first polarity of DC voltage substantially opposite to the impedance provided by said signaling means at the time of said replacement; and circuitry responsive to changes in impedance between said predetermined pair of conductors for applying a detection signal between said predetermined pair of conductors to determine if said change in impedance was caused by the substitution of said alarm indicator for said signaling means.
Claim 7
Dependent Claim
55 words
The combination in accordance with claim 4 wherein said circuitry includes a means for removing said first polarity of DC voltage from between said predetermined pair of conductors and connecting a second polarity of DC voltage between said predetermined pair of conductors in response to a change in impedance between said predetermined pair of conductors.
Claim 8
Dependent Claim
57 words
The combination in accordance with claim 5 wherein said circuitry includes a means for generating an alarm signal each time the impedance between said predetermined pair of conductors in response to said second polarity of DC voltage is different than the impedance between said predetermined pair of conductors in response to said first polarity of DC voltage.
Claim 9
Dependent Claim
203 words
An alarm protected telephone system comprising; a subscriber set including a switch for selectively applying voltage polarity independent low impedance between a pair of conductors to which a first polarity of DC voltage is applied or a voltage polarity independent high impedance between said pair of conductors; an alarm indicator exhibiting a low impedance in response to one polarity of DC voltage and a high impedance in response to the other polarity of DC voltage; means responsive to the occurrence of an alarm situation for replacing said switch between said conductors with said alarm indicator; means responsive to said switch for controlling said alarm indicator to provide an impedance between said conductors in response to said first polarity of DC voltage substantially opposite to the impedance provided by said switch at the time of said replacement; means responsive to changes in impedance between saId conductors for replacing said first polarity of DC voltage between said conductors with a second polarity of DC voltage; and means for generating an alarm signal each time the impedance between said conductors in response to said second polarity of DC voltage is different than the impedance between said conductors in response to said first polarity of DC voltage.
Claim 10
Dependent Claim
203 words
An alarm protected telephone system comprising; a subscriber set including a switch for selectively applying voltage polarity independent low impedance between a pair of conductors to which a first polarity of DC voltage is applied or a voltage polarity independent high impedance between said pair of conductors; an alarm indicator exhibiting a low impedance in response to one polarity of DC voltage and a high impedance in response to the other polarity of DC voltage; means responsive to the occurrence of an alarm situation for replacing said switch between said conductors with said alarm indicator; means responsive to said switch for controlling said alarm indicator to provide an impedance between said conductors in response to said first polarity of DC voltage substantially opposite to the impedance provided by said switch at the time of said replacement; means responsive to changes in impedance between saId conductors for replacing said first polarity of DC voltage between said conductors with a second polarity of DC voltage; and means for generating an alarm signal each time the impedance between said conductors in response to said second polarity of DC voltage is different than the impedance between said conductors in response to said first polarity of DC voltage.
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) | 1976-07-23 | 1977-01-22 | 1977-07-24 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-07-23 | 1981-01-22 | 1981-07-24 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-07-23 | 1985-01-22 | 1985-07-24 | $7700.00 | Window Closed / Lapsed |