US4101741A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Line circuit for key telephone systems
Assignee: International Standard Electric Corp
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Filing: 1977-03-14
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Granted: 1978-07-18
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Expires: 1997-03-14
Abstract
Abstract A line circuit for a key telephone system using two relays, a ring delay (B) and a combined off-hook and hold relay (C), and solid state devices including a first and a second optical coupler. On a ring signal from the exchange, the first optical coupler is activated to cause the energization of the ring relay. On a station of the line going off-hook (busy), the conventional A lead ground operates the C relay and causes de-energization of the B relay. When a station of the line goes into hold, the circuit must differentiate this condition from a hang-up condition. This differentiation is performed by sensing the line voltage as low (continued loop closure at the start of hold) or high (open loop at the stations of the line). The C relay is held during this determination so that the circuit may enter the hold condition when indicated. On a high voltage condition, indicating a hang-up condition, the second coupler switches on to prevent the B relay from operating, and thereby preventing the circuit from entering the hold condition.
Inventors
- 👤 George Kunstatter
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 06:39
CPC Classifications
H; H04; H04M; H04M9/00; H04M9/002; H04M9/005; H04M9/006
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
141 words
A line circuit for a key telephone system which comprises a ring detecting means for causing operation of a first relay to initiate local signaling on occurence of ringing current applied to the line conductors, a second relay operated in response to an off-hook condition at a station of said line circuit, means for deenergizing said first relay in response to said off-hook signal, line voltage sensing means, means responsive to operation of said second relay for enabling said line voltage sensing means to determine the voltage across said line, said line voltage sensing means maintained in an off condition during off-hook and hold conditions, means for switching said voltage sensing means on in response to an open loop across said line conductors to prevent said first relay from operating and for preventing said line circuit from entering the hold condition.
Claim 2
Dependent Claim
141 words
A line circuit for a key telephone system which comprises a ring detecting means for causing operation of a first relay to initiate local signaling on occurence of ringing current applied to the line conductors, a second relay operated in response to an off-hook condition at a station of said line circuit, means for deenergizing said first relay in response to said off-hook signal, line voltage sensing means, means responsive to operation of said second relay for enabling said line voltage sensing means to determine the voltage across said line, said line voltage sensing means maintained in an off condition during off-hook and hold conditions, means for switching said voltage sensing means on in response to an open loop across said line conductors to prevent said first relay from operating and for preventing said line circuit from entering the hold condition.
Claim 3
Dependent Claim
31 words
A line circuit as claimed in claim 1, in which said ring detecting means and said line voltage sensing means each comprise in combination a rectifier bridge and an optical coupler.
Claim 4
Dependent Claim
47 words
A line circuit as claimed in claim 2, in which said line voltage sensing means includes a zener diode for preventing the switching on of the optical coupler of said voltage sensing means only when the voltage across the voltage sensing rectifier bridge exceeds a predetermined voltage.
Claim 5
Dependent Claim
41 words
A line circuit as claimed in claim 2, in which the coupler of said ring detecting means is switched on responsive to a hold signal applied to the line conductors and the coupler of said voltage sensing means is shut off.
Claim 6
Dependent Claim
133 words
A line circuit for a line of a key telephone system comprised of a pair of line conductors, means for detecting ringing current applied across said line conductors, said ring detecting means including a rectifier bridge and an optical coupler connected to output terminals of said bridge, said coupler responsive to detection of ring current across the line conductors for causing operation of local ring control means, means for preventing operation of said ring control means in response to an off-hook signal applied to said line circuit, means for causing operation of said ring control means during a hold signal applied across said line conductors to cause operation of said ring control means, and means for bridging a resistance in said ring control circuit across the line conductors responsive to a hold signal.
Claim 7
Dependent Claim
133 words
A line circuit for a line of a key telephone system comprised of a pair of line conductors, means for detecting ringing current applied across said line conductors, said ring detecting means including a rectifier bridge and an optical coupler connected to output terminals of said bridge, said coupler responsive to detection of ring current across the line conductors for causing operation of local ring control means, means for preventing operation of said ring control means in response to an off-hook signal applied to said line circuit, means for causing operation of said ring control means during a hold signal applied across said line conductors to cause operation of said ring control means, and means for bridging a resistance in said ring control circuit across the line conductors responsive to a hold signal.
Claim 8
Dependent Claim
61 words
A line circuit as claimed in claim 5, in which said preventing means comprises line voltage sensing means includes in combination a rectifier bridge connected across the line conductors, an optical coupler with its input terminals connected across the diagonal of said rectifier bridge, and a zener diode in series between an output terminal of said last mentioned bridge and coupler.
Claim 9
Dependent Claim
47 words
A line circuit as claimed in claim 6, in which there is a hold prevention circuit coupled to said line voltage sensing means to prevent said line circuit entering a hold condition when voltage above the breakdown of said zener diode is sensed across the line conductors.
References Cited (Backward Citations)
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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) | 1981-07-17 | 1982-01-16 | 1982-07-18 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1985-07-17 | 1986-01-16 | 1986-07-18 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1989-07-17 | 1990-01-16 | 1990-07-18 | $7700.00 | Window Closed / Lapsed |