US3748405A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Key telephone system line circuit
Assignee: COMDIAL TELECOMMUNICATIONS Inc A CORP OF DEL
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Filing: 1972-06-15
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Granted: 1973-07-24
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Expires: 1992-06-15
Abstract
Abstract A key telephone system line circuit provides the supervisory and control functions for initiating and terminating local signalling to a key telephone set and for placing the associated line in and out of hold conditions. Contacts of the line relay of the line circuit are connected in series with the dummy load placed across the telephone line during hold conditions to provide a positive release of the telephone line in response to a momentary change in line potential generated by the telephone switching center as a result of the outside party hanging up while the line is on hold.
Inventors
- 👤 P Saba
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 12:15
CPC Classifications
H; H04; H04M; H04M9/00; H04M9/002; H04M9/005; H04M9/006
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
83 words
An improved line circuit for interconnecting a key telephone set with a telephone line wherein a line relay is connected in series with the telephone line to be actuated by the flow of DC current therethrough and a dummy load is placed across the line in response to a hold signal from the key telephone to hold the line seized while the telephone set is temporarily disconnected therefrom, the improvement comprising contacts of the line relay connected in series with the dummy load.
Claim 2
Dependent Claim
83 words
An improved line circuit for interconnecting a key telephone set with a telephone line wherein a line relay is connected in series with the telephone line to be actuated by the flow of DC current therethrough and a dummy load is placed across the line in response to a hold signal from the key telephone to hold the line seized while the telephone set is temporarily disconnected therefrom, the improvement comprising contacts of the line relay connected in series with the dummy load.
Claim 3
Dependent Claim
162 words
A line circuit for interconnecting a key telephone set with a telephone line wherein the telephone set generates an off-hook signal when it is connected to the telephone line and a hold signal when it is disconnected therefrom while the line is held seized, comprising: first circuit means including a first relay connected so that said first relay is actuated by either ringing signals or a DC current flow through the telephone line; second circuit means including a second relay which is actuated in Response to the off-hook signal and is maintained actuated through contacts of said first relay when the hold signal is present; third circuit means including a third relay which is actuated through contacts of said first relay during ringing and through contacts of said second relay when the hold signal is present and is deactuated by the off-hook signal, and a dummy load for connection across the telephone line through contacts of said first, second and third relays.
Claim 4
Dependent Claim
162 words
A line circuit for interconnecting a key telephone set with a telephone line wherein the telephone set generates an off-hook signal when it is connected to the telephone line and a hold signal when it is disconnected therefrom while the line is held seized, comprising: first circuit means including a first relay connected so that said first relay is actuated by either ringing signals or a DC current flow through the telephone line; second circuit means including a second relay which is actuated in Response to the off-hook signal and is maintained actuated through contacts of said first relay when the hold signal is present; third circuit means including a third relay which is actuated through contacts of said first relay during ringing and through contacts of said second relay when the hold signal is present and is deactuated by the off-hook signal, and a dummy load for connection across the telephone line through contacts of said first, second and third relays.
Claim 5
Dependent Claim
44 words
The line circuit of claim 2 wherein said first relay has two windings, one connected in series with the telephone line for energization by the flow of DC current therethrough and the other winding connected across the telephone line for energization by ringing signals.
Claim 6
Dependent Claim
51 words
The line circuit of claim 3 wherein the series connected winding of said first relay is inhibited from operating while said third relay is deactuated, and said second circuit means momentarily provides energizing current for operating said second relay until said first relay is actuated after the hold signal is generated.
Claim 7
Dependent Claim
33 words
The line circuit of claim 2 including signalling means responsive to the simultaneous actuation of said third relay and deactuation of said second relay for providing local signalling to the key telephone set.
Claim 8
Dependent Claim
36 words
The line circuit of claim 2 including circuit means connected across said first relay contacts used to switch said dummy load for providing a current shunt path when said contacts interrupt the flow of DC current.
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 |