US3814870A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Telephone subscriber line terminating test circuit
Assignee: AT&T Inc
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Filing: 1972-09-19
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Granted: 1974-06-04
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Expires: 1992-09-19
Abstract
Abstract A telephone line terminating test circuit for simulating a subscriber line subset to provide a properly timed off-hook signal responsive to a ringing current applied to the line. During precutover testing of a telephone switching system, the test circuit connects a subset simulating resistance across the line under control of a thermal relay operated responsive to the ringing current to simulate an off-hook state. The thermal relay is delayed in both its operate and restore phases to provide proper testing periods.
Inventors
- 👤 H Miller
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 08:31
CPC Classifications
H; H04; H04M; H04M3/00; H04M3/22; H04M3/26; H04M3/28; H04M3/30; H04M3/301; H04M3/32; H04M3/323
Claims Analysis
Total Claims: 6
Claim 1
Independent Claim
184 words
A telephone subscriber line terminating test circuit for simulating a telephone subset during testing of a switching system having a source of ringing current and means for tripping said source of current responsive to an off-hook condition of said subset, said test circuit comprising a bridge circuit detachably connectable across the tip and ring conductors of said line, said bridge including a pair of parallel branches, one of said parallel branches including a thermal delay relay means and direct current blocking capacitor means, the other of said parallel branches including a resistor of a value substantially equal to the direct current resistance of said subset in its offhook state, said other of said parallel branches also including relay make contacts controlled by said relay means, said relay means closing said contacts after a predetermined interval responsive to the presence of ringing current applied to said line to connect said resistor across said line to simulate said off-hook condition to trip said source of ringing current, said relay means restoring said contacts after a second predetermined interval responsive to the termination of said ringing current.
Claim 2
Dependent Claim
184 words
A telephone subscriber line terminating test circuit for simulating a telephone subset during testing of a switching system having a source of ringing current and means for tripping said source of current responsive to an off-hook condition of said subset, said test circuit comprising a bridge circuit detachably connectable across the tip and ring conductors of said line, said bridge including a pair of parallel branches, one of said parallel branches including a thermal delay relay means and direct current blocking capacitor means, the other of said parallel branches including a resistor of a value substantially equal to the direct current resistance of said subset in its offhook state, said other of said parallel branches also including relay make contacts controlled by said relay means, said relay means closing said contacts after a predetermined interval responsive to the presence of ringing current applied to said line to connect said resistor across said line to simulate said off-hook condition to trip said source of ringing current, said relay means restoring said contacts after a second predetermined interval responsive to the termination of said ringing current.
Claim 3
Dependent Claim
105 words
A telephone line terminating test circuit comprising a bridge circuit detachably connectable across a subscriber line, said bridge circuit including a first parallel branch including a thermal delay relay means and direct current blocking capacitor means comprising a polarized capacitor included on either side of said relay means and a second parallel branch including normally open contacts controlled by said relay means and resistor means simulating the direct current resistance of a telephone line subset, said relay means being operable responsive to ringing current applied to said line to cause a delayed closing of said contacts to simulate an off-hook condition of said subscriber line.
Claim 4
Dependent Claim
105 words
A telephone line terminating test circuit comprising a bridge circuit detachably connectable across a subscriber line, said bridge circuit including a first parallel branch including a thermal delay relay means and direct current blocking capacitor means comprising a polarized capacitor included on either side of said relay means and a second parallel branch including normally open contacts controlled by said relay means and resistor means simulating the direct current resistance of a telephone line subset, said relay means being operable responsive to ringing current applied to said line to cause a delayed closing of said contacts to simulate an off-hook condition of said subscriber line.
Claim 5
Dependent Claim
141 words
In combination in a telephone switching system having a plurality of subscriber lines, a source of ringing current, and control means for applying said ringing current to a selected one of said lines and for terminating said ringing current responsive to an off-hook condition of said line: a line terminating test circuit for simulating said selected line comprising a bridge circuit adapted for temporary connection across the conductors of said selected line, said bridge circuit including a first parallel path including a thermal delay relay means operated responsive to said ringing current and a first and a second polarized capacitor included on opposite sides of said relay means; and a second parallel path including resistance means substantially equal to the direct current resistance of the subset of said selected line and relay make contacts controlled by said thermal delay relay means.
Claim 6
Dependent Claim
141 words
In combination in a telephone switching system having a plurality of subscriber lines, a source of ringing current, and control means for applying said ringing current to a selected one of said lines and for terminating said ringing current responsive to an off-hook condition of said line: a line terminating test circuit for simulating said selected line comprising a bridge circuit adapted for temporary connection across the conductors of said selected line, said bridge circuit including a first parallel path including a thermal delay relay means operated responsive to said ringing current and a first and a second polarized capacitor included on opposite sides of said relay means; and a second parallel path including resistance means substantially equal to the direct current resistance of the subset of said selected line and relay make contacts controlled by said thermal delay relay means.
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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) | 1977-06-03 | 1977-12-03 | 1978-06-04 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-06-03 | 1981-12-03 | 1982-06-04 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-06-03 | 1985-12-03 | 1986-06-04 | $7700.00 | Window Closed / Lapsed |