GB1494136A - Telephone exchanges - Google Patents

Telephone exchanges

Info

Publication number
GB1494136A
GB1494136A GB811175A GB811175A GB1494136A GB 1494136 A GB1494136 A GB 1494136A GB 811175 A GB811175 A GB 811175A GB 811175 A GB811175 A GB 811175A GB 1494136 A GB1494136 A GB 1494136A
Authority
GB
United Kingdom
Prior art keywords
output
earthing
key
exchange
currents
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
GB811175A
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Telefonaktiebolaget LM Ericsson AB
Original Assignee
Telefonaktiebolaget LM Ericsson AB
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Telefonaktiebolaget LM Ericsson AB filed Critical Telefonaktiebolaget LM Ericsson AB
Publication of GB1494136A publication Critical patent/GB1494136A/en
Expired legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M3/00—Automatic or semi-automatic exchanges
    • H04M3/42—Systems providing special services or facilities to subscribers
    • H04M3/58—Arrangements for transferring received calls from one subscriber to another; Arrangements affording interim conversations between either the calling or the called party and a third party

Landscapes

  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Interface Circuits In Exchanges (AREA)

Abstract

1494136 Automatic exchange systems TELEFONAKTIEBOLAGET L M ERICSSON 26 Feb 1975 [6 March 1974] 8111/75 Heading H4K In an exchange system in which a subscriber makes an enquiry call, e.g. to initiate an interim conversation with a third party, by earthing one of the speech wires La, Lb, e.g. by depressing a key K at his substation TA, this earthing is detected at the exchange by a circuit DA which includes voltage dividers R5, R6 and R3, R4 and a differential amplifier DF. The resistors R3-R6 are chosen so that for on-hook (no current in La, Lb ) and connection-established (equal currents in La, Lb) conditions, the output from DF, Fig. 2 (not shown) is substantially zero. However, on depression of key K the currents in La, Lb become unequal, resulting in a negative output from DF. This output actuates a coupling circuit, which brings about the necessary switching sequences for an enquiry call.
GB811175A 1974-03-06 1975-02-26 Telephone exchanges Expired GB1494136A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
SE7402969A SE7402969L (en) 1974-03-06 1974-03-06

Publications (1)

Publication Number Publication Date
GB1494136A true GB1494136A (en) 1977-12-07

Family

ID=20320429

Family Applications (1)

Application Number Title Priority Date Filing Date
GB811175A Expired GB1494136A (en) 1974-03-06 1975-02-26 Telephone exchanges

Country Status (4)

Country Link
DE (1) DE2508547A1 (en)
GB (1) GB1494136A (en)
IT (1) IT1033426B (en)
SE (1) SE7402969L (en)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL7904429A (en) * 1979-06-06 1980-12-09 Philips Nv FLOW DETECTION DEVICE FOR AN AUTOMATIC TELEPHONE CONTROL PANEL.
DE3108264C2 (en) * 1981-03-05 1984-05-30 Deutsche Fernsprecher Gesellschaft Mbh Marburg, 3550 Marburg Circuit arrangement for detecting the switching state of an earth button on a telephone set

Also Published As

Publication number Publication date
SE7402969L (en) 1975-09-08
IT1033426B (en) 1979-07-10
DE2508547A1 (en) 1975-09-11

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Legal Events

Date Code Title Description
PS Patent sealed
PCNP Patent ceased through non-payment of renewal fee