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Telephone Line Scanning Circuit Disclosure Number: IPCOM000095260D
Original Publication Date: 1965-Oct-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 39K

Publishing Venue


Related People

Croisier, A: AUTHOR


This scanning circuit is for a telephone exchange and provides self-checking facilities.

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Telephone Line Scanning Circuit

This scanning circuit is for a telephone exchange and provides self-checking facilities.

Telephone line L, which is to be scanned, receives its address of standard SLT levels. The And made up of diodes D1, D2 and D3 detects this address. If the telephone line is off hook, the voltage at point A is such that transistor T always stays blocked even if the circuit receives its address pulse. There is no response upon the repeated address circuits. If the telephone line is on hook, transistor T conducts when the line is addressed. The telephone line address pulse is sent through capacitor C and diodes D5, D6 and D7 to the response circuit. The address is repeated.

The system has the following self-checking features. If transistor T fails, the line is always off hook. If one diode D1, D2, D3 is open, unexpected bits are found in response to the scanning of other circuits. These bits define the faulty circuit. If one diode D5, D6, D7 is open, incomplete response results from scanning the circuit. If any diode is short-circuited, the circuit still operates. The presence of a failure is indicated by the amplitude of the signal on either the scanning or the response circuit.


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