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Browse Prior Art Database

PBX Trunk Circuit

IP.com Disclosure Number: IPCOM000093452D
Original Publication Date: 1967-Sep-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Garcia, J: AUTHOR [+2]

Abstract

Ringing signals and metering signals sent from a central exchange to a private branch exchange have the same frequency, e.g., 50 cps. Ringing signals are fed to either of the two trunk wires. Metering signals are fed, in phase, to both wires and referenced to earth.

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PBX Trunk Circuit

Ringing signals and metering signals sent from a central exchange to a private branch exchange have the same frequency, e.g., 50 cps. Ringing signals are fed to either of the two trunk wires. Metering signals are fed, in phase, to both wires and referenced to earth.

Previous trunk circuits are composed of a transformer TR, the primary winding of which, shunted by a diode limiter, is connected to the switching network. The secondary winding of TR is connected to central exchange via two external trunks. A relay RL allows transmission of the dialing signal.

This circuit provides a device to detect the ringing and the metering signals and to distinguish between the two. This device is a symmetrical detector composed of a two transistor, full-wave rectifier with grounded median tap, an integrator, and a transistor T acting as a current detector.

When either ringing or metering pulses are sent through the trunk wires, the T output circuit delivers a signal which is detected by the trunk scanner. The distinction between the two signals is obtained by associating, to the scanner output on one hand the calling trunk status and on another hand the called trunk status.

A signal appears, on the calling status line when the PBX is calling. A signal appears on the called status line when the Central Exchange is calling.

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