This PAX is designed specially for small organisations having a requirement of up to 10 telephones.
GENERAL CONSTRUCTION METHOD OF OPERATION
This P.A.X. has a capacity for 10 extension lines and permits one conversation at a time. It operates from 24 volts DC which are obtained from a built-in battery eliminator.
The P. A. X. comprises 10 line relays and 13 relays in the speech circuit. BPO type relays are used and require no special adjustments. The P. A. X. is housed in a metal case painted hammered grey which is fixed to a wall by two screws. The dimensions are:
230mm x 370mm x 138mm (9.1" x 14.75" x 5.5")
Weight: approximately 12Kg (26lb) The battery eliminator is housed in the upper part of the case and is separated from the relays by an isolating plate.
The cover is secured by a single nut and the section opposite the eliminator is louvered to permit good ventilation.
The plate on which the relays are mounted is hinged and when opened the terminals are completely accessible.
The terminal block is fitted at the base of the frame and cabled to the relays in a way which permits free movement of the relay mounting plate.
The battery eliminator is of the full wave type, fitted with a suitable filter and supplies 24 volts DC 0.5A for the relays and 70 volts AC for the ringing current.
The ringing current is passed through a low capacity condenser and a rectifier to provide the dialling and ringing tones.
The mains input can be 110 or 220 AC ±6%, 50 Hz.
An extension desiring to originate a call removes the handset from the telephone. This complete a DC loop to cause the line relay (L) to operate which prevents any other line relays from operating should another extension try to originate a call.
On receipt of dial tone, the calling extension may dial the desired number. The called extension will be free because only one speech circuit is incorporated in the exchange. Thus, on completion of dialling, interrupted ringing current will be automatically applied to the called extension’s line to ring the telephone bell and ring tone will be returned to the calling extension to inform him that the required extension bell is being rung.
When the call is answered, the removal of the called extension’s handset extends a DC loop to the line relay which operates to connect the two lines together.
Extension “0” can intervene in an existing conversation by pressing the button on his instrument which, actuates relay L 10. For this purpose the telephone of extension “0” is fitted with a button and the line has 3 wires. Under these circumstances, extension “0” requests both parties to replace their handsets and he also restores his own.
On removing his handset again, he receives dialling tone and can proceed with his call under normal conditions.
At the end of a conversation, all relays are released when the parties replace their handsets.
Taken from sales literature 200/1 by Plessey Automatica Electrica Portuguesa (SARL)
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