1959 - History of Ericsson - History of Ericsson

Fig. 3 X2464
Trunking diagram
LR line relay
SNR connecting circuit
REG register
Technical Data
The resistance of extension lines may be up to 500 ohms. Using 0.5 mm
conductors this corresponds to a distance between switchboard and telephone
of 2.5 kilometres.
The power unit is supplied wired for 220 V and can easily be adjusted
for 110, 127 or 150 V after removing the protective cover over the power
terminal block. Fluctuations in mains voltage of ± 14 % are permissible.
The power unit delivers 24 V operating voltage, 85 V ringing voltage, and
a dial tone of about 100 c/s.
Operation
The switchboard contains equipment for 15 extensions and 2 link circuits.
The line equipment for each extension consists of two relays, one for link
circuit 1 and the other for circuit 2. The link circuits are selected alternately:
after one has been occupied, the other is selected on the next call.
In addition to line equipments and link circuits the switchboard contains
a common register.
When an extension user calls the switchboard, one of his line relays,
corresponding to the link circuit due for selection, operates and connects
the extension to that circuit. None of the other line relays associated with
the selected circuit can then operate, so that two extensions cannot seize the
same link circuit simultaneously.
The register is connected to the link circuit and returns dial tone to the
extension.
The number dialled by the extension is stored by a relay chain in the
register.
On the completion of dialling two ringing signals are emitted in quick
succession, provided that the called number is free, and ringing tone is
returned to the caller. The called extension is connected to the calling
circuit. The register is disconnected and no further ringing signal is transmitted.
When the called party answers, speaking conditions are immediately
established. For the line to be cleared on completion of conversation both
parties must replace their handsets.
If a called extension is engaged, busy tone is returned from the register
until the line is cleared, i.e. until the caller replaces.
The register is equipped for time release. Thus, if an extension does
not start to dial within about 6 seconds of being connected to the register,
the register is disconnected and the extension is locked to the link circuit.
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