TRAFFIC CONTROL TELEPHONE SYSTEMS Circuit - Sam Hallas

PART 2
4001-A SELECTOR KEY
Selector Key Case (capacity 40 Keys) comprising 4002-A
Base Unit and 4002-B Extension Unit
Fig. 6.
The function of the selector key (Fig. 8) is to control the operation of the
battery relay and the battery reversing relay of the system, so that the appropriate
sequence of current reversals required to operatethe selector at the station called, will
be transmitted to line. The selector key is operated by twisting the handle P one
quarter turn and releasing it. On release, the key returns to normal driven by a
clockwork mechanism, the speed of which is controlled by a governor Q. At the end
of the shaft and rotating with it, is mounted the impulse wheel A with its coding
segments C. The keys are mounted in a wooden key case, supplied in units with a
capacity for 20 keys. The units may be bolted together if more than twenty keys are
required, as shown in Fig. 6.
The code of the base unit is 4002-A, and the extension unit 4002-B Selector
Key Case.
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