TRAFFIC CONTROL TELEPHONE SYSTEMS Circuit - Sam Hallas

Page 28
After the ringing period, one impulse is transmitted to line by the calling key
and all selectors are advanced one step then return to the normal position.
A similar sequence is followed in the operation of a selector with a different
code setting.
General Call
When it is necessary to communicate with all stations simultaneously the
Controller operates the General Call key which transmits an uninterrupted train of 17
impulses. These impulses advance all selectors on the line, irrespective of the positions
of intermediate code pins, to the ringing position, thus calling all Way Station
Operators to the telephone. The ringing period and clear down of selectors is identical
to that described for individual calling.
Time Sending
Selectors are set to the time receiving position by an unbroken train of 22
impulses. Again all selectors respond and irrespective of intermediate coding pins
arrive in position 22. Instead of the normal holding pin they are held by the holding
finger engaging with an are which covers four code wheel positions commencing in
position 22. Single impulses received while the selector is held in this position will
cause the code wheel to advance to position 23 and fall back into position 22. In
position 23 there is a contact connected in parallel with the normal ringing contact so
that the momentary contact made with the code wheel contact spring results in short
strokes of the bell thus repeating the time signal code.
As the time arc on the selector covers four code wheel positions it follows that
to clear this condition more than three impulses must be sent to line. Therefore to
restore the selectors to normal, operate any key other than General Call or Time
Sending.
Test Requirements
General. — As a rule, adjustment is not recommended unless the fault is quite
obvious and easy to rectify. If the cause of the failure is not easily seen or corrected,
we recommend that a spare selector be substituted, and the faulty selector tested
with the 4001-B Selector Test Set (described in this book) or returned to Standard
Telephones and Cables Limited for investigation. When a selector is returned, a
statement of the conditions and as nearly as possible, the manner in which the
selector acted, should be sent to assist in determining the cause of the failure.
Extreme care should be taken when any adjustments have to be made.