TRAFFIC CONTROL TELEPHONE SYSTEMS Circuit - Sam Hallas

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SA wiper 2, the circuit for relay DC, through its 1,000 ohm winding, is broken when
this switch steps one step from its normal (home) position, and during subsequent
impulses Relay DC is held over its 3 ohm winding in series with IR1 contact and line
switch SA operating coil. Being slow to release, Relay DC does not release during
impulsing.
Line switch SA will take one step for each dial impulse, which, in the case of
code 53, will be five steps, leaving line switch wipers SA3 and 4 connected to line
switch SA bank contacts 6 and line switch SC bank contacts 12 and 10 respectively.
After the tens impulses are completed there will be a pause, whilst the controller reoperates
the dial to send the three (unit) impulses.
During this inter-digital pause, Relay IR will remain operated and Relay DC
releases after a short interval. This causes the digit switching Relay DS to operate via
50 volt negative, Relay DS winding e-a DCl, line switch wiper SA2, G2, GC3, TS2,
to 50 volt positive.
Relay DS locks up via DS1, leaving it independent of DC1 and line switch SA2.
Contact DS3 changing over causes Relay DC to re-operate via 50 volt negative, Relay
DC winding e-d DS3, line switch wiper SB2, G2, GC3, TS2, to 50 volt positive.
Relay G remains operated via IR1, Relay G winding, DC2, Relay DC 3 ohm winding
with resistor YA 50 ohm in parallel, DS2, line switch SB operating coil to 50 volt
negative.
The Controller now dials the three (unit) impulses and Relay IR releases with
the first impulse (break of dial) and line switch SB operating coil will be energised via
50 volt negative, SB coil, DS2, Relay DC 3 ohm winding b-a with resistor YA 50 ohm
in parallel, DC2, IRI, G3, to 50 volt positive. Note. — The operation of IR1 momentarily
short circuits Relay G, but this short circuit makes it slow releasing and it
remains operated during impulsing. Relay IR is again operated when the dial remakes
the impulsing contact after the first impulse, this removes the short circuit from
Relay G at IR1, and connects the winding of Relay G in series with line switch SB
operating coil, which releases and steps the line switch wiper arms. At line switch
wiper SB2, the circuit for Relay DC is broken when this line switch steps one step
from its normal (home) position, and during subsequent impulses Relay DC is held
over its 3 ohm winding in series with IR1 contact and line switch SB operating coil.
Being slow to release, Relay DC does not release during impulsing.
Line switch SB will take one step for each dial impulse (three in this case),
leaving line switch SB 3 and 4 wipers connected to line switch SB bank contacts 4 and
line switch SC bank contacts 23 and 25 respectively. When the dial has returned to