TRAFFIC CONTROL TELEPHONE SYSTEMS Circuit - Sam Hallas

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20, so that the true readings will be 2.5 milliamperes. Then restore the “low”
key and throw the “release” key (KRL on diagram), after which the rheostat
knob marked " release " should be adjusted till the microammeter reads 140.
This is a direct reading of the release current. Finally restore both the “release”
key and the "meter " key, after which the selector is ready for test.
N.B. — No adjustment of the selector currents for the “high” or the “saturate”
conditions of test are provided, but by throwing the “meter” key (KM on diagram)
and leaving all other keys normal the saturate current can be read on the meter, and by
throwing in addition to the “meter” key the "high" key (KH on diagram) the high
current can be read. In both these cases the meter multiplier is 80.
To Test the Selector
1. For release-throw the “saturate” key. This puts the saturate current through
the windings of the selector. Observe that the armature of the selector is attracted to
one of the poles. Then throw the “release” key, after which the armature should
return to normal. Repeat this test for the other pole of the selector by throwing both
the “saturate” key and the “rev.” key (KRV on diagram) when the armature should be
attracted by the saturate current to the other pole. On throwing the “release” key, the
armature should return to normal.
2. For high current-throw the “high” key (keeping “meter” key normal) and
operate the test selector key. The selector should step to its ringing position, and the
buzzer should sound for approximately 2 seconds, after which the selector should
restore to normal as the selector key completes its run. Repeat this test with the
“rev.” key thrown in addition to the “high” key. This circuit switching directs the
impulses the opposite way through the winding, and should allow the selector to
step correctly to its ringing position and release as in the first part of this test.
3. For low current-throw the “low” key (keeping “meter” key normal) and
operate the test selector key. The selector should step to its ringing position and the
buzzer should sound for approximately 2 seconds, after which the selector should
return to normal. Repeat this test with the “ rev.” key thrown in addition to the “low”
key. With the impulses passing in the opposite direction through the windings the
selector should step to its ringing position and release correctly as in the first part of
this test.
The three terminals, K1, K2 and K3 provide facilities for connection direct to a
selector key case. When so used, the selector key case must be completely disconnected
from its associated selector case.
To Test a Selector Set
Connect L1, L2 of the selector set to L1, L2 of the Test Set, and proceed as
above, except that the meter key KM must be held operated.