TRAFFIC CONTROL TELEPHONE SYSTEMS Circuit - Sam Hallas
TRAFFIC CONTROL TELEPHONE SYSTEMS Circuit - Sam Hallas
TRAFFIC CONTROL TELEPHONE SYSTEMS Circuit - Sam Hallas
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swing of the meter needle either side of zero during impulsing will be equal. This<br />
shows that the positive impulses are of the same duration as the negative impulses.<br />
To get the best result of this test it is preferable to use a heavily damped meter.<br />
The relay SR is shunted by a rheostat and by adjusting this the release time of<br />
SR can be varied thereby controlling the impulse ratio of the impulses transmitted. To<br />
increase the time during which SR is on its back contact, turn the adjusting screw of<br />
the rheostat in a clockwise direction. If, in the above test the swing of the meter needle<br />
either side of zero is unequal, the rheostat should be adjusted until the ratio is correct.<br />
It is assumed, of course, that the selector key originating the test impulses has itself<br />
been checked for impulse ratio (prior to the test) as described in Part 2.<br />
<strong>Circuit</strong> Breaker No. 4001-A<br />
The <strong>Circuit</strong> Breaker opens the line battery circuit if excessive current is taken<br />
from the battery, such as would be caused by a short circuit on the line or line circuit.<br />
Its resistance is 2 ohms and it is normally adjusted to trip at 0.6 ampere. On<br />
resetting the circuit breaker after it has been operated, care should be taken not to hold<br />
it in forcibly by hand, so that, if the short circuit still exists, the circuit breaker will<br />
have an opportunity to re-open the battery circuit.<br />
Controller's Telephone <strong>Circuit</strong><br />
Since the controller is normally listening on the line, a head-set is the most<br />
convenient form of receiver and transmitter to employ. The head-set is connected to<br />
the talking circuit by means of plug and jack, so arranged that two sets can be used at<br />
the same time. When no head-set is connected an alarm circuit is completed through<br />
the jacks. This circuit may be used to operate an extension bell or an amplifier and<br />
loud speaker. In the former case, way stations would require a magneto for calling the<br />
controller while the second arrangement retains the normal method of operation, but<br />
enables way station calls to be heard at a reasonable distance from the control position.<br />
Foot Switch No. 4001-A<br />
The Foot Switch is used instead of a speak-listen key, thus leaving both of the<br />
Controller's hands free for recording messages. The Controller's talking circuit is of a<br />
high efficiency type, so arranged that by operating the foot switch when talking, the<br />
impedance matching is made optimum for both the transmitter and the receiver.<br />
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