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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Page 54<br />
1. Voltage measurements of Test, Main and Line Signalling Batteries.<br />
2. Measurement of external resistance by simplified Wheatstone Bridge.<br />
3. Line resistance measurement by simplified Wheatstone Bridge.<br />
4. Earth leakage measurement direct reading in ohms.<br />
5. Earth fault location, by simplified Murray Earth Test, direct reading as<br />
percentage of line.<br />
6. Resistance measurements by voltmeter method.<br />
7. Line resistance measurement by voltmeter method.<br />
8. Line to earth resistance measurement by voltmeter method.<br />
9. Measurement of incoming volts from line.<br />
10. Impulse ratio check on selective signalling.<br />
11. Operational check for Traffic Control Selectors on reduced voltage.<br />
12. Telephone communication with line under test.<br />
The voltmeter movement resistance is 100 ohms with series and shunt resistors<br />
to give the various rest conditions. This instrument is centrally pivoted and has two<br />
scales, 350-0-350 and 70-0-70 volts.<br />
When used on Wheatstone Bridge and Murray Earth tests, it is most important<br />
that an approximate zero reading be obtained before attempting to make the final<br />
balance test by operating the sensitivity key, SK. Failure to do this may result in<br />
irreparable damage to the voltmeter movement.<br />
If, in measuring line loop or line earth resistance, difficulty is experienced in<br />
obtaining a steady balance with Wheatstone Bridge or Murray Earth Test, the voltmeter<br />
method should be used.<br />
When making any line tests it is important that the terminals T1 and T3 should<br />
be isolated, and conversely, when measuring an external resistance, the lines should<br />
not be connected.<br />
Installation Notes<br />
The Test Set should be installed adjacent the main frame so that it can be<br />
connected to any line by inserting test plugs into the appropriate Protector Mounting.<br />
The various battery supplies, ringing supply and earth should be connected as<br />
indicated on the Test Set. It is essential that a separate 50 volt battery should be used<br />
for the Test Set battery, since under fault conditions it is possible that the main 50<br />
volt battery may be connected in some way with the line under test, and this might<br />
give rise to false reading if the main battery was also used to operate the Test Set.