TRAFFIC CONTROL TELEPHONE SYSTEMS Circuit - Sam Hallas

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