This is a handy little unit for testing the voltage on a model railway track.
It is supplied as a Printed Circuit Board (PCB) with two brass contacts along
the bottom, and a voltmeter and other components mounted on it, including a
red/green LED to indicate track polarity. It is designed to work with track
from Z scale to O scale.
To use, simply press the unit down on the rails, (where the label says
track) and check the LED and the voltmeter.
If the LED lights up red, then the track has a DC voltage on it, and the
right rail is positive. If the LED lights up green, then the track has a
DC voltage on it, and the left rail is positive. This is indicated on the
face of the unit as “Gn (for green) L +ve,” meaning left positive, and
similarly for Rd (red) meaning right positive. If both sections (red and
green) of the LED light up, then there is an AC voltage on the track. It
is assumed this implies DCC, hence the labelling “Or DCC” meaning Orange
indicates DCC. However, this must be interpreted - there may be an AC
voltage from an AC controller. The labelling is meant to provide a simple
reminder of the state of the LED. The light may not be seen as orange,
but the red and green sections will possibly be separately visible.
The voltmeter will start to indicate with around 5 volts on the track.
Because of the diode bridge on the unit, the voltage indicated is
approximately 1.5 volts lower than the track voltage. Thus, a reading
of say 7.8 volts should be interpreted to mean the track voltage is
approximately 9.3 volts. The unit will read up to 30 volts.
Although the approximately 1.5 allowance must be made in interpreting
the readings, the readings will be consistent. That is to say, if a
reading of say 10.2 volts is given near to the track supply point, and
a reading of 9.6 volts is obtained further away, then there has been a
loss of some 0.6 volts between the two points, which possibly indicates
a problem in the wiring. There is a built in load resistor in the tester,
which will draw approximately 100mA at 12 volts, thus helping to show
up any poor connections in the track circuit – if these are there, the
track voltage will drop as the test is made further away from the
The diagrams above show (from left to right) the unit, detail of the
face of the unit, and the unit in use, with the right rail positive,
and approximately 10.4 volts on the track.
All kits available from :
Aztronics Pty Ltd       Phone 8212 6212
170 Sturt St,                     Fax 8212 4212
Adelaide, SA, 5000.