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Appendix 2 - Commoning Feeder Cable Cores
Although the RTM300 sensors are polarity independent, the RTM500 interface
card drives the sensors with a supply and return line. Any number of sensors on
one interface card can therefore be commoned so that for all four channels, only
one common core and four sensor cores are needed - a total of five cores.
To identify which cores can be commoned together:
Remove all feeders from the backplane and fit an interface card with all
four channels turned on.
Use a DVM set to measure at least 20V.
Measure the loop feeders on each channel. With no sensor present
these will show a dc voltage of about 15V. The low side of each feeder
can be commoned and the high side should be treated as a separate
core.
Where a phase has either X,Y,Z detection (or for MOVA IN, X, SL) then all three
detectors may be connected back to the controller on a four core feeder. This has
to be broken into at the Z location and extended to the Y and then two cores run
to the X.
It is suggested that the black is used as the common, with the red being the
furthest detection point and blue and yellow used for the two closer detection
points.
It is recommended not to common between RTM500 cards.
Note. RTM500 outputs are protected against short circuits. If an error is
made during commoning, the channel fault LED will flash at about 2Hz
indicating a short circuit on that channel output.
