Digitrax PM42 Manual - Halaman 4

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The PM42 offers four settings for short circuit detection sensitivity. These four

settings let you optimize your PM42 for operation with other equipment you

use on your layout.

When a short circuit occurs on any layout, the voltage at the booster will col-

lapse. The purpose of the PM42 is to preempt the booster shutdown to mini-

mize disruptions to layout operations by automatically re-starting the layout

when this happens. In most cases, you will not notice any power interruption in

the operation of DCC equipped locomotives. This is because most DCC

decoders store energy to keep their CPUs alive in case of brief power interrup-

tions and the inertia of a moving locos will usually keep it moving as long as

the short does not last too long. Because power storage characteristics vary

from decoder to decoder, some are more sensitive to short circuits than others.

To compensate for more sensitive decoders, the PM42 can be set for faster or

fastest short circuit detection. Slower short circuit detection may be a better

choice if you are running locos with lots of incandescent lamps or lighted pas-

senger cars because when you turn these on, there is a brief current spike that

may be indistinguishable from a short circuit to the system.

3.2 Auto-Reversing

When a train enters a PM42 reverse section sub-district that is set up for "Auto-

Reversing" and there is a polarity mis-match, the PM42 will automatically

change the polarity of that sub-district and the train will continue to run

through the reversing track section. The "SUB-DISTRICT STATUS" LED for

that sub-district will light red or go off, depending on the polarity needed to

correct the auto-reversing polarity mis-match.

When auto-reversing occurs on the layout the direction of travel of non decoder

equipped or "conventional" locos WILL be affected depending on where they

are on the layout and on which part of the track has its polarity reversed to

allow for auto-reversing. We recommend that analog locos not be run on

any layout that is using auto-reversing because they may suddenly change

direction when track polarity is changed by the auto-reversing feature.

Since the PM42 operates "downstream" of the Digitrax boosters it is con-

strained by the operating characteristics of the boosters; i.e. the current avail-

able during a short circuit and the timing setup of the boosters. A correctly

wired and configured PM42 will operate before booster fault shutdown and dis-

connect any load detected as a "short circuit". The PM42 will automatically

attempt to reconnect any short circuit detected until the short circuit is cleared.