I am using the DCCOD to detect my layout. I am in the process of installation
now. Here is a commentary by Dr Chubb on detectors vs price and features.
To C/MRI Users:
There has been considerable discusson on the Layout Design SIG Group
about Staging Yard Detection. In reply to some of the discussion I
posted the following message that I thought might be of interest to
this group so I'm repeating it here for your use as well:
Dear Peter and Andy:
Looking at the BDL16 is fine but checking it out against other DCC
compatible detectors the price quoted of $8 per block is somewhat on
the high side for what you get, or better yet for what you don't get.
Many think it's great so consider that input as well. Some of the
important factors I recommend looking for in detectors are discussed
High sensitivity is critical to providing maximum protection of
single cars, true prevention of throwing switchpoints under any part
of a train, reliable OS occupation lights where track sections are
short and single car detection is critical to prototypical
A good test is if you can lay your finger across a section of track
and the detector shows detection you have good sensitivity. Or put a
70K ohm resistor across the track and if it shows detection have
pretty good detection. Many DCC detectors on the market require 10K
or less across the track to acquire detection.
Having a built in turn-on and turn-off delay is equally important to
minimize dirty wheel problems and even some level of dirty track
problems causing lack of detection. A good turn-off delay should be 2
seconds or more.
Having the sensitivity adjustable is absolutely paramount to
achieving maximum performance out of any detector. The leakage
resistance between the two rails varies all over the map from layout
to layout, from block to block, is a function of humidity, type of
ballast, type of glue, number of turnouts in block and everything
else under the sun. Having sensitivity factory preset at some nominal
value is an extremely poor substitute for having a built-in
potentiometer for optimally setting the sensitivity separately for
Having a built-in LED before the above noted time delays is essential
to being able to quickly and effectively set sensitivity to its
maximum value per block without generating false detection. Typically
for example, OS sections are short with typically lower leakage
resistance between rails thus you can set its detector to higher
sensitivity which is exactly what you need for short OS sections
where one or two cars occupy the complete OS section.
Avoiding detectors that rely on diode voltage drop for detection is
also advantageous for DCC layouts. These cause changes in train speed
when go from undetected to detected trackage, unless you add series
diodes in all non-detected track section feeders.
The series diodes are pretty well required for DC railroads but there
is no excuse for using that approach for DCC where you have an 8KHz
power-signal that can easily be sensed with a pulse transformer as
part of the detector circuit
Modularity is also an important factor. Having one plug-in detector
per block is great when it comes to detecting where shorts exist.
During an operating session, even with series problems, fault
isolation is rapid and corrective action is just as quick. Also
suspect a detector problem change it out in a matter of seconds.
I could go on and on with the list of features required for good
detection, but I don't want to make this posting too long. Taking a
serious look at the BDL16, and many other detectors as well, you will
not find many of the above features included.
However, several detectors on the market do offer some of the above
important features. The sad part is that most users purchasing
detectors aren't aware of the important features and which detectors
include which features. It's also important to realize that the
better line of detectors don't cost much, if any more, than the less
capable detectors. In fact some of the less capable detectors are the
highest in cost.
In summary, don't take picking the correct detector lightly as it's
an important parameter in optimized layout design. Fundamentally, it
really pays to shop around for the optimized detector that provides
the above listed features at the best price.
Bruce Chubb, MMR