DBD22 - DCC Block
Detector
The DBD22 is a dual block
occupancy detector. It provides complete isolation from
the track by using small transformer type sensors. This
also means there is no drop in track voltage as there is
with sensing diodes. The DBD22 is designed to work well
with the SIC24AD signal and indicator
controller.
MSRP - 21.95 USD
Manual in PDF format - 180K
Color
Picture
Board size: 1.5" X 1.8"
Operation:
The DBD22 is capable of sensing current in two isolated
sections of track called blocks. This provides for
detecting the presence of locomotives or other rolling
stock that draw current from the track.
The track feeder wire for one rail of the block is passed
through the hole in the sensor (see diagram below) before
connecting the feeder to the track. When the current in
the feeder going though the sensor reaches the trigger
level, the output is turned on and the LED lights showing
the block is occupied. Passing the feeder though the
sensor more than one time will increased the sensitivity.
However, this is NOT recommended because the maximum
sensor current specification will be greatly reduced.
Locomotives and lighted cars draw enough current to
trigger the DBD22. In order for other rolling stock to
draw current, resistive wheel sets will have to be added.
For HO scale, one 4.7K ohm resistive wheel set will work
per car. If you want to use 10K resistive wheel
sets you will need two wheel sets per car.
Duty track can cause intermittent current flow. A built
in filter keeps the DBD22 from rapidly turning off
and on if the current flow is interrupted. Additional,
there is a small amount of hystersis so that small
changes in track current near the trigger point do not
cause the DBD22 to turn off and on. The filter keeps the
output on after a train leaves the block for a short
period of time. This time is typically about 1 to 2
seconds. The amount of track current has an effect on
this time.
Since the DBD22 does not use diodes to sense track
current there is no drop in track voltage. This allows
you to “double sense” a block. For example, suppose you
want to add a grade crossing with gates and flashers to a
section of track that already has a diode sensing block
detector. The block could be cut into three smaller
blocks to detect traffic on each approach and island
blocks. DBD2s can be used for the three new blocks with
out interfering with the operation of the original
detector or causing an additional track voltage drop. See
the SIC24AD signal and indicator
controller for information on implementing a grade
crossing.
Specifications:
Operating voltage: 5 to 15 volts DC
Typical operating current (unoccupied): 3 ma @ 5 volts, 8
ma @ 12 volts
Typical operating current (occupied): 8 ma @ 5 volts, 20
ma @ 12 volts
Maximum load per output: 150 ma
Typical trigger current: 3 ma @ 5 volts, 6 ma @ 12
volts
Maximum sensor current: 5 amps w/one pass of feeder wire
