Zonker's Defect
Detectors Clues Page
http://BayLUG.org/zonker/railfan/detectors.html
This page is dedicated to showing some of the different Defect
Detectors I have found, and (hopefully) as I learn more about them, I
can share that knowledge with folks that read my
railfan pages.
Legacy Equipment
There are a variety of problems that can crop up on a moving
train. Crews inspect their loads before they leave the yard, and
there are sometimes yard crews who lend their eyes to departing
trains, to make sure things look good as they depart. But, once they
are underway, lots of things can still go wrong...and without a
conductor riding in a caboose behind most long freight trains, it's
hard for the train crew to notice problems that are a half-mile
behind them.
Automated Defect Detectors were designed to look for some
of the more common problems (and the critical problems), such as;
- Hot Box (a wheel bearing run out of grease and heats
up)
- Axle Count (have you lost the back half of your train?)
- Dragging Defect (is something dragging under or
alongside?)
- Speed (does reported speed agree with your
instrumentation?)
- Excessive height or width to protect bridges, tunnel
entrances, and other structures with restricted clearances near
the tracks.
Some detectors can report to local display devices (in a yard, for
example), while others report their data to distant dispatchers. Some
talking detectors have a low-power radio transmitter on the
local Road Channel, and a speech synthesizer. The detector will
announce itself on the radio as the train starts to cross the
detector, so the engineer will know that it is operating properly. As
the train passes, the detector will count the axles...and if it
notices any other defects, it will report them by axle location.
(Example: Hot Box on Axle 47, or Dragging Defect after Axle 98.)
After the last car has passed the detector, these talking
detectors will report their finding(s) via the radio. Usually, the
report includes the number of axles, followed by "No Defects", and
often followed by the train speed. This way, the crew will know that
they still have all of the axles that they expected to have, and they
can check their reported speed against the speedometer in the cab.
The radio and antenna technology used are different, because these
defect detector systems have been developed over time. Once a
railroad has a good 'recipe', they'll use that design for any new
installations, but they may not upgrade older units unless they are
failing. Then, as railroads merge, the new owner usually doesn't
spend money to replace working units with their designs. As a result,
different detectors may sound different, report different
information, and the radio signals may be weak or strong. (Most of
the transmitters are low power, but the listening distance can vary,
depending on whether there is an antenna outside the equipment
chassis, and what type of antenna (directional or omnidirectional,
and how high it is mounted above the local terrain.)
Spotting the pieces
Click on any of the thumbnails to see larger pictures.
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 Axle Counters are often magnetic
devices. Notice the rusting metal shavings on the top of
this sensor. The sensors usually have two magnetic fields,
and the sensor can detect when the large wheels come close
to these magnetic fields. These sensors are usually mounted
on the inside of the rails.
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 Hot Box Detectors are thermal sensors,
and they are looking for HOT bearing cases. Since
these bearings are on the ends of the axles, the sensors are
located on the outside of the rails, looking upwards.
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 Dragging Defect Detectors use a
mechanical switch, coupled with a set of replaceable flaps.
Notice that these flaps are located between the rails, as
well as on the outside of the rails. The switch doesn't move
much, so the flaps end up taking the brunt of any impact
with something being dragged along with the train.
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 Cable Connections are actually welded
to the rails. The mechanical connections are often painted,
probably to help prevent corrosion. You will find these near
block signals, as well as level crossings. For the
connections around level crossings, there are usually more
than one set of connections; some are closer to the
crossing, and some are farther out (so the gates can be
triggered from farther away if the trains are approaching at
high speed, while slower trains (switchers) won't trigger
the gates until they are very close to the crossings.
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 Bonding Wires or "bonds" are used to
connect adjacent rails (joined end-to-end), to make the
rails look like one electrical conductor.
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 Cable Junctions are sometimes found
near detectors and signaling equipment. Cables near level
crossings seem to normally be buried directly from the rails
back to the control box near the crossing. I don't know if
these are just the vented access points for underground
conduits, or if they are just splicing junctions for cable
runs.
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 High and Wide Detectors are loops of
wire suspended beside and above the track, and are used to
protect tunnel entrances, and other close structural
clearances along the right of way, by alerting train crews
in time to stop the train before they get to the protected
site.
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Defect Detectors I have found;
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Warm Springs Sub, MP1.5 (talker)
  Viewed facing South,
Lake Elizabeth is to the right
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  Dragging Defect detector
switch
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    Hot-Box Sensor
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  Magnetic Axle-Count
sensors
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 Underground Cable Junction
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 Viewed facing Northeast (dragging defect
detector is black, near the right edge, while the wiring
junction and hot-box detectors are near the center of the
image, near the large post. The equipment locker has a
Sinclair-type antenna (black) on top.)
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 And I found a bunch of these, spaced at
regular intervals, along the gauge near the detector. These
tarps spanned three ties, and were stapled with heavy wire
staples. I couldn't tell if there were any sensors
underneath them, but there were usually some cables coming
out from under the ballast near each of these tarps, and
there were the white, round cable junctions spaced about
every three tarps. (I found two more on the UP Milpitas sub,
within a mile of this series along the Warm Springs sub, but
there didn't seem to be any detector equipment in the area
on the Milpitas line. I don't know if they have anything to
do with each other.) If you have any ideas whet these may
be, I'd love to hear about them. I'm guessing that they are
for sensing the speed of the passing train. (All of the
adjacent rails near the tarps had bonding wires between
them...)
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Coast Sub, MP 28.9 (talker)
  Notice the horizontal,
"Sinclair style" antenna mounted on top of the box...
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You can see the dragging equipment detector
and the hot-box detectors, but this detector also counts
axles and speed.
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Oakland Sub, MP 23.0
High and Wide detectors are typically silent, and
only alert the passig crew if there is a defect noted
(caused by the passing train pulling down the wire loop).
This High and Wide detector is located
near the South Hayward BART station, and it is protecting
the tunnel in Niles Canyon. It is visible from the north end
of the South Hayward B.A.R.T. southbound platform
(seen in the background of this photo).
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 The loop of wire is supported by
insulated anchors. If a passing train snags the wire, the
wire is pulled away, tripping the detector, which would
alert the crew. (Of course, if the train snags the wire, it
would likely strike parts of the tunnel...)
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This detector also has a dragging defect sensor, as well
as axle counters. The axle counters here have shields to
protect the detectors from dragging equipment in both
directions. (The camera battery died before I could get all
the pictures I wanted.)
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I found an open signal locker once...
 This is the Niles sub, facing south, from the
southern end of the town of Niles. While taking this picture
(with the Alameda Creek crossing in the distance), I noticed
the open door on the signal locker. (The right-hand of the
two lockers shown in the foreground.) I checked for vandalism,
and I was surprised how clean it was inside. The lock was
missing, and the hasp was broken, so I could only close the
door, but not secure it. I called the UP emergency number
(from the local crossing signal box signage), and I reported
it to the signal maintainers. The maintainer found two more
signal lockers in the area with broken hasps while looking
for the one I reported. (It seems the one I found was an
abandoned WP locker, related to the wye in Niles, long since
retired.)
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 This relay, on the top shelf, seemed to be
heavier-duty than I would have expected. I don't know how
old the part is, but it would probably have performed will
for another decade or more. (Look at the shock-mounting
under the relay!) The cables also seem much smaller gauge
than what I notice near grade crossings, but maybe there is
a backboard on the other side of that locker, where the big
cables meet the smaller ones in the locker? I'd like to find
a long-time signal maintainer, and listen to some stories.
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 I was surprised to see the date on this
maintenance slip. I was much happier when I heard later,
from the maintainer, that the signal was retired any years
earlier. Those lockers sure keep the weather and the dust
out, though!
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More pictures and more text will go here as I find them.
Updated: October 2003
Copyright 2001-2003,
David K. Z.
Harris, N6UOW
Questions? Comments? Additions? Email railfan at
baylug.org
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