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Zonker's Defect Detectors Clues Page

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;

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.

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.

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.

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.

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.

Bonding Wires or "bonds" are used to connect adjacent rails (joined end-to-end), to make the rails look like one electrical conductor.

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.

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.

Defect Detectors I have found;

Warm Springs Sub, MP1.5 (talker)
Viewed facing South, Lake Elizabeth is to the right

Dragging Defect detector switch

Hot-Box Sensor

Magnetic Axle-Count sensors

Underground Cable Junction

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.)

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...)

Coast Sub, MP 28.9 (talker)

Notice the horizontal, "Sinclair style" antenna mounted on top of the box...

You can see the dragging equipment detector and the hot-box detectors, but this detector also counts axles and speed.

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).

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...)

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.)

Coast Sub, Milepost 26.11 (Alverado Road crossing, silent)
(I found one like this at the Decoto Road crossing on the Niles Sub; I've never heard either of them talk.)
(Maybe these are for detecting RF-Powered ID Tags?)

Facing Northward, (towards Oakland) from the street crossing

The graffiti has been there a while (a problem in that area)

Looks like microwave antennas to me
(how do these work? They are offset...)

A different type of magnetic sensor (look for the metal filings.)

Coast Sub, Milepost 33.5 (North of Stevenson Blvd. private crossing, silent)
This is only a dragging defect detector, and only talks if there is a defect.

Facing Northward, (towards Oakland) from the street crossing.

The dragging defect detector had a pretty clean gap on the day I visited, after some recent roadbed work in the area.

- - Notice the Sinclair antenna, and the scotchlite reflective strips facing the approaching trains (but there were no other marks on the housing).

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.)

I was interested to see the labeling, and the wire dressing. This reminded me of old telephone signaling equipment, including the battery-backed DC power supplies. I would later learn that much of the signaling gear is usually either 12- or 24-volt lamps, and usually 1.5-volt or 3-volt DC used for sensing trains on the track. That would lend itself well to easy troubleshooting, and commonly available components (at least for relays and bulbs).

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.

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!

More pictures and more text will go here as I find them.

Updated: October 2003

Copyright 2001-2003, David K. Z. Harris, N6UOW
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