Eastern Railroad Discussion > How does a DED calculate train length / speed?

GRS train MOPO (Mohawk-Portland) crawls upgrade past the Wendell Depot Dragging Equipment Detector (DED) with GP40 and GP35 dragging an off-line SD26 and 80+ cars. When the last car passed by the DED, it reported temperature @ 60 degrees, axle count @ 334, train length at 5,300 feet, and train speed as "too slow!" Question: Does the DED uses axle count and duration of train passage to estimate length and speed? If so, what assumption does the DED make re: the avg length per 4 axles? Or is there a radar gun associated with the DED?

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Here's the freeloading SD26...

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I have heard a train stop just west of Roanoke because the TSA (track sied analyzer) said it was going too slow. It had to stop and restart.
I have also heard trains contact dispatcher when the DD did not match the train's axle count. I suspect there is an optical sensor to begin and end the DD process. Hopefully a maintainer is reading who can give detailed answers.

The best one that I heard was just around the Ohio/NY line (I think) off of I90. The detector went off with a "level 2" and a "level 3" defectect, annouced the cars by its reporting marks, axle, side, feet from headend, and the train symbol. Never heard that before, but it was pretty cool.

JPB Wrote:
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> Does the DED uses axle count and duration of train
> passage to estimate length and speed?

Yes.

> If so, what assumption does the DED make
> re: the avg length per 4 axles?

It doesn't make the calculations that way.

> Or is there a radar gun associated with the DED?

No.

The detectors have magnetic wheel sensors a couple of hundred feet on either side of the detector, plus one at the detector. They measure the time it takes to get from the outer sensor to the detector, which gives them the average speed. Knowing that, they can add up the distances between axles, and work out a total length.

On the auto train got a defect detecker defect,they had to walk the train before going on.

Pj Wrote:
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> The best one that I heard was just around the
> Ohio/NY line (I think) off of I90. The detector
> went off with a "level 2" and a "level 3"
> defectect, annouced the cars by its reporting
> marks, axle, side, feet from headend, and the
> train symbol. Never heard that before, but it was
> pretty cool.


Sounds like it was tied in with the railroad's computer system and an AEI scanner. There's some pretty cool new advances being made in bringing computer into railroading. Being a computer major, this really interests me since it means more possibilities for me to get a job doing what I love, railroading and computing!

A foaming nerd or nerd foamer! One of my degrees is in CS and I don't use it anymore than my poly sci degree. Hmmm...what else can I get and not use?

I doubt the "too slow" message is in reference to the train's performance, but more that the speed is too slow for the detector to accurately measure.

Signal Computer Consultants (the guys who do the Train Dispatcher simulations
for the PC) also do AEI readers, and they have software for a "smartscan" hotbox
detector that integrates this AEI data with the data from the train. Sounds like
what Pj mentioned. If anyone is interested in looking this stuff up, they have
brochures on their website: http://www.signalcc.com Click on the AEI Tags and
Readers link.

filmteknik Wrote:
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> A foaming nerd or nerd foamer! One of my degrees
> is in CS and I don't use it anymore than my poly
> sci degree. Hmmm...what else can I get and not
> use?


Hmm, Liberal Arts? They seem wholly unmarketable degrees!

ED3 Wrote:
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> On the auto train got a defect detecker
> defect,they had to walk the train before going on.



IIRC all passenger trains and solid haz mat trains have to be walked in entirety when a defect is found.

The UP (former CNW) detectors I'm familiar with come out with "Integrity failure" when the speed gets below a certain threshold.

That was a cool message, all right, giving car number for the defect.

The "hottest" message I ever heard was when UP 3985 passed over the local detector. Started right out with a defect on Axle 1, Axle 2, etc. The dispatcher asked whether that was normal, and the engineer (can't remember which one) said something along the lines of "Yeah, don't worry about it."

The detectors that we have use two transducers (magnetic wheel sensors mentioned previously) located 24 inches apart. It uses the time for the last eight axles to pass over the detector to calculate the speed using the set distance (24 inches). It then uses the speed and time the full train was occupying the detector to determine the length of the train. If the train alters it's speed at all over the detector, this can "throw off" the true length a little bit since it only uses the last eight axles to determine speed, but uses the full time to calculate length.

Xingman
http://home.internetcds.com/~xingman/

Boy JB you have a lot of guts putting Guilford pictures on here! lol.