choochoochoo
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Given planes have 'weight on wheels' sensors, how feasible would it be for trains to have 'wheels on rails' sensors ?
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How feasible would it be for trains to have 'wheels on rails' sensors ?
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Planes leave the ground as a normal part of their lives...
choochoochoo
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But it wouldn’t be a very normal part of their life for the landing gear to be allowed to retract whilst on the ground.
a_c_skinner
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It ought to be practical to devise sensors that tell the driver to stop and examine if there is sustained and hugely excessive vibrations in any vehicle in the train, certainly in passenger stock which has (the potential for) complex comms between vehicles. Not as a quick cheap retrofit but aeroplanes do tell their pilots about the engines vibrating.
choochoochoo
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Might be a bit naive in my understanding of how electricity and track circuits operate, but if track circuits are completed by wheels on an axle touching the rails, could a sensor be placed on that axle to detect when its completing a track circuit and thus send an alert if it might have derailed and is no longer completing a track circuit ?
Cherry_Picker
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Yes, but then you just have another thing with a sensor on it that throws up more faults than it's worth.
Kentish RYS
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No, because not all the railway is track circuited. A lot is Axle Counters (they detect the electromagnetic field of a passing wheel flange, but do one side therefore counting axles, on the entrance and exit of a track section). Also a lot is non continuous train detection or tablets/token/radio tokens or Signaller looking out the box window for a tail light (or using a tail light camera or train crew using train arrived complete plunger). Ive probably forgotten something in that quick list of the many ways the GB Mainline network knows where trains are. Also different track circuit types use very different frequencies or voltages and traction return on the Mainline goes through the axles. It probably isn't impossible to have a comparison list to work out if it is a track circuits not traction return but would be very expensive and not worth it for the little benefit (low derailment rialsk and %of Network that is not Track Circuited
43096
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Track circuits are fail safe i.e. the wheels/axle break the circuit.
D365
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It's temperature sensing, rather than vibration, but onboard "hot axle box detection" systems have been fitted to some new build fleets.
a_c_skinner
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Didn't know that and the level of vibration when an axle derails is so sustained and so marked it shouldn't be difficult to make such a system that isn't hugely costly and doesn't produce too many false alarms.
Peter Mugridge
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Surely, though, for that to detect a derailment the entire train needs to be off the rails, as a single bogie still on would still provide the short circuit?
By that point, it would be blindingly obvious to all on board that it was off the road anyway.
Nicholas Lewis
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The bogies are naturally subjected to high g forces in all directions that are damped by suspension so any sensor has to be able to distinguish between normal and chaotic behaviour and that probablys means processing power on each coach. Given how unusual it is is it really worthwhile retrofitting a solution.
That's not what a weight on wheels sensor is for.
a_c_skinner
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I've never been in a derailed vehicle but from the descriptions of passengers who have the magnitude and character of the vibration is completely different to normal service, hugely different. So different that it really ought to be an easy proposition to detect. Yes it would need processing power, everything does and it would need comms to relay the answer, and yes we don't have that many derailments so I doubt retrofitting would be worthwhile but it seems an obvious refinement.
HSTEd
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The US Federal Railroad Administration backed electronically controlled pneumatic (ECP) braking standard supports vibration sensors, axle temperature sensors and a great deal else besides.
But fitment would cost a few thousand dollars per freight vehicle and the freight operators won't want to spend it.
But fitment would cost a few thousand dollars per freight vehicle and the freight operators won't want to spend it.
choochoochoo
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I understood it's part of a air/ground logic system that involves preventing/enabling certain functions on the the ground. Preventing gear retraction being one of them. Thrust reverser/ground spoiler deployment being prevented in air being another.
Of course. Sorry, I'd misread the context of your post!
Presumably you could fit load cells into the bogies which measured the intensity of vertical movement and also the frequency of that movement, registering an alarm when "out of range"
Removing background noise, especially on old track, might be a problem though - as also may be reliability given the constant vibration
Removing background noise, especially on old track, might be a problem though - as also may be reliability given the constant vibration
InvernessTMD
Member
Can someone smarter than me tell me why this is at all possible? Surely some sort of basic sensor setup to check whether a wagon is still on the rails is possible.There was a freight on the Gospel Oak-Barking line who managed to go more than two miles without noticing before the brake pipe separated and the brakes applied. It absolutely chewed up the track sleepers and cabling.
Report 12/2020: Derailment of a freight train near Wanstead Park
Derailment of a freight train near Wanstead Park, London, 23 January 2020www.gov.uk
Maybe it could check if the wagon isn't at an extreme or impossible angle, that the bogies are not at an extreme or impossible angle and that the wheels of the wagons are still turning and haven't become significantly slower (or faster I suppose) than other wagons in the consist. If one of these is true the driver is alerted (to avoid trains stopping constantly for false alarms) and if two of these are true the emergency brakes are applied.
I understand this would probably be rather expensive. But is there a technological or logistical reason why you couldn't implement something like that? Obviously not exactly what I have said as there's probably much better ways to figure out if a wagon is still on the rails.
Ashley Hill
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It would detect a slip but not a derailment.
HSTEd
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I think vibration could be measured by a weight on a spring in a sealed tube, with a contact at one end (fitted on a short buffer spring) that detects when the weight reaches end of travel in the non-spring direction. I believe vibration from derailment or wheel-flats makes "normal" vibration appear silent by comparison.
We can already measure the weight of the vehicle using suspension height, as automatic adjusters on Westinghouse AIr brakes do. Load cells could get quite expensive I would tink!
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choochoochoo
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I was thinking wouldn’t dragging derailed coaches be noticeable as an unusually large reduction in speed if the train was coasting or unusually slow acceleration if the train was trying to speed up ?
HSTEd
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It is far from unheard of, and when it happens it can cause enormous damage.
Given a comparatively small fleet of freight wagons in regular use, some sort of technical solution is likely to be justifiable in cost terms.
Nym
Established Member
These freight wagons that have literally no electrical systems on them at all and are maintained with a nut rounder and a hammer?
Electronics won't make it's way onto legacy wagons, no matter how much industry 'experts' want it to so they can sell more things.
Electronics won't make it's way onto legacy wagons, no matter how much industry 'experts' want it to so they can sell more things.
ac6000cw
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With freight trains it can easily happen if it's something like a simple 'wheel climbing over the railhead' type derailment, resulting in one wheel on an axle running along the sleepers and ballast on the the outside of one rail and the other wheel running along on the inside of the opposite rail. The traction/tension forces along the train will tend to hold the vehicles in line.
Often in that situation the train only breaks in two (and pulls the brake pipe apart, which applies the brakes) when the derailed wheelset hits an obstruction like a set of points which deflects the vehicle sideways (or normal braking bunches up the train so the tension forces disappear)
Nicholas Lewis
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The Wickford train was 2 x 720s which pack in a lot of power and with a lightly loaded train nothing was untoward to the driver.
My supposition here being is the rear bogie is unmotored so its ligher than a motored bogie and at speed the leading wheelset would have been forced above each sleeper so presents only a little extra resistance compared to normal and with standard sleeper spacing there is little space for the wheelset to sink into the ballast. Also it appears, RAIB will clearly tell us in due course, the wheelset stayed on the sleepers or some time as its pretty straight along there. Thus it was only when a brake application was made that the train dynamics changed on that bogie resulting in the vehicle moving into the cess.
I was involved in clear up operations from several freight train derailments where only one bogie/vehivle had derailed and the drivers only became aware when the trains parted and brakes came on.