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Post by class411 on Nov 5, 2022 9:47:33 GMT
I mentioned all this, in somewhat less detail, several posts back. The first of your explanations (and the second of mine, upthread) is, I would have thought, unlikely. It would mean that every time there is a power failure, or the clocks change, someone would need to reset the clock exactly right. (And station clocks do seem to be, in the main, exactly right, according to my radio synched watch [yes, I know it's pointless, but the technology fascinated me].) Also, pulses inevitably get lost, so the clocks would tend to drift. In the full synch each second case, it's even harder to see how this could happen. If there was a fault with the least significant bit on the minute register (or the path that sets it), then, if the bit was permanently up, or down, the minutes would jump by 2 every two minutes, and if the bit was inverted, the minutes would run: 1, 0, 3, 2, 5, 4 ... But the reason I was so surprised by the OP was that, according to the poster, this has been going on for 22 years. I would think it's moderately unusual for clocks to run that long with no maintenance, let alone maintain a one minute error for such a long period. The fact that the clocks in question are very close together certainly indicates that the problem is with a synch signal, rather than being within the clocks themselves. (Unless they have 'nudge' buttons and some LU employee at SB Central Line thinks it's funny to have the clocks perpetually running slow ) Whilst I'll certainly bow to your superior knowledge of LU technology, As a systems designer, I have a lot of experience with all sorts of fault tolerance and data integrity issues, and I still find this particular case bizarre.) ETA:I think I may have inferred the system employed. Given that the OP says he saw this in 2000, then it is at least this old, and quite possibly older. That means the system was probably specified in the early nineties. Back then, no one would have considered linking things like station clock via the internet, and electronics/computers were more expensive and less capable, so bunging encoded time signals around would not have been a likely solution. What they probably did was us a one second pulse sync, with a separate 'reset' signal that would reset the clock from the master, every 24 hours. Cheap, and pretty robust. So long as pulse loss was reasonably rare, the clocks should not drift for more than a few seconds for a day or two. That just leaves the problems of why two clocks, that are physically close, both exhibit exactly the same behaviour, and how something can reset a minute behind the correct time (a second ahead is reasonably easy).
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class411
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Post by class411 on Nov 4, 2022 18:12:33 GMT
I remember it (in carriage pilot light) as a very violet tinged blue.
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Post by class411 on Nov 4, 2022 17:01:08 GMT
For an analogue clock, the explanation is simple.
However, the OP clearly states the clock is digital.
I thought I was going mad reading the last few posts, until I checked said OP. (Not that I recollect any analogue displays at SB Central Line).
Oops. Sorry, I just noticed we’d moved on from Shepherds Bush and digital displays.
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Post by class411 on Nov 4, 2022 13:50:27 GMT
The clocks I mentioned are at the far ends of the platform, only visible if less than a carriage length away due to the low ceiling and recessed walls, and poor lighting. I'd guess they were installed back in the day for departing drivers to keep to time? Of little passenger benefit given the location. Even if they are not particularly useful, it is quite bizarre behaviour. - If the clocks were free running, how come they are continually set incorrectly every time they need resetting (power failures, drift, BTS changes)?
- If they were synchronised by a per second pulse from a central location, pretty much the same question applies as above.
- If they receive the entire time every second, or once a day (or other time period), and then free run - how do they manage to keep getting it wrong in exactly the same way?
The only way I can see that this would happen - and it's a hell of a stretch - is if case 3 is correct, for some reason the time is always reset on an odd number of minutes, and a data transfer is always losing the least significant bit, at some point.
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Post by class411 on Nov 3, 2022 21:59:27 GMT
The clocks at both ends of the eastbound platform at Gloucester Road on the SSR have both been exactly one minute slow to the second since at least 2000 when it became my local station. They do however adjust perfectly for daylight saving each clock change. That is truly bizarre. It is hard (impossible) to envisage any sensible system that could behave like that.
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Post by class411 on Nov 2, 2022 22:06:37 GMT
That would be the Uxbridge road warp in the space-time continuum.
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Post by class411 on Oct 31, 2022 8:23:27 GMT
This sounds like the station to visit if you want to get a feel for what The Underground used to be like decades back.
Certainly stations are now cleaner, brighter, and more modern looking, but there was something incredibly appealing about the dusty old utilitarian nature of stations in the past.
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Post by class411 on Oct 29, 2022 14:13:59 GMT
With the current economic situation, is it likely that HS2 will go ahead - at least in the short term?
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Post by class411 on Oct 28, 2022 8:57:26 GMT
This photo is from about 20 years ago. I have also seen instances when people have to queue in the pedestrian tunnel before being able to get to the station entrance. Looking at that photo has clarified what it was that I found unusual - although I didn't realise the detail at the time. That photo shows a fairly normal busy exit. There are people crowded at the bottom of the stairs and others approaching the crowd. In each of the cases I referred to in the OP, there was a crowd at the base of the steps, and the remainder of the platform areas were just lightly loaded. As if a lot of people had got off a train and the last of them were making their way up the stairs. This is obviously something that happens a lot, and it was presumably just a statistical anomaly that I saw it happen three times in a row. It was definitely the last occurrence that made me think: "I'll ask about that on DD".
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Post by class411 on Oct 27, 2022 8:49:25 GMT
I don't understand how you've never noticed it before if you are so familiar with the station! Yes, it is odd. It's true, the station has always seemed busy when I have used it, and I dare say there may have been a couple of people waiting to use the stairs, but in this case, over the course of two weeks, on three occasions, the was a 'pool' of people, 8-10 deep, around the base of the stairs. The platforms, on the other hand, seemed to have the usual occupancy, and there was no congestion at the gate-line, meaning the steps were a definite pinch point
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Post by class411 on Oct 26, 2022 18:24:19 GMT
Several people have mentioned the museums, but they have always been there. (Well, at least since well before anyone on this site was born).
Indeed, that is the reason I'm so familiar with the station.
Admittedly I sometimes use the tunnel, but until last week I've never seen congestion to the extent it's been in evidence recently.
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Post by class411 on Oct 25, 2022 17:43:15 GMT
Does anyone know why South Kensington is so busy at the moment?
I used it twice last Tuesday, and passed through it today, and on each occasion there was a massive queue of people waiting to use the exit steps to street level. (All observations outside rush hour.)
I've used it many times in the past and never seen congestion before.
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Post by class411 on Oct 25, 2022 17:38:44 GMT
At Shepherd's Bush (Central line) they tried to dig a shaft for a step free lift but had to abandon it as it kept filling with water. As opposed to one with steps? Sorry, I know what they mean. I wonder how the lift shaft could be under the water table but not the track bed. And why the couldn't waterproof the lower few feet. Thanks to Grand Designs I've seen a building successfully completed where the lower part flooded until waterproofed.
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Post by class411 on Oct 15, 2022 16:38:06 GMT
Can anyone explain the rather odd way the line is represented on the diagram at Paddington? Diagrams solely of the Elisabeth line appear as a continuous line at Paddington, but on the complete version it looks as if you have to get out and go walk-about. Currently and until through running begins, trains from Abbey Wood to Paddington terminate at the Elizabeth line station which is below Eastbourne Terrace, the road that runs alongside the southwest (platform 1) side of the mainline station. Trains from Reading and Heathrow terminate in the main station, typically platforms 11 and 12. Interchanging takes about 5 minutes (excluding waiting time). From 6 November, all* Elizabeth line trains will call at the belowground Elizabeth line station platforms and no walking will be required to change services. *During normal operation anyway, the possibility exists for services from the west to terminate in the main station during planned or unplanned disruption. Thanks, Chris. I was a bit confused because I realised that although I'd gone for Heathrow to Paddington and from Paddington towards Abbey Wood, I'd never actually been through Paddington, and hence could not answer from experience what happened. An 'in carriage' diagram (I assume) that I found on line showed the line without interruption.
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Post by class411 on Oct 14, 2022 17:46:03 GMT
Can anyone explain the rather odd way the line is represented on the diagram at Paddington?
Diagrams solely of the Elisabeth line appear as a continuous line at Paddington, but on the complete version it looks as if you have to get out and go walk-about.
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Post by class411 on Oct 6, 2022 9:25:25 GMT
I'd never heard of this Elstree museum before and I been commuting through the place for 30 years or more. Must stop off one day***. *** mind you, I been saying that about RAF Hendon museum for the same 30 years and still done zilch about it. Same for me with Bletchley Park. [/OFFTOPIC]
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Post by class411 on Oct 6, 2022 9:23:02 GMT
So what changes to cause the spacer to move? (Possibly) When a train starts drawing current from the section of which the rail in question is a part, where the current flows, a magnetic field will be induced in the rail. And as trains can draw quite a lot of current so the effect can be noticeable.
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Post by class411 on Oct 5, 2022 16:41:00 GMT
In the example in the video, probably the current rail is bearing heavily on the adjacent insulator pots either side of the one shown and the shimming isn't quite right at the one shown, leaving the shim loose. Yes, that makes sense. So this clicking is not a particularly common phenomenon, nor an (or a side effect of) intended design feature?
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Post by class411 on Oct 5, 2022 11:45:39 GMT
Yes, that was my first thought - if it was supporting the rail then there would be no space between it, the rail and the pot. Then I wondered whether it was a temperature-related thing - i.e. the plate supports the rail when it is hot (or cold) but not when it's cold (or hot)? The gap seems much to large to be a result of (or in place because of possible) expansion. Watching the video full screen, it appears that the piece that moved was one of a number stacked - indeed, as if they were spacers, but they took up far too little space vertically to have any effect. We really do need a track engineer.
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Post by class411 on Oct 5, 2022 8:59:06 GMT
I'm more inclined to wonder why the plate is there in the first place, and if its behaviour is intentional. I understood these to be spacers intended to lift the rail surface to correct contact height. Surely, if that was the case, they would be fixed.
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Post by class411 on Sept 28, 2022 8:44:53 GMT
Grinding won't make the ride smoother - it reprofiles the rails to eliminate conditions such as Rolling Contact Fatigue and Gauge Corner Cracking, both of which if left untreated can lead to sudden catastrophic rail failures with associated risk of derailment - think Hatfield which was as a result of untreated Gauge Corner Cracking. The solution for a smoother ride may be additional tamping to consolidate the existing ballast under the sleepers, reballasting, or, depending on the ballast condition, complete renewal; but not grinding. Thanks for this explanation. I've noticed people mentioning grinding in relation to both increasing and decreasing rail noise, so it's good to get a definitive answer to a question I kept meaning to ask.
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Post by class411 on Sept 24, 2022 18:37:13 GMT
What was there before? Something went wrong on my first attempt to post that message (I accidentally pressed the F12 key which opened an on-screen box of computer code and by the time I realised what had happened my entire message had been deleted!) and I had to start again and its possible that an 'auto-fill' function inserted something else into the thread tittle box. I thought it was autocorrect because ‘Action’ also appeared in the body of the text, and autocorrect is a bit ‘variable’ with proper nouns.
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Post by class411 on Sept 24, 2022 4:31:40 GMT
Aggressive autocorrect?
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Post by class411 on Sept 11, 2022 18:07:02 GMT
See my other post, Is a dedicated workshop and staff constantly applying sticking plaster to current displays well past their life and in a lot of cases non-compliant a good use of funds ? [ ] yes [x] no Yes, my response was more directed at changes that were introduced for the sake of style, rather than those for more pragmatic reasons.
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Post by class411 on Sept 10, 2022 10:38:45 GMT
Is changing an existing serviceable display for a different serviceable display a good use of funds? [ ] Yes [X] No
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Post by class411 on Sept 9, 2022 10:48:45 GMT
Though, the Central is reliable for having accurate indicators (SSR Lines I'm looking at you!) There is the occasional moment where it will go blank, and display Westbound Trains: Central Line or something like that.. Presumably the logic in the display is responsible for those types of message, so they will show whenever there is a glitch in the feed.
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Post by class411 on Sept 9, 2022 8:17:10 GMT
I thought that this, from the Guardian was rather nice, and also on topic, here.
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Post by class411 on Sept 8, 2022 8:17:13 GMT
However back to the topic, trains in the snow before the mods come for us! A pair of black helicopters are being readied for delivery to DD's enforcement division as we speak.
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Post by class411 on Aug 27, 2022 17:33:56 GMT
If a shoe did weld itself to the rail, either a real weld, or an ice weld, would it be likely to pull away from the rail, or would it destroy the shoe's mounting, if any motor was powered and the train tried to move?
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Post by class411 on Aug 23, 2022 9:51:28 GMT
I hadn’t noticed before, but the rail sides are actually brown. It doesn’t come like that, does it? It’s that sort of detailing that makes it look so good.
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