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It's kind of annoying that they don't go into specifics about why this is good. The problem with traditional accelerometers is that the error accumulates, and so even small errors accumulate. The article doesn't really address what makes this different - and in fact I don't think it is different. You're still just measuring acceleration using a sensor and that sensor will have errors that accumulate. So the question…
Cool technology, but seems a bit of an extreme effort just to check train position. Why can't they just use markers on the tunnel walls (or under the tracks)?
Agree in principle though, is this extreme precision really needed?
I would have thought a simple device that counts the number of times the wheel has rotated would be vastly simpler and cheaper, and surely accurate to within a few centimeters.
But fiberoptic gyro navigation is already a thing, and has been for decades. It's not super cheap, but it's cheap enough for an industrial application like this one. So I'm not sure what problem is being solved here.
Cool technology, but seems a bit of an extreme effort just to check train position. Why can't they just use markers on the tunnel walls (or under the tracks)?
> Naturally, trains already have track-based location systems, but they are usually based on a train being within a “moving block”, so their accuracy is down to metres rather than centimetres. If you want to monitor track conditions, the more accurate the location of the suspected fault, the less time staff spend repairing it. Agree in principle though, is this extreme precision really needed?
I would have thought a simple device that counts the number of times the wheel has rotated would be vastly simpler and cheaper, and surely accurate to within a few centimeters.
It wouldn't. Wheels slip in the wet, they develop flat areas with differential friction, minor differences in wheel circumference would soon add up over long distances, and all dimensions change with temperature. But fiberoptic gyro navigation is already a thing, and has been for decades. It's not super cheap, but it's cheap enough for an industrial application like this one. So I'm not sure what problem is being sol…
* What would the Central Limit Theorem give us if a significant number of wheels on loco's and carriages were instrumented and ID logged over the years.
* What drift patterns and correction factors can be observed and fine tuned by passing {many} wheel streams through station to station and line end to line end "known distance" corrections.
For half a century or so aircraft height was largely done with air pressure alone.
To this day GPS accuracy is "improved" by logging the "drift" of fixed point stations giving us filter coefficients to correct for atmospheric wobble, acute angle uncertainty, as yet uncorrected time drift, etc.
It's kind of annoying that they don't go into specifics about why this is good. The problem with traditional accelerometers is that the error accumulates, and so even small errors accumulate. The article doesn't really address what makes this different - and in fact I don't think it is different. You're still just measuring acceleration using a sensor and that sensor will have errors that accumulate. So the question…
Don't trains run on a fixed path, meaning we can use more traditional "positioning systems" like, umm, math? Or placing passive sensors or paint a big number on the wall?
That said, I'm not buying that quantum INS is required for this over more established techniques like visual-inertial odometry. However, the UK seems to have a whole bunch of active quantum INS research projects, so I wonder if the tube stuff is just a weak public cover for the military/civil emergency applications that make the technology actually interesting.
https://www.railengineer.co.uk/controlling-the-elizabeth-lin...
> The signalling is essentially hands off and is timetable driven. The latter includes GoA3 reversing moves at Paddington and Abbey Wood which are fully automatic as are all entries into and out of a depot. The line uses axle counters for secondary train positioning information other than where neutral sections for the overhead power exist, where track circuits are deployed, these being seen as less vulnerable to any spark interference from the overhead catenaries.