News: 1590054911

Overhead wires for trains carry AC current at 25kV. Current draw runs into the thousands of amps when a train is passing by.

A really powerful UK electric locomotive is 5MW, which is only 200A at 25kV. The current draw never gets near a thousand amps, let alone "thousands". The conact wire is only about 120 square millimetres.

Not ALL trains are running at 25kV AC. For example the Tyne and Wear Metro in the UK is 1500v DC and I remember as a trainee working in the substation watching the ammeters climb well past 1000amps.

I seem to remember that Holland is also 1500v DC which is why they bought locos originally built to work the Manchester-Sheffield route back in the early 70's.

"It is unclear whether three similar magnetometers would have been immune to the strong electromagnetic field generated by a passing train."

Sorry, but its perfectly obvious that ANY magnetometers would have been affected - it was the field being 'unexpected' that was the problem, not the readings, so three independent devices would NOT have helped.

You really don't want to have any electronics anywhere near active overhead railway lines.

In a previous job I remember we had some problems with electronics that was sited close to railway lines with overhead cables - it was the other side of the fence but kept getting weird glitches. Enquiries were made to BR engineering and they said that any induced voltages at the distances we were talking about "should only ever be low voltage, so there should be nothing to worry about".

It took a little while to realise that the "low voltage" they were referring to was according to the IEC definition, i.e. up to 1000V.

In Minnesota, the light-rail Metro Green Line between downtowns Minneapolis and St. Paul runs on 750 VDC. It passes right through the heart of the main University of Minnesota campus and displaced normal vehicular traffic on what used to be quite the busy avenue.

From Wikipedia: "A particular area required exclusive attention and support, that being outside the University of Minnesota's biology department. Between Pleasant and Harvard streets there was 1/8" of tolerance between design and as-builds. Control factors used in the biology labs would be impacted by the electromagnetic radiation emitted from the nearby light rail. The 1/8" tolerance is said to cancel out any EMR that the light rail may produce."

The press during time of design and build said the tolerance was 1/4", and "cancel out" is a misnomer -- we all know EMI would follow an inverse-square law (radius from conductor center since it's a line, not a point source) and be reduced but never truly zero unless one uses a Faraday cage, but the building(s) in question were older affairs which couldn't be upgraded that extensively.

There have been no public reports of any issues during testing or full operation. Kudos to the contractors who pulled it off.

Of course, if they had gone with a different routing this wouldn't have been an issue(!), but that would have entailed a new bridge over the Mississippi River, a bridge/tunnel option -- U of MN opposed that also due to seismic-sensitive projects -- or sharing the brand-spanking-new I-35W bridge that was built to be ready for such a task (I may have mentioned the 2007 collapse before). Politics and engineering just don't mix.

Okay, so you decided to launch your drone on a bridge, likely made of metal but not specified in the article, and next to an electrified train line.

Instead of launching from a field in the middle of nowhere.

Were you specifically testing the drone's ability to navigate in complicated electromagnetic environments ? Because even without a metal bridge, an electrified train line is going to have an impact on compasses, as you found out the hard way.

Given the people concerned knew about the "Network Rail (Route Control and Air Operations)" (why does Network Rail have an air department - they can barely run the things on the ground!) and they were flying a £30k commercial drone I would assume they were either investigating the bridge or the rails so operation near them was essential

https://www.networkrail.co.uk/running-the-railway/looking-after-the-railway/our-fleet-machines-and-vehicles/air-operations/

They have an air department because they use drones (and sometimes helicopters) to inspect the railway network without having to close parts of it so that engineers can wander up the track safely.

The bridge may have been metal, but it only spanned two rail lines, so there is a good chance it was masonry.

Given the value of the drone and that they knew who to contact at Network rail, this sounds like the drone was being used for some form of survey probably on behalf of NR, or at least on an asset immediately adjacent to the rail line. The bridge presumably provided a (the best? the only?) vantage point for the drone pilot to keep the drone in visual sight at all times (which I think is a legal requirement).

Presumably not any DJI type drone anyway - mine bitches about an unknown magnetic field if I've got so much as a keyring in my pocket when doing the initial calibration.

"Electromagnetic interference has been blamed for a number of unforeseen problems in electronic devices over the years"

Who knew! Unforeseen only by designers who know nothing about EMI!

I appreciate that you can't design out poor decision making, but this should have been taken into account in the drone's flight software.

It has three-axis gyro data available, and even a rudimentary architecture should have made the drone fail-over to this inertial positioning when the compass data became erratic and implausible. It doesn't need to know which direction it's going from a magnetic point of view, and I'm surprised that it even takes that into account for primary heading data. Basic stabilisation should, in my opinion, be solely from the IMU.

Magnetic heading can be used to compensate for gyro drift, but I'd have thought derived GPS track is likely more accurate anyway.

New monitors had to be bought anyway. Flat screens still a new thing and somewhat expensive. So management opted for (rather big) CRTs. New site near rail roads, so all CRTs where flickering like hell whenever a train passed, and that was all the time. And there is no practical way to stop the flickering (shielding with a thick iron box not being practical). CRTs were sold off for pennies, and flat screens bought.

Manglement ------>

...with Max-8 style "technology" built in!!

Third rail systems are DC and have traction return currents appearing everywhere that they shouldn't. They must have alarming effects on magnetic compasses nearby