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Early NX panel question

British signalling of the past (UK, excepting Northern Ireland)

Early NX panel question

Unread postby Signal-sighter » Sun Nov 26, 2017 4:11 pm

I've recently been reading the second edition of 'Railway Signalling and Communications Installation and Maintenance' from 1946, which has some really fascinating old information and photos in it as well as some wonderful period adverts for the likes of Sykes, Tyer and SGE at the back.

One picture which particularly intrigues me shows a panel captioned "N.X." Route Relay Interlocking Panel. The track layout is very odd, about the only comparison I can imagine is the discharge loop at a merry-go-round power station but it would surely predate this concept by at least 20 years. I'd also like to know what the big black control in the middle of the panel is for. Does anyone recognise it?

https://image.ibb.co/dfCYQ6/IMG_0652.jpg

EDIT - the thought has just struck me that it might not be from the UK....
Last edited by Signal-sighter on Sun Nov 26, 2017 4:32 pm, edited 1 time in total.
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Re: Early NX panel question

Unread postby davidwoodcock » Sun Nov 26, 2017 4:31 pm

One of the terminal "stations" of the underground Post Office railway in London, perhaps?
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Re: Early NX panel question

Unread postby Mike Hodgson » Sun Nov 26, 2017 7:14 pm

The layout looks remarkably like many model railway "fiddle yards" or hidden storage loops!
One notable characteristic of the layout is that there are no dead-end sidings for locos or cripples.

Scandianavia or southern Africa might well have had something of this nature long before we had MGR. It needn't be the discharge end though - it could equally well be the loading end - opencast mining company loading facility perhaps? It doesn't show any discharge/loading facilities though, unless it's the 6 tracks bang in the middle.

The wider gaps beteween tracks 2&3 and 4&5 could represent island platforms if it's a passenger facility.

Nor does it seem to show any lineside signals for that matter.
So was it purely signalling or was it an early system controlling driverless trains?
Or perhaps a drive-on-sight system, controlling only the points - a suburban tramway for example?

It seems strange that your write-up doesn't identify the location, as this would have been state of the art and you would expect both contractors and operator to be bragging about it.
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Re: Early NX panel question

Unread postby Baffled boffin » Sun Nov 26, 2017 7:14 pm

It's possible a model railway was built and controlled by it to serve as a demonstrator. The large control could be an all signals on switch, at a guess.
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Re: Early NX panel question

Unread postby John Webb » Sun Nov 26, 2017 7:26 pm

I have seen diagrams of the GPO railway and some photos of the control panels - the track layouts and the panels looked nothing like the photo - but regrettably I can't recall my source. Might have been the "Railway Magazine" a year or two ago when the proposal to open up part of the GPO railway to tourists was announced.
According to O S Nock's "Fifty Years of Railway Signalling", the first N-X panel ever was at Brunswick on the Cheshire Lines circa 1937, but he comments that the outbreak of WW2 brought a halt to the development of the N-X style of panel. Perhaps it's more likely that the panel illustrated is from the USA?
The black object might be a loudspeaker?
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Re: Early NX panel question

Unread postby Andrew Waugh » Sun Nov 26, 2017 9:23 pm

It's the Transbay terminal in San Francisco, brought into use on 15 January 1939.

This was a Metro operation, with interurbans crossing the brand new San Francisco - Oakland Bay suspension bridge. The regular (pre war) service was 1000 trains a day (probably counting each return trip as two trains). It was a third rail system, with trains of three companies using it: Interurban Electric, the Key System, and the Sacramento Northern.

(Edit - two power supplies were provided - 1350V overhead for the Interurban Electric/Sacramento Northern, and 625V third rail for the Key System.)

The signalling was provided by GRS, and used ATC over the bridge.

The funny thing is almost certainly a microphone, to communicate with the operator at the other end of the bridge (Oakland Yard) where a similar panel was provided.

The Transbay terminal was still in use when I was there 20 years ago, but the trains had long been replaced by buses.
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Re: Early NX panel question

Unread postby StevieG » Sun Nov 26, 2017 11:02 pm

Not easy to be 100% certain but the photographed panel looks to be, either the same or similar as, or some other relative of, those of Metrovickers / GRS - type installed at, e.g., Mile End, Bow Junction, Stratford, Faversham and Amsterdam Central, with other variants in the Brunswick panel(s), Potters Bar, and Barking.
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Re: Early NX panel question

Unread postby Andrew Waugh » Sun Nov 26, 2017 11:32 pm

Some notes on the panel.

It was, of course, an NX panel. Each location had an entrance button (large and with a light and a subsidiary button) and an exit button (smaller, black, and no light) (US, so everything is bi-directional). Long route selection was possible, where the operator could push the button at the entrance to the station, and then the end route button at the entrance to the platforms and the intermediate routes would be all automatically set. It also automatically selected the best possible route automatically if the normal route between two points was occupied by a train.

A single light was provided in each track section, which was white for route set and red for track occupied.

Point position was shown by moveable relay controlled vanes which meant the set route was a solid white line, and the unset route was a thin triangle.

The line of controls inside the loop are three position telephone keys used to manually set the points. Centre for route setting, up/down for normal/reverse.

On the right hand side (adjacent to the double line representing the bridge) is the train describer - very similar in operation to the UK SGE describers. The buttons are at the bottom of the panel - one button for each of 15 destinations. The lights at the top are for the approaching trains. The vertical rows of lights show the origin of the first three approaching trains (15 possible origins, in two rows). The next seven trains are simply indicated by a single white light (so the operator knows how many trains are approaching).

The first set of incoming points (adjacent to the train describer lights) was worked automatically by the train describer. They would be called one way for Key System trains, the other way for Interurban electric trains. This automatically separated the trains into the two halves of the station (the double line at the top of the panel is actually two single lines for arriving trains - one line for each company). Minimum headway was 1 minute, and this was expected to save the operator a considerable amount of work. A manual point control for this set of points was provided - this was the control at the extreme bottom right.

The two controls at the bottom left were switches to dim the signal lights, and to control the brightness of the panel indications.
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Re: Early NX panel question

Unread postby Mike Hodgson » Mon Nov 27, 2017 8:40 am

Thank you very much for that excellent and very detailed explanation Andrew. I am amazed that this was pre-war.

It does leave me wondering how a single light aperture could display red/white as LEDs were only invented in 1962. Two separate filament bulbs behind the bezel, one clear, one painted red? An electromechanically operated moving red filter, as found in traditional searchlight signals? I would have thought it much easier/cheaper just to fit two lamps side by side. We are acciustomed to track circuit indications being duplicated in case of filament failure, but I suppose an alternative would be lamp proving as provided for signal heads.

We are also used to seeing signal repeaters and fault alarms on NX diagrams, but I suppose aspect repetition is unnecessary if you rely on the signals working automatically in accordance with the route set up, and drivers can call in if there is a fault. Or perhaps there was a separate fault panel for technicians - S&T presumably had somebody on site all the time in view of the criticality of this panel to such a busy service.
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Re: Early NX panel question

Unread postby kbarber » Mon Nov 27, 2017 10:06 am

In the UK examples at Stratford & Bow Junction (so presumably similar at Brunswick), the entrance 'button' was in fact a switch that turned through a right angle. I have an idea the US examples offered that facility for putting a route into automatic operation but used it as a pushbutton for one-shot operation (confirmation welcome, also comments on switch design - was the pushbutton the centre of the switch or did the whole switch depress?) UK examples didn't offer the pushbutton for the entrance function. In the early examples, signal indications (red & green only) were shown through the centre of the entrance switch, so no need for other indication apertures. In the late (1960) example at Barking, there were very small (about the size of a typical early LED) separate indicators but no representation of the signal itself (so would be effectively invisible in a photo of this quality), and the 'through the switch' indication was used for filament failure.
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Re: Early NX panel question

Unread postby Signal-sighter » Mon Nov 27, 2017 10:31 am

Thanks everyone, and especially Andrew, for the information and identification.
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Re: Early NX panel question

Unread postby StevieG » Mon Nov 27, 2017 1:11 pm

Signal-sighter et al, Re this topic, in case of interest/further help to those who do not have a long history with these forums, some more scraps of additional relevant information / detail might be found within this previous thread : -

viewtopic.php?f=2&t=668
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Re: Early NX panel question

Unread postby Andrew Waugh » Tue Nov 28, 2017 12:58 am

Mike Hodgson wrote:It does leave me wondering how a single light aperture could display red/white as LEDs were only invented in 1962.


Actually, you are right. The track sections don't show red/white. I read too quickly the details...

The correct sequence of operation is:
* Push the entrance knob. The light behind the knob begins to flash.
* Push the exit button. Route setting commences. The route indicators move and 'red "lock lights" behind the pointed ends of the route indicators' light to show that the points are locked. When the route is set, the white light in the entrance knob becomes steady (showing that the signal has cleared).
* Train passes the signal. *White* lights illuminate in the track to show track occupancy (one per track section). The white light in the entrance knob goes out to show that the signal has gone to stop. As the train passes over the points, the red lock lights go out as the points are released.

So the light in the entrance knob is the signal indication. The white track lights show track occupancy. The mechanical route indicators show the route set.
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Re: Early NX panel question

Unread postby Andrew Waugh » Tue Nov 28, 2017 1:13 am

kbarber wrote:In the UK examples at Stratford & Bow Junction (so presumably similar at Brunswick), the entrance 'button' was in fact a switch that turned through a right angle. I have an idea the US examples offered that facility for putting a route into automatic operation but used it as a pushbutton for one-shot operation (confirmation welcome, also comments on switch design - was the pushbutton the centre of the switch or did the whole switch depress?)


(I should have said earlier that I'm working from GRS Bulletin 173 "Railway Signaling on the San Francisco-Oakland Bay Bridge".)

The booklet has detailed photos of both the entrance and exit buttons.

The exit button is a simple T shaped button, black with an white arrow engraved on the top.

The entrance button is considerably more complex. It has a white light in the centre with a large black arrow. Around this is sleeve with a milled edge (suggesting the ability to turn). At the back of this sleeve is an extension with a small white button on the top.

The written description is clear that the entrance knob is pressed to start route selection (with a photo showing a finger pushing the centre of the knob). It twice mentions that the knob can be pulled to cancel the route (with a photo showing a hand grasping the side of the knob). No further details are given, so I don't know the function of the white button, or if the knob can actually turn.

(The Bulletin, incidentally, is one of the best presented I've ever seen. It's black and white, of course. But it has *gold* spot colour throughout. And I'm not talking about any yellow ink, it's a true gold colour.)
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Re: Early NX panel question

Unread postby Andrew Waugh » Tue Nov 28, 2017 1:27 am

Ahhh.

I found a further description in the California Highways and Public Works magazine for September 1938 (pp24-5). The department built the bay bridge and the associated works (including the railway). The magazine is available on the Internet Archive for those that want to read along...

The description is very high level, and is primarily about the matching NX panel at East Bay Yard (at the other end of the bridge) which was clearly installed first.

It says "It is possible to set up a route for a succession of trains. When this is done, the signal knob is rotated 90 degrees rather than pushed in; but the completion button is operated as for one train. The wayside signal will automatically clear for the next train while the route remains locked."

So turning the knob fleeted the signal.

(The article includes a nice photo of two techs connecting the cabling from the relay room to the back of the panel. The number of terminals required is impressive - as is the packed vertical portion with the buttons, route indicators, lights, and wiring.)
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