Signalling System

[official.h12]

Why are signalling systems changing from NX to WestCAD VDU? Also what are the benefits of WestCAD VDU over NX?

 

[Welly]

Easier to change the displays when tracks are re-modelled than it is to change the NX panels.

 

[Tim M]

It’s also easier to interface Westcad with other digital systems such as Computer Based Interlockings (e.g. SSI, Westlock, Westrace, Smartlock), legacy remote relay based Interlockings using Time Division Multiplex communications and train describers. There are probably other digital interfaces.

By the way WestCAD should be regarded as mature technology having being initially used in Australia and Norway (Oslo T-banen commissioned in 1996 included an Ebilock interface as well as Westrace) for many years, it was called Mimic back then.

 

[68000]

Essentially NX panels and the design of them are becoming obsolete if not already

 

[John Webb]

NX panels are complex arrangements of electrical switches and indicators, usually built up from 'tiles' which have to be purpose made (at least to the overprinting of details) to form the required display. They take up a lot of room - the NX panel from 1979 at West Hampstead PSB, replaced by 4 VDU screens just over a year ago, was some 50foot (15m) long! Take a look at https://www.swindonpanel.org.uk/ who saved and restored the NX panel from Swindon and have it on display at the Didcot Railway Centre.

Both mechanical switches and indicators have finite operating lives, as do VDU screens, but the latter are much cheaper and quicker to replace.

 

[Annetts key]

NX panels are complex arrangements of electrical switches and indicators, usually built up from 'tiles' which have to be purpose made (at least to the overprinting of details) to form the required display. They take up a lot of room - the NX panel from 1979 at West Hampstead PSB, replaced by 4 VDU screens just over a year ago, was some 50foot (15m) long! Take a look at https://www.swindonpanel.org.uk/ who saved and restored the NX panel from Swindon and have it on display at the Didcot Railway Centre.

Both mechanical switches and indicators have finite operating lives, as do VDU screens, but the latter are much cheaper and quicker to replace.

Actually the Henry Williams NX type panel (as used extensively on Western) is remarkably good. The biggest maintenance issues are:
Replacing the filament indication lamps (which I swear blow within minutes of you having just checked them, with a signaller telling you within seconds, you've missed some...),
Occasionally cleaning button or switch contacts,
Occasionally having to refit a switch knob (either because it's been reported loose or it's become completely detached),
Or having to order a new top plate because the fingers of thousands of operations of a switch have rubbed away all the markings (paint).
The only other routine maintenance is dusting and cleaning.

Not much else goes wrong or needs doing.

That sounds like a lot, but given how many lamps, switches and buttons there are on a typical large installation, it's small fry compared to the maintenance of just one set of points.

The Henry Williams NX type panel is completely modular. Given the correct spare parts, any part can be built-up and hence repairs or alterations are not difficult (unless wiring changes are needed). But this work is time consuming. I know, I've rebuilt various configurations of switches, buttons and lamp units.

The only parts that are custom made for each tile are the top plates. The painted part that you can seen in the pictures (mostly green for Western). Well, apart from the blanks that are completely green...

The Henry Williams NX type panels are also far more durable than the more modern plastic tile panels that some places got in the 1990s or thereabouts.

The main reasons for the removal of these is that alterations are expensive because of the labour cost. They are seen as old and obsolete. And if you want to connect them to computer based Interlocking systems, you need a panel multiplexer system.

Also the powers that be think that banks of computer screens in "modern" control centres are better.

 

[edwin_m]

It actually costs quite a lot to alter the screens, because the original supplier has to be commissioned to amend all the data and install on site. I used to do this for the original IECCs 30+ years ago, but it's probably a bit more high-tech these days than setting out on the train with a rucksack full of replacement memory chips...

 

[MarkyT]

Actually the Henry Williams NX type panel (as used extensively on Western) is remarkably good. The biggest maintenance issues are:
Replacing the filament indication lamps (which I swear blow within minutes of you having just checked them, with a signaller telling you within seconds, you've missed some...),
Occasionally cleaning button or switch contacts,
Occasionally having to refit a switch knob (either because it's been reported loose or it's become completely detached),
Or having to order a new top plate because the fingers of thousands of operations of a switch have rubbed away all the markings (paint).
The only other routine maintenance is dusting and cleaning.

Not much else goes wrong or needs doing.

That sounds like a lot, but given how many lamps, switches and buttons there are on a typical large installation, it's small fry compared to the maintenance of just one set of points.

The Henry Williams NX type panel is completely modular. Given the correct spare parts, any part can be built-up and hence repairs or alterations are not difficult (unless wiring changes are needed). But this work is time consuming. I know, I've rebuilt various configurations of switches, buttons and lamp units.

The only parts that are custom made for each tile are the top plates. The painted part that you can seen in the pictures (mostly green for Western). Well, apart from the blanks that are completely green...

The Henry Williams NX type panels are also far more durable than the more modern plastic tile panels that some places got in the 1990s or thereabouts.

The main reasons for the removal of these is that alterations are expensive because of the labour cost. They are seen as old and obsolete. And if you want to connect them to computer based Interlocking systems, you need a panel multiplexer system.

Also the powers that be think that banks of computer screens in "modern" control centres are better.

The Henry Williams 'Domino' panels were made under license from Swiss company Integra, who sold similar panels to their home market and many other places worldwide. Integra became part of Siemens in 1992. Here's a Swiss example:

https://www.hmmueller.de/DVDA_x1000/60-077.jpg

While button colours etc are different, the switch mechanisms and lighting under the face plates were the same as the UK ones. ISTR some WR signallers changed blown lamps themselves, as it was easy to lift up individual faceplates to access them.

 

[Belperpete]

It actually costs quite a lot to alter the screens, because the original supplier has to be commissioned to amend all the data and install on site. I used to do this for the original IECCs 30+ years ago, but it's probably a bit more high-tech these days than setting out on the train with a rucksack full of replacement memory chips...

Agreed - the idea that it is easier to change software than hard wiring is something of a fallacy when you are dealing with safety-critical systems. The changes to the software have to be thoroughly tested, to include all possible implications and potential impacts of the change. As I recall, with early IECC systems, ANY change to the data, no matter how small, required the WHOLE IECC data set to be retested!

The main advantages of screen-based control systems such as WestCAD, IECC and the like are:
they take up much less space
they allow easy relocation of the control point
they allow automatic route-setting
they are significantly easier to interface with computer-based interlockings
it is not hard to interface them to existing relay interlockings
they can be used to add extra features and safeguards to older relay interlockings (such as Train Operated Route Release and over-run protection)

So if an existing relay interlocking is being replaced with a computer-based interlocking, either because of its age or because a major layout change is being made, then consideration will usually be given to replacing the NX panel with a screen-based system. Other relay interlockings that are not being replaced can then be recontrolled from the same system.

Most relay interlockings generally have some form of electronic remote-control system to interface them to the NX panel, especially where the relay interlockings are remote from the panel. Many of these systems are obsolete, and so problematic to maintain. Replacing the NX panel with a screen-based control system allows these old electronic systems to be abolished.