Talk:Tyer's Electric Train Tablet

Globalise

This article talks about Tyers No.7 Tablet as though it was specific to New Zealand; it wasn't. Since I don't think separate articles for every kind of electric token instrument are justified, I've proposed that content from this article be merged into Token (railway signalling).

As an interim measure, I tried to move this article to "Tyers Electric Train Tablet in New Zealand", but that name is protected so cannot be used (which is interesting - this suggests it has previously existed then been deleted). I've added a "Globalize" tag, but as stated above, I think this article should be merged. –Signalhead ^< T > 17:03, 10 August 2008 (UTC)

I can understand the sense in globalising this article and combining it with other Electric Train Token (UK GW parlance) systems. Although this, the Tyers No.9 syatem and various staff systems all function in similar manners there is disagreement in terminology.

Perhaps this should all be brought under one umbrella heading of Single Line Systems?7severn7 (talk) 08:34, 14 August 2008 (UTC)

The South African Railways used to use a tablet system as well.Nolween (talk) 16:59, 30 June 2009 (UTC)

Sri Lanka Railways is still using this method. So this article should not be localized to one country and article should be in globalized manner. නිපුන දොඩන්තැන්න (talk) 07:11, 26 December 2011 (UTC)

+++++++++++++ I found the page confusing and incorrect in many places. It would seem far more sensible IMHO to talk about ETT instruments in the order in which the various types were introduced. And, if you're going to start by talking about No 7(the last 'main' type) then surely it os better to illustrate it with a picture of that type rather than a No 6?Railwest (talk)

Technology

It's not clear to me from the description how it worked, but I suppose it worked like this:

• There was a Tyer's apparatus at each end of the section. Each contained quite a few tablets. When a train approached one end of the section, the officer stationed there withdrew a tablet and gave it to the train driver. The removal from the apparatus caused it to lock, preventing the removal of another tablet, thus ensuring that a second train from this direction could not get authority to enter the section. At the same time, the apparatus caused a signal to be sent to the distant apparatus that made it impossible to withdraw a tablet from it too, so a train approaching from that direction could not be issued a tablet and therefore had no authority to enter.
• The first train now had the tablet and authority to enter. When it arrived at the distant end, the driver gave the tablet to the officer, who inserted it into his apparatus. This freed both machines to issue tablets again.
• The machines held a stock of quite a few tablets, because during the course of the day there could be several trains in succession from one direction. Overall however, there would usually be a net balancing out, so it would be rare for one end to run low on tablets. If one end did begin to accumulate too many tablets, perhaps there was a special lever that would issue a tablet on each pull so the driver could carry some to the other end to make up the deficit?

Is that basically how it worked? Akld guy (talk) 00:55, 12 January 2017 (UTC)

@Akld guy: Mostly correct. However, the normal state was that both machines were locked; the phrase "the officer stationed there withdrew a tablet" is true, but they couldn't do this without first informing the signaller at the other end, which brings me to the phrase "At the same time, the apparatus caused a signal to be sent to the distant apparatus that made it impossible to withdraw a tablet from it too", which is kinda redundant but long-winded to rewrite. When signalbox A had a train to dispatch to signalbox B, A would send the bell code for "is line clear" to B; to this, B would respond with "Line clear", and B would then press a button that released the Tyer instrument at A, allowing A to withdraw a tablet. In turn your sentence "This freed both machines to issue tablets again." is almost the opposite of the truth: both became locked, but either could once again be released by sending a signal from the other end. Here's an amended version of the first two bullets:

• There was a Tyer's apparatus at each end of the section. Each contained quite a few tablets. They were mutually locked. When a train approached one end of the section, the officer stationed there would request release from the other end. The officer receiving this request would press a button that released the Tyer instrument at the first end, where the first officer withdrew a tablet and gave it to the train driver. The removal from the apparatus caused it to lock again, preventing the removal of another tablet, thus ensuring that a second train from this direction could not get authority to enter the section. At the same time, the apparatus caused a signal to be sent to the distant apparatus that use of the release button at the distant apparatus made it impossible to withdraw a tablet from it too, so a train approaching from that direction could not be issued a tablet and therefore had no authority to enter.
• The first train now had the tablet and authority to enter. When it arrived at the distant end, the driver gave the tablet to the officer, who inserted it into his apparatus. This freed both machines to issue tablets again.

This isn't quite right, but it indicates the fail-safe nature of the system: there is a positive "release" signal, the absence of which is taken as a "lock" signal, and the "normally both locked" state means that should the connecting wires be broken, the apparatus at both ends would become (or remain at) "locked" instead of both suddenly being released while a train was passing between them.

Regarding your last bullet, there may have been such a feature, but I imagine that it was locked and/or sealed in such a way that it could only be used with appropriate authority. Alternatively, I expect that an appropriate individual from the railway's Signals & Telegraph department would rectify any imbalance during periodic maintenance of the apparatus. --Redrose64 🌹 (talk) 09:58, 12 January 2017 (UTC)

@Redrose64: Thank you for that very clear (and prompt) explanation. I suggested a lever pull to release tablets if one end accumulated too many, but a key (itself kept in a locked cabinet) might have been more appropriate. Anyway, thanks for making the signalling clear. Akld guy (talk) 10:59, 12 January 2017 (UTC)