dibber25 Posted October 25, 2016 Share Posted October 25, 2016 Please can someone with some technical knowledge tell me the correct title for this piece of kit photographed at Barnstaple in 2009. I believe it is a TPWS grid for the end of the line but is it for incoming or outgoing trains? I'd like to be able to describe it correctly in an article. (CJL) Link to comment Share on other sites More sharing options...
Mark Saunders Posted October 25, 2016 Share Posted October 25, 2016 If it is at the end of the line there will be another one a few yards infront of it. the first one is the Arming Loop and it starts a timer on the train, after this it passes a Trigger Loop that if passed over before the timer has timed out it will trigger a Brake Application as the train is deemed to be going too fast! All TPWS ariels/loops come in pairs it is only the distance betweem the two that differs at Stop Signals they are next to each other to initiate an immediate brake application! Mark Saunders Link to comment Share on other sites More sharing options...
RMweb Premium phil-b259 Posted October 25, 2016 RMweb Premium Share Posted October 25, 2016 Please can someone with some technical knowledge tell me the correct title for this piece of kit photographed at Barnstaple in 2009. I believe it is a TPWS grid for the end of the line but is it for incoming or outgoing trains? I'd like to be able to describe it correctly in an article. (CJL) It is a 'mini' TPWS grid and will be part (you need two grids per TPWS installation) of an overspeed sensor (ISS) designed to bring a train to a stand if it is entering a terminal platform too fast. Full sized grids were found to be giving too many false positives and tripping unnecessarily - something to do with the radiated signal interacting with the platform structure Link to comment Share on other sites More sharing options...
Edwin_m Posted October 25, 2016 Share Posted October 25, 2016 I believe the small grids are actually needed because the field produced by the larger ones is too inaccurate to monitor speed at the low speeds needed on approach to buffer stops. But yes that's what it will be doing. Link to comment Share on other sites More sharing options...
Wheatley Posted October 25, 2016 Share Posted October 25, 2016 Full sized grids were found to be giving too many false positives and tripping unnecessarily - something to do with the radiated signal interacting with the platform structure Which although a 'right side' response was actually causing real problems and a lot of passenger injuries. On the approach to a platform line half the passengers are standing up, rummaging in bags, rounding up kids, coats, shopping etc, anything except holding on. And when the TPWS trips at less than 10mph the unit stops absolutely dead, none of the several seconds of violent braking but time to brace you get when it trips at 60mph, Link to comment Share on other sites More sharing options...
Edwin_m Posted October 25, 2016 Share Posted October 25, 2016 It also meant drivers were approaching the grids really slowly to avoid being caught by the TPWS, and once clear of the grid had to apply power to get the train to its normal stopping position. Applying power on the approach to a buffer stop isn't really conducive to avoiding collisions with it. Link to comment Share on other sites More sharing options...
RMweb Gold The Stationmaster Posted October 25, 2016 RMweb Gold Share Posted October 25, 2016 It also meant drivers were approaching the grids really slowly to avoid being caught by the TPWS, and once clear of the grid had to apply power to get the train to its normal stopping position. Applying power on the approach to a buffer stop isn't really conducive to avoiding collisions with it. It was a very real problem at Paddington with HSTs in the early days as the normal running-in speeds were more than enough to result in a brake application and stopping short. Which encouraged exactly what you have identified as a consequence. Link to comment Share on other sites More sharing options...
RMweb Premium John M Upton Posted October 26, 2016 RMweb Premium Share Posted October 26, 2016 Still a problem in some places where the mandatory approach speed is observed over the grids but then a squirt of power is required to keep going as the remaining track slopes uphill! Link to comment Share on other sites More sharing options...
RMweb Gold Dunsignalling Posted October 26, 2016 RMweb Gold Share Posted October 26, 2016 If the driver stops the rear sensor of his/her unit on top of one, you also get fun and games when they change ends. It occurs quite often at Exmouth, where the frequent variations in train formations must make it hard to remember how far back the other end is. John Link to comment Share on other sites More sharing options...
Rivercider Posted October 26, 2016 Share Posted October 26, 2016 I think this photo shows the two grids at Barnstaple in context to the station 143603 in the platform 27/3/2015 cheers Link to comment Share on other sites More sharing options...
dibber25 Posted October 28, 2016 Author Share Posted October 28, 2016 Many thanks for all the help. Now I'll see if I can put together something that resembles it. (CJL) Link to comment Share on other sites More sharing options...
Turbo_Tim Posted November 1, 2016 Share Posted November 1, 2016 If the driver stops the rear sensor of his/her unit on top of one, you also get fun and games when they change ends. It occurs quite often at Exmouth, where the frequent variations in train formations must make it hard to remember how far back the other end is. John Same problem potentially at Batnstaple. If it's longer than 2 carriages then stop with front cab by the gents toilet. The other problem is that it's gently downhill into the platform so picks up speed. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.