I’m pretty sure you’re correct. Isn’t that why all the buffer stop grids are of the smaller type.
I recall the original ones kept having spurious interventions because the timer would reset before the trigger loop was reached.
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710112 collision with Buffers at Liverpool Street Station (15/10/2026)
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I recall the original ones kept having spurious interventions because the timer would reset before the trigger loop was reached.
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RailUK Forums
357
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The timer should reset before the trigger loop is reached - it's reaching the trigger loop before the timer resets that trips you isn't it?
edwin_m
Veteran Member
It was related to the shape of the electromagnetic field produced by the loops - known as "side lobes". This didn't matter at normal speeds but when they tried to use it for buffer stops (which it was never designed for) it wasn't possible to get the timing accurate enough.
357
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I think we are both saying the same thing but using different terminology!
My understanding has always been that when the train goes over the first loop the timer starts, then the timer should end before you reach the second loop.
If you reach the second loop before the timer ends, you'll have a brake application because you passed between the two racks too quickly.
Tell me if I'm wrong!
PudseyBearHST
Member
You both are saying the same thing I think.
Are the mini grids different frequency to the normal grids which cause freight train and passenger train to be set at the same speed? Or is it different 10/12.5 or whatever?
Are the mini grids different frequency to the normal grids which cause freight train and passenger train to be set at the same speed? Or is it different 10/12.5 or whatever?
Signal Head
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Originally set at 10mph (Passr), but there were 'false' interventions on trains running at or very close to that speed. In part caused by the signal from the loops being reflected back by the platform causing the antenna to encounter the 'trigger' frequency a little too early and so appearing to be doing a higher speed.
To counter the problem, 'mini loops' were designed specifically for use in platforms, and the 'set speed' increased slightly to 12.5mph to provide a suitable margin for error.
apologies.Sorry for belated reply as I was out all day Friday. 6 foot is indeed not a coach length. Trains presumably could stop a few feet from the buffers but they often stop a coach length or more away. I was womdering why.
dk1
Veteran Member
It can often depend on which class of train & include things like stopping points for pantographs such as platform 1 at Ipswich as the OHL does not run the full length of the platform and as an example to stop a station roof pillar or other furniture from blocking wheelchair ramp access at train doors. Platform 6 at Norwich is another issue for 755/3s. They stop further back as if not the opposite cab stands over the TPWS grid.
At Liverpool St in certain platforms such as platform 8 a 12-car train needs to get fairly close to the stops or it will stand foul at the rear.
rogercov
Member
And slightly more recent (my photos)
Amazing that it had hardly changed in over 60 years!
