On Mon, 7 Jun 2010 04:56:16 -0700 (PDT) someone who may be D7666
wrote this:-

Speed control relays have been around on LT / LU for eons, they are
nothing new introduced post Moorgate.

Holding a signal and/or train stop at danger and only releasing it
if a train operates track circuit(s) in more than a specified time,
thus proving the train is going slowly enough, was certainly done
before the crash at Moorgate. Sharp curves and approaching signals
with a short overlap are examples. Presumably the way the front of
trains used to enter platforms while the rear of the previous train
was leaving [1] is another example. However, this was greatly
extended after Moorgate to cover dead end tunnels. The original
posting was not so much misleading as incomplete.


[1] IIRC the equipment was fitted as part of 1930s schemes and
removed during the "managing decline" era of the 1970s when it was
thought trains would not need to be run close together again. There
still seems to be some of this, but not as extensive as it once was.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000...#pt3-pb3-l1g54

On Jun 7, 2:24*pm, David Hansen
wrote:

Speed control relays have been around on LT / LU for eons, they are
nothing new introduced post *Moorgate.

Holding a signal and/or train stop at danger and only releasing it
if a train operates track circuit(s) in more than a specified time,
thus proving the train is going slowly enough, was certainly done
before the crash at Moorgate. Sharp curves and approaching signals
with a short overlap are examples. Presumably the way the front of
trains used to enter platforms while the rear of the previous train
was leaving [1] is another example. However, this was greatly
extended

I dis-agree, still, with this term ''greatly extended''.

The use of timed relays is and always has been much much much more
extensive than curves and overlaps indeed is the very essence of
headway control across the entire LU network, everywhere, including
plain line with no restrictions. don't try and apply main line
practice ''approach control'' to this, it is very very different. Even
plain line LU automatic signalling is different - there are - in non
signals engineers over simplified terms - 2 track circuits between
every signal for every 1 on main lines. This is fundamental to LU
signalling practice.

The quantity of additional relays for TETS is not that significant.
Baker Street Met IMR for example - a location I have visited several
times for work - is (I think) about the number of fingers of one hand
timed relays for the 2 bays TETS , but there are around a couple of
dozen others (off the top of my head) doing non TETS stuff, to protect
the 2 convergence points (the Met. City junction, and the north end
throat, and always have done.

Edgware Road for example does not have TETS, but it has - and indeed
again always has had - *huge* numbers of timed relays. I've never been
in Edgware Road cabin or relay rooms - much that I'd like too - and
probably will one day legitimately get a professional related visit -
but I travel through the place almost every day and looked up the
signals diagrams to understand it all.

--
Nick






--
Nick