[PRCo] Re: MetroRail Signalling

[Phillip Clark Campbell]

> From: J Aurelius <jaurelius at centurytel.net>
> To: Phillip Clark Campbell <pcc_sr at yahoo.com>; alschneider2 at juno.com; etennyson at cox.net
> Cc: rejmhj at netzero.net; j_swindler at hotmail.com; pittsburgh-railways at dementia.org;
>  jack.may at americomm.net; gary-elaine at comcast.net; nawdry at bga.com; crvlkotula at aol.com;
>  philgcraig204 at yahoo.com; billvigrass at verizon.net; bob.dietrich1 at verizon.net;
>  bbente at bellsouth.net; trams2 at comcast.net; allmanr at verizon.net;
>  shadow at dementia.org; akftrain at aol.com; miklosfrank at comcast.net; russell.jackson at stvinc.com
> Sent: Sunday, June 28, 2009 4:21:21 PM
> Subject: Re: MetroRail Signalling

 
> Audio-frequency (hundreds of hertz) track circuits 
are common on modern rapid transit systems.
> These frequencies aren't good 
for railroad track circuits (except as an overlay to control
>  grade crossing 
gates) because they don't propagate down the track far enough for the
>  1 mile 
plus railroad signal blocks.  On rapid transit lines, blocks typically are 
500-750 feet long. 
>  With audio frequency circuits it isn't necessary to cut 
the rails and provide a path
>  (impedance joint) around the insulated joints for 
traction power return, as was used
>  on older systems.  The device at the 
block boundary keeps the audio energy from
>  moving into the next block and 
injects energy at a different frequency into the nextblock.  
> The energy 
from the first block is detected by a relay (or other device) that works
>  only 
from the first frequency - if it's present it has traveled down the block 
without
>  being shorted out by a train; if it isn't present the signal system 
decides the block is occupied.
 
> This is probably over-simplified but I think it's 
right in principle.
 
> John Aurelius


Mr.Aurelius;


Thank you very much;  I now understand the basic concept.

With the old relay system, fail-safe was built into the system.  'A'  weak
link in this system was the human element;  operators could miss the signal
or otherwise ignore same.

It now seems  'computers'  or electronic circuitry somewhere takes the
place of the human operator,  even to the point of not recognizing occupancy
and thus resulting in an accident.  I hope a successful resolution is found
soon.



 Phil
Without  a   'coast'   but  not  a   'cause.'
--  --
"If thou wouldst rule well, thou must rule for God,
and to do that, thou must be ruled by Him ...
Those who will not be governed by God...
........will be ruled by Tyrants."
William  Penn,  founder  of  Pennsylvania



________________________________


----- Original Message ----- 
>From: Phillip Clark 
>  Campbell 
>To: alschneider2 at juno.com ; etennyson at cox.net 
>Cc: rejmhj at netzero.net ; j_swindler at hotmail.com ; pittsburgh-railways at dementia.org >  ; jack.may at americomm.net ; gary-elaine at comcast.net ; nawdry at bga.com ; crvlkotula at aol.com ; philgcraig204 at yahoo.com ; billvigrass at verizon.net ; bob.dietrich1 at verizon.net ; bbente at bellsouth.net ; trams2 at comcast.net ; allmanr at verizon.net ; shadow at dementia.org ; akftrain at aol.com ; 
> miklosfrank at comcast.net ; jaurelius at centurytel.net ; russell.jackson at stvinc.com 
>Sent: Sunday, June 28, 2009 11:58 
>AM
>Subject: MetroRail Signalling
>
>
>Mr.Alan 
>  Schneider;
>
>
>Thank you very much for this report.  Thank you to 
>  the many contributors on
>this subject.  The news reports  
>  'seem'  well done and I was able to glean
>much information from 
>  them;  comments from contributors underscored these
>observations and 
>  brought much clarity to this disaster.  The postings have been
>most 
>  productive  --  'mostly.'
>
>I have changed the subject line and 
>  have questions to seek a greater understanding
>of the signaling 
>  system.  I found the URL for the included article:
>http://www.fredericknewspost.com/sections/news/display.htm?StoryID=91910
>because 
>  I wanted a closer look at the included photo:
>http://www.fredericknewspost.com/photos/09/06/26/91910_large.jpg
>
>It 
>  is already established that  'computers'  handle the signals 
>  through  'ATC;'  while I
>understand the concept I am not familiar 
>  with the details.  My reference is the US&S
>signals as used on PRC 
>  interurbans.  Rails were gapped and insulated;  an impedance
>bond 
>  allowed ground return around the insulated rails while keeping the signal 
>  circuit
>current within the block.
>
>'Parallel'  construction is 
>  evident in the MetroRail photo but the rails are not gapped and
>insulated 
>  are they.  Please note the dual set of cables between the rails in each 
>  track
>that arc through a half circle before attachment to each of the 
>  rails;  this  'suggests'  an
>insulated gap in the rails 
>  which, again, is not clearly evident.  There are far more 
>  cables
>between the rails than the parallel US&S impedance 
>  bond.
>
>Also noteworthy is the large gap in the 600-volt(?) 
>  3rd-rail.  As the cabling between the rails
>of each track seems 
>  identical and the 3rd-rail is gapped on both tracks I am  
>  'assuming'  that
>such a gap in the 3rd-rail exists wherever such  
>  'signal cables'  exist.   Is this true?  Why is
>it 
>  necessary to gap the power supply at signal cabling locations?  Why 
>  aren't the running
>rails gapped, or are they?  I assume each truck has 
>  a 3rd-rail shoe on each side;  it then
>'seems'  that current is 
>  never disconnected from the train as the gap  'seems'  shorter 
>  than
>truck spacing, or is it?  The right hand track has ties that 
>  extend further than standard
>'apparently'  to accommodate 3rd-rail in 
>  the gap area;  the same may be true of the other
>track but the ties 
>  could be covered by the ballast.
>
>If someone is able to give some 
>  clarity to the computer style ATC signals circuits it will
>be most 
>  appreciated.  Thank you to one and all for such efforts.
>
>
>
> Phil
>Without  a  'coast'  but  
>  not  a  'cause.'
>--  
>  --
>"If thou wouldst rule well, thou must 
>  rule for God,
>and to do that, thou must be ruled by Him ...
>Those who 
>  will not be governed by God...
>.......will be ruled by 
>  Tyrants."
>William  Penn,  founder  of  
>  Pennsylvania
>