[PRCo] Re: MetroRail Signalling
Phillip Clark Campbell
pcc_sr at yahoo.com
Tue Jun 30 13:53:17 EDT 2009
> 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: Monday, June 29, 2009 5:43:14 PM
> Subject: Re: MetroRail Signalling
> Audio frequency track circuits and their block
boundary devices have been around longer than
> computers have, probably from
right after World War II. The signal source can be an analog
> audio
oscillator and the detector can be a relay. The fail-safe principle is
still there as long as
> the frequency can't wander to that of an adjacent block:
if the oscillator quits there isn't a
> signal to detect; if the relay fails it
won't pick up (to announce a clear block).
> Signal systems that use computers are designed with
considerable care using fail-safe principles.
> That said, track circuits of all kinds live out in
a punishing environment (heat, cold, strong forces from
> track
expansion-contraction and trains passing, vandalism) and block boundaries.
They CAN fail to the
> unsafe side - an insulated joint can fail so it
isn't insulated; an electronic boundary device can
> lose its
integrity. Unsafe failures of signal systems ARE RARE but have always been
with us.
> Unsafe actions by human drivers, while also rare, are a more
common cause of accidents.
> John Aurelius
Mr.Aurelius;
Even as I wrote the first email inquiring about the signal system I thought about
'signal corruption' or, as you put it above, the audio signal passing its 'block
boundary device.' For the system not to detect the train ahead, would it be 'possible'
that the signal in the track section//block of the following train was passed to the block
ahead where the stopped train was found? The 'system' may have then recognize
both trains as one. Would this be a possibility?
>From other descriptions here it seems the intermittent nature of this one block should
have tripped a fail-safe device to prevent the accident. This obviously didn't happen.
However, it was known for several days that this 'block' showed intermittent detection
wasn't it. It would seem that an alert dispatcher would have noted the detection of trains-1
and trains-3 but not train-2 stopped between them. This dispatcher should then take
immediate action to notify train-3 to institute control to avert a 'possible' collision.
Mr.Craig mentions something similar; this should already be in place or something
easily noticed by that alert dispatcher.
Did San Francisco install 'computer' operation in its Lrv subway about a decade or two
ago? Before that they had cab signals and manual control; equipment would automatically
stop if the cab signal speed was exceeded. How does this compare to Wmata?
The 'unsafe' feature is a 'given' because this is an imperfect world. But when found
these unsafe situations need to be resolved don't they.
I need some explanation // definitions please:
ATO== Auto Train Operation -- operator simply a doorman.
ABS== ? something Block System. (Certainly not Auto Brake System.)
Other acronyms?
Thank You.
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
>
>> 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
>
>
>
>
>
>----- Original Message -----
>From: Phillip Clark
> Campbell
>To: J Aurelius ; 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: Monday, June 29, 2009 1:32 PM
>Subject: Re: MetroRail Signalling
>
>
>
>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
>>
>
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