Life on the Rails

[Iormlund]

No one seemed quite sure what fit for duty meant.  Harish finally managed to chase down an Australian rail medical guide.  It was 210 pages long.  I sent it to our company nurse.  She immediately called me back and asked "Isn't there someone there who could go?"

It's the same in Spain. Every worker gets a check up once a year to make sure you are fit for duty (the company only receives a yes/no answer, you get the full report). Without these papers (and more) you won't be able to enter most plants.

I oversee contractors working on my project. Most of these come from Germany and the Netherlands, where this is not mandatory. It's a pain in the ass. So we made a deal with our insurer to offer those to our contractors. We have similar problems with risk assessment paperwork. To make matters worse nobody in our Health & Safety staff speak English fluently.

[Savonarola]

The mysterious Vector Network Analyzer (VNA) from yesterday's post is a device which measures loss and reflection in cable over various frequencies.  You probably learned in physics at some point that Voltage (in Volts) is equal to the Resistance (in Ohms) times the Current  (in Amps) run through the circuit; that is: V=IR.  This is true for DC circuits, for AC circuits it's slightly difference.  The resistance factor is now called impedance (but still measured in Ohms.)  Impedance changes as frequency changes; so that a circuit can have a very low impedance at one frequency and a high impedance at a different one.  Low impedance means that most of the power passes; high impedance means that most of the power put in is changed to heat and absorbed by the circuit.  In communications theory we call this "Insertion Loss."

Radio frequency is a type of alternating current; rather than the 50 or 60 Hertz (cycles per second) used in your home it's at a much higher range from several hundred thousand Hertz used in AM radio to several hundred million Hertz used in your cellular phone to a few billion used by your WiFi (Hertz is an SI unit so these become KHz, MHz and GHz respectively.)  One function of the VNA is that it can measure the insertion loss over a range of frequencies; the one that I had with me can go from DC (that is 0 Hz) to 6 GHz.

A second type of loss that's found in all communication circuitry is reflection loss.  That is every device in line will reflect a small amount of power back.  So if you plug your stereo cable from your console into a graphic equalizer and another from the equalizer to a speaker some of the signal will be reflected back by the first cable, some by the graphic equalizer, some by the second cable and some by the speaker.  This loss is called "Mismatch loss;" and, once again it is frequency dependent.  In the old days (and even today in certain applications like Ham radio) the concern was in the amount of power being reflected back in damaging the radio; so we measure the amount of power coming back in.  In the old, old days the only way to measure this was with a Voltmeter at two different points, so the most commonly measurement of this is called Voltage Standing Wave Ratio or VSWR (pronounced Vis-War.)  (Today it's possible to measure the power directly at the source; that's called Return Loss or RL.)

VSWR is best visualized as a window with a Venetian blind.  At near perfect match the blind is horizontal and almost all sunlight can come through.  At complete mismatch all the sunlight is reflected out and none of it enters the room.  Complete mismatch, in communications engineering, means that there is either a short circuit or a break in the line (open circuit.)  So a high VSWR indicates a problem.

The third function of the VNA is that it can measure the time of each individual reflection point used in VSWR and use that to calculate the distance.  It can only do this at a single frequency and measures out the distance.  We call this "Distance to Fault" or DTF.  If there is a fault (a short or open) we will see that as the most prominent reflection point.  Usually the antenna is the most reflective element, so we use this as a safety check (and to measure the length of the cable run.)  Electricity moves slower than the speed of light through copper; the actual speed depends on the size and composition of the cable.  Each manufacturer rates their cable at a certain "Propagation velocity" which needs to be put into the VNA to get the right(ish) result.

So you can see my concern at having to explain this TSA agents; I have trouble explaining this to other Electrical Engineers.  I think I've been over this half a dozen times with WD by now (to be fair what he does is a mystery to me as well.)

[Savonarola]

and (my specialty) high-powered lasers.

I would just like to point out to the rest of Languish that I am not the poster most likely to become a super villain.



Safety is a big issue in rail too.  We have yearly inductions and daily briefings on all days we're out on the tracks (in North America and Australia, I mean.  They have a different understanding of safety in Colombia.)  The concern that is unusual in rail is that people without an occupational background can get right up next to trains.  It's sometimes hard to convince people how dangerous those really are.  We're working on a high speed rail from Miami to Orlando right now.  One of my co-workers was installing switches down by West Palm Beach^1..  When he was there a woman was stopped at a light when the gates came down.

John:  Ma'am you have to move your car.
Woman:  What?  Where?
John:  Just go around the gate.
Woman:  That's stupid, I'm not moving.
John:  There's a train coming, why are we arguing about this?

Fortunately she did get out of the way.  The train has been in operation since the beginning of the year and there have already been four deaths from people either trying to beat the train or pedestrians crossing the tracks away from a crossing.

1.)  Right across the estuary from Mar-a-Lago; which probably explains this as well as anything.

[Savonarola]

Good info and you're working on some interesting engineering items.  When we had some bad train accidents a few years ago I was really surprised that some kinds of systems weren't already in place. It seemed crazy that if a train approached an area way over the track speed limit that there was little or nothing to slow it down. As you say, it takes time and money to install the systems.

Nothing in rail ever happens quickly.  The accident which touched off the legislation mandating PTC (Chatsworth train collision) happened a decade ago.

[Savonarola]

I really enjoy these stories.  Your writing is excellent.

Thank you, Grumbler

[Iormlund]

and (my specialty) high-powered lasers.

I would just like to point out to the rest of Languish that I am not the poster most likely to become a super villain.

I lack an advanced degree though. I'd probably make a good henchman. Or perhaps the villain's love interest.

Safety is a big issue in rail too.  We have yearly inductions and daily briefings on all days we're out on the tracks (in North America and Australia, I mean.  They have a different understanding of safety in Colombia.)  The concern that is unusual in rail is that people without an occupational background can get right up next to trains.  It's sometimes hard to convince people how dangerous those really are.  We're working on a high speed rail from Miami to Orlando right now.  One of my co-workers was installing switches down by West Palm Beach^1..  When he was there a woman was stopped at a light when the gates came down.

John:  Ma'am you have to move your car.
Woman:  What?  Where?
John:  Just go around the gate.
Woman:  That's stupid, I'm not moving.
John:  There's a train coming, why are we arguing about this?

Fortunately she did get out of the way.  The train has been in operation since the beginning of the year and there have already been four deaths from people either trying to beat the train or pedestrians crossing the tracks away from a crossing.

Having crossings with trains that do 200 mph doesn't sound very safe. Over here bridges are built over (or under) high-speed tracks. Which is another reason why they are so expensive to build.

[Savonarola]

I lack an advanced degree though. I'd probably make a good henchman. Or perhaps the villain's love interest.

Damn

Having crossings with trains that do 200 mph doesn't sound very safe. Over here bridges are built over (or under) high-speed tracks. Which is another reason why they are so expensive to build.

We don't go anywhere near 200 MPH anywhere in the United States ( ).  To the best of my knowledge the fastest is 110 MPH; the max speed on standard track.  In this case, since there's no radio system between West Palm Beach and Miami, the maximum speed is 79 MPH.  In areas where there are multiple gates, such as a city, the speed is restricted even further.

[Savonarola]

At first blush the Amtrak train collision in South Carolina this morning looks similar to the Chatsworth train collision I mentioned yesterday.  A train track is divided into a series of sections we call "Blocks".  Usually a train is given absolute right to the block which it occupies; which means no other train can enter the block.  The blocks are separated by a series of signals; if you don't have authority to enter the block then you're not allowed to go past the signal.

In the case of the Chatsworth train collision the conductor blew past a signal and right into a freight train coming the other way.  In this case the freight train was stopped on the tracks; so it could have been a mistake by the Centralized Traffic Control (CTC) rather than the locomotive operators.  In any event this is the problem PTC was created to solve.

[KRonn]

At first blush the Amtrak train collision in South Carolina this morning looks similar to the Chatsworth train collision I mentioned yesterday.  A train track is divided into a series of sections we call "Blocks".  Usually a train is given absolute right to the block which it occupies; which means no other train can enter the block.  The blocks are separated by a series of signals; if you don't have authority to enter the block then you're not allowed to go past the signal.

In the case of the Chatsworth train collision the conductor blew past a signal and right into a freight train coming the other way.  In this case the freight train was stopped on the tracks; so it could have been a mistake by the Centralized Traffic Control (CTC) rather than the locomotive operators.  In any event this is the problem PTC was created to solve.

Thanks for that insight because I was really wondering how the two trains collided. As far as I know, usually a freight train has priority while passenger trains move to sidings to allow freights to pass. Given that being accurate, it sounds like you're saying the passenger train missed the signal, or the signal was wrong, to move to a siding? The freight train being stopped on the tracks - why would it be stopped? Could it be that it was signaled the other train on the tracks as to why it was told to stop?

[KRonn]

I just saw a news update on the crash. They're saying the Amtrak train was diverted to a siding where the freight train was stopped.

[Savonarola]

I just saw a news update on the crash. They're saying the Amtrak train was diverted to a siding where the freight train was stopped.

Yes, from the reports whatever train control system CSX was using was down.  Usually you change switch position from your CTC; in this case the switch was thrown manually on site and either the person who threw it didn't report this to their dispatch or the dispatch didn't report this to the Amtrak crew.

This is the fourth fatal incident Amtrak trains have been involved in during the past four months.  Only Tacoma was Amtrak's fault; the North Carolina and West Virginia incidents were caused when people tried to run the gates.  This one is almost certainly CSX's fault.

[Savonarola]

Here's some rail lingo for you guys.  A rail switch is set to "Forward" when you continue on the track you're currently on; and "Reverse" when you switch tracks.  The CSX crew had left the switch in reverse; which moved the Amtrak train onto a siding.

Rail operation is done by signals as well as dispatch.  (That is there are electric signals which tell the train operator is occupied or empty.)  Areas where there is no signalling system are called "Dark Territory;" and all train control is done entirely by radio.  Because the signalling system was down; this crash occurred in dark territory.

[Savonarola]

We have some senior engineers in from France.  One worked on the Paris Metro.  He said that the Metro cannot leave trains parked on the track overnight, since they will be defaced by graffiti.  Instead they are kept behind locked doors in a depot with men and dogs to guard the trains.  There have been instances where roving gangs of artists have broken into the depot and fought off the guards in order to paint the trains.  That's dedication.  Anyone can suffer for his art; but it takes a real artist to make other people suffer for his art^1..

He later went to work on the Tram system in Geneva.  The workers there thought the story was... well, not hilarious, but whatever the Swiss equivalent of hilarious is.  Unbelievable, maybe?

1.)  John Cage did for over sixty years.  Now that's real dedication.

[Jacob]

I enjoy "roving gangs of artists" as a turn of phrase

[KRonn]

I just saw a news update on the crash. They're saying the Amtrak train was diverted to a siding where the freight train was stopped.

Yes, from the reports whatever train control system CSX was using was down.  Usually you change switch position from your CTC; in this case the switch was thrown manually on site and either the person who threw it didn't report this to their dispatch or the dispatch didn't report this to the Amtrak crew.

This is the fourth fatal incident Amtrak trains have been involved in during the past four months.  Only Tacoma was Amtrak's fault; the North Carolina and West Virginia incidents were caused when people tried to run the gates.  This one is almost certainly CSX's fault.

This explains it nicely.