>> Well I thought impedance bonds allowed the traction current to passand>> attenuated the signal frequency of the particular track circuit. > >I think they're short pieces heavy of heavy wire. Do we have the same >things in mind?The heavy duty wire is to get around joints in the track. When a track circuits section ends then it needs to be isolated from the next section, this is where impedance bonds are used. Obviously in electrified rail you cannot just stick an insulating joint between the track circuits as the return current needs to continue. Impedance bonds allow the return current to continue while blocking the track circuit signal. This keeps the track circuits isolated from one another.>>> That makes sense, but it requires narrow-band selective filters. Noise>>> filters in addition don't make a sensible part of that picture. >> >> Could you please explain this slightly more? What do you mean by noise >> filters in addition? > >Presumably, your noise filters would pass the interesting signal and >block the noise that occurs at other frequencies. The tuning (channel >selection) filters would do the same thing.Yeah, What I meant by an active filter was simply an op-amp bandpass filter centered at the signal frequency. As the noise should be a lot less due to the isolation transformer the frequency response of the filter shouldn't have to be too sharp.>I hope you're right. I guess you are, but it needs to be confirmed bytest. I'd love to go out and test these things on a real track or even a section of test track, but unfortunately in order to be allowed to do this I would have to do a safety course, which the university isn't willing to pay for. The calculations which led me to the above decision was from the initial characteristics of a general railway line. So modelled as a transmission line we have it R, G, L and C characteristics. From there we were able to work out the attenuation constant and use that to determine how much a signal attenuates over a given distance. Obviously this will change over time, especially when it rains, the ballast conductance will increase heavily.
Filtering options for reflected signal with noise
Started by ●April 15, 2008
Reply by ●April 30, 20082008-04-30
Reply by ●April 30, 20082008-04-30
John121 wrote:>>> Well I thought impedance bonds allowed the traction current to pass > and >>> attenuated the signal frequency of the particular track circuit. >> I think they're short pieces heavy of heavy wire. Do we have the same >> things in mind? > > The heavy duty wire is to get around joints in the track. When a track > circuits section ends then it needs to be isolated from the next section, > this is where impedance bonds are used. Obviously in electrified rail you > cannot just stick an insulating joint between the track circuits as the > return current needs to continue. Impedance bonds allow the return current > to continue while blocking the track circuit signal. This keeps the track > circuits isolated from one another. > >>>> That makes sense, but it requires narrow-band selective filters. Noise > >>>> filters in addition don't make a sensible part of that picture. >>> Could you please explain this slightly more? What do you mean by noise >>> filters in addition? >> Presumably, your noise filters would pass the interesting signal and >> block the noise that occurs at other frequencies. The tuning (channel >> selection) filters would do the same thing. > > Yeah, What I meant by an active filter was simply an op-amp bandpass > filter centered at the signal frequency. As the noise should be a lot less > due to the isolation transformer the frequency response of the filter > shouldn't have to be too sharp. > > >> I hope you're right. I guess you are, but it needs to be confirmed by > test. > > I'd love to go out and test these things on a real track or even a section > of test track, but unfortunately in order to be allowed to do this I would > have to do a safety course, which the university isn't willing to pay for. > > The calculations which led me to the above decision was from the initial > characteristics of a general railway line. So modelled as a transmission > line we have it R, G, L and C characteristics. From there we were able to > work out the attenuation constant and use that to determine how much a > signal attenuates over a given distance. Obviously this will change over > time, especially when it rains, the ballast conductance will increase > heavily.Oh, this modern world! When I was a kid, I occasionally played in the rail yards. It would have been possible to scramble trains around, but we didn't. (Did you know that two kids can move a car along a level track by pushing steadily for long enough?) We used freight cars to roll out pennies, and discovered to our (and the engineer's) dismay that a penny jammed tight against each side of a locomotive drive wheel (so at least one would be well rolled when the train started) effectively serve as chocks and prevent the train from starting? I live now near the East Coast Corridor railroad line, what used to be the Pennsylvania Railroad main line. There are places nearby where no fence keeps me from the rails, and the track is straight enough to see approaching trains a long way off. The line is electrified. Maybe I'll go down and make some DC measurements and use headphones to check rail-to-rail noise. (In these times of terrorism para^H^H^H^H alertness, I'll need to be sure to bring no implements remotely capable of causing a derailment.) Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●May 1, 20082008-05-01
On Apr 30, 6:36 pm, Jerry Avins <j...@ieee.org> wrote:> > I live now near the East Coast Corridor railroad line, what used to be > the Pennsylvania Railroad main line. There are places nearby where no > fence keeps me from the rails, and the track is straight enough to see > approaching trains a long way off. The line is electrified. Maybe I'll > go down and make some DC measurements and use headphones to check > rail-to-rail noise. (In these times of terrorism para^H^H^H^H alertness, > I'll need to be sure to bring no implements remotely capable of causing > a derailment.)I don't know about you Jerry. Regardless of what you did as a kid, the railroad is a very dangerous place. An electric railway is even more so. I don't know for sure, but I would expect that anyone found trespassing on the tracks would be arrested and prosecuted. I know when I worked for the railroad we would chase the kids off of the right of way. Electric rails a very dangerous and I can't imagine that you would entertain the thought of trying to make an electrical measurement on them. Don't get toasted! Rick
Reply by ●May 1, 20082008-05-01
rickman wrote:> On Apr 30, 6:36 pm, Jerry Avins <j...@ieee.org> wrote: >> I live now near the East Coast Corridor railroad line, what used to be >> the Pennsylvania Railroad main line. There are places nearby where no >> fence keeps me from the rails, and the track is straight enough to see >> approaching trains a long way off. The line is electrified. Maybe I'll >> go down and make some DC measurements and use headphones to check >> rail-to-rail noise. (In these times of terrorism para^H^H^H^H alertness, >> I'll need to be sure to bring no implements remotely capable of causing >> a derailment.) > > I don't know about you Jerry. Regardless of what you did as a kid, > the railroad is a very dangerous place. An electric railway is even > more so. I don't know for sure, but I would expect that anyone found > trespassing on the tracks would be arrested and prosecuted. I know > when I worked for the railroad we would chase the kids off of the > right of way. Electric rails a very dangerous and I can't imagine > that you would entertain the thought of trying to make an electrical > measurement on them. > > Don't get toasted!Thanks for thinking about my well being. The switching yard in the Bronx during WW II was not electrified, the yard locomotives rarely exceeded 5 MPH, and when we were shooed away it was /pro forma/, from a distance. that said, you are certainly right. As for making measurements along the right-of-way (overhead catenary; no third rail), what danger do you anticipate? Signs in the stations warned riders to use the crossover tunnels rather than walk across the tracks, but many people walked across the track anyway until fences were installed between the north- and southbound sides. (Track workers hate those fences.) I'm still inclined to go out there, but in no hurry, and quite willing to be guided. Those Acelas come pretty fast! Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●May 1, 20082008-05-01
On May 1, 10:08 am, Jerry Avins <j...@ieee.org> wrote:> rickman wrote: > > > I don't know about you Jerry. Regardless of what you did as a kid, > > the railroad is a very dangerous place. An electric railway is even > > more so. I don't know for sure, but I would expect that anyone found > > trespassing on the tracks would be arrested and prosecuted. I know > > when I worked for the railroad we would chase the kids off of the > > right of way. Electric rails a very dangerous and I can't imagine > > that you would entertain the thought of trying to make an electrical > > measurement on them. > > > Don't get toasted! > > Thanks for thinking about my well being. The switching yard in the Bronx > during WW II was not electrified, the yard locomotives rarely exceeded 5 > MPH, and when we were shooed away it was /pro forma/, from a distance. > that said, you are certainly right. > > As for making measurements along the right-of-way (overhead catenary; no > third rail), what danger do you anticipate? Signs in the stations warned > riders to use the crossover tunnels rather than walk across the tracks, > but many people walked across the track anyway until fences were > installed between the north- and southbound sides. (Track workers hate > those fences.) I'm still inclined to go out there, but in no hurry, and > quite willing to be guided. Those Acelas come pretty fast!Certainly the overhead wires are safer, but they still use the rail as the return path, no? So at any time a section of faulty track can become energized to the full potential of the wires if a train is anywhere near, moving or not! But all that just ignores the issue of the train itself! I worked in a signal gang one summer and my job had long periods of standing around waiting to fetch something a maintainer needed. One day while standing on the track, I heard an engine coming and turned around only to see it about 200 feet away and coming at over 60 miles per hour! It was a double engine deadheading back from pushing a train over a ridge and they were booking! It also ran much quieter without the huge load of cars. If I had ignored the sound for even another second, I may not have been able to get out of the way in time and would not be here to tell you how dangerous a surprise along the right of way can be. And this is not to mention the stories of people getting whacked by loads that have come loose and hang off the side of the train or even a simple piece of stone that gets on the rail and shoots off like a bullet when the engine hits it. I know I don't need to lecture adults, but a lot of times people don't realize how dangerous industrial environments are from just looking around. Many of the hazards are not obvious.
