How are locomotives controlled if they are in the middle from the lead loco ?I know airbrakes are connected but what about mu hoses?
They are not hard wired MUed with the head end. They are “distributed power units” (DPU) controlled by telemetry from the head end. The same is usually true with locomotives at the rear. DPU is pretty commmon in today’s railroading.
How does it work?
It’s all radio control. The engineer has the choice of tying the head end and the DPU together (electronically) or running them separately, where the lead loco would be run by traditional means, the DPU via the control box. If they are tied together, whatever the lead loco does, so does the DPU.
If Jeff Hergert will access this thread he can explain it all in detail - he is a Engineer on the UP and operates DPU trains on many of his trips.
Thankyou very much
Even at my age still learned something new today
One interesting thing about DPU, since it is a radio based control sysytem, is how it deals with communication failures between the head end and the DPU units, which can easily happen on a rail line. My understanding of how this works (subject to correction by those who know more about the technology than I do) is that, when there is a communication failure, the DPU units will, at least initially, continue to operate based on their last command. But this will stop if something happens that is out of “correspondence” with the last command.
For example, if the last command was “run 8” and there is a communication failure, the DPU units will continue in run 8. But, if there’s a brake application from the head end, the computers on the DPU units will sense the drop in train line pressure that initiates a brake application, recognize it as being out of “correspondence” with the prior run 8 command, and drop the DPU units to idle without any command from the head end. Someone with more expertise than I have may want to further comment on this.
I know of a horseshoe curve in central Texas that is unlike the Horseshoe Curve near Altoona. It does not have a valley between the legs of the curve. The curve winds its way around a sizeable mountain. Actually, it is more like a large hill, but we Texans have a habit of exaggerating stuff.
When a long train is going through the curve, the locos on the back are out-of-sight of the lead locos. What happens to the commands from the lead locomotive?
One answer to this is the same as the answer to LOS in tunnels or winding ravines. Repeaters or passive antennas.
Remember that the actual data rate being transferred across the radio is comparatively slow, so things like multipath interference are not critical, and it becomes possible even in analog to code the data for typical MU-style commands so that multiple repeating sources won’t functionally interfere with each other.
A simple repeater setup might take the signals from the ‘master’, transmit them up the ‘mountain’ in the example, and then rebroadcast so that you had the equivalent of 50 microvolt contour at all points along the track (or more precisely the path of the antennas on the slaves). The number of locations needed for this would be determined by the length of consist, number of slave locations, and a few other relatively simple factors.
It is possible that a tuned passive antenna could be provided along the track route along the ‘trouble’ areas, with the signal being repeater-amplified if desired. A similar approach was used to put FM radio into the bores of the Lincoln Tunnel years ago, which is technically far more demanding than servocontrol of Woodward governors and the like.
Modern developments for the cellular-telephone industry have of course made it not only ‘trivial’ but cost-effective to implement remote signal assurance for any number of midtrain slaves, and to allow a computer on the head end to calculate all the different positions for throttle and DB relative to GPS/GIS to control things like node position and predictive throttle up/down for sensible train handling of very long consists over comparatively difficult profiles with minimum difficulty for the engineer (compared to what w
Here’s a incident that resulted from improper train handling and operation of the Locotrol II system. The current DP system has many of the same features.
https://tsb.gc.ca/eng/rapports-reports/rail/1996/r96c0086/r96c0086.html
Later report on the same thing:
https://bst-tsb.gc.ca/eng/rapports-reports/rail/1997/r97c0147/r97c0147.html
While we are on the subject of ignorance of Locotrol, what was the Canadian case involving the two midtrain helpers left configured to ‘pull the other way’? You provided the reference in a different thread but search won’t find it now, and I can’t tickle Google with the right search params to cough it up.
One of the most terrifying things I’ve seen is that initial video (the one that was taken down within 30 minutes) of the accident – I think at Panhandle – where the lead unit’s control equipment was so rapidly and thoroughly demolished that the rear DPU kept pushing the consist at fairly high speed into the developing debris field…
There is a confusing forumla on exactly where mid DP’s are to be placed in the train. The length permits a 20 car count either direction and a 1,000 ft barrier that cannot be outside of that. Mid Dps are a waste of time and have created much rework w/trains leaving an initial terminal out of compliance which then creates issues of the train crews being pulled from service. If there is an issue, one needs to contact their RFE or the rules hotline help desk and be goverened by their instructions. Personally I have not encountered any issues but being called for one still makes me nervous.
DP is an updated version of Locotrol, Locotrol lll I believe.
During communication loss (comm loss) DP consists will continue operating at the last command they received in power throttle for 90 minutes. If it was a dynamic brake command, it will stay in dynamics until comm is restored.
During comm loss it is possible to signal the DPs to go to idle by using the automatic air brake. For comm loss in power, just making a service application is supposed to get the DP to idle down and cut out it’s brake valve. In dynamics during comm loss, an emergency application is needed to get the DPs to go to idle/brake valve cut out.
Jeff
Thanks for your input.
With the exception of takeoffs and landings, many of the tasks of flying a sophisticated airplane that had been handled by the pilot are now handled by the onboard computer. The pilots put settings into the computer, i.e. desired altitude, speed, etc., and the computer actually flies the airplane.
To what extent has computer technology taken over some of the tasks of operating a modern railroad locomotive?
Both GE and NY Air Brake have systems that come close with regard to train handling.
Just like your car, most of the functions are now computer based.
I turned off Trip Optimizer (GE) last night going through a series of hog backs. (It had the DP in dynamic brake 8 when our guide lines for the territory call for the DP to be in throttle 1 or 2, pushing the slack in. Not pulling it out.) LEADER (NYAB) isn’t much better. They are thinking of making that official, turning off the EMS (energy managment systems) in ‘challenging locations’ because they have been tearing up the larger trains we are running. (Normally, I wouldn’t have turned it off. They want it to be used as much as possible and 9 times out of 10 the ems gets away with bad train handling. So I usually give them what they want. Last night I just wanted to get in without having to be delayed by putting a train back together.)
I think it’s because all they (ems) take into account is speed. They don’t take into account the terrain they are traversing. In this, Trip Optimizer is worse because it ‘plans’ the trip and then runs the train to that plan. If it plans on going over the top of a hill at 27 mph, it will go over the top at 27 mph. Even if it has to back off the throttle or even go into dynamics to do it.
LEADE
Do the EMS systems take into account where the DPU is located in the 15K foot trains and where the hog backs are in relation to the DPU.
I get the feeling that the longer the train and the more varied the gradients encountered the more deficient the EMS software actions are.
Have YOU seen or heard of any of the EMS system designers/programmers riding trains to observe how well or poorly their programming is actually woking in the field? I have the sneeking feeling that their algorithms were designed and encoded before PSR sized trains became the norm. Software anticipating 9-10K foot trains would always be deficient with a 15K foot or larger train has to be hancled. Despite being able to dial in the actual length of the train, is that length figure actually being acted upon in view of the terrain condition that you are operating upon?
Jeff, if given the choice, would most engineers draw a bye on these systems entirely?
Tree and Jeff,
Thanks. Very helpful insight.