It seems AC-traction-motor diesels don’t use ammeters-- instead the computer screen (?) shows the locomotive’s current tractive effort. What exactly does this mean?
Do the front and rear couplers have gauges (or whatever) that measure those forces directly, and the computer subtracts them?
If so, the engine will show 8000 lb less TE on a 2% upgrade than it does at the same speed on the level. Do they try to “correct” the reading somehow?
Can the engineer push a button and get total TE for the MU consist?
I don’t know exactly what is driving them, but I do know there’s no load cell or strain gauge involved It’s an algorithm based on actual HP and actual speed. I was around during discussions when the builders were talking about what should replace the load ammeter for the AC units but I can’t remember which builder came up with the idea. At that time, all the details were yet to be worked out. I don’t think there are any that trainline, tho’ that would be a good thing to have. The goal wasn’t to give the engineer a 1% precsion measurement tool, but to give him an idea of the dynamics of loading other than the seat of his pants.
Sounds ingenious and simple enough, since actual speed is easily available, and HP isn’t all that hard to compute, given voltage and current which are probably easily availabe too (I hope!).
That said, aircraft turboprop and turboshaft engines almost all have torquemeters (some older piston engines of the giant economy size class, too). A few – a very few – of these are based on a load cell, but most of them use a dismayingly ingenious system involving measuring the torsion of one of the shafts in the gearbox. No strain gauges needed, just a couple of magnetic pickups… Details on request!
We can go into the computer screen and see what each individual traction motor is putting down to the rail. If an engine doesn’t seem to be loading the way it should, that’s one of the things I’m looking for.