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Re: The Davis blog lives!

Postby Typewriters » Sat Feb 01, 2014 11:17 am

I saw the request too, and I actually have a copy of that instruction on the way here, Bright Star! Hopefully we can figure out more about the introduction date, but I don't think we'll narrow it too much further.

Allen - CHEC picks up rotational speed of the turbocharger rotor, using a probe that sticks into the intake area with its tip right near the nose piece of the rotor on the air intake side. Two magnets on the rotor nosepiece transfer signal to the probe. For turbos built for, or modified for, CHEC excitation but which aren't being used in a CHEC equipped locomotive there's a blanking plate to insert where the probe is mounted. This allows a higher degree of interchangeability.

I'll have to read through the GE instruction to fully answer your questions, Allen, but let me just slip in a note here. It's really up to each manufacturer of equipment of any type to determine what, analytically, falls inside of any designatory envelope. So we might say in guessing that "CHEC excitation" includes wheelslip control as is called out in your request for information, but wheelslip generally doesn't fall fully under "excitation control" in old GE's. For example, there's no interface at all on the U25 except that the wheel slip detection / correction system can energize the ORS solenoid on the governor to reduce excitation by moving the load regulator wiper arm toward minimum field position. (There's also the more important air system interface that triggers the slip suppression valve and if slip continues the sanders.) That really only involves the governor and has nothing to do with any of the equipment that generates the field for the main generator other than the fact that the variable resistance of the load regulator is in the circuit between the exciter and the generator. My point here only is to say that I'll have to read GE's actual "stuff" to determine how best to answer your question. I already have the details on the older equipment - the two variations during the U25, the 300 Hz system for the U30, the later 400 Hz system for the U33. Using those materials I can bounce the CHEC excitation off to see the differences. Of course -- the most obvious difference is the use of a turbocharger rotor speed input to excitation control in order to infer the upper limit of excitation level (as I now understand it) as compared previously to using an intake manifold pressure signal to limit fuel injection and/or excitation (interfaced with the engine governor and not the electric /electronic control system, by way of manipulation of the load regulator wiper arm.)

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Re: The Davis blog lives!

Postby Allen Hazen » Sat Feb 01, 2014 7:41 pm

Many thanks! The bit about the magnets and the speed probe is… neat! Turbocharger rpm is, I take it, WAY too high to make any mechanical link to a tachometer practical, but exploiting electromagnetic phenomena provides a work-around for that.
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