Which Controller?

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Sailor - 31 Dec 2007 21:22 GMT

The discussion referred to was on a somewhat different topic - this
one was more specific - that of which controller might be
recommended?
I too would love to know just exactly what is fed back in terms of a
signal in order to achieve what?

Are we discussing a power source which sets a desired voltage level
but compares the actual instantaneous output with the desired or is it
some measure of a pulsed variable frequency square wave which is
regulated by the reflected component voltage?

I thought that all my years in electronic control engineering left
little room for non knowledge but I am definitely lacking in this
area!

Regards

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Mark Thornton - 31 Dec 2007 21:51 GMT

> The discussion referred to was on a somewhat different topic - this
> one was more specific - that of which controller might be
[quoted text clipped - 10 lines]
> little room for non knowledge but I am definitely lacking in this
> area!

Feedback controllers use a pulse output (the power is switched on and
off). While the power is off the motor is still turning and acts as a
generator producing a voltage proportional to its speed (BEMF). A feed
back controller measures this voltage and adjusts the pulse duty cycle
(ratio of on to off time) to maintain a constant speed.

In analog systems the pulse frequency is quite low (and audible) as the
signal has to travel some distance from the controller to the loco. In a
digital system a BEMF controller is inside the loco, resulting in quite
short wire runs, which allows a much higher frequency to be used. This
frequency can be outside the audible range.

Mark Thornton

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Model Forum / General / Railroads / December 2007

Which Controller?