Mike Keitz schrieb:
>
> On Mon, 10 Aug 1998 19:04:16 -0400 Chris Eddy <ceddy@NB.NET> writes:
> >Stefan..
>
> >The back EMF on a DC motor is a very good indication of speed.
>
> Of a permanent magnet motor it is.  But the original poster was asking
> about a series-wound motor.  With these, the magnetic field strength is
> not constant like with PM.  It depends on the field current and any
> residual magnetization of the field core.  If you were to measure the
> motor (field and armature since they are in series) current and > armature vol
tage, the speed could be determined something like this:

The article in the electronic world describes howto ... with a
DC-Motor.

Well ... it suggests following Idea to me:

When switching PWM of,  still supplying the field-coil ( with less
current ) and use "generated" Voltage as Speed indicator.

what kind of disadvantages do I have to expect ?

still more suggestions ?

Kind regards

        Stefan Sczekalla-Waldschmidt
        ssw@oikossw.de