Re: Plasma Voltage Servo

Mariss and Tom, In the "real world" the theory has been being used
for some time in commercial applications, it just controls the
direction of a dc moter by reversing polarity rather than using a
stepper.
Also Mariss, I wonder how hard it would be to add a feature of the
axis being raised all the way up when the voltage drops to zero, then
lowers again to the previous height when the plasma is activated
again. this would be to give more safety room between cuts to avoid
tip ups, etc. from damaging the plasma cutter. I would assume this
would need to be handled in the software. What would happen if I were
to wire up both this circuit and a computer output to the same gecko
drive? In theory, they would be not be sending commands at the same
time.
Thanks,
Dale



--- In CAD_CAM_EDM_DRO@y..., "mariss92705" <mariss92705@y...>
wrote:

> Hi,
>
> The circuit I drew up has a 30Hz bandwidth; any signal frequency
> component above that value will average to its DC value. The

trimpot

> would allow you to adjust the torch to any height between 70 and

140V.

>
> It would be useful for me to see a 'scope picture of what the

actual

> voltage looks like in operation. You mention a sawtooth waveform.
> What is the amplitude and frequency? What is desirable to servo to?
> Since I lack any practical knowledge on this subject, I would need
> this info to make a sensible comment.
>
> Mariss
>
>
>
> --- In CAD_CAM_EDM_DRO@y..., "ths992001" <thscarince@h...> wrote:
> > WRT plasma arc voltage vs torch to work distance:
> >
> > Once I read an Amercan Welding Society paper on this subject.
> > According to this article, the arc voltage wavform is something

of

> a
> > sawtooth. At the beginning of the cycle the arch starts at the

top

> > of the material at a certain voltage. As it rapidly burns its

way

> > down the face of the cut, the voltage ramps up to some peak at

the

> > bottom surface of the material. At this point, the arc jumps

back

> to
> > the top surface and the cycle begins again.
> >
> > This means that the average arc voltage may not be an ideal
> > indication of the torch height in all conditions (material,
> > thickness, feed rate, amps, target height...). The author

proposed

> > using the "peak low" (the base of the sawtooth) voltage as this
> best
> > represents the actual height under varying conditions.
> >
> > Got an extra op amp for an averaging peak (or valley, in this

case)

> > detector Mariss? Seriously, his design will probably do the

trick

> > just fine in the real world.
> >
> > Tom Scarince