Re: Plasma Voltage Servo

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