Re: CNC Plasma

>
> It seems that any torch should be able to use the auto height
> control. A simple op-amp used as a comparitor to keep the current

in

> a set proportional band style control would be easy to implement.
> any current measurement, feed back or feed forward, from most any
> part of the torch, from the wall to the tip should offer a place to
> monitor current used.
>
> (notice generous use of 'seems' and 'should')
>
>
> Dave

It is my understanding (possibly incorrect) that the thing that
varies with the torch height is the voltage. I suspect that the
circuity in the plasma cutter attempts to maintain a more or less
constant current by adjusting its voltage (notice I said "suspect"
most manufacturers are pretty vague about HOW their units work) The
circuits I have seen use a voltage divider in the main plasma cabinet
to sample a portion of the output voltage (50:1). It then is simple
to compare that against a variable logic level reference voltage and
for a given type and thickness of material keep the torch height
constant. The problem comes in where the initial strike distance for
the arc and the initial starting voltage (until you get burn through)
is different than what is needed for a optimum cut.

The guys at Rutex (www.rutex.com) have some mechanical as well as
electronic torch height kits. More importantly they have documents
that describe the processes involved and the solutions.