Plasma and Ethercat?

As far as the slug dropping or crossing the kerf, the arc voltage can spike, but it will never pass the limitiations of the plasma it self. The plasma has a maximum power it can output . Example the a maxpro200 can output 33kW, if you cut with 200A, the voltage can go only so high before the plasma hits its limit.

Umm no.

That assumes that the plasma output has no series inductance or parallel capacitance. This is far from the case. The problem is that the arc starts and stops at nanosecond rates, generating voltage and current spikes far in excess of the plasma power supply ratings.

The AMAX-4817 might be a better choice than beckhoff as its a seperate analog Input module with stronger isolation. Add an AMAX I/O module and its all you would need
www.advantech.com/en-au/products/cf678dc...63-97e4-27475418e86f

Nice one, have not seen that before. It's quite expensive though? And maybe a bit overkill with 8 x 16-bit ADC (for a single plasma). Would be nice to find a mixed signal one with something like16 I/O and few ADC and few PWM. Maybe one day I will have time to make one.

Maybe I misunderstand something here. I assumed we were talking about work to electrode voltage and further than that, the divided one.

So apart from the ignition or ohmic sensing the cutting itself is nothing dramatic, well at least to me its not. What do you mean by the "nanosecond" rates?

So purely from work to electrode voltage point of view the plasma does not "instantaneously" turn on the cutting power. The current is ramped up in the tens or hundreds ms time frame. This is all depending on the torch/consumable design. Same goes when you stop cutting, the arc is "extinguished" in a controlled manner.

Typically the IGBT's switch around 50kHZ, I have seen some a bit higher, some a bit lower but all that I came across switch under 100kHZ. The arc itself I see as a purely resistive load.

Now for crossing a kerf, the arc lags behind for a few degrees, depending on speed and material. When you cross a kerf, the top of the arc will touch the material before the bottom and makes the arc "jump" over the kerf. This extends the arc to a certain degree and makes the arc voltage higher (longer arc). Something similar happens when the center slug drops and the arc follows the slug for a moment, extending the arc.

Anyone can test their plasma's max output voltage during cutting by incrementing the cut height and seeing when the arc goes off. A plasma rated for example 200V cannot sustain an arc that requires 300V.

I will try to remember to scope the kerf crossing and hole cutting next time I have a chance, maybe not this year but for sure start of 25.

I'm eager to learn new things and it would be great if someone corrects me if I am wrong.

When an arc stops or starts, the connection is broken or established in a fraction of a nanosecond.
This generates a large current transient what starting and because the plasma source has substantial output
inductance, it causes a large voltage transient when the connection is broken.

This is the reason relay contacts typically have arc suppression devices, not just to preserve the contacts
but to suppress the massive EMI generated by the near instantaneous current interruption.

Sorry not sure what you mean, but when the arc is turned on or off its done in a controlled way. The ”whole” idea is to stabileze the molten hafnium, tungsten or whatever the electrode material is.

I think we are tallking about different things, sorry about that.