THCAD selection including ohmic sensing

I don't think the contractor is required as the hypersensing circuit is impervious to high voltage.
Currently when the voltage exceeds 24 volts, the component is seeing an arc voltage and it never breaks now. The thcad always sees a bit past the full scale and the 390k resistor sets full scale to 23.5 volts anyway.

So what if you mux the  THCAD calibration instead? once it is > 24 volts, recalibrate it to be fullscale 200 or 300 volts?

Yes will need 2 factors one for the arc voltage and one for the Hypersensing, also the QtplasmaC need to change from THC to Hypersensing Mode.
 

The mode can be automatically selected based on voltage sensed. You know at startup its not cutting, start in hypersensing mode but if the voltage exceeds 24 volts, calibrate to THC range and stay there until it falls to say < 5 volts, go back to hypersensing mode.

I have a fundamental problem to follow the discusions on ohmic and/or hypersensing.
It would be great if someone can point to the mistake in my thinking.
All of the pilot arc torch heads I know have an electrode connected to the plasma voltage (negative) and a shield connected to the workpeace.
With a HF pulse on the plasma voltage (relative to the shield / workpeace) the arc is started.
This means that the torch head tip (shield) which is electrically connected to the workpeace can't be used for ohmic sensing because it's alrerady connected to the workpeace.
What's wrong ?

except you are confused between the torch tip and the shield. Some torches (Hypertherm, and Thermal Dynamcs for example) Have a seperate shield that is not shorted to the workpiece.

So in general if you have an exposed tip you can't do ohmic sensing because its shorted to the material.

Some machines (ie Swiftcut) lower a seperate probe and ohmic probe off that. This can be done fairly easily in QTplasmac with a pneumatic cylinder as all the required signals are there.

roland206 wrote:

All of the pilot arc torch heads I know have an electrode connected to the plasma voltage (negative) and a shield connected to the workpeace.

Oh no!!!!!
Nozzle is not shield.
Nozzle can not be connected to workpiece, although in some "high voltage pilot arc" plasma's it may seems so when measuring, transformers n stuff...
Nozzle is connected to high voltage/high frequency when pilot is on
Shield is an extra layer not connected to anything internally, usually there is a retaining ring and a wire connected to it leading to ohmic sensing parts of the electronics, or not used at all electrically, just for protecting the air stream on multiple gas systems.
Pilot arc is between electrode and shield.
Cutting is between electrode (negative as you already stated) and material/table/clamp that is positive.
During cutting nozzle must be "off or electrically detached" otherwise it would burn to a crisp in 1-2 seconds.