THCAD

phillc54 wrote:

I am looking at some document changes and I want to mention some practical options for users.

At the price point, nothing can compare to the THCAD. A friend costed some of the components on it and could not work out how PCW did it for USD $69!

You keep coming back to encoder inputs. There must be other methods to get an analog signal into linuxcnc.

You might be able to use the GPIO on a Raspberry .

But we are not talking about done for you modules and you come back to the THCAD as the only viable option unless you are using ethercat. But if you go that way its not something for the hobbyist and you will want deep pockets.

And they definitely won't need your instructions.....

The real issue for THC is that for best performance you need an isolated sensor
this is because you want to measure the voltage between the work and the torch
The work connection is theoretically at ground potential but may differ by a few volts
DC and worse may have significant continuous HF noise and large spikes when the arc
is established. (due the the finite inductance of the ground path and the ability of the arc to generate very fast current steps)

In addition to measurement considerations, you really don't want the very dirty plasma source ground connected to the control system ground, creating a ground loop.

This is not saying you can not make a simple isolated measurement system, heck, you could use a 555 timer rigged up as a V-F converter and a low cost OPTO and have a
working isolated measurement system for less than $1.00. (though you still need an
isolated power supply and this is a bit tricky since this isolated supply may provide
a path for HF currents into the control system)