Thankyou: PrimeCut60 +Mesa 7i76_THCAD-10+Linuxcnc PlasmaC Axis Success

Thanks to all on these forums for helping in getting my machine up and running. Today we finally got the THC going. On the PrimeCut 60 machine I originally used the internal 300K ohm résistance pins to feed the THCAD-10. This worked sort of, but took me a while to realize that even though I had frequency changing, Arc Volts readout changing, ..... that I was hitting a 40V limit for the Full Scale voltage range. So THC did nothing as the actual voltage during cutting were around 92v. Rather than increase (external to the PrimeCut60) the resistance for a larger FSV, I opted to use their internal divider pins. Pins 11 and 12 on the CNC port provide 1/16 arc voltage. This output has about a 10K ohm resistance. That solved the issues and all is well. After recalculating..... the voltage scale is 0.000432, voltage offset 3803, divide ratio 1.1, full scale voltage 11. Measured arc voltages are about 8V lifted torch and about 6v while cutting. GUI display tracks an external voltmeter. One last question:
???? It would be nice to have a second or third digit on the arc voltage display. Let me know please is this is feasible. I can see the Up/Down THC indicators change but not much changes to the rather constant 6V GUI when cutting.
Thanks again,
Dennis

kramerda wrote: One last question:
???? It would be nice to have a second or third digit on the arc voltage display. Let me know please is this is feasible. I can see the Up/Down THC indicators change but not much changes to the rather constant 6V GUI when cutting.

It does 3 digits (probably more) by default.

It seems to me like you missed the fact that you are now using a 16:1 voltage divider. It seems like you are displaying divided voltage rather than re-correcting for that fact.

Here is a handy calculator: Scale and Offset calculator .

You would enter your Max Voltage frequency, 0v frequency, jumper setting for the frequency, THCAD model, and lastly type in your divider ratio (16 for you).

Hope that helps.

sorry for my confusion - yes the gui works as prescribed for arc volts - I was in error using the formula in the plasma guide based on added series resistance for scaling not the voltage divider option. Using your 'calculator' with a divide ration of 16, GUI shows reading < 2 volts arc off, about 124 volts arc on, which matches an actual volt meter measurement X16 power unit.
Just to double check - from HAL Config Watch, on the encoder pin of the 7i76, Frequency is around 4000 arc off and 23,200 with arc on (about 1/5 of full frequency range).
Obviously no need for decimal places in my 3 digit reading now. Thanks for catching this.

kramerda wrote: sorry for my confusion - yes the gui works as prescribed for arc volts - I was in error using the formula in the plasma guide based on added series resistance for scaling not the voltage divider option. Using your 'calculator' with a divide ration of 16, GUI shows reading < 2 volts arc off, about 124 volts arc on, which matches an actual volt meter measurement X16 power unit.
Just to double check - from HAL Config Watch, on the encoder pin of the 7i76, Frequency is around 4000 arc off and 23,200 with arc on (about 1/5 of full frequency range).
Obviously no need for decimal places in my 3 digit reading now. Thanks for catching this.

Are you using a THCAD-300?

Using THCAD-10
Now I'm trying to tune things - i.e. Using Cut Voltage (as measured around 80) not auto volts, with same settings as without THC for pierce ht., cut height, delay (.2) etc. Weird things like movement stops about 10mm into a straight cut. ???? No velocity lock or errors reported???

I think that when you are starting out you should use Auto Volts.

You can only use Cut Voltage if you are 100% sure that the displayed arc voltage is exactly the same as the measured arc voltage and also that the cut chart is correct for that machine.

When you have a control system capable of Auto Volts, I do not see a reason why you would want to go back to specifying the cut voltage. In my experience different temperatures and different steels that are suppose to be the same cut differently depending on certain environmental and quality conditions.

With my old CandCNC system I had to specify the cut volts and I was always having problems. I have NEVER had a cut voltage issue withe PlasmaC, and I do ALOT of cutting!.

Just my opinion.

Hi Phil.....I did try the auto mode but either my delays were off and it never really settled down. I also don't have ohmic sending so when my float is used, the variable due to material flex or a bounce contributes to a bigger error in starting height. With a fixed cut voltage target based on lots of earlier non THC cutting I'm confident in the voltage target and false starts seem to have been solved. That said ohmic is on the horizon as I work with other materials and thicknesses. i.e. I've seen differences in dross between hot and cold rolled steel all else being the same. Thankyou for ur continued guidance.