Another plasma component...

Stefan, also look at the other alternative voltage divider settings that you board can be set to. The default 30:1 on my Thermal Dynamics is near perfect (300 volt full scale) . On a pierce it goes out of range but PCW says this is fine and is a valid way of getting more accuracy as you use more of the fullscale when cutting.

rodw wrote: Stefan, also look at the other alternative voltage divider settings that you board can be set to. The default 30:1 on my Thermal Dynamics is near perfect (300 volt full scale) . On a pierce it goes out of range but PCW says this is fine and is a valid way of getting more accuracy as you use more of the fullscale when cutting.

Just checked my Hypertherm and there is a 30:1 scale on the board so I will set it to that.

phillc54 wrote: I pushed another update:
- remove duplicated ini file entry - doesn't really affect anything, just a tidy up
- change resolution for arc voltage input scaling and offset
GUI files changed are:
configs/sim/axis/plasmac/native/plasmac_axis.py
configs/sim/axis/plasmac/gladevcp/plasmac_panel.py
configs/sim/gmoccapy/plasmac/plasmac_config.py
configs/sim/gmoccapy/plasmac/plasmac_panel.py

rodw wrote:
The on screen scaling does not work because of enforced upper and lower limits in the config screen as I can't enter an offset of 3659.375 (0-100 enforced)

Also the maths in my earlier post says the frequency counts per volt is 83.73 and you have to input the reciprocal of this which is 0.011943151 which is not logical. So I would recommend that the maths be changed to do the reciprocal stuff internally and also remove the enforced range on the scale. If that was the case I think it would work well with some explanation in the docs.

I have fixed the upper and lower limits, hopefully by enough to cover everything.
I don't want to change too much as I don't want the component itself to be dependent on any particular hardware.

I rigged up a 7i76e with a TCAD connected to the encoder input and two batteries for testing:
- run LinuxCNC
- open halshow and watch plasmac.arc-voltage-in and plasmac.arc-voltage-out
- set arc-voltage-scale to 1
- set arc-voltage-offset to the value read from plasmac.arc-voltage-in
- measure battery voltage
- connect battery to THCAD input
- set arc-voltage-scale to battery-voltage / plasmac.arc-voltage-out
could probably fine tune further but it was good enough for the purpose of the exercise.
My values were:
arc-voltage-offset = -3805
arc-voltage-scale = -0.000406

Cheers, Phill.

In my machine.hal I don’t have arc-voltage-offset I have somthing listed as scale and filter. Where are you finding the actual arc voltage ofset settings? I did find settings in the mymachine_config.cfg file.

thefabricator03 wrote: Just checked my Hypertherm and there is a 30:1 scale on the board so I will set it to that.

I thought I saw they had different options. Good find. I think that will yield a better outcome as you will have a higher count per volt which will give better resolution.

@JTk, sorry I can't help there as I'm not in front of a machine.

'03

Ok, my advice is going to be contrary to others. The documents are correct.

1. The docs method of calculating the required offset and scale values does work. 1st, just use a 9V battery and your THCad card without the plasma CPC port connected. This will get your THCad card and display on the same page, the changes you will make going forward will be less than 2 orders of magnitude (powers of 10). The displayed voltage will be noisy. Look at the velocity output of the encoder component ( it will be noisy but will not change with changes to the scale or offset) while you are changing the offset and scaling values in the GUI. When you can get the displayed voltage to jump from 0 to the batteries voltage when you connect it you will be good, again this will be a little noisy.

2. I will assume you do not have a high voltage regulated power supply or don't want to mess with lethal voltages. Connect your THCad to your plasma power supply through the divided voltage on the CPC port. Connect a DVM with a 200VDC scale between your work piece and the torch electrode ( if you don't like this then put your DVM across the THCad input). Do a series of line cuts and record the voltage displayed on the gui and the voltage on the DVM If you have the DVM connected across the work piece and the torch electrode the ratio of the two voltages should be very close to the value that you need to adjust the scale to, it most likely will not be exact because of component tolerances. You will need to do this several times adjusting your offset and scale factors each time. You will get very close in the end. You can do all this by calculation (as I have done) and adjust the offset and scale to make the displayed value equal the measured value. Remember that you will need to change the offset value every time you change the scale value (check 0 between trials).

Sorry, I know this is clear as mud. If you can post the max and min values that came with your THCad we can at least get you within an order of magnitude of the correct offset and scale values.

I know this sounds crazy but having the perfect values really doesn't matter that much because you always want to do a series of line cuts to verify the book settings to your equipment anyway. I realize you run a job shop and need to be able to just plug in book cutting values to keep setup time to a minimum. This just means more time spent upfront getting your scaling and offset values close. You will still need to figure out a global offset between your measured cut values and the book ones. No one has made either measurement with the same calibrated equipment (unless you buy so much HT equipment they sent a rep to your shop).

John

In my machine.hal I don’t have arc-voltage-offset I have somthing listed as scale and filter. Where are you finding the actual arc voltage ofset settings? I did find settings in the mymachine_config.cfg file.

If you are using the plasmac gmoccapy config they are on the Plasma Config tab.

Cheers, Phill.