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Hu Gemox,A plasma cutter generates a huge amount of electrical noise, so all signals should be galvanically isolated.For this reason, I would not recommend the Mesa 7i97. Instead, I would use a 7i83 for the analog outputs, since it provides galvanic isolation from the rest of the control system.To determine the complete hardware configuration, the machine’s existing electrical schematics would need to be reviewed.A THCAD2, or an equivalent interface, is necessary to measure the plasma arc voltage. This voltage measurement is used by the torch height control to maintain the correct distance between the torch and the plate.I would not recommend using a stepper motor for the Z axis, as it may not be able to achieve the required speed.How are you planning to generate the G-code?

Hi, I'm building a plasma table (QtPlasmaC, THCAD-300) around a 7I80HD-T and would like to run the ST8_PLASMA config — 8 stepgens plus the two encoder inputs is exactly the right fit for this machine.

I see PIN_ST8_PLASMA_72.vhd ships in the 7i80hdt.zip hostmot2 source, but there's no prebuilt 7i80hdt_st8_plasma.bin among the stock configs, looks like it was only ever built for the Spartan 7I80HD.

Any chance of getting a Trion build of that config a test. If it's easier to point me at the Efinity project setup to build it myself, that works too.

Thanks!

tommylight wrote:

That would be redundant as LinuxCNC is the motion controller.
In short:
-buy a Mesa 7i96S and a THCAD

I was wondering if I should buy direclty the 7i95T as it has all needed i/o and encoder feedbacks for up to 6 axis.
What you suggest ?

I plan to set up a separate head in the future for plasma and who knows maybe even a spindle for drilling.

Thanks Heaps Stefan and Rod I just received the THCads and am about to draw up my Transition drawings from masso to linuxcnc.
Have either of you used Qelectrotech for drawing before as I am about to give it a go. Supposedly there are libraries for Mesa boards available.

qplasmac is a complicated GUI. Normally, it is set up assuming a mesa card using pncconf. 
I think I  would try running up pncconf and build a rough config for a 7i96s. You just need a template for all of the plasma specific pins so pick a mesa pin to use for each. don't worry about scaling the axes etc
Then I would copy the pin layout to your hal file and make sure any plasma  specific stuff in the ini file is copied to your ini file, then replace the Mesa pins with your lcec pins. 

With linuxcnc running open another window and type halcmcd show pin lcec should list all your Ethercat pins and you could probably filter out just the inputs or outputs

Also reviewing recent plasmac configs on the forum may help
I have one but its a very complex one with lots of custom stuff so would not recommend following it github.com/rodw-au/showstopper/tree/master 

In the qtplasmac GUI, there is a couple of fields for THCAD parameters. Set the offset to 0 and scale to 1 and use the actual torch volts. You may need to use mult2 to calculate the full scale voltage. Alternatively, use the scaling field which might be better.

Good luck
 

tommylight wrote:

Yes you should leave them out, as noted above the only usable way for DMM drives is in Position mode as they have a delay in position signal outputs.
Also the encoder input will be used for THCAD if you want plasma.

By "leave them out" I meant to not connect them at all. But then how the linuxcnc will know where it is at certain point ? I will probably loose a part of precision with not connecting the encoders feedback.

tommylight wrote:

Yes there is, Mesa 7i85 or 7i85S should have 4 encoder inputs.

I see this card has a DB25 connector to connect it to the computer I suppose, or does it gets connected to the
7i96s ? Sorry for dumb questions.
Is the DMM Dyn4 encoder output supported by the Mesa 7i85 ?

tommylight wrote:

No, not per se, but LinuxCNC can be programmed as you need it, so a simple G04 P1800 will make the machine wait for 30 minutes at the first cut to preheat the material.
Same for outputs and solenoids, everything can be automated and even add a side panel with settings and buttons and stuff.

OK for this, I will take a look better on it once I install it in a virtual machine.

saxa wrote:

I see the board has only one input for the encoder feedback. But I have 3 drives, so should I leave the encoders
signals from the drive to linuxcnc out ?

Yes you should leave them out, as noted above the only usable way for DMM drives is in Position mode as they have a delay in position signal outputs.
Also the encoder input will be used for THCAD if you want plasma.

saxa wrote:

Or there is a way to connect all 3 encoders to the board ?

Yes there is, Mesa 7i85 or 7i85S should have 4 encoder inputs.

saxa wrote:

Also has LinuxCNC some settings to make the preheat , and open the various gasses vales at ceartain time already in or should I be doing this from zero up ?

No, not per se, but LinuxCNC can be programmed as you need it, so a simple G04 P1800 will make the machine wait for 30 minutes at the first cut to preheat the material.
Same for outputs and solenoids, everything can be automated and even add a side panel with settings and buttons and stuff.

In an Ethercat world, I think you can use a Beckhoff 0-10 volt analog interface as it has similar over voltage specs as the THCAD. People have cracked the Hypertherm Ethercat machines here. But do use industrial Ethercat cables in a HF world

I recently bought an old plasma + oxyfuel machine to retrofit and resell. I awaits me first finishing some other projects. I plan to connect ethercat servos directly to a linuxcnc pc. I have not yet studied the serial interface for the big XPR plasma power unit that came with it. On a previous project I used mesa + THCAD, never heard any complaints from that one.

Welcome. Have a look in the ethercat section. There are a couple of stickies. There is a seperate Ethercat master application that runs on the Linuxcnc  PC and there is another driver that connects Linuxcnc to the Ethercat master which in turn talks to all your slaves. You should be able to use a Beckhoff analog input (0-10 volts) to read the divided torch voltage. Other than that, it will be similar to what Tommy described for Mesa hardware. The Beckhoff modules are rated for over voltage of 500 volts, same as the Mesa THCAD. I'm uncertain that other brands of analog inputs have this protection. I can't help with oxy.

During cutting or at idle?
-
If during cutting, check grounding, if it is shallow under ground, the ground getting dry will cause that.
If at idle, there are a lot of things that can cause that, like other machines in the shop, changing the power socket, stepping on the wiring, wiring isolation failing somewhere due to fatigue and/or strain, and if in Europe, even your neighbor installing a new air condition unit, etc etc.
A simple solution to remedy the latter, use a 0.01 to 0.022 uF (also known as 100-220nF) capacitor on the THCAD input.
I use a 0.1uF electrolytic one rated for 50V but that might lower the reading speed, although for me it works perfectly fast till 6m/m, i have not tested it faster.

Hey when i first built my table my thc would read only + or - 1-2 volts over time its gotten worse and worse now it reads + or - 8 volts or so. Any idea whats causing this? Its running off raw arc voltage with a bunch of resistors in series. 

saxa wrote:

Now recently I have visited some exhibition and I saw today most of industrial things are on EtherCAT.

Yes, it does seem so...

saxa wrote:

My plan is to make linuxcnc act as an master node, and send signals to the motion controller which will then through some adapters transform the signal to pulse/dir and send to the drives.

That would be redundant as LinuxCNC is the motion controller.
In short:
-buy a Mesa 7i96S and a THCAD
-a used Entrprise PC
-A network cable
-Wire, install LinuxCNC, start wiring drives and motors
-those drives will have to be set in position mode, hence 7i96S
-yeah, wiring, you will need very good quality shielded cables for everything as cables that long will collect a lot of interference, not very important for oxy cutting, but a mist for plasma cutting.
-....well, that is it.

Most people on this forum in your position have ditched CommandCNC and moved to QTplasmac with a Mesa THCAD to measure torch voltage and let Linuxcnc manage the THC function internally.

I still have machines running LinuxCNC (named EMC2 back then) on Ubuntu 8.04, and 10.04 and...
It is all dependent on how you look at things, but i would definitely not discard parallel port as it is extremely reliable, extremely cheap be it as a old PC for 20-50$ or add on card for 10-15$, does not need a BOB (although it is recommended for new users as it adds a bit of safety for wiring).
Overall, when you realize you can have a fully functioning and very reliable machine control for under 50$,that will control whatever contraption you can think of by adding some cheap drives and motors found on old photocopiers, the possibilities rise sky high.
So no, parallel port and 32bit are not obsolete, nor will they be any time soon, they are the perfect setup form learning CNC on a very low budget.
Go out, scavenge some motors and belts and linear rods, build something, then build something else even better, then...
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Personally i use Mesa cards for everything and by now i have installed over 70 or 80 or 100 (probably more but i have no clue of the exact number), but still sometimes i build machines using a parallel port, even plasma machines that produce huge amounts of interference and THCAD wired directly to parallel port with no BOB, using HF start plasma sources work perfectly but do require very strict wiring and shielding and grounding.
Visit the "show your stuff" section, find topics started by me, plenty of pictures and videos of machines i have built and/or retrofitted, and some other stuff...