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Wrong polarity on THCAD input, or wiring not correct from THCAD to Mesa 7i96S.
Open the "halshow" and check if the encoder is counting correctly.

       

 

# ---ARC VOLTAGE ENCODER---
net plasmac:arc-voltage-in <= [HMOT](CARD0).encoder.00.velocity
setp [HMOT](CARD0).encoder.00.counter-mode 1
setp [HMOT](CARD0).encoder.00.filter 1
setp [HMOT](CARD0).encoder.00.scale -1

this is how it look like in hal. my board is 7i96s

Once your encoder velocity is responding correctly, 
enter your thcad calibration data into the qtplasmac gui as per the instructions.

the light on the board  shows your wiring to the thcad is correct.
Next step is to confirm that it is being read correctly by the mesa encoder.
open halshow and find the encoder you are using. Does the velocity pin ove at all or does it stay static.

If its static, then this is probably missing from your hal file.I thought it was added by pncconf

Screenshot when cutting, not cutting, and settings page

     
Hi, I have a new plasma machine which I bought recently that has CNC ports and has 1:1 ratio divider and am using 1M ohms at each leg of + and - of the plasma machine which will give you 21:1 ratio but the THC doesn't move up and down but I can see the THCAD-10 LED light blinking fast when cutting and blink slowly when not cutting. i have attach my logs.

Hello, CNC Friends
So I spent a lot of money the last coupler of days. I have purchased a lot of stuff for a cnc table. hopefully I wasn't to cheap....I probably was but the price of things have gone way up .  So I went with the LattePanda. probably a bad choice, I was waiting for experts to join in but did not hear nothing. If you have better options for around the same price let me know, I could always return this. My original plan was with rack and pinion but after reading some of   tommylight   posts I decided to go with cog belt. I would like to use aluminum but the price is so high I will be making it all steel. My gantry with be made from 1.5"x4" tubing 1/8" thick. not as light as I would like it but it will have to do. My width of gantry will be around 62" with around 48" usable cutting with and around 60" cutting length. I will be using nema 23 motors 425oz for the x and y and 178oz for the z. I will ride on linear bearings HGR15s. For the Z axis i will use a double 10" draw slide as  tommylight  suggests and I will use a 8mm acme thread. I ordered the Mesa 7i96 board with THCAD2 boards. I am not sure if the THCAD2 would be the best but I contacted Mesa and that's what they recommended for the hypertherm powermax 85. So after looking, my plasma cutter doesn't have the built in voltage divider, so I will have to purchase that also to get it set up.  So I have screen recording of my 3d drawing.
<iframe width="560" height="315" src="" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" allowfullscreen>

yes, plasmac has had a lot of changes.
I have attached my larest component and a stand alone hal file which you can just load from your ini file

I had a bit of a mission getting ohmic sensing working.  I sort of rushed and just followed the examples I found, but none worked for me, so had to make my own hal connections.  Just thought I would post them here in case it helps someone in the future.  I am using LinuxCNC 2.8, Mesa 7i76e with THCAD-10 for ohmic wired to 7i76e encoder B pins.  Base setup made with Pcncconf, then with the plasmac configurator.  Using plasmac in axis.

Thee original post for this topic shows:
The manual pages say (manpages.ubuntu.com/manpages/kinetic/man9/ohmic.9.html):
The plasma cnc primer says (linuxcnc.org/docs/html/plasma/plasma-cnc..._with_a_mesa_thcad_5):
But what I had to use was:
So it looks like some pin names and debounce pins have changed across versions.

Thanks.

I did try with and without the earth wire but no difference. The top THCAD is the arc voltage one, lower is for ohmic.

I cant get to the machine right now to try hal show (after I work out what that is!), but in the hal scope list, there was only one encoder 00 listed.

I do have the *pl.bit files, downloaded them tonight. So will install tomorrow (after I work out how!).

Try removing the green earth wire from the THCAD. I have seen an AC ripple with it connected.
Also, if you go through halshow, and look at your mesa pins, if you have more than one encoder you have the right bit file installed (file name ends in *pl.bit if you need to install it.)

This is my first post so go easy on me please!

I have built a plasma table and finally up to the part of configuring Plasmac.  This is my first time using LinuxCNC so still getting used to how it all ties together.  So far so good though, the machine moves nicely and I have got as far as completing Plasmac configuration.

I am stuck on a little problem where the arc voltage is unstable.  In fact, it is oscillating like crazy in the HAL scope.  My configuration is:
 - Mesa 7i76e
 - THCAD 10 wired F0+/- pins to ENCA+/- pins.  Analog side connected to PowerMax pins 5/6. Freq/32, unipolar mode

What I tried:
 - Bridging the analog input terminals to ensure it was not oscillating on the input.  No change.
 - Changed the frequency divider jumper.  The amplitude of the oscillation in hal scope changes but not the frequency, so is sort of working!
 - Reading lots of form posts!

I did read tonight that there is a special firmware for the 7i76e for using dual frequency inputs (I have two THCAD, one for ohmic).  I need to work out if I have the right firmware in it.  I think I did install it a few years ago when I got it, but honestly don't remember (cant access the machine tonight).  Is special firmware even required to get the one frequency input going for a start? 

I have attached some pictures and files, please let me know if anything else is needed.  Thankyou in advance.
 

Etkoehn wrote:

Question. Why is the Mesa 7i96s a better option then the 7c81

Maybe I'm biased but the pi has questionable performance for linuxcnc although the new 2.9.1 image seems OK.
If you have a 7i96s you can move to a PC if the pi does not cut it.
The mesa cards are designed to work with the THCAD2 for reading torch voltage, the 7c81 probably can too but is the performance the same? I don't know.
I think stepgen performance may be better on the 7i96s
The Mesa 7i96s has additional firmware  to allow up to 3 encoder A's so you can add an extra THCAD for ohmic sensing (if it can be supported on your torch).

But the most important feature is redundancy as you are not tied to the Pi