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The Everlast has a voltage divider builtin. Why reinvent the wheel?
The only issue is that with a THCAD, the internal resistors are seen by the thcad so what the THCAD sees is distorted.
Set yout THCAD to use a 10 volt range, no resistor and use the 16:1 range on the everlast.
The divider seen will be 24:1 (not 16:1). This will give you a full scale reading of 240 volts.
Just calibrate your software to 24:1 instead of 16:1
Do not ground the HV side of the thcad as that will allow a mains 50/60 Hz ripple show up.
You must use a RFI filter on the control panel mains power entry. 

Ah, that makes a lot more sense on why I was confused. Thanks for clearing that up.

The 2.4M resistor should be on the negative input (the plasma voltage)
Ground is positive on plasma machines.

The division ratio can be specified in the setup (/32 suggested)

Hello,

  I have an Everlast 82i with a 7i96s and a THCAD-2. I'm very new to linuxcnc but I'm slowly catching on and enjoying learning everything. I have a few questions about the THC that I haven't been able to find the answers to:

So, a lot of what I have read says the best way to get voltage from an everlast is to connect directly to the ground and the torch inside the machine, which I have done. I have a little bit of confusion on which side goes where on the THCAD-2. My thought is that I go from the ground clamp side to a HV resistor 2.4m and then to the Negative side of the analog in on the THCAD-2. Then just connect the side from the torch to the positive. Is this correct? 

Second question is if I leave the frequency divide ratio jumper on the 1 if I am using the raw voltage through the resistor?

Finally I do see that if I'm using the raw voltage I should've purchased the THCAD-300. At the time of my purchase I thought I would be using the 50:1 divided voltage. Right now I am waiting on the resistor to run the raw voltage and just wondering if the 50:1 is worth trying and the main question that has already kept me from trying is what would I put the jumper for the frequency divide ratio on? 

Thanks for any help.

Set your scaling so that 24 volts is a bit under 10 volts eg. say 9.5 volts. That way the component will know that 24v or greater is actually the torch cutting (that will do no harm)

Thanks Tommy !

Yes, you can use THCAD10 instead of THCAD5, just set the scaling and offsets correctly for it.

Hi all,

We are looking at adding ohmic sensing to our plasma table. The plasma cutting primer shows the use of a THCAD-5, but is it possible to use a THCAD-10 (we have a spare one of them as we build our controller with a THCAD-10) ?

Cheers, Peter

P.S. By the way, our plasma table with QtPlasmaC works well, cuts everything from 1.6mm to 25mm or thicker with a Hypertherm 125. Haven't had any major hiccups for a long time, except for the computer getting a bit tired !

yeah it was an early design.  i built big before i learned to think big.  with what i use it for, its actually not the aluminum extrusions that are my weak point.  99% of my deflection comes from the delrin vgroove wheels and the fact that the mounting point on the z axis is only about 50mm wide.  combine that with a high z axis which is always a weak point and it was a recipe for disaster.  its replacement will be using aluminum t-slot for the gantry, but 80x160mm heavy beam.  according to the the specs, i am looking at < 0.1mm deflection with a load of 100kg.  considering it is only for wood and acrylic and occasionally aluminum clad, that is well within my tolerance levels.  


this z was an aftermarket unit that i came across and used it as an upgrade for the original one that was using a tr8*4 with a delrin nut, but that was way undersized for a spindle that heavy.  this one has a lot of travel, but i just went out and got some better pics of it, and i was mistaken.  it is acually a 1605 ballscrew with a pair of 20mm rods.  granted a 1605 is slower than a tr8, but i gain in resolution and it of course runs so much smoother than the tr8.  originally i had intended to recycle the parts of this machine to create a 'lathe' which was basically a 4 axis with a super short y and horizontal z that i could use to do gun stocks and furniture turnings.  but then i decided i could do more with a plasma so the lathe got back burnered until i get better situated.  

i know that this z is definitely overkill for a plasma, but i have it and that will keep me from having to buy another one.  actually, it would have been tolerable for a router had it only had another set of bearings on the rails and could mount a bigger plate on it.  in addition, i am going to recycle the aluminum for the gantry which is again overkill, but i have it and its already the size i plan on using as well as the aluminum rails.  so far i have picked up 1500/1000 hgr20 rails to use instead of those stupid v wheels.  i have broke so many of those its truly pathetic.  i would buy them in bulk just to keep them on hand and never again.  well, they were actually great when i first got started, but as i have gotten better and more ambitious, its time to stop beating a dead horse.  i got my thcad2 from jt the other day, and of course all the electronics will be swapped over.  i may need to order some power supplies because its been a while since ive been inside of the control box and i cant remember if the ones in there are 24v or 48v.  i know one machine is 24 and the other 48, but i just cant remember which one is which.  my aluminum also got here the week before last, so i can start cutting at least some of the plates.  the gantry plates are going to be 10mm and 6.35mm for the x carriage.  now all i am waiting on are getting my steel parts cut and my pulleys for the reduction coming in from china.  then we seriously start to build!

linuxcnc.org/docs/devel/html/plasma/qtpl...lasma:parameters-tab

Scroll down to "Configuration -THC"

Probably not exactly what you're looking for.  I can get my parameters from my machine (65XP), but I think they are the default settings.  A lot of the tuning parameters depend on the speed of the Z axis, etc.  

But as another place to start, I would verify that the voltage readings are not noisy/don't have interference issues, etc.  When I was doing mine, I opened up the halscope and continually plotted the output from the THCAD.  I was able to see that having the ground connected to the shield was causing all sorts of noise, which calmed down then I removed the shield connection.  I also then hooked up a DC power supply to it and verified that it showed the correct voltage value.  I cant remember I either used a 9v or a 24v power supply I had laying around etc.  Lastly, I did some looking at the voltage under a long torch pulse, etc.  Erroneous noise in this system can cause you a lot of grief.  The GUI updates arent fast enough to really show everything, so it's best to use halscope to plot the voltage under the aforementioned conditions, as well as cut conditions  on thicker material (with the THC disabled), etc.  

Hopefully that helps give you some places to look before you start turning the knobs

Hey Guys,

   Is there a manual somewhere that defines the THC parameters for QTPlasmac? Just something that specifies what parameter does what. I'm having some serrated looking cuts on thinner metals (14-18 ga) due to what I believe is the torch moving up and down to quick. I have a 7i96S with THCAD-10 using 45XP and my settings are pretty much the same as I've seen others post:

50 Sample counts
1.00V Sample Threshold
1.00V Threshold
10 Speed (PID-P)
90% VAD Threshold
500V/Sec Void slope
0 PID-I
0 PID-D

I tried going down to 65% VAD threshold as suggested in another post but did not see a change. Also, I've been pausing the cut, making the change, saving, and resuming the cut to look for differences. I'm assuming the save parameters button takes place without having to restart QTPlasmaC.
 

Hello, this is a reply to beauxnez post from few days ago.

"hello, is it possible to make an nvem card work with qtplasmac?"

 The answer is yes, another friend and myself are right at the end of a plasma machine build, were using a ec500 as the controller and it works fantastic with qtplasmac. I will say the THC is the only thing that we don't have working at the moment. On ours the plasma output is just on output 1, torch is either on or off. It goes from the board and turns a relay on and off which is the actual switch. For ours we have a Everlast 82i for the plasma cutter which has a 50:1 voltage divider, that gives us a 0 - 5v output for the torch voltage but from my understanding there aren't any analog inputs on these boards. A analog to digital converter may be a option. I'm not sure what the output of the mesa THCAD boards looks like, there may be a way to use one of those. I'm just getting started on trying to setup a arduino to take the analog voltage, work some magic on it, and send the info to linuxcnc that way using modbus.  The downside I'm seeing to this approach is effectively I'm setting up a second controller to take just one analog input, and I'll have to put a switch inline on the ethernet cables.  The upside is another controller and analog input, so now I can dream up more features to add to this machine (During our build process it started as a basic machine, we now have individual limit switches for every axis, probing, etc. , touchscreen interface, and so on..) 

Hello Beauxnez, firstly could I ask you what your native language is? I speak Spanish and some English, it might help you to know this in case you want to communicate with me in another way.
The problem becomes technical because it is a hardware design problem that these boards present, these boards were not designed to attach any encoder to the input pins and even less so for an encoder that varies signals A and B quickly.
The THCAD modules, for example, would have to be connected to these boards through an instance of the QDC module or encoder module software (the latter I don't know how fast it can count) I advise you to take a look at the LinuxCNC documentation more specifically 1 -Plasma Cutting Primer for LinuxCNC Users and 2-PlasmaC User Guide, then in this forum there is a lot of information about THCAD and MESA boards.
The development of the QDC module has been a challenge at least for me as I had to code it, thanks to Scott for his ideas on how to do it, after all that work I carried out functional tests and found many tracking errors for closed loop configurations due to because the integrated circuits that protect the inputs (optocouplers) do not switch fast enough and the signal that reaches the microprocessor is quite distorted.
Having said all the above, I could tell you two things:

1- Can the NVEM/EC300/EC500 boards be used to connect THCAD encoders, etc.?
Yes you can do it.
2- Can this connection be made directly to the inputs of these boards?
Yes, but it would be very slow, this to follow an axis (max velocity700mm/min encoder 1000ppr or 4000 counts), I imagine that THCAD also has problems.

Another thing I can tell you is that this is a project that is being developed so don't expect to connect everything and have it work the first time, greetings

tommylight

yes I think that on this side it will not be too difficult for me, the most complicated thing will be to modify the ini file, hal.......

Torch ON = digital output (through relay for safety)
ARC OK = digital in , optional as it can also be derived from arc voltage quite reliably
ARC Voltage = encoder input in counter/velocity mode, directly from Mesa THCAD if it can handle 5V, use a resistor for 3.3V input.