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tommylight wrote:

It is usually like that, no interest for a while, then all of the sudden several people gunning for them.
 

maybe you were right, the 7i80HD-16 is sold and shipped.
but i still have the THCAD-10 if anybody needs it.

i have a couple used Mesa boards i don't need, on my store website:
www.tjfhome.net/shop/index.php?route=pro...age=en-gb&path=66_68
i assume i set Paypal up right (USA shipping only)... if not, it won't go through, i guess. never had a purchase from my site yet to test it.
I have laid eyes on the 7i80HD-16, but the THCAD-10 i have not looked for yet, but know where it is.

7i76e_7i76x1_Dpl.bit is the firmware needed for a 7I76E and multiple THCADs

The load resistor for Ohmic sensing determines the sense current
I would not use higher than 25K

Note the if you use a lower value you need to make sure that you do not exceed
the resistors power rating with the open circuit plasma voltage.

Next I want to add ohmic sensing. With a Thad. 

I have downloaded the Firmware files from mesa. There are many files in the hostmot2 folder but have no idea which file I need to flash unto the 7i76E mesa board. What is the file name?

other question is about the serial resistor between positive and Thcad recommended is 390k but in one of the threads 25k is recommended can I freely experiment with resistors? Or does it need a high value to protect the Thcad?

You remember the episode lol, I was the one who bought thcad, and I had them held up in customs. Thank you very much for doing your best to get the plates to me.

Bit of an overdue update ....

Electronics cabinet has come a long way and know looks like mostly respextable.

With THCAD for ohmic sensing installed
 

I setup ohmic sensing on shielded and unshielded consumables. As I was not able to easily source a machine shield for the PTM80 torch I got a gouging shield, mount it in the lathe and turned the end down so there as 0.5mm gap back to the nozzle.  I did a similar approach to the hand torch standoff.  I had to make a mandrel to mount it on and clamp with a hose clamp. But once that was done turning it down was easy.
 

 

Next I made a "fence" on X0 (X is my long axis compared to the YY one).  This was done using 3adjustable triangles which i then aligned using a DTI.  Accurate to within 0.02mm over the whole travel.
 

Final update is some work I have been doing to enhance the YY axis travel.  My machine had been 610 x 1240mm on YYX config.  This allowed for indexing full 2400x1200 sheets through the machine even though I did  not have room for a machine of that size (hence the fence).  But I wanted to try and improce on the YY travel. I have figured out how to get it to 700mm.  Stage 1 gets me to 690mm and these new over travel flags support that extended travel.
 

 

Finally the machine making parts for the machine:


Cheers - J.

 

RDA wrote:

tommylight wrote:

I do not have any torch with shield, so i can not test although i do have 2 of THCAD for now.

 
I assume you mean that the tip ”sticks out” from the torch? You could always wire the sensing between the tip and work.

I have my 30XP setup like that but I use a cheap solid state relay rather than a THCAD.

RDA wrote:

If you have an HF start plasma, the HF is created between tip and electrode, you might still not believe me but anyways.
There could be some HF in the tip so keep that in mind.

Yes, that is the reason i never advise using such torches with ohmic.
And all the plasma sources i have are HF/HV start ones.
I am sure i can cobble something together to avoid the high voltage but not worth it, i like my THCAD's not crispy
Oh, i do have a Hypertherm MAX 43 that has blow back start but i have no consumables for it, despite ordering them several times.

tommylight wrote:

I do not have any torch with shield, so i can not test although i do have 2 of THCAD for now.

 

I assume you mean that the tip ”sticks out” from the torch? You could always wire the sensing between the tip and work.

I do not have any torch with shield, so i can not test although i do have 2 of THCAD for now.
I have to go pick up a Hypertherm 3070 as i do have it's torch and cables in my shop, but the transformer was to big to fit in a Skoda SuperB!

Tommy, We use a 24k 5W resistor as suggested by PCW a long time ago.
You need to calibrate the adjustable voltage on the power supply to be 24 volts.
And you need to monitor the ohmic voltage when configuring it and ensure the ohmic threshold is above the off voltage when the torch is wet.
Initially, Steve had this set too low even though it worked for me.
I was going to ask Steve to try a threshold of 24.9 volts to see how reliable it is as an experiment. I have always seen a full 24 volts on contact.
There are so many advantages of using a THCAD for Ohmic sensing, it would be good if a few like minded people could experiment further.
 

In regards to Ohmic triggering, did anyone try to add a resistor in parallel to THCAD input?
That should raise the current required to trigger, and might improve usability a lot.
A 220 ohm 5W should be a nice value to try, it raises the reuqired current to roughly 120mA, instead of uA. Should be more than enough to eliminate water induced triggering.
470 ohm will be under 50mA, if that proves to be problematic on dirty and rusted sheets, although i doubt it.

SteveatSteelCut wrote:

increasing the ohmic threshold to 23.5 seems to have solved this issue for me.
After the nozzle got wet from the watertable the ohmic voltage was showing at above 22volts.

Great news. All it took was a little tuning. Perhaps the settings that worked for me were not appropriate for a default setting. Also, many may have forgotten that the reason why the pulse torch feature was added to Plasmac was to get air flow running before the first pierce to keep water off the material on the initial probe. This was added for islander261 who adopted plasmac during the early development days. Islander261 also contributed the original ohmic relay circuit detailed here linuxcnc.org/docs/stable/html/plasma/pla...r.html#ohmic-sensing

@snowgoer, thanks for the refresher. Its been a long time since we did all the experimentation on THCAD ohmic. There are many people using it sucesfully including James in New Zealand, Joey in Ireland, Santiago in Portugal  to name just a few recent users. I can't help but think making the same change Steve did would have solved your problem. There is enough data on the forum that proves the voltage caused by a water induced short is lower than full contact. Your video shows instant failure when probing starts so the threshold is clearly too low. We need to set the threshold high enough to be above the wet voltage. 

 

SteveatSteelCut wrote:

Yes it is usable.
When it let's me use ohmic probing it is working great.
It's a lot faster than the float switch, doesn't put pressure on any adjustments, and it doesn't push the material down. It seems like a much more accurate measure for pierce height.

Deleting the var file was a placebo. When you receive that error, it's because the ohmic probe tripped prior to reaching probe height. Generally speaking, this is due to either the torch being wet, a piece of slag completing the circuit, or in the case of my Powermax 65XP, when I used the THCAD Ohmic sensing the voltage used to accumulate for no apparent reason (though I was told this is impossible (by those without a Hypertherm)). After months of testing, I did away with THCAD ohmic sensing in favor of a few diodes, relays, and a resistor or two which sounds complicated but is much cheaper and easier to implement and has required 0 dickering, I can find a post with the diagram if you're interested. You can decrease the sensitivity of the THCAD ohmic by adding resistor(s), but ultimately I still had the issue of the accumulating voltage. You can plot this and see if it might be your issue using HALSCOPE. After a few cuts my voltage would hover near the trip voltage even when the torch wasn't wet.

PCW wrote:

Funny aside: We had to change the name of the THCAD on a invoice for a
shipment to Brazil as anything with the letters THC gets held up in customs...

I wonder why, they should check for stuff containing THC LEAVING the country!