I just got a Burny DNC 2.8 and...

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19 Feb 2022 01:59 #235303 by PCW
"All that aside, in the end, after a TON of testing with both circuits, and now months of experience with both circuits, we found that there is no benefit to THCAD-Ohmic (yes, I know it is "less parts"). Sure, it "works", and it's an alternative, etc. But I can't see a good reason to spend the extra money, to add the extra complication (I am not talking part count), and frustration necessary to make it work. A quick search will reveal the many who struggle to make it work."

Sensing with a A-D (like the THCAD) is faster, more accurate and more flexible for setting thresholds than a relay. The fact that you have a >20:1 difference is sense current is the reason for your issues..
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19 Feb 2022 02:28 #235304 by phillc54

One thing I've noticed is that QTplasmac does not handle such an issue gracefully. I'm awake to it now. It blindly tries to lift the torch to break the circuit but if its at top of travel it can't as it tries to go out of bounds. maybe it could issue a warning if a job starts in that condition or raises an error if the ohmic sense is on and the Z axis is above probe height at the beginning of the probing sequence.


Currently when ohmic probe is detected at cycle start if should give an error message and pause wherever it is currently located. When a ohmic probe is detected during a cut it should give an error message and moves Z to the maximum limit minus 5mm.

A quick test seems to confirm that it is working correctly.
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19 Feb 2022 02:49 #235306 by rodw

Sensing with a A-D (like the THCAD) is faster, more accurate and more flexible for setting thresholds than a relay. 

Yes, my experience too. I think Tormach has similar experience.

Also in this thread it was mentioned that you must have a shield cap on your torch to do ohmic sensing. This does not apply for hypersensing.
The THCAD can handle the full brunt of the torch voltage and keep your electronics totally isolated. You just need to make sure that there is no continuity between the material and torch tip (ie not shorted in the torch tip) and  devise a way to connect your wire to the tip.

The same can't be said of a relay circuit unless the relays are rated to handle the torch voltage and amperage without burning up.

Phil, I got a number of warnings, not sure exactly what they were.

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19 Feb 2022 03:06 #235308 by phillc54

Sensing with a A-D (like the THCAD) is faster, more accurate and more flexible for setting thresholds than a relay.

 
Yes, my experience too. I think Tormach has similar experience.


I halscoped the SSR that I used for relay ohmic and for both the on and off cycles the state was changed in the next servo thread so it is fast enough.
The Z height plots after probing showed that the repeatability was similar to "hypersensing".
I have been using the relay ohmic for around six months without issue.

Also in this thread it was mentioned that you must have a shield cap on your torch to do ohmic sensing. This does not apply for hypersensing.

I also use relay ohmic directly via the tip because my finecut tip protrudes past the shield.

Phil, I got a number of warnings, not sure exactly what they were.

Me either. :)

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19 Mar 2024 15:39 #296329 by Amin646
Hi Javier,

I'm Amin from Malaysia,

Are you still using this Burny 2.8?

I have an issue with the board. there are two capacitors that burnt.
I just want to check the capacitor 11C and 12C farad value.

Thank you.

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06 May 2024 14:24 #299947 by tovarna
Hi Amin646. Sorry but we did not keep the board when we bought it.

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