THCAD selection including ohmic sensing
- Uthayne
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05 Apr 2020 20:12 - 05 Apr 2020 21:47 #162793
by Uthayne
So I've flashed my 5i25 with the firmware you provided in this post and have verified that I do in fact have three "A" pins
I've got the THCAD-5 for ohmic sensing wired into what was encoder B+/-. When I start up linuxcnc it cannot find any other encoder pins. Here's a ss of what's available when viewed from my router config.
Following along with the documentation in the primer, it says hm2_7i76e.0.encoder.02.velocity. I'm trying to parallel this with a hm2_5i25.0.encoder.01(or 02).velocity . Obviously I'm missing something about how the 2 additional A channels are connected.
EDIT: Figured it out, forgot to enable the 2nd encoder in the machine hal file. "loadrt hm2_pci config=" num_encoders=2..."
Now it's running
Replied by Uthayne on topic THCAD selection including ohmic sensing
Yes the 5i25 --> 7I76 config is wired the same as the 7I96 and 7I76E configs:
The encoder connector has 3 encoders with only 'A' channels so instead of
the standard 1 encoder with A,B,IDX you have 3 encoders with only 'A' pins
So I've flashed my 5i25 with the firmware you provided in this post and have verified that I do in fact have three "A" pins
I've got the THCAD-5 for ohmic sensing wired into what was encoder B+/-. When I start up linuxcnc it cannot find any other encoder pins. Here's a ss of what's available when viewed from my router config.
Following along with the documentation in the primer, it says hm2_7i76e.0.encoder.02.velocity. I'm trying to parallel this with a hm2_5i25.0.encoder.01(or 02).velocity . Obviously I'm missing something about how the 2 additional A channels are connected.
EDIT: Figured it out, forgot to enable the 2nd encoder in the machine hal file. "loadrt hm2_pci config=" num_encoders=2..."
Now it's running
Last edit: 05 Apr 2020 21:47 by Uthayne.
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- grijalvap
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04 Nov 2024 17:45 - 04 Nov 2024 17:47 #313765
by grijalvap
Replied by grijalvap on topic THCAD selection including ohmic sensing
PhillC54.
This is an interesting aproach, basically we are muxing the THCAD input, may be some processing power can be saved using only one encoder.
I re-draw your schematic just to make it more readable, I think this will require some changes to PlasmaC componet.
This is an interesting aproach, basically we are muxing the THCAD input, may be some processing power can be saved using only one encoder.
I re-draw your schematic just to make it more readable, I think this will require some changes to PlasmaC componet.
Attachments:
Last edit: 04 Nov 2024 17:47 by grijalvap.
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- rodw
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04 Nov 2024 19:12 #313773
by rodw
Replied by rodw on topic THCAD selection including ohmic sensing
I don't think the contractor is required as the hypersensing circuit is impervious to high voltage.
Currently when the voltage exceeds 24 volts, the component is seeing an arc voltage and it never breaks now. The thcad always sees a bit past the full scale and the 390k resistor sets full scale to 23.5 volts anyway.
So what if you mux the THCAD calibration instead? once it is > 24 volts, recalibrate it to be fullscale 200 or 300 volts?
Currently when the voltage exceeds 24 volts, the component is seeing an arc voltage and it never breaks now. The thcad always sees a bit past the full scale and the 390k resistor sets full scale to 23.5 volts anyway.
So what if you mux the THCAD calibration instead? once it is > 24 volts, recalibrate it to be fullscale 200 or 300 volts?
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- grijalvap
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04 Nov 2024 21:15 #313785
by grijalvap
Replied by grijalvap on topic THCAD selection including ohmic sensing
Yes will need 2 factors one for the arc voltage and one for the Hypersensing, also the QtplasmaC need to change from THC to Hypersensing Mode.
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- rodw
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04 Nov 2024 21:50 #313786
by rodw
Replied by rodw on topic THCAD selection including ohmic sensing
The mode can be automatically selected based on voltage sensed. You know at startup its not cutting, start in hypersensing mode but if the voltage exceeds 24 volts, calibrate to THC range and stay there until it falls to say < 5 volts, go back to hypersensing mode.
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- roland206
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19 Mar 2025 12:28 #324288
by roland206
Replied by roland206 on topic THCAD selection including ohmic sensing
I have a fundamental problem to follow the discusions on ohmic and/or hypersensing.
It would be great if someone can point to the mistake in my thinking.
All of the pilot arc torch heads I know have an electrode connected to the plasma voltage (negative) and a shield connected to the workpeace.
With a HF pulse on the plasma voltage (relative to the shield / workpeace) the arc is started.
This means that the torch head tip (shield) which is electrically connected to the workpeace can't be used for ohmic sensing because it's alrerady connected to the workpeace.
What's wrong ?
It would be great if someone can point to the mistake in my thinking.
All of the pilot arc torch heads I know have an electrode connected to the plasma voltage (negative) and a shield connected to the workpeace.
With a HF pulse on the plasma voltage (relative to the shield / workpeace) the arc is started.
This means that the torch head tip (shield) which is electrically connected to the workpeace can't be used for ohmic sensing because it's alrerady connected to the workpeace.
What's wrong ?
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- rodw
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19 Mar 2025 20:17 #324313
by rodw
Replied by rodw on topic THCAD selection including ohmic sensing
except you are confused between the torch tip and the shield. Some torches (Hypertherm, and Thermal Dynamcs for example) Have a seperate shield that is not shorted to the workpiece.
So in general if you have an exposed tip you can't do ohmic sensing because its shorted to the material.
Some machines (ie Swiftcut) lower a seperate probe and ohmic probe off that. This can be done fairly easily in QTplasmac with a pneumatic cylinder as all the required signals are there.
So in general if you have an exposed tip you can't do ohmic sensing because its shorted to the material.
Some machines (ie Swiftcut) lower a seperate probe and ohmic probe off that. This can be done fairly easily in QTplasmac with a pneumatic cylinder as all the required signals are there.
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- tommylight
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19 Mar 2025 20:41 #324318
by tommylight
Nozzle is not shield.
Nozzle can not be connected to workpiece, although in some "high voltage pilot arc" plasma's it may seems so when measuring, transformers n stuff...
Nozzle is connected to high voltage/high frequency when pilot is on
Shield is an extra layer not connected to anything internally, usually there is a retaining ring and a wire connected to it leading to ohmic sensing parts of the electronics, or not used at all electrically, just for protecting the air stream on multiple gas systems.
Pilot arc is between electrode and shield.
Cutting is between electrode (negative as you already stated) and material/table/clamp that is positive.
During cutting nozzle must be "off or electrically detached" otherwise it would burn to a crisp in 1-2 seconds.
Replied by tommylight on topic THCAD selection including ohmic sensing
Oh no!!!!!All of the pilot arc torch heads I know have an electrode connected to the plasma voltage (negative) and a shield connected to the workpeace.
Nozzle is not shield.
Nozzle can not be connected to workpiece, although in some "high voltage pilot arc" plasma's it may seems so when measuring, transformers n stuff...
Nozzle is connected to high voltage/high frequency when pilot is on
Shield is an extra layer not connected to anything internally, usually there is a retaining ring and a wire connected to it leading to ohmic sensing parts of the electronics, or not used at all electrically, just for protecting the air stream on multiple gas systems.
Pilot arc is between electrode and shield.
Cutting is between electrode (negative as you already stated) and material/table/clamp that is positive.
During cutting nozzle must be "off or electrically detached" otherwise it would burn to a crisp in 1-2 seconds.
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- roland206
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20 Mar 2025 07:27 #324344
by roland206
Replied by roland206 on topic THCAD selection including ohmic sensing
rodw and tommylight thanks for your answers. Although I have to admit I am stil confused.
I bought a cheap pilot arc plasma to play arround. It has an explicit connection between the tip and the workpiece. Ohmic sensing can't be done. Right?
Anyhow, I build a CNC Plasma and I am looking for a suitable frontend (plasma and torch) my wishlist includes:
1 plasma cutter (hopefully < $1000) with a european distributor
2 Ohmic or hypersensing (willing and able to build homemade electronics if I know what)
3 THC with a THCAD-x (best case with an avaibale THCAD-300)
Can someone propose a setup ?
I bought a cheap pilot arc plasma to play arround. It has an explicit connection between the tip and the workpiece. Ohmic sensing can't be done. Right?
Anyhow, I build a CNC Plasma and I am looking for a suitable frontend (plasma and torch) my wishlist includes:
1 plasma cutter (hopefully < $1000) with a european distributor
2 Ohmic or hypersensing (willing and able to build homemade electronics if I know what)
3 THC with a THCAD-x (best case with an avaibale THCAD-300)
Can someone propose a setup ?
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20 Mar 2025 11:53 #324353
by tommylight
Replied by tommylight on topic THCAD selection including ohmic sensing
Stahlwerk
www.stahlwerk-schweissgeraete.de/Plasmaschneider-CUT
Good quality and cheaper than china, vertical machine torch is 40E in Germany, with 5 meter cable is 90E, bought both.
Mind the pilot arc, there are some without it so do not get those, it is easy just look for a red knob on the bottom front and usually it is written in spec info.
www.stahlwerk-schweissgeraete.de/Plasmaschneider-CUT
Good quality and cheaper than china, vertical machine torch is 40E in Germany, with 5 meter cable is 90E, bought both.
Mind the pilot arc, there are some without it so do not get those, it is easy just look for a red knob on the bottom front and usually it is written in spec info.
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