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List of available THCs?

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FeralCutter
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List of available THCs?

Postby FeralCutter » Wed Jun 07, 2017 3:51 pm

As the title says, anyone have a list of THC manufacturers?

attila0216
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Re: List of available THCs?

Postby attila0216 » Fri Jun 16, 2017 5:33 pm

The cheapest Proma Thc 150 and Proma SD. They do good job, simple installation but not too many features. And threre is Candcnc DTHCIV. I had this before, but because I'm from Europe support is zero. And i have to tell too expensive and i had too much problem with it. What i have now is Neuron lite. This is far the most professional i have ever used. And support is 5 star. Razordance is another option. One more i know is Minithc and Thc300.

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Re: List of available THCs?

Postby DanM » Mon Aug 21, 2017 6:41 pm

How do you like the neuron and how do you get in contact with them. Their website is messed up right now and I’m trying to figure out if their system is compatible with Teknic Servo and drive system.

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Re: List of available THCs?

Postby jimcolt » Tue Aug 22, 2017 10:29 am

The best THC's are those that are built as an additional axis integrated on the same CNC and software that operates the whole cnc machine. It is necessary that the THC intimately communicates with the x and y axis in order to control real time cutting height to eliminate diving, collisions or other height issues that affect plasma cut quality and consumable life. If you want the lowest cost...then the low cost standalone height controls will certainly work better than no height control, but do not expect identical performance or results. Jim Colt Hypertherm

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Re: List of available THCs?

Postby DanM » Tue Aug 22, 2017 3:17 pm

Hey Jim have you checked out the Neuon any thoughts on it, the pro version?

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Re: List of available THCs?

Postby tcaudle » Tue Aug 22, 2017 3:52 pm

It's a bit like "show me a list of all the cars I can buy with 2 doors"

THC's are in one of two categories:
1, Totally Stand Alone (they do everything including fire the torch, touch-off, delays, rapid height , and piercing with little or no control from the motion software.
2. Control software Dependent THC (they have to have a specific type of control software to run.)
Within that 2nd category you have units that are tightly integrated with the control software and bring features that are inneractive with the toolpath. and others that just send basic commands to the software . MACH3 has hooks for THC (external THC just sends UP and DOWN "jog" commands ) Some of the least expensive ones use the internal MACH3 THC logic. The game changed when MACH3 was declared obsolete (about 2 years ago) and unsupported from the authors , and they announced MACH4 that is a totally different application requiring different drivers and different THC. MACH4 is still under development.

So to really quantify a model you have to first define the control software and the OS platform (windows or LINUX) That will narrow your list of choices down from from dozens to a few. Some of the units are more than just a THC and also have the control interface (BoB) or even the entire control including motors.

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Re: List of available THCs?

Postby Rodw » Tue Aug 22, 2017 4:48 pm

jimcolt wrote:The best THC's are those that are built as an additional axis integrated on the same CNC and software that operates the whole cnc machine. It is necessary that the THC intimately communicates with the x and y axis in order to control real time cutting height to eliminate diving, collisions or other height issues that affect plasma cut quality and consumable life. Jim Colt Hypertherm


Jim, this is now possible with LinuxCNC using an experimental development branch. I'm the first to implement it last weekend. There's still a bit of tuning to do to suit my hardware but the very first cut was well within the limits of +-5 v you have quoted previously using parameters determined using a LinuxCNC software simulation of my hardware. Currently, I'm seeing a +2-4 v range from the commanded voltage. This has not been an easy journey because as you know, the devil is in the detail, implementing corner height lock, kerf crossing and initial voltage sampling.

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Re: List of available THCs?

Postby robertspark » Sun Aug 27, 2017 3:44 am

As a customer, the neuron is good imho.
Andrew goes by the handle of shad on several forums.
Having used mach3, mach4 and uccnc, Look toward uccnc + neuron for a better plasma system. I don't have experience at Linux so am unable to compare hence my viewpoint is confined to a windows experience.

Like cars everyone thinks one or the other is better, but most settle on what you can afford plus a bit the sales rep can convince out of you...

I have owned (and still have)
Proma 150 THC http://proma-elektronika.com/index.php/ ... ct-thc-150

Mini THC (contact Denis goes by handle po-mo) http://minithc.com

Neuron lite (contact Andrew, goes by the handle shad) http://neuroncnc.com/products/lite
The neuron will work with a few different motion softwares (mach3, mach4 uccnc)

I was offered the tmc3in1, but turned it down as I'm afraid ( but wish it were not true ) the development of the warp9 Ethernet smooth stepper is way too slow at integrating mach4 functionality (still have the usbss and the ess, unfortunately only the ess will provide THC functionality)
http://texasmicrocircuits.com
https://cnc4pc.com/tmc3in1-torch-motion ... -3in1.html
(USA based, been around a long time, one of the early manufacturers along with sound logic / Bob Campbell for THC's)

There is also:
https://www.candcnc.com
(been around a long time, Tom Caudle well supports this forum with responses and they have developed since ~2002 with what was probably the original THC's for the "hobby" / commercial market, do a lot of really detailed and good technical manuals, USA based)

And,
http://razordance.co.uk/THC.htm
(UK based, you'll find Sterling on the Mach3 forum as well as a few other forums from time to time)

An arduino based one:
https://www.pricecnc.com
(Ireland based, seems to be taking off in the UK with R-tech offering their units, not sure that Arduino is up to the resolution or sample rates required at faster cutting <200"/min on thin metals with 45Amp + plasma cutters)

An DIY arduino one:
https://github.com/regeg/ArdunioTHC
(not sure about the sample rates / resolution for THC at faster cutting thin metals)

To be fair + comprehensive we should also probably mention Hypertherms own THC's although I don't think they are priced for the hobby / semi-commecial market that all of these other products are generally ranged for, but if you want top of the range performance and cost wise with huge R&D + experiance + backup support then they are probably for you.
https://www.hypertherm.com/en-US/hypert ... ensor-thc/
Last edited by robertspark on Mon Aug 28, 2017 6:45 am, edited 2 times in total.

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Re: List of available THCs?

Postby robertspark » Sun Aug 27, 2017 6:30 am

As others have said previous, there are generally two groups, ones that read the voltage and send "up" and "down" signals to the parallel port or motion controller and those that control the z axis directly.

When it comes to THC bottom line you want fast response and accurate voltage tracking.

This means you really will want (or end up with) one of those that control the z axis directly, especially when your feedrate rises to the 200inch per min and above.... BUT you will also need / require a fast acting z axis which means looking at around 2-3 turns per inch and a lightweight carriage for acceleration

You also will want a motion controller / motion control software that can control THC without affecting motion (mcodes which are activated in synchronisation with motion (mach3 = m10px+m11px, mach4 = m62+m63, uccnc m10+m11, or m205m206 or any of the other m sycron functions.... Uccnc is way ahead of the others in my opinion

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Re: List of available THCs?

Postby Rodw » Sun Aug 27, 2017 6:49 am

robertspark wrote:You also will want a motion controller / motion control software that can control THC without affecting motion (mcodes which are activated in synchronisation with motion (mach3 = m10px+m11px, mach4 = m62+m63, uccnc m10+m11, or m205m206 or any of the other m sycron functions.... Uccnc is way ahead of the others in my opinion


Don't forget LinuxCNC also supports this through M64/M65 and M67/M68 and that CandCNC gave it a vote of confidence when they migrated from Mach to LinuxCNC. For the last few years, I've been OS agnostic but I have to say there are fewer and fewer reasons to choose Windows in a cloud based environment and CNC isn't one of them.

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Re: List of available THCs?

Postby robertspark » Sun Aug 27, 2017 8:02 am

To be fair, I did say...

robertspark wrote:I don't have experience at Linux so am unable to compare hence my viewpoint is confined to a windows experience.


Windows is just what most people seem familiar with (I've tried for 20 years on and off with linux in many flavours but just could not get my head around it, and considering I manage ok at learning VB, cypress VB, C , C++, c# lua and arduino variants coming from windows I've always found linux difficult.

The issue with linuxcnc seems to also be motion controllers or lack thereoff and compatibility (but that is just my own personal impression of when in the last 18 months I looked at something better than mach3 and considered many options, and motion controllers)

In my opinion if you are choosing a motion controlller and software then look at not just "product support" (the bit that gets you up and running) but "product developement" which is a bit more all encompasing and should not be hardware based as once you've spent you're cash on hardware you dont want to be updating it too often but it is helpful if whoever you are dealing with can provide frequent software updates and listen to users generaly via a polling sytem and debate .... there is zero point in providing a feature for one user... you may as well see how many of your subsribers it affect and provide an update to the advantage of many but maybe educate or steer that user in the right direction of others as to why the other way may be seen as "better" by the majority

[we digress from the original topic.....]

another manufacturer is PureLogic.... problem is their website is largely in Russian, although they do provide a large degree of their manuals in english. an you will need their motion controller to use their THC (which I did consider 2 years + ago) which works with MAch3. Having just looked on their website they too appear to have their own motion controller software (puremotion) ( but know zero about it)
https://purelogic.ru/news1/zapuwen_v_pr ... mt1plcmt2/
https://purelogic.ru/files/downloads/do ... CM_eng.pdf

There is a capacitive torch height controller -CHC-200D / 300 or 400 (all very similar)
http://www.robosan.com.tr/pdfs/CHC-200E%20MANUAL.pdf
http://www.soldgreat.com/user_manual/Laser_CHC_300.pdf
(although I supect that this may be better at oxy/acetylene than plasma...)

At this point the manufacturer manuals get a bit thin on information as to how they work, and what you need to make them work (each to their own and you'll more than likley be wanting something else soon too)

another manufacturer appears to be StarCut [India] although a manual is hard to find on the unit:
http://www.star-engineers.com/Plasma-To ... V-THC.html


Another one is the SH-HC30 which appears to be from china
http://www.startsh.com/eng/sh-hc30.html

___________________________________________

Dispite a large number of users using a proma, having owned one, I would not recommend them as the amount of control parameters is very thin for what is a complex control algorithm, and also they largely use dry contacts (relays) which are slower to respond than something a little faster (optoisolators, reed relays or high speed relays ,..... MOSFET's anything but a clunky relay really).... go with a proma and after a while you'll want something more when you begin to understand a little more. It all depends what setup you want I guess and how much you want to expend.

Note I did use the Proma THC 150 and not the "SD" variant.... although I suspect that this one i not going to be much faster and still employ relays
Proma THC 150
http://proma-elektronika.com/index.php/ ... ct-thc-150
http://proma-elektronika.com/download/PDF/thc150_en.pdf
Proma THC SD (Step & Direct output)
http://proma-elektronika.com/index.php/ ... act-thc-sd
http://proma-elektronika.com/download/PDF/thcsd_en.pdf
Last edited by robertspark on Mon Aug 28, 2017 6:25 am, edited 2 times in total.

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Re: List of available THCs?

Postby Rodw » Sun Aug 27, 2017 8:52 am

robertspark wrote:The issue with linuxcnc seems to also be motion controllers or lack thereoff and compatibility (but that is just my own personal impression of when in the last 18 months I looked at something better than mach3 and considered many options, and motion controllers)


Robert, you are missing the point. LinuxCNC IS_THE _MOTION_CONTROLLER. Unlike Mach (which I never used as it failed my user requirements analysis), LINUXCNC does it all so does not need any of the add on Motion controller boards. Having said that, it interfaces with a huge number of high end interface cards but all of the motion control is inside the LinuxCNC application.

By definition, LinuxCNC does not interface with other motion controllers like ESS becasue it IS_THE _MOTION_CONTROLLER.

Some of the control systems such as Pico Systems, Ethercat and Mesa allow you to build enormously complex systems that Mach does not even kown exist!

The basic install of LinuxCNC is so painless I was gobsmacked. I downloaded an ISO, ran the install and had a perfect working system in under an hour.

I did a similar exercise as you did before selecting LinuxCNC. Of course, I knew I had a journey in front of me as I did not know Linux that well but once the OS was installed and functional, it works like any PC so the focus quickly becomes configuring LinuxCNC itself.

For a developer who knows C, LinuxCNC is a no brainer. You can write your own components that are then installed and become part of the system with a single command "halcompile --install youraddon.comp"

An underrstanding of Python can be helpful to write command handlers for custom screens. I've used this a bit to get gcode commands to update screen parameters (like torch target voltage).

robertspark wrote:Despite a large number of users using a proma, having owned one, I would not recommend them


I tend to agree. I did consider buying one. They seem popular in Europe where they were developed. I've never used one but I know of a couple of EU plasma manufacturers that use them. There is a good LinuxCNC integration for them but I've never tried it as I wanted more functionality.

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Re: List of available THCs?

Postby robertspark » Sun Aug 27, 2017 9:36 am

With regards to linuxcnc, I think you are missing the point....

What does it run on?

A microcontroller or pc?

How does it output the signals?

Linuxcnc is just a software application ... Similar to mach3, mach4, winpc uccnc. I'll chat later I've got to drive 7hrs

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Re: List of available THCs?

Postby Rodw » Sun Aug 27, 2017 4:55 pm

Thats all right, I was sleeping while you were driving.
LinuxCNC runs on a PC. I use an ultra small form factor PC about 4" square. Some have got it running on a Raspberry but it does not have the grunt to also run a graphical IDE.

Because LinuxCNC is the motion controller, most people are using it to control the Z axis internally. That means they just need something to read the voltage. There is a THC component in the standard LInuxCNC build that people say works well. There is also an experimental development branch that has additional features embedded in the LInuxCNC core that allows you to embed THC right within the trajectory planner. Thats what I'm using.

The easiest way to read the torch voltage is with a USD $69 THCAD card from Mesa which is designed to measure voltage in a noisy plasma environment. It easiest to connect this using another Mesa board but it can be used on its own. I'm using the 7i76e which I think is ideal for stepper based plasma machines.

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Re: List of available THCs?

Postby robertspark » Mon Aug 28, 2017 4:26 am

Thanks Rodw, I learnt something new.

I looked at linuxCNC when I was looking at converting from a Warp9 Ethernet Smooth Stepper, so was looking for something pin wise compatible.
I came across this linuxCNC wiki page http://wiki.linuxcnc.org/cgi-bin/wiki.pl?HardwareDesign
Which seemed to suggest that the options were:
Parport (SPP and EPP)
PCI and PCI-Express
ISA (extremely limited availablity on new hardware)
Ethernet (new in LinuxCNC 2.7; with "uspace" realtime only)


Hence I looked at parallel port as a step backwards (back to Mach3) and did think about options to run multiple parallel port cards to increase the number of IO's.

But then kind of thought when reading that wiki page that becasue of the 1kHz loop that the speed was not really there for some of the things like THC. I was aware from reading the page that there was a the "fairly fast" loop which appears to max out at 50kHz, then you get back into the relms of motion controllers (basically external processing) of which I looked at the MESA boards as they appeared well made but the documentation kind of went over my head (kind of like when I looked at KFLOP from Dynamotion .... all looked a little too much hard work at setting up and everything was a custom setup).

I've also just reciently upgraded to a small fanless PC [probably similar to yours]
http://p.globalsources.com/IMAGES/PDT/B ... ini-PC.jpg
which has allowed for a bit of a faster setup.

In the past I always had hardware setup issues with Linux (although it's probably because like most we get use to plug & play with windows, and are not good at scratching around at setting up drivers in linux so a few of the periperals never seem to work [although Ubuntu did change a lot of that ~10 years ago (thanks to Mark Shuttleworth)].

Looking at the MESA cards again I may have another go at setting up a linux OS under dual boot / second HDD with linuxCNC and see how it pans out.
That 7i76e appears to be a good I/O board equivelent to the UC300 or SmoothStepper equivelents.
Thanks for the headsup on that and the THCAD card from MESA
http://store.mesanet.com/index.php?rout ... uct_id=290
0-10V input (for 50:1 type divided output plasma cutters)
http://store.mesanet.com/index.php?rout ... uct_id=127
0-300V input for raw voltage output plasma cutters
http://store.mesanet.com/index.php?rout ... uct_id=128

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Re: List of available THCs?

Postby robertspark » Mon Aug 28, 2017 6:18 am

One of the things to note when looking at that THCAD from MESA THC interface board is the sample rate.

Sample rate is one of the things that affects a large number of Torch Height Controllers and is one of the things that some manufacturers are not keen to publish or openly disclose.

The THCAD board has an A/D 10 bit resolution at 1kHz and 12 bit resolution at 250hz.

For a plasma cutter running at say 200"/min (~5m/min) which is not that high and probably fairly common target parameter from the plama cut manuals
1kHz sample rate is 1 sample per 5mm (0.2"), add to this a degree of filtering / averaging then the response will be slower dependant upon the final sample rate.

Also 10 bit is 1024 bits of resolution ( i.e. the THCAD either has a full scale range of 0-10v or 0-300V) which means that the sample resolution will be
10V / 1024 = 9.765625mV per Bit x 50 (50:1 voltage divider) = 0.48828125V per Bit

or 300V / 1024 = 0.29296875V per Bit

So, now you need to consider that 1V of plasma voltage variance is approximatly 1/32 - 1/64" (0.8 to 0.4 mm), but your THC's maximum sample resolution is either ~0.5V or ~0.3V [dependant upon THCAD variant], you only have either 2 or 3 bits of resolution per actual plasma torch volt you now begin to realise that you do not have may bits that you can loose with drift or ADC accuracy..... hence you should really be looking for a THC with 16 bit resolution to allow for better filtering and also a higher sample rate than 1kHz again for better filtering

I am aware that the MiniTHC and the Razordance THC have similar sample rates (not sure about the sampling resolution), Minimum hysterysis setting on the Proma 150 is +/- 1Volt (i.e. 2 volts) which when you then consider that 1/32" to 1/64" is approximilatly equivelent to 1 torch volt you now begin to consider how important resolution is given the cut height is 1/16" (you only have between 2 and 4 volts of error before a potential torch crash)

this is why I went with the Neuron [Lite / Pro are the same sample resolution and sample rate, just increased IO's for other bits like fan / Oxy/Acetylene controls].

The Neuron gives you a torch height position control with a set point resolution of +/-0.125 mm (.005") and an arc voltage control with a set point resolution of 0.25 volt.

There other bits like sample and hold, and a whole load of other settings available (andrew is very proactive and easy to discuss things with and get integrated), screenshots of the UCCNC Neuron settings are below.


There is a bit more reading here on THC other options
http://opensourceecology.org/wiki/Sensi ... Work_Piece
There is also very good information around page 6 of this manual http://candcnc.com/images/Manuals/LCTHC-Manual_REV7.pdf


_____________________
In my opinion, it is possible to improve the resolution of the THCAD by narrowing the voltage sensing range from say 0-10V to 0-5 or even 0-3V which with a 50:1 divider will be 0-250V or 0-150V (better) via changing the resistors and also offsetting the sensing voltage from zero volts upwards given plasma tends to be in the range 75 - 140V, you can now see that adding 50V offset will move the range to 50-200V when you lower the range from 0-10V to 0-3V and add in 1 Volt of offset so the range becomes 1-4V with a 50:1 divided input.
You will need to add in something like a zener diode to clip off input voltage above 200V which is not really of any use given the arc should transfer and stabalise below this and closer to the cutting height of ~ 1/16" above the work
Attachments
2017-08-28 20_01_30-3.png
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2017-08-28 19_59_18-1.png
2017-08-28 20_00_06-UCCNC-1.png
Last edited by robertspark on Mon Aug 28, 2017 3:04 pm, edited 1 time in total.

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Re: List of available THCs?

Postby Rodw » Mon Aug 28, 2017 6:29 am

Robert, your PC should be perfect for LinuxCNC and a Mesa 7i76e and even better if its a Celeron J1900 or N3160. If it has onboard wifi it will generally be useless as it leads to high latency. But a USB wifi dongle will be fine. Thats what I've done as I only have one ethernet port.

The latest Linux builds are pretty seamless on installation and driver support. I'm using Linux Mint and compiled LinuxCNC from source.

If you use a parallel port, there are two threads. the fast base thread for step gens and the 1 kHz servo thread. Mesa Hardware dispenses with the base thread as stepgen (up to 10 Mhz) is offloaded to the Mesa card. This substantially relaxes latency requirements.

One of the config issues with the Mesa Ethernet cards is that you need to be running a preemptive realtime kernel. I had to compile it from sources but I was able to distill this down to a 10 line or so bash script. Once I got this far, compiling LinuxCNC from source was a walk in the park! Just after I built my machine one of the forum members wrote an awesome tutorial (he says he took some inspiration from my journey) on how to install Linux Mint and LinuxCNC.

This may have been superceded recently with the prerelease of a LinuxCNC ISO with the preemptive kernel and the latest version of Debian. LinuxCNC faces constraints bundling their product with a Linux ISO due to licensing on some platforms would you believe.

The other consideration a plasma machine builder faces is that gantry machines become significantly simpler to build and calibrate if you use the development branch, not the stable release. This is a 5 minute job if you install from the ISO as a .deb package is available for it. I've only ever used the development branch (master). THis is becasue master includes the joint axis enhancement that makes squaring the gantry when homing a trivial matter.

So for inbuilt THC, you have 3 choices.
1. Use the existing THC component for the Mesa THCAD written by John Thornton (who you will also buy your Mesa hardware from, See http://mesaus.com/). This is a more conventional "bit bang" type.

2. Use a conventional external "bit bang" THC

3. Compile LinuxCNC from source and checkout an experimental branch that supports external offsets that are unknown to the trajectory planner. It includes a PID based THC component which I am using. After the developer apologised to me this morning for forgetting to tell me one config setting needed to be modified on a metric config, I am expecting it will be well within Tom Caudle's +- 1 volt target tomorrow morning. I expect to be able to get this down to +- 0.2 V with live testing.

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Re: List of available THCs?

Postby Rodw » Mon Aug 28, 2017 6:48 am

Robert, When you are reviewing the THCAD, you are making similar mistakes to beefy, another mad Aussie plasma nerd who I've been swapping notes with.

Here's what Peter from Mesa had to say to me this morning in answer to a question I asked
Previously he had said to use the THCAD 1/32 divider with LinuxCNC. I wanted to know if I should be using the 1:1 divider with my PID setup.

The advantage of using the divided mode is that you can set the encoder filter to a lower frequency
and gain better noise immunity on the THCAD ==> ENCODER INPUT path. If this path is short It probably doesn't matter

The divider ratio does not significantly affect the resolution

This is because of the way the encoder velocity estimation works, it does not just count input cycles, it counts input cycles/ time between the first count and the last, so gives high resolution numbers even at low input frequencies.


So its all about the cable length between the THCAD and the MESA encoder. My 2 cards are almost kissing each other so I might try the 1:1 setting. In my config, don't forget there are 2 bits of "smarts" supporting the THCAD. The FGPA processor on the 7i76e and LinuxCNC itself. THe LCNC developer wants me to do a few tests so I can capture the response of the THCAD to a sudden change in volts so he can enhance his software simulation. I think he will get it to a stage that wou willbe able to fully tune your system in software before transferring a handful of settings to a live table. Finally I think many of the settings on the Neuron screens you shared become unnecessary with torch height control embedded into LinuxCNC. Here's my touch screen compatible screen. There has probably been some slight changes since this screen shot was taken. This screen has a few "tabs" in it selected by the buttons on the left

Image

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Re: List of available THCs?

Postby robertspark » Mon Aug 28, 2017 7:14 am

Rodw thanks for that detailed post, you've got me thinking now about looking at it again (yes I've got the N3160), it's got wifi, but that is just for setup [windows for software loading and updates as it will be offline in the garage just using the ethernet for CNC I do not believe a machine should be online it should be offline and just feed it memory sticks of gcode, less chance of polling / other network related latency potential issues, plus a firm believer in everything being wired for plasma (keyboard + mouse)

definatly look at the ISO for the idot proofing with me on a second HDD.

I've been chatting a bit to Beefy (keith) on the UCCNC / CNCdrive forum + Mach3 for a little while now and we're pretty good at bumping each other along (not sure what happened to Terry (Vmax) / TP though)

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Re: List of available THCs?

Postby Rodw » Mon Aug 28, 2017 7:33 am

robertspark wrote:In my opinion, it is possible to improve the resolution of the THCAD by narrowing the voltage sensing range from say 0-10V to 0-5 or even 0-3V which with a 50:1 divider will be 0-250V or 0-150V (better) via changing the resistors and also offsetting the sensing voltage from zero volts upwards given plasma tends to be in the range 75 - 140V, you can now see that adding 50V offset will move the range to 50-200V when you lower the range from 0-10V to 0-3V and add in 1 Volt of offset so the range becomes 1-4V with a 50:1 divided input.
You will need to add in something like a zener diode to clip off input voltage above 200V which is not really of any use given the arc should transfer and stabalise below this and closer to the cutting height of ~ 1/16" above the work


I'm no electronics guy but you can scale the THCAD-10 to whatever scale you want simply by adding a resistor of the correct value as its described in its manual. I think from memory it can handle a 500v overload indefinitely so there is no reason why you could not use the raw arc voltage and scale it so that full scale 10 volts = 200 volts.

Also the THCAD uses a Sigma Delta voltage to frequency converter chip which is one of the best ways of measuring a noisy voltage. The voltages I've observed with LinuxCNC's built in Oscilloscope are remarkably clean. If you ever get to understand Mesa's range of cards, you will find they are very clever people. I think if we could improve on their products, we shouldn't be on this forum! Don't forget that there is a FGPA doing the heavy lifting before signals get passed to LinuxCNC across the ethernet cable. I'm not sure of its clock speed but its probably up around 500 Mhz+ I can tell you the THCAD is highly accurate as they are individually calibrated, it works and it works very well!

You will have no problems with your N3160 if you take the plunge to the dark side. Just turn off all power saving features in the BIOS first. Because latency is critical to success of a LCNC machine, any network connections would be taken into account during initial testing so its quite safe to use it. I push files from my network to my Synology NAS where my Plasma machine has its own home directory so I can pick up files from there. Glad you also know Keith. He's been very helpful recently. Even if he's wrong, it makes me think and evaluate stuff.

Whilst I'm writing this on a Windows PC, earlier posts were written on a chromebook and sometimes from my LInuxCNC Unix machine. I'm officially OS agnostic, very cloud focussed and prefer to use the right OS for the job. There are only about two applications that require Windows left in my world.

motoguy
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Re: List of available THCs?

Postby motoguy » Mon Aug 28, 2017 12:10 pm

Out of my depth doesn't begin to describe my involvement in this discussion. However, I would like to add a router table to the stable. I'm also very pleased in my move from Mach3 to CommandCNC. Particularly in motion control. I've read this becomes even more of an issue in the 3d world. As such, I'd like to use a Linux based system for a router table. I'm sure this is all helpful, if I can figure out what you're talking about. ;)
Bulltear 6x12 w/ Proton Z axis & watertable
CommandCNC/Linux w/ Ohmic & HyT options
Hypertherm Powermax 85 w/ machine torch
Solidworks, Coreldraw X7, Inkscape, Sheetcam

tcaudle
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Re: List of available THCs?

Postby tcaudle » Mon Aug 28, 2017 1:15 pm

While its nice to talk about 16 bit resolution versus 10 , try this sometime: get a flat piece of material, level it and set you torch at .063" thenmake a straight line cut without a THC ON. In theory it should be dead on. Instead what you will see is a volt or more of changes as it cuts simply from things like the change in metal density and molecular compensation and the fact you are vaporizing metal with an arc and blowing it out with shop air. The point? it's a lot more important about the response time to a change rather than the resolution. Narrowing the range of voltage will not change the resolution because the bits are spread across the full range of the input on the chip. So if the A-D has a range or 3V (0-3V) at 10 bits it can read 1024 distinct values in that full range. to get it to 3 v you have to scale it externally and lower the range so you only put in 1/2 the range also gives you 1/2 the number of data points. The step between each point stays the same. It would only improve if you made the 0-3V range just 50 to 250 volts aka "expanded scale" (that would take some amp circuitry in front and you would have to clamp the upper end to prevent damage to the a-d.

So, back to resolution. 1024 gives you 1/4 volts of 256, 12 bit (what we use) gives you .06 volt in 256. 16 bit gives you .008 volts resolution. 8 millivolt. of 256 Volt range. So what good is being able to resolve an 8 milivolt signal when a WONDERFUL tracking would be + - .5 volt and 1 volt holds about + or - .01" in height? If you add in filtering (averaging) and dampening (in the PID loop ) that is a bunch of info you simply cannot use. Then you have noise: at 50:1 divided ratio you signal to noise ratio say .020 volts of noise equals 1 volt of change at the other end. In theory a lower divide ratio should yield a better signal to noise ratio. So again I assert its the RESPONSE (Speed) of the Z and the entire loop response that determines tracking. Higher resolution makes it smoother up to a point.

I do not adhere to the concept that a VtoF method is the best way to do remote voltage sensing. But what do I know....just an old tired EE with 40 years of design experience. :geek:

BTW CommandCNC ships with a router Config and a POST and has a "Manual" toolchange that can use a touch pad. The next release of hardware / control software will have built in Spindle Speed with tach feedback.

robertspark
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Re: List of available THCs?

Postby robertspark » Mon Aug 28, 2017 1:44 pm

All torch height control, and voltage sensing related, nothing router related in this thread.

One of the things I picked up recently was a calibration PCB as I've got a load of different items that measure voltage as well as plasma bits, but none i'd say had been calibrated reciently and I asked Andrew about the neuron lite and how it was calibrated as the hypertherm "book feed & voltage settings" are taken as a gospel starting point.... Andrew told me they were all hand calibrated, but he has since added a correction / calibration setting to the uccnc plugin given I did wonder how much drift there may be over time or temperature. Always a good question when people report a book cut voltage issue... Are you sure that your THC is accurate? Or at least giving you / comparing the right number (one reason why sample and hold is useful to check settings on the neuron which now also has graphs and logging) I will update my earlier posted screenshots shortly as they were unfortunately old ones without the k factor voltage calibration parameter of the log/ plot graph.
http://m.ebay.com/itm/181863456673?_mwBanner=1

Thanks for your post tom, I didn't say use 16 bits, I said have 16bit sampling, that way you can truncate (via bitshift) the last 2 (maybe 3) bits of the 16bit ADC which you could consider as error and or offset.

Tom, I was wondering if anyone has tried kalman filtering on THC?

robertspark
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Re: List of available THCs?

Postby robertspark » Mon Aug 28, 2017 2:52 pm

Here is another one for general discussion... How many are using PID, or are you using PI?

Also, what are you using it for (what are you measuring)? Voltage?

What are you trying to control with it? Measured voltage to setpoint voltage?

That being the case you are then controlling an output via digital control (up or down) which is near enough bang bang control.

Are you employing hysterysis (+/- error).... But the "I" part of the PID loop will increase the error every measurement loop... Hence are you not just better with filtering with hysterysis?
-Averaging
-Complementary
-Kalman?

If you are controlling the speed of THC up or down then that makes a little more sense for PID given if the error is great (or increasing rapidly) you want the z to be moving quicker than if the error was smaller or closer to the target. Or also considering the actual feedrate for your PID to provide error correction relative the the current X Y feedrate.

I struggle with PI or PID control if all you are doing is bang bang control


This is more for the Linux THC guys as the others I expect will keep quiet as the Linux side of things is a little more open than windows or proprietary THC's when it comes to talking about inner workings of how they do it (have tried or intend to)

beefy
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Re: List of available THCs?

Postby beefy » Mon Aug 28, 2017 4:58 pm

I made my own version of the Mesa THCAD and it worked great. However, my sample rate was too low at 62 times/sec. What got me interested in the THCAD ?? Well, in the beginning it was simply that it was an easy interface method all ready to go. When I got the board I checked out the components and that's where I learned about the onboard VF converter chip which is a Sigma Delta type. The talk of the town was this type of "AD converter" is great for noisy signals. THAT describes the plasma arc.

Real life tests and results are what matter to me. So not being happy with the THCAD I'd just bought and had I my disposal, I built my own version and connected to my existing plasma system while it was running. I had a microchip reading the output freq, converting the freq to something which represented voltage, and sent it through a serial connection to a PC. I was very surprised at the results. The voltage readings spewed on the PC screen at 62 times/sec and had very good stability between readings, way more accuracy than what could be taken advantage of with a spurious plasma cutting arc. As Jim Colt says the plasma arc varies spuriously during a cut in any case.

THAT is all I'm interested in RESULTS.

Then recently I hit myself on the head when I realised I'm an idiot because at 62 times per sec the Z could move further than I'd want it too between samples. So I will be upping the sampling rate significantly and doing more real life tests.

Regarding all this talk of super fast sampling rates. How can all this super fast sampling rate be taken advantage of in plasma cutting. I'm hearing 1000 times/sec for example. If the plasma arc is so spurious during a cut then that means we don't have a nice stable voltage to measure in any case. From one 1/1000th second (1 millisecond) sample to the next one, you could have different readings simply due to the spurious arc. Also can your Z react to changes within 1/1000th second, I don't thinks so it's a mechanical device with mass and inertia. To me that means you would have to take a bunch of 1/1000 th second readings and average them to get a useful voltage reading. That effectively means the sampling rate is being reduced in any case due to the averaging.

OK so let's add voltage filtering into the mix to smooth out the plasma voltage before reading it. That in itself adds delay so even if you could smooth the voltage out and sample it 1000 times/sec you are sampling a "late" arrival, so the super fast sampling rate is not much use anyway.

With a longer sampling period you can have more averaging of the noisy plasma volts, and thus a more accurate reading. So my thoughts are sample less frequently but frequently enough to give fine control over the torch height. Time will tell how this works for me.

All I ever here is about super fast THC. That can actually be a disadvantage on thicker material where the torch is travelling slower. What happens when the torch crosses a void. The THC can react so fast that the voltage never raises enough to cause the anti-dive to kick in and the torch dives down into the metal. OK so you need to reduce your THC feedrate for these cuts (point being we don't always need super fast THC control).

I'm no expert but what I do is talk to experts and ask them questions. The above is based on answers I've got from electronics engineers, etc, guys who do only electronics for their living, not a mixture of disciplines.

The best way to sort all this out is to SHOW what a system can do. Show every available feature in action (slow motion videos would be good). Technical talk will baffle most users, many of whom I've came to realise find it too much to single step through gcode when they have a fault.

Also, how many users are going cut thin metal at high speed and need super fast THC reaction as the metal distorts with heat. Who needs to cut corrugated sheet, etc. There's a lot more to a good plasma system than just high speed, accurate THC and turning off the THC at corners. My bet is a great many users could get away fine with moderate speed THC so long as it's REASONABLY accurate.

As for the “bang bang” THC vs the PID controlled THC, many users are perfectly happy with a bang bang system. PID comes into its own when fast accurate reaction time is a necessity but it also needs fine tuning to make it work well. And that goes back to that question – do you need it. Will a decent Ford with electric mirrors, electric windows, power steering, etc, work for you, or do you need a Ferrari.

Oh, and Rod, I'm a Pom, not an Aussie, sorry LOL.

Keith.
8 x 5 water table
Powermax 1250 with Duramax torch
Candcnc MP3000 / Mach3
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