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Another cheap option for reading thermistors is LM331, a voltage-to-frequency converter
www.ti.com/lit/ds/symlink/lm331.pdf?ts=1760588182451
Or an industrial solution by Mesa, the THCAD

Hello
I'm having a weird Qtplasmac 2.9.238.315 bug where my torch goes down when it should be going up - but only during THC corrections.
Normal Z axis movement is OK as it should, with homing, probing, etc.

THC is being used from voltage (THCAD-2) and arc OK signal is present. 

I tried reversing the Voltage Scale (from 0.009 to -0.009) and no changes. - it still is correcting in the reverse way. how weird is it!

Where could i start?

Thanks everyone

Here is a suggestion:

forum.linuxcnc.org/plasmac/55286-servo-d...ofit?start=10#331245


( pncconf has more built-in QTPlasmaC/THCAD support  so may be an easier path)

PCW wrote:

If using a THCAD for ohmic sensing has issues with water. the most likely issue
is that the sense  resistor is too high a value.

I agree and I am pretty sure i mentioned somewhere a long time ago that a lower value resistor should be used for sensing. Something that will result in 20-50mA current should do just fine, maybe more as the water used will get lower resistance the more cuts are done and as it evaporates.

Thanks everyone for the feedback. I’ll keep you posted as things progress.

If using a THCAD for ohmic sensing has issues with water. the most likely issue
is that the sense  resistor is too high a value.

Looks great. I will be interested in how you go with the My Ohmic Pro. I was sent an evaluation one and its beautifully engineered. I just had nothing to try it out on. The THCAD for Ohmic struggles on Water tables so hopefully it proves a more robust solution. Lukaz at Proma said he was very proud of the water handling of the  My Ohmic Pro

Be sure to add an EMI filter on your mains input to avoid electrical noise. You can get them built into an IEC connector. even with a power switch and fuse built in.

I thought the THCAD can do the job of the Promo Ohmic sensing system?
Or perhaps one need an additional THCAD arc-voltage reader.
Plasma-guys, you know this.

It looks like you have most of it sorted out, but feel free to ask any questions if you get stuck.

Depending on what the mystery control board is, it might be compatible with Remora firmware.

Hi all and thank you for checking this topic!

Little intro to my project and why I cam here.
I'm here asking for help with upgrading my table. I've bought a CNC plasma cutting table with the hope of starting my own thing and because it looked like a lot of fun. Couple of months down the road it turned out that the table is more on the hobbyist side than I would like. So I decided to start upgrading it in order to have higher quality cuts that I can be proud of.

My current setup.

PLASMA SOURCE

• Unit: Sherman CNC 130 (CNC variant).
• Divided arc output: 1:20 divider present on the machine (available for THC feedback).

CONTROL

• Unknown motion  control board
• Unknown THC controller

MOTION, DRIVES, AND POWER

• Motors: stepper-based system in use - Nema 24 - 60bhh86-300e-24db 
• Stepper drivers: 3 × CW-5045 in use for X, Y1/Y2, Z. (
• X/Y motion: rack & pinion, 
• Z motion: drive type ballscrew.
• Installed Power: 400VA transformer labeled “230V / 12A” and “SMT 400VA”. This is a step-down transformer: it takes the 230VAC mains in and produces about 30VAC (at up to 12A) on the secondary. After a bridge rectifier and filter capacitor, that 30VAC becomes roughly 42VDC.

CONTROL AND SOFTWARE

• CAM: SheetCam (current workflow).
• Machine control (current): Mach3.

TABLE

• 3.5 × 2.0 m with water bed.

My plan.

• Move to LinuxCNC with QtPlasmaC.
• Move to Mesa 7i96S: Ethernet motion interface
• Move to Mesa THCAD-2: for 1:20 arc-voltage THC input
• Move to MyOhmic PRO
• Install limit switches
• Use 18 AWG (0.75mm2) shielded cables for the up to 24V connections
• Use 16 AWG (1.5mm2) shielded cables for the connections that are more than 24v

In short: to replace the controls, cables, add limit switches and keep the rest

The diagram.
I've reused a diagram from the forum (I believe that it's LOWRIDER3) which turns out to be immense help, I'm not sure I would be able to come up with anything useful if it wasn't for it!

I'm adding the diagram itself so that you good folks can make comments, recommendations, critiques. Thank you all in advance!

Yeah, somehow i managed to miss this.
When in doubt, more C4 !!!
Use relays as you have in the drawing for ARCOK, do not wire anything to Mesa, do a test cut and check if the relay closes while cutting. Do the same thing for TorchON but reversed, meaning contacts go to plasma and coil on the Mesa side but do not wire to Mesa just use whatever can give 15-24V and trigger the relay with it see if the torch fires. After this, you can wire stuff to Mesa, one at a time, test, wire, test....
As for the Arc Voltage, find the big rectifiers, usually with big aluminium heatsinks and find the positive and negative, wire two short wires to each, wire 2 of 1MOhm/2W resistors to each of those wires, on the other side of the resistors wire two thinner wires prefferably shielded and send those to Mesa THCAD, mind the polarity, although nothing will happen if you do mix the polarity but you will have no voltage reading on screen.
Make positively and ultimately sure you have the power cord and plug under your foot while adding this, i do that always to prevent someone somehow getting the idea that it belongs plugged to the wall...while i have both hands inside!

There is a wire between the torch- and the old thc's interface. I think the interface has resistors and they sampled the work+ side at the thc. But i'm guessing and there's no useful documentation for it. There is a spot on the old interface for divided arc volts, but it was never hooked up. 

So I have to do at least a little wiring inside either way, so I was thinking may as well put the thcad inside the plasma while I'm at it. 
It's a high frequency machine so maybe that'll help with emi.



 

I am trying to figure out how to interface a thcad2 and mesa 7i97t with a hypertherm hsd130.
Originally, this machine was hooked up to an external hypertherm thc.
The hsd130 has an internal 37 pin connector that goes to a "phc interface" that has am external 15 pin connector that connected to the old thc.
Unfortunately, the phc interface's manual doesn't explain what the pins on the 15 pin connector are for or how they should be wired and the hsd130 manual doesn't even mention it.
The manual does have all the information for the internal 37 pin connector. 

 Should I just remove the phc 15 pin connector and use the 37 pin? That seems easier than trying to reverse engineer the "phc interface"?

I will try to attach the relevant pages from the manual.

The example circuits are above my head.
Do I need any relays for the arc ok and start i/o's or can they connected directly to the 7i97t?
Should I use 24v from my controllers power supply?
Can I use 2 or 3 1mohm resisters connected directly to the torch/work leads for the thcad2?

 Hello everyone,This is my first post here on the LinuxCNC forum, and also my very first CNC build — so please forgive any mistakes or lack of experience on my part. I'm doing my best to learn as I go.I'm building a plasma CNC machine and using a Mesa 7i92 card. For my setup, I’ll be connecting two 5-axis breakout boards — one on P1 and one on P2. I’m looking for a suitable firmware that would allow me to:

• Use 4 or 5 encoder inputs (for THCAD and potentially other uses)
• Have at least 10 inputs and 5 outputs for general machine control

I’ve checked the Mesa site and the firmware list, but I’m not sure which bitfile would suit this configuration best. If anyone has a firmware file that fits these needs — or could point me in the right direction — I would be very grateful.Thank you so much in advance for your help and patience. I really appreciate the knowledge and support shared in this community.Best regards,

Hello All, I'm using this post processor (PlasmaCv2.1) in Fusion 360. My issue is that my first round hole in the gcode cuts no problem, machine come downs and probes, makes a perfect cut and then the Z axis rises 1-2inches and continues along the path in the gcode but doesn't come back down to start the plasma arc, it just runs the whole program without coming back down to initiate arc and cut the material. I don't get an "arc okay" error which is odd .I went back into Fusion360 and set my retract height and clearance height to 0 to see if that would help and maybe the THC via THCAD through a MESA 7i76 board would work but it just gave me an error. "Safe Traverse Height has been reduced to 0.23in"


Images attached of my cut parameters ,material properties , gcode from Fusion 360 and some misc info. 

The machine cuts simple parts using the conversational in QTplasmaC no problem, and my THC works so I've isolated it to the Fusion 360 Gcode and unsure how to fix my issue. Possible bug maybe?

I feel like I'm doing something really dumb and overlooking something really simple, in an effort to not waste another couple days going in circles, could anyone point me in the right direction, i greatly appreciate it!