Ohmic resistor location?

[binfordw]

Hi,

Our shop has a plasmacam table. I was talking to one of the assembly guys today, and pointed out a beveled cut on a bracket. He told me the table has been messed up, and the Z wasn't working right.

I took a peek at it, first time I've seen a plasma cam table. It has an Ohmic retainer (on a 85PMax), and the wire running back to the tiny little controller on the frame. A quick search pointed out the need for a resistor, which I didn't see. Can anyone tell me where these are generally located on this wire? At the spade connector for the torch? inside the controller where the wire is landed?

Thanks!

[weldguy]

I am not a PlasmaCam guy but I am pretty confident the wire from the ohmic clip does not require a resister. The resister is to be on the arc voltage feed wire from the plasma cutter. A beveled cut is not uncommon and there are many things that can cause it such as worn nozzle, incorrect cutting height, incorrect air pressure, etc. Cut a 2" square and post a profile pic of it from 2 sides so we can see your bevel. Reading the bevel will help to narrow down your issue.

[binfordw]

Thanks for the reply, I'm not new to plasma in general, I ran a PM 45 and 65 on a homemade table for the last 10 years or so before finally retiring from the home work. Forums, (and Jim Colt!- glad to see he's still around), have taught me a good deal about troubleshooting issues along the way.

The bevel I mentioned is from the cut height being waay too high, as the Z isn't positioning right. The torch is meant to touch off, and it doesn't do this correctly, I can only assume because its not sensing the sheet/ zeroing the Z correctly. (My old home setup used a switch and a floating torch mount to locate the sheet).

[weldguy]

10-4 Maybe post the turn of events that takes place during touch off and I am sure one of the Pcam gurus here will chime in with a solution.

[binfordw]

The Z drives into the sheet, and continues to drive the Z, losing steps, jerking, for a few seconds before raising to (pierce height I assume?).

I guess I should actually look at it more, I was just probing for some more info in the meantime while in the comfort of my chair!

[adbuch]

--- resistor, which I didn't see. Can anyone tell me where these are generally located on this wire? ---

Welcome aboard!

On the Plasmacam table, the wire between the torch ohmic retaining cap and the motor cap should have an inline 47K ohm resistor installed (these normally come installed from the Plasmacam factory). Without this resistor it may be possible to damage your controller or cause erratic sensing problems.

The spade clip shown in the second photo is normally connected to the ohmic retaining cap terminal if ohmic sensing is being used (as opposed to "stall on material to zero" or "from previous location/cut height"). Look at the Settings, Height Control, Pierce Height Reference window to make selection.

David

ohmic sensing wire resistor.jpg

ohmic sensing wire resistor closeup.jpg

[adbuch]

The Z drives into the sheet, and continues to drive the Z, losing steps, jerking, for a few seconds before raising to (pierce height I assume?).

More information would be helpful, and also some screen shots of the Settings pages for Machine Control and Height Control. If the operator has the "stall on material to zero" option selected, then the sequence you describe above is normal.

David

[binfordw]

Ahh, thanks for the pics/ info, I’m fairly certain ours does not have that resistor anymore. I’ll have to check when I get back to work.

I do recall them saying they had to change a setting in order for it to cut at all- I believe it gave collision errors- as if it was always sensing the sheet when the “normal” setting was used. Wonder if that’s the one you had mentioned.

I’ll check the settings in more detail. I just looked through them, mainly trying to tell if this setup actually had a dthc or not. The software has the settings options for it, and the diagnostics screen had a voltage reading, but that was as far as I got. Dthc or not, I’d still have the problem of the z not sensing the sheet right before the pierce.

[adbuch]

Depending on how old your table is, you may (or may not) have ohmic sensing. If your height control screen looks like this, then your table would not have had the ohmic sensing option - and is most likely a DHC model running 3.11 software.

PC5.JPG

If your height control screen looks like this, then you have Design Edge with basic height control and no ohmic sensing.

Basic Height Control Settings Page.jpg

If your height control screen looks like this, then you have Design Edge with advanced height control which does include the ohmic sensing option.
David

advanced height control.jpg

[adbuch]

I do recall them saying they had to change a setting in order for it to cut at all- I believe it gave collision errors- as if it was always sensing the sheet when the “normal” setting was used. Wonder if that’s the one you had mentioned.

If they were having a problem with ohmic sensing not sensing the material and giving an error, then they most likely turned off the "sense material to zero" option and instead selected "stall on material to zero".

David

[binfordw]

Great info thanks!

We do have the last screen shown- design edge with advanced height control. I’m fairly certain the table is only a few years old, I just started working for them a few months ago.

I believe they turned off “retract z if contact” to get it to cut. I’ll check it out when I go back in.

So just to be certain, if the software we have is the advanced height control, the table has digital height control based on voltage from the arc? So it uses ohmic to find sheet, reset Z zero, then presets for pierce height and initial cut height, then voltage takes over and the torch will follow sheet in Z, if there’s bowing, etc?

[Joe Jones]

binfordw,

Where are you located? Sometimes you might be close enough to another PlasmaCam owner (like me ) that he or she might just jog over to help you set things up.

Some PlasmaCam table owners view other owners in the area as "competition" and they won't give you the time of day. however, I see no problem with other PlasmaCam owners in my area. There is enough business out there for everyone.

If the height control wire coming out of your carriage motor has been cut short, and it does not have that resistor, you can (and should) order a new carriage motor wire harness from PlasmaCam.

Part # 2-301 for $49.00

It is easy to install onto the motor.

Joe

CARRIAGE HARNESS.jpg

[adbuch]

So just to be certain, if the software we have is the advanced height control, the table has digital height control based on voltage from the arc?

Yes. To auto-calibrate your Z shift and Arc Voltage shift, go to the Settings/Height Control page/Cutter Location Adjustment and check the boxes for "Autozero Z shift on next cut" and "Autozero arc voltage shift on next cut". (These boxes will be automatically unchecked after your first cut.) You would normally do this after you initialize your machine and before you start cutting. Under Settings/Height Control/Pierce Height Reference if you select "Sense material to zero" then the z shift will be set using ohmic sensing. If you select "Stall on material to zero" then the z shift will be set by lowering the z axis until the material is contacted and the stepper motor stalls out. Once z shift and arc voltage shift have been calibrated, the torch height control will monitor the divided arc voltage and raise or lower the z axis in an effort to maintain a constant arc voltage - which in turn will maintain a constant cutting height.

Robert Johnson has an excellent Youtube video titled Design Edge Settings Explained explaining all the settings - what they do and how to set/adjust them - here.

David

https://www.youtube.com/watch?v=7rcm0DdDPfo

[binfordw]

Thanks again for the info- and I appreciate the offer above for a possible hands on visit`, I'd have to politely decline though, this is at a business not owned by myself. Not a plasma cutting business mind you, we use the table mainly to help prevent outsourcing covers and panels for automation equipment made in house.

[adbuch]

Happy to help! I hope you get it sorted out.
David

[binfordw]

So just to be certain, if the software we have is the advanced height control, the table has digital height control based on voltage from the arc?

Yes. To auto-calibrate your Z shift and Arc Voltage shift, go to the Settings/Height Control page/Cutter Location Adjustment and check the boxes for "Autozero Z shift on next cut" and "Autozero arc voltage shift on next cut". (These boxes will be automatically unchecked after your first cut.) You would normally do this after you initialize your machine and before you start cutting. Under Settings/Height Control/Pierce Height Reference if you select "Sense material to zero" then the z shift will be set using ohmic sensing. If you select "Stall on material to zero" then the z shift will be set by lowering the z axis until the material is contacted and the stepper motor stalls out. Once z shift and arc voltage shift have been calibrated, the torch height control will monitor the divided arc voltage and raise or lower the z axis in an effort to maintain a constant arc voltage - which in turn will maintain a constant cutting height.

Robert Johnson has an excellent Youtube video titled Design Edge Settings Explained explaining all the settings - what they do and how to set/adjust them - here.

David

https://www.youtube.com/watch?v=7rcm0DdDPfo

A late response-

But seems we still have yet to resolve our issues here.

I watched Roberts video, and it seems to point towards our machine setup having an issue. I've noticed the boxes to check for "Autozero on next cut" are not selectable for me.. Any reason why this would be?

Thanks!

[Francisco]

"Autozero" checkboxes are enabled after machine initialization. Once a cut is started, the Z shift and arc voltage shift are set automatically and the checkboxes disabled. Not being at the machine now, I am not 100% sure, but I think you have to initialize again if you need to repeat the "autozeroing" (which would be odd).

[Francisco]

BTW, the 47kOhm resistor is easy to replace. Use a 1/2 Watt one. You'll need two short sections of 1/8" Ø shrink tube to insulate the soldered areas and a one inch or so length in 1/4" Ø to provide mechanical support.

[adbuch]

A late response-

But seems we still have yet to resolve our issues here.

I watched Roberts video, and it seems to point towards our machine setup having an issue. I've noticed the boxes to check for "Autozero on next cut" are not selectable for me.. Any reason why this would be?

Thanks!

Yes - as was mentioned above, your table must be initialized before the "auto zero z shift on next cut" and "auto zero arc voltage shift on next cut" options become active.

David

[rdj357]

A late response-

But seems we still have yet to resolve our issues here.

I watched Roberts video, and it seems to point towards our machine setup having an issue. I've noticed the boxes to check for "Autozero on next cut" are not selectable for me.. Any reason why this would be?

Thanks!

Make sure the machine is initalized as David says and also make sure that you have height control enabled. It won't be an option to check the arc shift autozero box if it is off and it won't be an option for the z shift autozero of the pierce height reference isn't set to sense material (it will work on stall as well but not preferred). You will have to enable these options, click OK and then reopen the settings window to be able to check the autozero boxes.

[binfordw]

I had a bit of time today to check this table out, I did find a break in the ground wire. I replaced the wire- with no resistor however- and we are back to having height control. The torch touches off properly, and cuts at a fairly reasonable height. I just need to brush up on the cut settings next, I set the cut height at .065, I assume changing that value will change the actual automatically controlled cut height. On my old table, I ran Mach3 software, and just adjusted the voltage to match the Hypertherm cut sheets, more or less. There was a pierce height, then a manually set cut height (usually .o65ish), then DTHC took over and it went by voltage.

The cut quality is lightyears better than what we had for sure.