Ohm-sensing torch issues

[durantc]

Our shop recently purchased a Fab-cut plasma table (replacing our old vicon).

The torch uses an ohm measurement on the material to sense the metal prior to each cut (this is new compared to our old table) and I am continuously having trouble with the torch not sensing the metal.

Fab-cut claims the table is working perfectly and are blaming the metal industry for changing something or having uneven zinc coating on our 26 and 24ga (mostly) metal. They told us to spray water or scuff the material, randomly do a sensing in various spots for better readings but I get sheets where nothing works.


Does anyone have an idea or information on solutions or finding an actual issue with the machine so we can make fittings consistently?

Thanks

My boss and

[djreiswig]

I'm not sure how their ohmic is wired, but you need to have a continuous connection from the plate side of the circuit to the material. When I wired up my ohmic initially, I hooked the plate wire to the gantry and it conducted through the table structure. I found out this wasn't reliable, so I ended up running a wire down the cable carrier and attached it directly to the water pan. It works lots better.
I would try attaching a wire to the torch tip and go around the table and test to see if there is a bad connection between the module and the material. You may need to add a wire to make the circuit more reliable. If the issue is between the material and the slats, you could add a wire with an alligator clip to attach material to the slats.

[weldguy]

Are you only having this problem on galvanized material?

[durantc]

We only use galvanized since 99% of what we make is purely duct work. However, we had the ohmic sensing completely stop working (we even tried some mild steel and still nothing). Connecting directly from ground to tip did not work even.

Our ground runs through a magnet we attach to the sheet which runs through the table ground then to the plasma machine.

Today they replaced the board in our plasma (thermal dynamics) and the ohmic sensing works 100% better during our initial tinkering. Tomorrow will be a full fab day and really test if it’s consistent and stops chewing through consumables.

[weldguy]

Sounds like your making progress. Curious to hear how it works out for you. Best of luck.

[Rodw]

What model Thermal Dynamics? I have an A120 which use the SL100 torch. I'm not understanding what the plasma cutter has to do with ohmic sensing as its really a controller function. Is it High Frequency start?
I have an idea but need to know more about your machine first.

[RDA]

What model Thermal Dynamics? I have an A120 which use the SL100 torch. I'm not understanding what the plasma cutter has to do with ohmic sensing as its really a controller function. Is it High Frequency start?
I have an idea but need to know more about your machine first.

The latest version of the automation pcb has ohmic and tip sensing built in (so you can use exposed and shielded consumables to sense the plate). You get a closing dry contact relay output from the pcb in the plasma to your CNC.