How to setup an ohmic sensor

[Greolt]

I am going to add an ohmic sensor. Want to avoid the spring back on light material.

Sensor will trigger probe input. Presently the floating Z does this.

How do I incorporate the floating Z switch as a backup if ohmic fails for any reason?

I am guessing you just set the switch as a Z axis limit but that will just trigger a limit fault and stop the program.

Is there a way to have the switch revert to its present function and have the job carry on?

[Vmax549]

You set teh switch to use Zhome and use G28.

[Greolt]

Sorry I am bit slow sometimes,

How does setting the floating head switch as limit and calling G28 work as a backup to G31 and the ohmic sensor?

How do I get them to work together? I am guessing it can be done with some clever trick in the macro, but it is beyond this carpenter's ability.

[Robertspark]

the way I did it (before the neuron THC):

I wire both the ohmic and floating head switch to the same probe input pin. the wiring has both inputs in parallel and they act as an OR gate.... whichever is triggered first will stop the probe / skip signal input.


then i cut the ohmic input and run that via a relay.

this allows me to test the ohmic input before probing and also to determine which input has been triggered and set the correct offset distance for the floating head switch or the ohmic input via a single macro.


my macro is as follows:

when called it checks the probe input, if it is active (indicating a possible ohmic probe fail: crud in the shield), it will drop the relay out and recheck the input. if it is active it will raise the Z (20mm) and retest again.... if it fails this time.... it will STOP and throw a message up to check inputs...... if the ohmic test fails at any point it will thow a WARNING (check ohmic sensor / shield) but continue the probing as normal.

providing the initial check passed.... it will probe the plate.

when the probe / skip signal is triggered it will test via dropping the relay out which input was triggered and it will set the correct offset according to which one was triggered... if the ohmic was not triggered it will throw a WARNING (check ohmic / shield) to the status bar and continue with the operation.

[Greolt]

Thanks for that Rob.
I will need to think about that for a bit.
The bit about both triggers in parallel makes sense.
The rest will take some more thinking for this old brain.

If using the shield as the touch would it make any difference which input triggered?

If it was the ohmic, that's good, but if the floating head then it is as it has been for the last two years.

[Robertspark]

it's all to do with the offset really.

the ohmic input normally has 0mm (zero) offset as it triggers as soon as it touches the plate.

the floating head is your backup... and that as you know has the switch offset.

also my experience was that when I ran the ohmic .... it all started out great (clean shield / cap new consumables etc) that all of a sudden maybe I got a miss probe because of crud in the cap (pierce splatter / buildup) and my (simple g31) probing routine set the wrong probe height as soon as it was called.. so the pierce height was all wrong etc.

hence I did a custom macro and added a relay to test which input was active, and to test an warn if the ohmic routine had failed or was not used and the correct switch offset was applied.

the miniTHC is where I started doing this as that is how that works.... have a read of the manual as there is a bit on ohmic input and sensing plus showing some solder bridges on the PCB that allow you to do what is explained previous.

https://minithc.com/pub/MiniTHC2_EN.pdf

https://minithc.com/pub/Ohmic_Sensor_EN.docx

https://minithc.com/

[Greolt]

it's all to do with the offset really.

the ohmic input normally has 0mm (zero) offset as it triggers as soon as it touches the plate.

the floating head is your backup... and that as you know has the switch offset.

Of course! I was forgetting the offset when the floating head switch triggers.

I will read up on the info you have sent me to.

Thanks again.

[Robertspark]

also maybe best to ask on the plasma spider forum for suggestions..... note a lot of mach3, and linuxcnc use but the wiring for two input sources should be the same.... or similar suggestions

https://www.plasmaspider.com/search.php ... mit=Search

[Greolt]

I will do some reading over there too.
Thanks Rob

[Greolt]

Rob

I am trying to imagine how you used the relay.

Maybe a double pole relay. Ohmic trips the relay. One pole sends a probe tripped signal.
The other pole sets a flag (spare input) which is read by the macro to see what tripped the probe. Ohmic or switch.

Does this sound right?