Ohmic enable relay lopgic

When does the ohmic enable relay get energized?

Linuxcnc ohmic input

bevins wrote:

When does the ohmic enable relay get energized?

Linuxcnc ohmic input

Bevins, the digital output signal is triggered by the plasmac ohmic enable pin.

If you want to try the bleeding edge, with the help of PCW and a THCAD-5 he donated to the cause, I am working on finalising documentation of our hypersensing (ohmic sensing on steroids)



This is combined with a component I've written which allows a digital voltage threshold to be set to give very precise sensitivity control with these advantages:

1. Costs are not significantly higher ( I removed AUD $60 in opto isolated relays and added an AUD $100 Thcad.)
2. Much simpler circuit, no need for diodes to protect from reverse arc voltage
3. no voltage loss
4. Instant sensing for faster and most accurate sensing.
5.no relays which are often quite slow to respond (have a look at the opto22 specs for example)
6. bulletproof in relation to arc voltages,
7. High noise immunity due to the THCAD design
8. Logic circuit is decoupled from the noisy plasma environment so no possibility that the ohmic sensing wire being used as an antenna to introduce spurious faults in a HF environment (eg 200 amp and above).
9. precise sensitivity adjustment

rodw wrote:

bevins wrote:

When does the ohmic enable relay get energized?

Linuxcnc ohmic input

Bevins, the digital output signal is triggered by the plasmac ohmic enable pin.

If you want to try the bleeding edge, with the help of PCW and a THCAD-5 he donated to the cause, I am working on finalising documentation of our hypersensing (ohmic sensing on steroids)

This is combined with a component I've written which allows a digital voltage threshold to be set to give very precise sensitivity control with these advantages:

1. Costs are not significantly higher ( I removed AUD $60 in opto isolated relays and added an AUD $100 Thcad.)
2. Much simpler circuit, no need for diodes to protect from reverse arc voltage
3. no voltage loss
4. Instant sensing for faster and most accurate sensing.
5.no relays which are often quite slow to respond (have a look at the opto22 specs for example)
6. bulletproof in relation to arc voltages,
7. High noise immunity due to the THCAD design
8. Logic circuit is decoupled from the noisy plasma environment so no possibility that the ohmic sensing wire being used as an antenna to introduce spurious faults in a HF environment (eg 200 amp and above).
9. precise sensitivity adjustment

You sound like Sheldon on big bang theory....lol

I don't have a thcad-5. I just have thcad. Is there firmware on the thcad and up gradable to thcad5? lol,

Back to the thc enable relay. These are getting energized via mesa. What is telling linuxcnc to turn on those outputs?
Certainly not the ohmic sensing relay since that relay will never be energized until the ohmic relay is energized. one side of the ohmic sensing relay passes through the contacts of the thc enable relay.

What am I missing?

/Edit I just reread your post. there is an ohmic enable pin. When does that get set? and by what?

bevins wrote:

What am I missing?

/Edit I just reread your post. there is an ohmic enable pin. When does that get set? and by what?

Bob, its a standard Plasmac Pin.
linuxcnc.org/docs/devel/html/plasma/plas...ml#_i_o_requirements

So the intent is that both sides of the ohmic enable circuit are disconnected from the torch and table unless we are probing. This is based on a design by Islander 261.

tommylight wrote:

one thing is perfectly unclear :
You mention the raise in price due to THCAD5 and that is all good, but is it being used also to measure the plasma voltage or just for sensing.
If there is no need for THCAD10, then the price is lower by those 60 pesos.

Sorry I missed one thing which Is important. The THCAD only ever uses the Encoder A input. PCW wrote new firmware for the 7i76e and 7i96 that puts 3 encoder A input on the board by reconfiguring the Encoder B and Encoder IDX pins. This firmware is included in the zip file you can download from Mesa and the file names end in "pl.bit"

I guess for Bevins, he might need an additional 7i77 encoder input but maybe PCW can do the sme trick for the 7i77

So you end up with two THCADs. A THCAD-10 for torch voltage and A THCAD-5 for the isolated Ohmic sensing circuit. PCW did not want anything other than the scaling resistor and the THCAD-5 on the sensing side and its not even necessary to turn the AC power supply off. So the probe enable pin is basically redundant. I did try enabling it with spindle.0.on and having it hard wired with no AC isolating relay through cutting and it all worked perfectly. In fact becasue it is scaled for 24.5 volt and the power supply is 24 volts, I added an pin which turns on at full scale which denotes the arc is cutting. Both the THCAD5 and the Meanwell Isolated power supply are rated for 500v overvoltage.

And yes, you should be able to use a THCAD-10 with a different scaling resistor

EDIT: and we set very wide switch hysteresis with the signal coming on at say 18-22 volts and off at say 1-5 volts. We saw the voltage risse over 0.04 volts of z axis movement (0v, 12v, 18v, 24v) per each 0.01mm moved with my jog wheel. Because the THCAD is so responsive, we seem to sense the surface reliably earlier and the Plasmac probe up to break contact appears to be much faster (as it has less travel to go as there are no slow relays in the circuit).

ok for the non-steroid types, the plasmac component will handle enabling and disabling the ohmic enable relay if I understand correctly.

bevins wrote:

ok for the non-steroid types, the plasmac component will handle enabling and disabling the ohmic enable relay if I understand correctly.

Correct. I meant to grab my hal file but forgot and now I am not at work!

I don't have a thcad-5. I just have thcad. Is there firmware on the thcad and up gradable to thcad5? lol,

The only difference between a THCAD10 and a THCAD5 is one resistor
Both would work fine for a Ohmic sensor

As would a THCAD-300, just use a 300V sense power supply...

(That's not as dangerous as it sounds since the current at the probe would be
limited to 100 uA, and 300V might be a bit better at sensing through dirty metal)

bevins wrote:

I don't have a thcad-5. I just have thcad. Is there firmware on the thcad and up gradable to thcad5? lol,
?

I was thinking later that if you had a THCAD-10 spare, a 48 Volt isolated power supply is the same price as the 24 volt one I used. A 470k resistor would set the full scale to 52 volts or a 452k resistor would give full scale of 50.2 volts. Either would be perfect!