Probing/Ohmic faults.

snowgoer540
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27 Jan 2023 16:41 - 27 Jan 2023 21:44 #263013 by snowgoer540

Replied by snowgoer540 on topic Probing/Ohmic faults.

rodw wrote:
The example I quoted was a real life example of a recurring production job cut on my table and you trivialise it.

Nah, I was just acknowledging your strawman by embellishing him.

That is not respectful.

Ad hominem. I'm not sure how anything I wrote could be considered disrespectful.

Its really pointless continuing the conversation.

Agreed.

You clearly have no interest in incremental improvements to qtplasmac anymore.

False dilemma. Example: Bill don't think this particular idea has merit, therefore Bill's not interested in any "incremental improvements".

The update list very clearly shows otherwise.

Which you've both benefitted from and complained about in the past.

But the point is QTplasmac is manufacturing an error for no valid reason.

Agree to disagree? I'll even help you get started with an alternative solution:

You could write your own component to take inputs from ohmic and float, do whatever you want to them, and then output them from your component to the plasmac component.
A starting place might be:
1. determine if float or ohmic fired first
2. if float, pass float signal to component
3. if ohmic, pass ohmic signal to component and ignore float signal until the float signal resets
4. reset the works so the next probe is evaluated in the same way

This will allow you to still gain your incremental improvement.

Do bear in mind that any overshoot has to be made up when the axis picks the torch back up off the material, so this effort may become a wash when compared to just adjusting the float travel a smidge longer.

I know I see things differently because of the many hours I spent getting to understand how plasma worked back when there was no viable plasma config. Who else plotted 16000 realtime readings from halscope and analyised the data statistically and graphed the results? I look for the exceptions to see what can be improved. One example is the spotting algorithm which came from observing behaviour after accidentally doing something similar. Others might have missed it but I didn't and now its in QTplasmac.

There's no doubt that this project is where it is, because of the contributions of many, yours included.

Last edit: 27 Jan 2023 21:44 by snowgoer540. Reason: editor

The following user(s) said Thank You: Clive S

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phillc54
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28 Jan 2023 03:42 #263046 by phillc54

Replied by phillc54 on topic Probing/Ohmic faults.

I haven't been able to replicate this even with reduced Float Switch Travel. My normal table setup is:
Probe Height = 10
Probe Speed = 400
Float Switch Travel = 1.51
Z Max Velocity = 200
Z Max Acceleration = 3000
which makes me think even with my longer travel that I should have seen it at some stage.

Is it possible there was some other influence to cause your situation?

Before I do any more can you confirm which one of the messages was the one you noticed:
"float switch activated. program is paused"
"float switch detected before probing. probe test program is paused"

When you say that you adjusted the hysteresis, do you mean the Float Switch Travel

Float Switch Travel = 0.9999999999999996
(wonder why it wasn't 1.0?)

Me too, that is odd. If I set mine to 1.00 then the .prefs file shows 1.0, I checked on both Bullseye and Bookworm so I don't think it is a python thing.

I might add its possible that the hypersensing with THCAD-5 could be a factor becasue its so quick to respond with no relay hysteresis in the system.

I don't think so, when I did my exhaustive comparison between SSR ohmic and THCAD ohmic there were no delays apparent with SSR, I think the on/off times are quoted as <250uS, plenty fast enough for a 1mS servo thread.

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rodw
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28 Jan 2023 11:09 #263068 by rodw

Replied by rodw on topic Probing/Ohmic faults.

I'm not sure what the error was but it mentioned it was probing in the error so seems like it was the second one.
Yes, I have an adjustment screw which reduces float switch travel and I always set it very fine.

From our investigation and testing:
A relay will have voltage hysteresis beng the turn off voltage and the turn on voltage. Measuring it with a variable voltage power supply can yield quite different thresholds to any published specs. The 24v one we tested said its turn off voltage was 11 volts and we measured 5. It turns on in 250 us and off in < 2 us. Your 250 us is from the on threshold being crossed. Don't forget the probe height is set by the switch off point so the turn on speed is not important.

As the probe contacts the plate voltage rises as pressure increases and it will fall as it lifts from the plate. I was able to see this with the THCAD-5 but you can't using a relay.

With hypersensing, it looks at the moving average voltage vs actual voltage as the torch probes away. It turns off the probe once a fall in voltage is confirmed by the actual voltage falling below the moving average. On a 24 v system, this could even be at 23.9 volts. Thats a long way before the 5v turn off on the relay would kick in. I never measured the speed improvement but it definitely appeared a lot quicker to us.

I might add that the moving average algorithm was not designed with speed in mind. It was designed to handle the very minimal voltage drop observed on Hypertherm machines if they got a bit of water in the torch. I might add under these conditions, a relay simply cannot probe sucessfully as the turn off voltage is never reached... Hypersensing handles it with ease.

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phillc54
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28 Jan 2023 11:26 #263069 by phillc54

Replied by phillc54 on topic Probing/Ohmic faults.

Thanks, I will have another look tomorrow.

We are getting a bit OT with this SSR vs THCAD talk but since you mention water I have no issues with water and SSR ohmic, during my comparison testing I was successfully and consistently probing with the material submerged.

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