Hypersensing questions

I tried disabling the encoder filter, did not see any change.

Here's some plots of a "wet torch" condition. Both touching the plate and not. The data was taken right after a pulse command, which had no real effect on lowering the voltage.

My low voltage is 23.8v and high is set at 23.9v

The noise seen on the floating picture is about 0.5v, maybe more, just eyeballing. Sometimes it gets as high as 24.5V, which is above what the PSU is set at (exactly 24.00V)

SHIELD on THCAD-5 is connected to frame ground.

tommylight wrote:

snowgoer540 wrote:

tommylight wrote: Above post deleted due to some new information, will report back after sifting through it.

Well i guess i can put the 4 resistors away then? :laugh:

Patiently waiting in suspense...

As i mentioned before somewhere, i have 4 o the THCAD on the way to me, so i can not test anything for now, but PCW reminded me that the ohmic sensing is not disconnected after probing, and that is a bit of a doodle as it can catch the wrath of the HV/HF start from the plasma and cause all kinds of havoc.
For now i have to wait, and even when i get them i have to find a plasma cutter with a shielded nozzle, all i have use no shields for that.
Then again, those THCAD can withstand quite a lot, so thinking differently for now.

Well, the nice thing is you have at least two guys who are stuck inside due to this pandemic stuffs, and willing to do tests. So you can live vicariously through us

Uthayne wrote:
Here's some plots of a "wet torch" condition. Both touching the plate and not. The data was taken right after a pulse command, which had no real effect on lowering the voltage.

My low voltage is 23.8v and high is set at 23.9v

great. It would be good to see a plot of the transition from the on to off state to see the voltage fall off. That is something I will be doing.

I have written a new version but need to make sure it compiles. With a bit of luck I will test today.

So 2 new pins. mode 0 to select current method and mode 1 to follow the trend. The other pin is the number of readings the trend must be seen for (eg up or down for x cycles).

I was a bit worried about the noise you show might prevent a simple trend with x successive readings being lower than the last. I do have some code that computes a moving average which I was hoping to avoid incorporating.

But the plan is that if there is a downward trend, the probe will turn off the moment the voltage falls below the high volt threshold.

rodw wrote:

Uthayne wrote:
Here's some plots of a "wet torch" condition. Both touching the plate and not. The data was taken right after a pulse command, which had no real effect on lowering the voltage.

My low voltage is 23.8v and high is set at 23.9v

great. It would be good to see a plot of the transition from the on to off state to see the voltage fall off. That is something I will be doing.

I have written a new version but need to make sure it compiles. With a bit of luck I will test today.

So 2 new pins. mode 0 to select current method and mode 1 to follow the trend. The other pin is the number of readings the trend must be seen for (eg up or down for x cycles).

I was a bit worried about the noise you show might prevent a simple trend with x successive readings being lower than the last. I do have some code that computes a moving average which I was hoping to avoid incorporating.

But the plan is that if there is a downward trend, the probe will turn off the moment the voltage falls below the high volt threshold.

Forgive me if I'm noticing something everyone else is already aware of. So I have my shield grounded to earth. The interesting thing is that when i dip the tip into water, I can make the false ohmic trip go away by removing the powermax ground from the table. The ohmic goes back to working like normal then (I can trip it with my fingers as it makes about 5 volts).

I havent had enough time to really wrap my head around the whole thing, but for some reason, I feel like a well placed diode would solve the problem. Obviously it's feeding back through the torch, to the ground, and then through the table to complete the circuit.

Am I on to something, or do i have my head up my ...

Also, when I dip the torch in water with the ground on the table my voltage spikes to 25+ volts, even though my PS is only set to 24.5.

Just more data points.

One other thing, can someone explain the 390K resistor. I know it's a "scaling resistor", but if you can put that into laymens terms for me as to what it's doing?

snowgoer540 wrote: One other thing, can someone explain the 390K resistor. I know it's a "scaling resistor", but if you can put that into laymens terms for me as to what it's doing?

Its described in the THCAD manual. Internally the thcad-5 has a 0-5 volt range with a voltage directly connected but that added resistor changes it to read 24.5 volts per the maths in the manual.

So I changed my mind and kept coding. I figured noise would likely be a problem. I decided that if we did a moving average of (ohmic-volts - ohmic-threshold), a positive average would be an upward trend and a negative average would be a downward trend. Whilst this involved some cut and paste of some (complex) earlier code I wrote, it actually simplifies the calculations to something like:
where avgvolts is the moving average of the last N readings (defined by a hal pin)
I just hope we can see the voltage drop away as I did in my testing. Halscope plots needed to confirm this.