THCAD-300 and Plasmac User Guide questions

Long time lurker, first time posting... First thanks to everyone who has inadvertently contributed to my success via all my lurking!

I recently converted a working gmoccapy install to Plasmac, and I am trying to get things right for my THCAD-300. It seems the Plasmac userguide specifically shows examples for the -10, and I am having some trouble getting numbers that make sense for the -300. I am in fact using F/32 as a jumper setting.

0V = 120 kHz
300V = 920.4 kHz

Under 22.1, the divider ratio for the THCAD-300 is said to be 29. I am wondering where this came from? I am guessing it is a known value from Mesa?

For 22.2, the example shown is for a 10v board. Being that mine is a 300v board, is the new formula simply Divider_Ratio/((300v_frequency-0vfrequency)/32/300)? When I plug in my numbers I get 29/((920400-120000)/32/300) = 0.347826. This leaves my display on Plasmac bouncing around between 5-8 volts. It seems like I am missing something simple here? But maybe I made incorrect assumptions when using the 10v formula for the 300v board.

Lastly, for 22.3, there's a new line since the last time I looked at the documentation:

setp hm2_7i96.0.encoder.00.filter 1

I am assuming that this just turns on the low pass filter as specified in section 4.11? Which also makes me assume that you need to add the line: setp plasmac.lowpass-frequency 100 to the HAL file as well? I am not quite sure I follow what this is useful for? Where did 100 kHz come from?

Thanks in advance for the help!

-Greg

You do not have a divider so do not use the 29.
That is all, as 29 multiplied by 4 to 5 you are getting will give 116 to 145.

tommylight wrote:

You do not have a divider so do not use the 29.
That is all, as 29 multiplied by 4 to 5 you are getting will give 116 to 145.

That makes sense. Sounds like the voltage divider should actually just be 1 then.

But I am curious, why does the user guide say that it is 29?

rodw wrote:

I've never really agreed with the idea that you need to do some maths to configure a piece of software. I really found this confusing when I started and thats why I wrote this component that lets you enter all of the parameters and no need to do any maths
forum.linuxcnc.org/plasma-laser/32585-scalethcad-component

I still use this today and set plasmac to have a scale of 1 and an offset of zero but I have dropped the included filter.

I think your offset = 120000/32 = 3750
So your full scale = 920400/32 = 28762.5
So your range from 0v to 300v = 28762.5 - 3750 = 25012.5
So your scale (frequency count per volt) 25012.5/300 = 83.375

So enter 3750 and 83.375 in plasmac and see how you go.

I will definitely have to check that component out, I didnt know it existed. I thought to myself "why cant my frequencies and which THCAD I have just be part of the configuration?". I am sure there are lots of other things on the priority list though.

I think the scale is looking for a really small number though. Everything you said makes it more clear, but I'm thinking it's looking for a really small number for scale though, would it be (1/83.375) = scale (0.011994)?

So you said you dropped the filter. Why? I'm still not sure I understand what the filter is supposed to do exactly.

Lastly, someone recently brought the hypersensing to my attention. Guess I have to order another THCAD now LOL. Good work there!

I think so as well, I think option 2 makes the most sense in my mind, without really understanding the system as a whole.

Good point on locking Plasmac to one vendor, didnt think of that.

Thanks for the reply, it helps a lot!

AgentWD40 wrote:

I made a little calculator for this a while ago

jscalc.io/calc/NTr5QDX6WgMThBVb

AWESOME! Thank you so much!

phillc54 wrote:

If those numbers are confirmed can I put a link to that in the PlasmaC docs.

This works out to what I ended up calculating. My machine has no voltage divider, so 1 makes sense there.