I believe I have bitten off a little more than I can chew with my first Arduino project.
Most of my project is complete as far as the logic goes but my elementary knowledge of analog circuits has a
gremlin rearing its head.
Here's my projects premise:
I'm using the arduino to sample the voltage between the torch and work piece on my CNC plasma cutting table and
using that voltage to adjust the height of the torch. DTHC (digital torch height control)
The plasma cutter is constant current and as the torch introduces heat into the metal it warps and varies the distance (as well as the subsequent voltage of
the torch height relative to the material.
I'm trying to keep the voltage constant by continuously adjust the steppers on the z-axis (torch axis).
Here's my setup thus far:
* probes from the work clamp(+) and electrode(-) send roughly 160-200vdc to a 50 amp bridge rectifier - I'm following someone elses lead on the rectification
* rectified signal is then passed through a simple voltage divider
* signal is then run through a low pass filter consisting of a 330 ohm resistor and 100uf/25v electrolytic capacitor
* MCP3201 12 ADC sends value to arduino via SPI
When arduino gets the value it runs some simple if/else functions based on height preferences relative to the material being cut.
When done with the calculations it encapsulates the control information and voltage information into modbus holding registers and sends them to my CNC control software to be read and acted upon.
Here's my problem:
As a beginner my understanding of the analog side of things is extremely limited.
I know my plasma is very noisy and has high frequency signals that are more than likely making there way into my ADC.
The reference voltage that I get from my ADC jitters.
It's not a huge variation but it's more than a couple volts and that equates to more slop than I want to deal with.
It also limits the speed at which I can cut.
I've been reading about two stage Pi LC low-pass filter because that's what commercial units use with success.
I just purchased an oscilloscope and could acquire some data but not exact sure what I'd be looking for just yet.
Does anyone have experience with these filters and willing to share some knowledge?
I've been studying these circuits and trying to visualize what is transpiring underneath but I'm in over my head.
Here's a pic of the circuit on the left and what I think is happening on the right???
This is the torch and workpiece: