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With water on the table and too low short circuit current configured,
we get something like the orange curve. A damped curve with reduced "swing".
No sharp transitions between open and short circuit.
 

Of course I tried to fix this in software, therefor the four conditions to trigger a sensing contact
The right thing to do was to lower the R1 value and increase the short-circuit current.

 

Hello I have this specific setup where my secondary turret is beyond my limit switch. What are my option if I want to use it and I still want to keep my security up? Is there a was to disable temporarily the limit switch with a specific tool? Thank you 

 

Here is what a sensing cycle looks like under good conditions.
Green: Sensing output signal: 1 if contact, 0 of no contact
Cyan: Voltage between plasma tip and work piece
Purple: Enable ohmic sensing signal
Red: Z-axle position.

First there is a 15 ms reaction time for the relay to switch on, I call it setup time.
After the setup time has expired, the contact evaluation starts.
There are several conditions.
1. Voltage drop below a set voltage limit like 12 V
2. Voltage drop from voltage at end of setup, like 5V drop
3. Overall voltage drop over one cycle, like 5V
4. Overall voltage drop over three cycles, again like 5V.
For good conditions like then one in the picture all conditions triggers at the same time in principle.

I have avidcnc from 2017 from wich i recently replace the breakoutboard with a mesa7i76EU to make it work with linuxcnc.
Everything seems to be working fine,

The only problem i have is that it doesn't seem to use the WCS coordonates after i zero my machine But keeps using only the absolute coordinates when im running my gcode
This causes the machine(zaxis) to move into the bed when starting the program.

can somebody help me please.
Thanks in advance.i added my gcodeand my hall/ini files for qtdragon.  

It's possible for my specific servo but there is not point to do this as my servo is not piloted by position but with analog (no ethercat drive)

Updated schematics 

Update of this project.
Regarding water on the table and difficulty to properly detect contact.
Yes, been there, done that. 
It seems to be caused by too low R1 resistance. Which means too low current at short-circuit.
Stray currents through water are in the same order of magnitude as the short-circuit current
and influences the voltage measurements. 
Too high R1 (low short-circuit current) and water on the table causes two things:
1. The measured voltage will only go to single-digit voltages, like 8V instead of 24V
2. The measured short-circuit voltage drop is only a few Volts. The voltage stays at some 8-3 = 5 V, where it should be 0V.
When looking at the voltage, well working means sharply up to some 23V, then sharp drop to 0V.
Not well working: Damped rise to some 10-ish V, damped drop of a few Volts at short-circuit.

Using R1 = 100 kOhm, short-circuit current = 0.24 mA. This is too low.
Using R1 = 2k7 kOhm, I = 8.9 mA works much better.