how to link the analog input in mode1 of qtplasmaq

Good evening everyone, my question is how can I link an analogue input to the hal, I'm reading this input through a plc via Modbus, I wanted to know where I have to link it for the thc to work in mode 1 of qtplasmac, I'm using Linuxcnc 2.9.2 , thank you in advance, I apologize if it's difficult to understand, I'm Brazilian and I'm using a translator

the pin you are looking for should be,    arc_voltage_in however not sure if modbus will be fast enought for the plasmac THC control loop,
if you are working in a "conventional"  plasma machine, the recomendation is to use MESA THCAD card to read the voltage. 

I also wanted to be able to use a table, but in Brazil it is not so easy to get a plate like that