Bon Jour,
By tension, I assume you mean torch voltage? There is an Opto isolator that translates voltage in to a proportional resistance out, You may be able to monitor the voltage by voltage divider into the Opto and use the resistive output for a Analogue input PIC.
If you wish to persue this idea I can look the opto number up, I picked a few up a while ago, meaning to experiment with them.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.