Works off the signal generator, every time it calls for a tool on command. You will need to add the G160 command to one of your Macros. If your table only has one tool being Plasma then likely you are using the M20 macro found under the menu Configuration > Programming > M-code Definitions, if you have more than one tool then you are likely to be using a different macro where the same applies. Open the M20 macro and after the M50 command which turns the tool on insert the line G160. Such as:
IF #AVHC = True THEN
M50
M101 I1 "No Pierce Signal Received"
M160
ELSE
M50
G04 x#piercedelay
M160
ENDIF