Question about THC parameters

For mode2 it is a percentage of Z maximimum velocity

For modes 0 and 1 it is mutliplied by the current height error, so the speed is determined by the PID-P value and the amount of height error.

sorry for a few more questions, how do you calculate or find out the current height error? Is the speed (PID_P x the current height error) in mm/ imperial unit or something else?

Theoretically it is not height but voltage. It is the difference between the arc voltage and the target voltage. The result is used as a height change in machine units per servo period.

Thanks for the explanation but I still don't know what speed my THC will be if I use PID-D in mode 1. My Z axis's max velocity is 4500mm, my PID-D is 10, my target voltage is 69 volt(cutting 1.2 mm stainless steel) and the arc voltage is 73 volt. From these information, can I calculate my THC speed? From your explanation, I will have 40 (10 x (73v - 69v). Is this 40 the speed of my THC in mm?

I didn't realise that you needed the exact velocity of your THC so I was only giving you a simplistic answer, it is more complex than that as it also takes into account the scaling and the resolution of the Z axis eoffset and it will change every one millisecond.
Why do you need to know the exact value?

Your torch speed will be up to your maximum velocity. The whole intent of a PID is it is a self adjusting algorithm that converges on the set point. If you google it, there are plenty of explanations.