Question about THC parameters

I have no intention of digging too much into the details of how a PID controlled THC works but I just want to control the thc exactly like what I want. The reason is that when I cut a rectangle, the torch will cut one edge of the rectangle at the target voltage(69v) but when the torch changes the direction, the voltage will change to 71v or 72v even in the middle of a long edge. I was wondering why the thc wouldn't cut all the same edges of the rectangle at the same voltage. Is that because my thc speed not fast enough or I missed something in the PID setting?

Disable VAD = Velocity Anti Dive

Is THC ENABLED on during the cut?

Is THC ACTIVE on during the cut0?

• if NO, is either VELOCITY A/DIVE or VOID A/DIVE on during the cut?
• if YES, is either UP or DOWN on during a cut?

It might be a good idea to disable VAD to see how it goes. I always enabled it to lock the torch around the corners. Will try it next time when I am around the machine.
Yes, THC ACTIVE is on and everything is working as expected(VAD, Up and Down led), just the cutting voltage is slightly different for each edge. By the way, the rectangle I cut is around 50x100mm, my feedrate is 3900mm, my acceleration for x/y/z axis is 1500mm/s/s. Is the dimension of the rectangle too small for the thc to kick in after the VAD lock?

If THS ACTIVE is on then that means VAD and/or VOID are not inhibiting it.

If UP or DOWN are on then the Z axis should be moving in the indicated direction and changing value in the DRO.

Attached are my sim settings and the z axis moving with a 1V differential between the target and the arc voltage.
 

I guess the real question is; Is the cut quality still OK  on the second and subsequent sides?
If so, don't worry.
Typically torch voltages changes 10 volts per mm so 1 volt is only 0.1mm
Say if you reduced to 80% and had to get back to cut speed, It will take 0.52 seconds so that might mean you travel say 3.5mm..
3900mm/min = 65 mm/sec so you will travel about 34mm in that time