Plasma Gap Control

One of the plasma kit people (I think Torchmate) has incorporated a
feedback device on their plasma cutters to maintain accurate gap control
over wavy steel and uneven surfaces, etc. I thought they were going to
sense changes in the cutting current, but it looks like they are using
proximity sensors instead.
This feeds a signal back to the controller to increment the Z axis
up and down to maintain good gap, and therefore more consistent cuts.