Thickness measurement: one sensor or two?
Whether your material is transparent decides the whole architecture.
On opaque material, thickness measurement needs two sensors facing each other and a frame stiff enough that the frame itself isn’t what you end up measuring. On transparent material, a single confocal sensor reads both surfaces at once and no frame is needed at all.
The frame is the hard part
In a two-sided system the C-frame is the dominant source of error. Carbon fibre and active temperature compensation exist because a steel frame that grows a few micrometres over a shift looks exactly like a change in thickness.
