Now that I’ve got my waxy work buttoned up (at least for the time being), I’m ready to get started on my next project…which is actually a return to an old one. Time to revisit my displacement sensor tinkering yet again.

But this time I want to up the ante a little bit. While my previous builds hit strong ‘top line’ repeatability numbers, their dynamic range and stability were not impressive….or even something I would consider acceptable for a commercial sensor.

My measured repeatability for my last iteration of sensor came out to +/- 2 µm (4 µm total) on a range of 400 microns. That’s only 1:100.

As a comparison, my chromatic confocal sensor (a commercial sensor that costs ~$10k) has a measurement range of 10 mm, and a measurement resolution of 0.25 µm. Now, I don’t care for using resolution, since that could just be useless digits, but the datasheet does not specify the repeatability. Going off of the resolution, the dynamic range is 1:40000. I usually ballpark it as being good to ‘about a micron’…granted, this is making me realize I’m very much due to actually characterize this thing a bit. But if we call it a micron, that’s puts it at 1:10000.

My reach goal for my new sensor is +/- 0.5 µm repeatability on a total range of 5 mm. With an uncertainty of 0.1 µm on each gauge block, I can’t even stack blocks and still stay within the 4:1 limit of measurer:measurand.