Hi Bruce,
My two-pennorth,

Go LVDT. Its relatively easy to get extremely good results, low drift etc. We use Schaevitz LVDTs. You can buy readout boards, or, I can supply you with a board with an analogue output if you are interested. We have 25 years of practice in making stable, low drift lVDT systems.

I'd mount your LVDT body on a un strained bracket just beneath your proving beam, so that you can eliminate thermal expansion in your systems. Bear in mind too that spring rate is ALSO temperature dependent, and you may or may not need to allow for that.

The capacitance method we used for our sensors would be even better, but takes a lot more setting up - it used my favourite technique of transformer bridges.We had a metal ring, with a ceramic plug in the centre perfectly suspended in the centre. On the plug are 4 capacitor plates, deposited by reduction firing silver oxide, which are wired to the bridge.



Steve