Hi there - I've been looking at using something along the lines of this bad boy. It's a variable inductor, essentially. The inductance changes as you move the core over the coil, allowing you to get a contactless linear position measurement. It's a lot like an LVDT, only it's not a transformer - just an inductor.

How would you suggest instrumenting such a beast? They say the excitation frequency is 112KHz. I'm guessing they mean that that is the maximum frequency that you should excite it at - but I could be missing something.

So here's my first pass at a plan for it:

Connect it to a full H bridge. Do a differential voltage measurement across it. Run the H-bridge at 112KHz with a square wave. Measure the current and voltage 4x per cycle, two times when it has positive current flowing through it, two times when it has negative current flowing through it. Find the di/dt of the first set of currents and of the second set of currents. Divide the voltage measured by these di/dts and you have two measurements of your inductance. Repeat this over and over and average the hell out of it.

Seem reasonable?