Hello all,

We have a device with which can be modeled as three parallel plates, with
the middle plate moving back in forth via a spring, affecting the
capacitances between it and the other two plates. We were hoping to measure
differential capacitance O(1-100fF), while at the same time actuating the
middle plate via electrostatic force using a large DC bias 50 - 200V. We are
looking for a circuit or sensor we can buy that will do this differential
measurement (probably via AC current) while allowing us to actuate the
middle electrodes. The only similar sensor we have found that you can buy is
sold at microsensors.com , however this uses a
reference DC voltage around 1V to make the measurements, thus not allowing
actuation using a DC bias.

We would like to avoid having to build our own circuit board to do this, but
if it comes down to it, how complicated would this be for someone with a
mechanical engineering background?

Thanks for your help.

Andrew O'Grady
Mechanical Engineering Department
Columbia University
[email protected]