Would not this device require a voltage source with a DC value of 0V?

An alternating current to me implies that it must go above and below 0V in equal amounts. If you measure 120vac with a DC voltmeter you get 0 volts.

I guess if you could get the circuit to work on a split supply and could make sure the voltage across the humidity sensor measured 0v... Seems like a lot of trouble to go thru tho.

 

It seems the sensor behaves like a capacitor and resistor , where its impedance alters with humidity at relative temperatures ( see datasheet), so you could use it in an oscillator circuit to vary the frequency, and then read the frequency or convert it to voltage using a F to V.

Datasheet...
https://www.google.co.uk/url?sa=t&s...&sqi=2&usg=AFQjCNFpjw8IHn5E6EULO-zjsVa1I7wpFg


One example here..

http://www.dzsc.com/dzbbs/uppic/200706140954107083.jpg