Parece que si hay efecto de Polarización en la medida de conductividad, por lo que me rectifico:
"When a DC voltage is applied across the electrodes of a conductivity cell, the ions present in solution will be discharged onto the electrodes and by surrendering or accepting electrons, be changed into molecular form. The flow of ions will then virtually cease within a very short time, and consequently, the current will decrease to virtually zero. Therefore, an AC voltage is used for conductivity measurements. Polarization, however, can still actually take place during a half cycle of one polarity, causing a space charge buildup around the electrodes, resulting in a loss of current flow. In addition to polarization effects, conductivity cells with higher cell constants require long, narrow passages to obtain these constants, which make the electrode contacts more susceptible to coating by oils, slurries, or sludges commonly found in streams of high conductivity."
Pues con lo que me habia molado el tema de la pila de 9V y el voltímetro. Mi exprimento funciona 100% con DC..... No sirvo para químico!!! XD XD XD
A parte de que mi novia ha flipado cuando he montado el tenderete en la cocina.....
Me imagino que tendrás que buscarte un ADC diferencial externo con gran resolución y un DAC para producir las señales AC. Por lo que parece también un sensor de temperatura, porque parece ser muy dependiente.
De todas formas, en google (buscando en inglés, como la mayoria de veces) salen muchas cositas....
http://gim.lx.it.pt/dicsap/artigoIMTC2006.pdf
http://nopr.niscair.res.in/bitstream/123456789/9572/1/IJPAP%2042(3)%20182-188.pdf