Conductivity Meter Circuit

Bearing in mind that conductivity is highly temperature sensitive, I don't think you will be able to measure it quickly unless the temperature is stable. Most measuring devices have substantial thermal lag.
Del

There are complex sensors + circuits that are far faster than that, such as 10kHz AC bridges, etc., like those used for fast profiling of the water column in lakes and oceans. It would be helpful to know your accuracy/stability needs, and your budget.

You should be aware that there are actually standardized units of conductivity, that are referenced to a temperature standard.

See my comments at the end of a year old CR4 thread on the issue of reading conductivity with an ohmmeter and the implications of reading "conductivity" in standard units of Siemens/cm or, something else, the reciprocal of resistivity.

http://cr4.globalspec.com/thread/57326/Conductivity-Resistivity-Measurement-with-an-Ohm-Meter