Well you can't do it with direct current; you will get a reading for less than a second, then nothing. The reason is that the conductivity is a result of the ions present in solution, and passing DC will alter this.
You need some kind of oscillator (Wein Bridge, or similar) to create a sine wave. Between 1 and 10 kHz seems to work well. Then using this current, and your probes (an audio cord with a gold plated phone plug works well,) measure the resistance of the water.
Well, it isn't really like a pH meter. The pH sensor acts like a very small battery; it puts out a very high impedance voltage, either + or -. at pH 7.0, the probe will put out 0.0v. With that one you have to offset, and scale the output.
Which probe were you thinking of? Post a link, so we can look at it.
Like Hero said, more info.
Well, it isn't really like a pH meter. The pH sensor acts like a very small battery; it puts out a very low impedance voltage, either + or -. at pH 7.0, the probe will put out 0.0v. With that one you have to offset, and scale the output.
Which probe were you thinking of? Post a link, so we can look at it.
Like Hero said, more info.