conductivity meter

asoe,

Sorry to "shoot down" your idea, but conductivity meters abound on the market.

In my current (print) edition of the Ben Meadows Company "Water Guide" catalog, there are more than ten pages of conductivity meters, ranging in price from < $100 (US) to over $900.00...

Here is a link to their online catalog, (specifically conductivity meters):

http://www.benmeadows.com/store/Water_Testing_and_Sampling/Water_Testing/Conductivity_Meters_and_Soluti/

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Just my $0.02...

asoe,

JMAN is right - if you want to develop such a device for business in order to sell it you should better burie that idea, there are so many instruments in the market that the chance of success is rather low.

If you - apart from that - want to build it for your own in order to learn something about electronics and have a little interesting and managable project then you should do that and I promise you will have a lot of fun and learn success.

I would recommend to take a cheap timer with some kiloHertz as a digital reference, an analog FET-switch like the 4051, a quad OP like the LM324 or meanwhile something better, some R`s and C`s and build a phase sensitive amplifier. Your investment will be not more than 2-3 dollars and you will be able to get an uncertainty of <= 0.1% which means a resolution of about 10+ Bits with a lo cost design like that.

Phase sensitive amps are very insensitive against noise and disturbances in industrial surroundings and so very reliable.

Have in mind that purified water has a practical and theoretical lowest limit of 0.055µS corresponding to about 18.2 MegOhm.

Hope that helps - regards Uwe

thanks for that ..

you are right i am not going to market that as you said those things are too much popular...

I would like to have that to test my mixed solution IPA/DI water... which is could purified to 100M.. could be higher than that indeed..

By the way I wonder if you know I could find the schematic on the internet?

One of the ways would be to study the Thornton conductivity and resistivity meters(usual disclaimer) first. Beware of copyright and patent infringements though!

BTW: water, which is probabaly the only fluid for which conductivity and resistivity are needed, has an absolute theoretical purity of 18.8MΩ.cm at 25degC ("Kohlrausch water") and therefore a meter reading to zero conductivity is not actually needed.