EC meter (or TDS or Electrical Conductivity)

Hi all,

I’m actually looking at building an EC meter which calculates the electrical conductivity of water (as the subject says so …).
This will then be doing some basic actions for correcting the solution (water) with some salts.

By the way, i’ve got a lot of problems gathering the informations on how these probes works.
I’ve got a pH probe too that will be interfaced thru a Phidgets 1130 module (this works pretty well by the way !).

I found this probe, cheap product compare to others : http://www.top-messtechnik.com/jtlshop/index.php?a=676&lang=eng
As my questions remains, i asked the owners of the site to help me a little on their probe. I hope they will answer with precious informations.

Thanks !

All I can recall about this is that such meters use AC to prevent gas build-up on the electrodes (and a very low current to avoid dissolving the electrodes too quickly!). My intuition is that a constant-current bipolar square wave is used and the amplitude of the resultant voltage across the probe is then proportional to resistivity of the fluid. The AC needs to be low frequency to avoid effects due to stray capacitance (water has an extremely high permittivity, about 80).

There might need to be several ranges since aqueous solutions differ 7 orders of magnitude in conductivity in worst case.

The AC output voltage may have super-imposed DC from electrochemical differences of the two electrodes, so I guess its important to measure only the AC component.

Based on the fact that EC probes seems to be selling (quite) everywhere, and for honests prices, is there a module that permits to connect the probe to it and gather the information (like the Phidgets 1130 module) ?

I prefer buying the module rather than doing it myself (and probably fails) because, when it comes to "precision measures" ... you know the deal !

Hope that someones knows where can i find this kind of module with BNC connector !

Thanks !

PS : By the way, i had found this page some time ago that talks about just sending voltage thru the solution : http://www.octiva.net/projects/ppm/ Basically, it says, if you send +5v between the 2 contacts of the probe (spaced by 1cm), if the reading is +3v, then the solution has a EC of 3 //for PPM -> x1000// 3000 ppm. I think this is too basic, and probably needs some tweaking. For example, i think that the EC probes (which are made of platinum), used at +5v should not last very long because of "hydrolysis". The more voltage, the more hydrolysis (i think, perhaps i'm wrong ... ?! hope that a great scientist will help me/us out of this :) )

Please forgive me for what i said, i did not even read the whole page before posting it. My apologies !

Hehehe !!!

FOUND IT !

So, after searching, i found the module i wanted !

It's something that works on +5v DC and uses a serial port based on RS232 (it works between GND and Vcc ; so it can be directly connected to the arduino).

Here is the link : http://atlas-scientific.com/Arduino-ph.html

Hope that helps a lot of people to do some wonderful works !

than you immensely for that link: http://atlas-scientific.com/Arduino-ph.html note to others, there are stamps and arduino code for dissolved oxygen, electrical conductivity, ph, and Oxidation Reduction Potential there.

These Kits provide everything you need to quickly set up your electrochemical monitoring system.

nice that all the ground work has already been done ready for you to discover. all we need now is the Chinese counter-part at discount prices XD

I had tried to make my own EC circuit back in the day. It was hard to do,...very hard to do. But I kinda got it working.

Then, like you I found Atlas Scientific. I got the pH stamp first. Worked great. So, I finally came to terms with the fact the my EC circuit was a not going to work. I broke down and bought there EC stamp.

As embarrassing as it is to admit,...I should have done it moths ago.

Anyway, I built a sick reef controller. I hope to sell it one day.

...just thought I'd add my two cents (because I went through the same thing).

Jay

You can also use these sensors. http://webpages.charter.net/tdsmeter/conductivity.htm