Water detector using conductivity but without corrosion

[schn]

Hello members, I wanted to make a water level detector. I used conductivity principle. But i used dc power and with a simple debouncing circuit i was able to detect water.But the electrodes corrode. If i use ac instead the problem will be solved. I am thinking of generating a square wave using 741 opampand then rectify the signal. will it work? i wd much appreciate ur help and ideas.

 

[davoud]

I think you should make AC voltage with 741 (contain Positive and Negative cycle ) and sensing without rectification

 

[audiomik]

What metal(s) are you using for your sensor probe?
Mik

 

[schn]

@davoud.. how do i sense ac? I want to use the coming signal in a logic circuit dat wl control a pump. As I said i hv already implemented the logic circuit using the dc signal i used before.. I used a nor gate ic and made a flipflop.. it controls a pump..

@audiomik... I am using a striped copper wire as electrodes.. I hv also tried a standard 2 pin connector.. Nthng lasts long.. I hv to change/strip regularly to expose new metal.. its frustrating wen my tank overflows..:/

 

[ZASto]

You should use Stainless Steel electrodes.

 

[schn]

@zasto.. thnx for the suggestion.. bt it wd be so much btr if i could use ac to sense.. i am trying a circuit for dat and wl soon post it here..

If any of u guys hv a proven circuit for dat plz share it with me..

 

[davoud]

Okay, I think you can use Square wave (contain + & - cycle) and connect it to one electrode and connect a resistance for biasing and rectifier for sensing to other.

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However you can use micro-controller for sending and receiving detection wave.

 

[audiomik]

As you appear to only need a level limit detector, why not use a float switch which has no exposed metal parts carrying any current
Mik

 

[chuckey]

If you built a two transistor multivibrator, feed each probe via a capacitor and a series resistor from the collectors. Then monitor the voltage between the actual probes. it should be 2 X supply when there is no water and some thing a lot lower when there is water present.
Frank

 

[Audioguru]

Pure distilled water does not conduct. Salty water and my tap water conduct.

 

[chuckey]

"Pure distilled water does not conduct", this is so , except for pure water is one of the most aggressive chemicals around, it wants to dissolve everything in sight. So in a non sterile environment, it will contain dissolved metals and salts which will make it slightly conductive, in the order of .1-2 micro Mhos /cubic cm ~ 10- .5 Mohms.
"hard" tap water is lower then 600 micro Mhos.
Frank