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From: liz@poppyrecords.invalid.invalid (Liz Tuddenham)
Newsgroups: sci.electronics.design
Subject: Re: Damned Projects!
Date: Tue, 31 Dec 2024 17:59:00 +0000
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Don <g@crcomp.net> wrote:

> Carlos E.R. wrote:
> > Don wrote:
> >> Electrolysis can cause the DC sensor to degrade over time.
> >
> > Use graphite. Two pencil leads.
> 
> You can probably adapt this technique to the task:
> 
>     Make your own non-inductive graphite resistors
>     <http://www.troelsgravesen.dk/graphite.htm>
> 
> Is electrolysis mitigation the sole benefit of using AC instead of DC?
> Is there any other reason to prefer AC?

There are two effects caused by electrolysis: it attacks the electrodes
and it builds up a non-conductive film of gasses.  Even if the
electrodes are made of something non-corrodable like carbon or platinum,
the sensor will rapidly go high imnpedance because of the gas film..
For both short and long-term stability, it is better to use AC.

Another problem is detecting the change caused by an increase in
conductivity.  A pair of electrodes will develop an electrode potential
of possible more than 1V, the sensing system for DC needs a signal
significantly greater than this for reliable operation.  High voltages
will overcome the gassifying effect but may lead to the formation of
reaction products between the electrodes and the electrolyte, which may
turn out to be poisonous.

The last thing you want to discover if your kitchen floods is that the
sensor has rendered tha puddle electrically live and toxic.


-- 
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk