Date: Wed, 15 Jan 1997 16:14:11 +1030 (CST) From: blymn@awadi.com.au (Brett Lymn) To: cp@opus.hpl.hp.com Message-Id: <aabcdefg191$foo@default> Subject: Re: measuring restivity of water
According to Zachary Kaufman:
>
>Several months ago I purchased a R.O. unit. Wanting to keep
>track of the membrane's health, I placed stainless steel
>wire sperated at a fixed distance into some R.O. water produced
>by the unit. I then attached my digital multimeter's leads
>to the two pieces of stainless steel wire. To my surprise,
>I did not get a steady resistance measurement diplayed on the
>digital multimeter. Instead, the value kept climbing.
>
:-) Oxidation/Electrolysis dude. You are probably building up a nice
layer of oxide on one of the electrodes - yeah sure they are stainless
steel but the stuff does oxidise. Actually, this is why SS stays
bright looking - the oxide is clear and actually protects the metal
from further corrosion except in some circumstances like in a reducing
atmosphere (if I remember my materials lectures correctly) where the
oxide layer breaks down and the metal corrodes.
Getting a resistivity measurement from water is tricky as you have
found out. I think that one way of reducing the effects of
electrolysis is to use and alternating current as the voltage source
and to use as low a voltage as you can. This is a bit difficult with a
multimeter because a) they use DC and b) they use a fixed voltage
depending on the range. About the only thing you could do would be to
be very quick when doing the measurement to minimise the effects of
electrolysis.
-- Brett Lymn, Computer Systems Administrator, AWA Defence Industries =============================================================================== "Upgrading your memory gives you MORE RAM!" - ad in MacWAREHOUSE catalogue.
This archive was generated by hypermail 2b30 : Tue Jan 02 2001 - 17:30:58 PST