In a message dated 97-12-14 17:17:04 EST, you write:

>
>  I would like to learn more on Resistivity, can someone clue me in on the
>  pupose. What is the meaning of Resistivity and why should inline cleaners
> have  meters to show what the Resistivity is at all times?
>

Peebos,
Resistivity is a material parameter.  It is based upon resistance, or the
resistance to the flow of electricity.  When used with a solution, resistivity
is measured in ohm-cm or megohm-cm.  A very clean deionized water sample will
read very high in resistivity because there are no ions to carry electrical
current.  Our laboratory DI water source outputs 18.3 megohm-cms.  For an in-
line cleaner, you would measure the resistivity of the wash or rinse solutions
in order to know when they have become contaminated.  As the solutions load up
with soils, the resistivity will drop.  In my opinion, you get far superior
cleaning with deionized water than with lesser purity water.  A good target
value for in-line cleaners is 2 - 6 megohm-cm water.  When it is in the range
of about 200 kilohm-cm to 1 megohm-cm, it is classified as reverse osmosis
(RO) water and cleaning is not as efficient.  If the resistivity drops even
lower, then you are dealing with tap water which does not clean as well.  On
the other hand, you don't want DI water that is too high, say on the order of
10-12 megohm-cm.  Jim Maguire at Boeing has some interesting stories about DI
water attack on stainless steel at consistently high resistivity levels.
FWIW.

Doug Pauls
Technical Director
CSL

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