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Conductivity Meter

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  1. conductivity meeters
    by wedman/ucsu.Colorado.EDU (WEDMAN DOUGLAS EDWARD) (11 May 92)

conductivity meeters

by wedman/ucsu.Colorado.EDU (WEDMAN DOUGLAS EDWARD)
Date: 11 May 92
Newsgroup: alt.aquaria,rec.aquaria

In article <1992May8.191659.25608-at-kong.gsfc.nasa.gov> mstephens.520-at-postman.gsfc.nasa.gov (mark stephens) writes:
>I've been hearing (or reading) a bit about conductivity meeters.  Would
>any body that has one relat what they have, when they use it and any
>thing else relevent...  
>
>I take it these devices replace, in some fashion, the test for hardness.
>"Hardness" is usually the amount of Ca, but it can vary.  Alkalinity is
>another confusing term, at least to the chemically challanged. I would
>hazard a guess that the conductivity meeters measure total dissolved 
>solids.  Does this include KH?
>
>         mark

Mark:
  A conductivity meter measures the ionic conductivity (or conversly, the 
resistance) of a liquid.  The number it gives can not directly be related to 
hardness, but rather, the total ion content of the liquid.  What the device
usually consists of is an probe which usually has two platinum electrode plates
parallel to each other and separated by some small distance.  The meter is
in its simplest form, a Wheatstone Bridge aparatus with a small oscillator and
a readout.  The oscillator generates a small amplitude (about 5 to 10 mV peak-
to-peak) sin wave.  The meter is zeroed by dialing in a resistance on one side 
of the Wheatstone bridge.  The resistance dialed in is then the resistance
between the two plates in the probe.  Relating this value to a calibration
curve for the probe will give you the concentration of ionic species in 
solution.
  I'm sorry that this is so technical, but it is neccessary that you know what
you are getting into.  These devices are not cheap and do not give you the 
kind of information that you are looking for directly.  You would need to do
other tests to be able to extrapolate out the information that you want.  The 
commont test kits for water hardness and densiometers are much more adapted to 
common aquarium type purposes.  
  I hope that this helps!  Let me know by E-Mail if there is more info that you
need, etc.

-Doug Wedman
 Ph.D. Student
 Chemistry Department.
 University of Colorado, Boulder
 CB 215
 Boulder, CO 80309-0215
 (303)492-8957
 (wedman-at-ucsu.colorado.edu)


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