A meter that reads out in uS [Microsiemens/cm] isn't a "TDS" meter.
Trem sells the Hanna PWT..it's not a TDS meter.
Trem says 1.2 uS/cm to 1 PPM, I say 1 to 1.
Saying uS on the meter without the /cm part... is a bit sloppy.
TDS meters read out in PPM.
The numbers are derived from measuring uS/cm and running that through a
water industry standard fudge factor for salt water to guesstimate PPM.
The fudge factor isn't a straight up 1 PPM = 2 uS/cm in silver water
using a salt formula, more like 1 to 1.8 and might even slide around
depending on where on the scale the measurement is being taken...but 1 to 2
is about as close as the meter is accurate and it's just an estimate to
start with.
There are 3 different commonly used formulas for converting uS/cm to PPM
in different dissolved solids that I'm aware of.
NaCl, KCl and 442. [I'm not aware of exactly what those formulas are]
A conductivity meter is far better than a TDS meter for this application,
but even then, it only reflects PPM in silver water under certain
conditions which may explain why Trem and I have come up with different
conversion factors after comparing uS/cm readings to AA Spec test results.
[1:1 vs 1.2:1]
Note: "reflects" PPM...not "measures" PPM and it's a fun-house mirror.
To be more specific [admittedly, in a bit of a broad and wobbly fashion],
uS correlated to PPM at 1 to 1 at 7-12 PPM at 75 deg F with 10-15%
particulate [unreadable] content.
Meters in general are a bit of a wobbly tool used in a context of an
extremely wobbly application where PPM applies to actual real world use of
CS/IES
Whether it's a 20 megaton bomb on the diamond or a 10 megaton bomb in
the ballparks parking lot, is pretty much a moot point if either can take
out the entire sports complex and the only argument left is how big each
crater is...and nothing but vapors left around to do the arguing. [An
edgemucated guess is good enough, so who cares if it's a 22 megaton bomb?]
or
the baseball only needs to leave the field to be a home run. If it goes
to Detroit from Shay Stadium or just makes it to the first row in the
stands, it's still a home run.
Using a cannon instead of a ball bat is just buying insurance.
Ode
At 12:43 PM 12/28/2005 -0500, you wrote:
I am a little confused on TDS measurements. Trem says that when using the
Hanna
TDS meter he supplied me for measuring EIS, that the ppm of the molecular
ionic
part and the reading on the meter are approximately 1:1. The meter says
that it
is reading uS, but that is a nonsense unit, it has to be uS/cm or uS/in or
something, not just uS. Ole Coyote says that the reading should be
multiplied by
2 to get the correct ppm, and Frank Key at
http://www.silver-colloids.com/Papers/CSProperties.PDF indicates that TDS
meters
are calibrated for calcium carbonate, that has a ratio of .5 ppm/uS, and that
ionic silver has a ratio of about 1.1. Thus one should multiply the
reading on
the meter by about 2.1 to get an approximation of the molecular ionic silver
content which argees with Ode..
Then http://educate-yourself.org/products/tdsmeterdescrip.shtml indicates
a 1:1
ratio again which agrees with Trem.
So I am confused if I should be multipling the reading by 2 or not. Trem,
do you
recalibrate the meter for EIS before shipping it out, or is it the standard
factory calibration?
Can anyone enlighten me on this?
Thanks,
Marshall
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