All this is why I bought an Electrical Conductivity meter instead of a
TDS meter. Much more direct at reading, and I have found it matches my
Faraday calculations when starting with pure water (zero conductance).
TDS meters seem much more imprecise.
Kathryn
On Aug 16, 2008, at 11:13 AM, Steven Foss wrote:
Hi Silver List,
"What multiplier do you use and how accurate do
you think your measurements are???"
I use 4 as the multiplier with TDS meters. Why?
To date no major reputable commerical manufacturer produces a meter to
specifically test for PPM levels for Colloidal Silver Suppensions.
When I asked (Hannah), "Not enough sales to justify manufacture, to
small a market."
A TDS meter is designed to measure Total Dissolved Solids in soltion
for applications such as hydroponic gardening, testing tap water and
Reverse Osmosis water, industrial uses for contaminants.
The typical TDS meter measures from 0 ppm to 999 PPM and was not
designed to measure small measurements with an accuracy of less than
50% under 100 of PPM
TDS meters measure transconductance (opposite of resistance) in micro
Siemens and then use circuitry to convert this measurement into a PPM
number (called a Conversion Factor).
The Conversion Factor circuitry "translates" roughly 1 micro Siemen
into 1ppm at Part Per Million readings of 100 PPM or higher at 90%
accuracy. At PPM levels lower than 100 PPM the Conversion Factor
translates 1 micro Siemen as 0.5 PPM, 50% of what is measured.
TDS meters were designed to measure dissolved solids conductivity and
are calibrated with Sodium Chloride (the "yellow" solution sold with
these meters) as a rough "Guesstimate." Salt is used as an average
approximation of the conductivity of the compounds and elements (and
polutants) found in water. (Potassium Chloride is the world standard
for calibration, but then TDS meters do not require scientific
accuracy.)
Soldium Chloride or table salt has twice the conductivity of Silver.
Or Silver has 1/2 the conductivity of table Salt. So any measurement
of Colloidal Silver will be half of that for dissolved solids.
TDS meters round off their measurements downwards after conversion. 0
to 0.9 PPM will read as 000 PPM. Likewise, 1 to 1.9 PPM reads as 1
PPM, etc.
Let's use some numbers. Let's say I have finished a batch of CS and
send half of it to a lab that runs an Atomic Aborption Spectragraphy.
The batch was made with Lab & Tech distilled water (0 PPM). The
test measurement is 10 ppm
I reach for my trusty TDS meter. The meter measures 90 % of the
transconductace (calibrated to Sodium Chloride which has twice
transconductance of CS) so 4.5 only is measured and the conversion
factor has a 50% error (under 100ppm readings) so 2.25, rounded down
becomes 2 PPM.
I have a batch of 30 PPM CS. 15 X 90%= 13.5 microS measured
multiplied by 50% Conversion=6.75 rounded down to 6 ppm
If I have a reading of 3 PPM X 4= 12 PPM (3 times 2 (for Conversion
Factor) times 2 (Salt factor) equals 12 PPM)
This doesn't account for Commerical Distilled water which measures
from 0 to 2 ppm (0 to 4 ppm if taking into account the Conversion
Factor from circuitry). The DW will measure as 0 ppm at levels as
high as 1.9 ppm (actual).
That is why I use the number 4 as a multiplier when using a TDS meter
to measure CS batches.
How accurate do I think these measures are with TDS meters?
Not very accurate, but better than nothing, or shelling out $400 USD
everytime I make CS to get an accurate reading.
Regards,
Steve Foss
If you are using Sodium Chloride or Sodium bicarbonate as an
electrolyte this muddies the water (and the measurement) further.
>Question for the group: What multiplier do you use and how accurate do
you think your measurements are???
Just make sure the TDS meter probe is not contaminated when measuring,
make sure there are no bubbles on the probe tips and do not try to
measure moving water (keep TDS meter still in water).
- Steve
<
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>..
Hi Steve. How does one use a TDS meter? Thanks. Faith G.
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