At 02:32 PM 6/16/2007 -0500, you wrote:
Evening Ode,
>> At 07:23 AM 6/16/2007, you wrote:
Are there any major differences in these meters.
PWT
TDS
EC
I think the PWT meter is mostly a sales gimmick name.
If you have pure water, why test it? Seems it should be simply called a
Water Tester Maybe the ranges are different.
You test pure water to make sure it's pure.
The ranges are different, so range read error is less with a lessor range
when testing nearly pure water.
EC is another name for conductivity meter, but doesn't indicate the range
used when checking pure water.
PWT indicates that range. Hanna has other EC meters that use higher ranges.
The COM-100 has an automatic dual range function, the low range similar
to the PWT and the high range double that, as well as 3 different salt
water conversions to PPM / TDS
## A TDS meter takes the conductivity and converts it to a PPM
equivalency for sodium salt water. It's range is generally huge, readout
resolution low and the fudge factor used for the conversion may only be
accurate to plus or minus 4 uS.
Two identical TDS meters calibrated in the same 300 PPM solution may read
two digits off from each other at 5 PPM with it's range read error spread
and that two digits can represent as much as a 16 uS difference. [Most are
Usually not that bad..some cheapos are worse.]
Re-calibrating them in a solution closer to the intended application make
them a lot more reliable and accurate [ I always do that ] but there's
still that resolution thing...no decimals on the display.
I realize that people like you need a variety of good instruments.
Seems that 90 % of the CS makers likely don't use instruments and don't
need them. That is, unless they have reason to suspect abnormal
impurities and low quality water.
Even though I have an EC meter I simply use the LED on my CS generator to
get a good idea of the water quality and often reject water simply by the
intensity of this LED.
## If the LED is in series with the electrodes, it will give an indication
of current draw [hence, water purity] with relative brightness...IF the
electrodes are always mounted the same and the water level is the same.
However, if there are no current controls, the current can get high
enough to burn the average 20 milliamp max LED out.
I think every CS generator should have an LED.
I add LEDs ( so cheap they are almost free ) to many control panels I
build. It allows me to make a near instant diagnosis when I walk up to a
panel. I even add one to show me when the phone company switches the
polarity on lease line circuits.
They don't do it every day, but they do it more often than I want.
Actually the higher priced CS generators could have 2 or 3 LED's and each
one could indicate a specific EC range for water rejection and other purposes.
# I *think* the SG6 does that with a red or green "go / no go" indicator
LED but they aren't hooked up in series with the output and don't give a
dimness / brightness indicator of degree. [If I recall correctly ]
If you have that dimness indication and current control and repeatably
spaced electrodes, the generator can be used as an EC meter of sorts by
determining at what electrode exposure the LED is at it's brightest and
measuring that exposure with a ruler, then comparing the exposed to water
length to a conductivity table established with an EC meter.
It's pretty easy to slowly pull the electrodes from the water and see
about where along in the process you are, if not the actual conductivity
measurement which is also possible but a bit more involved.
That's fairly accurate, but has severe range limits...fortunately, right in
the range of the most common use.
Ode
It does not take a very technical minded person to tell the Yellow, Green,
and Red LED from each other.
>> EC meter ..da best for DW.
Lots of other things also.
Wayne
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