Hey, stop barking! RTFM; the fact that you can find a meter that reads
over its nominal full scale - what it says on the 'range' dial that it is
competent to read at that position of the 'range' switch - has nothing to
do with lawyers or CYA. The 'range' is not the interval of values (call
them numbers if you want, doesn't make any difference, ) to which the
"percentage of full-scale" applies; the complete range of the instrument is
divided into segments, each one of which is scaled as, for example,
micro-volts, milli-volts, volts, or micro-amps, milli-amps, etc., reading
from minimum to . . . guess what?? "Full Scale".
Only two things are truly important about it all, and you've got one of
them dead on; if you want an accurate determination, get the right
instrument, and get it calibrated to a standard that's valid to your
measurement needs, which may cost Lots more than you want to pay; and for
CS the taste test and the Tyndall effect are probably calibration enough
for do-it-yourself purposes - unless you're a mad scientist.
Take care, Malcolm the Mad Scientist
At 07:52 AM 10/27/02 -0800, you wrote:
>Hanna's spec reporting is industry standard.
>Full scale and range are two different things. The range is a
>description of an interval of numbers in which the unit will perform
>within spec. Full scale (reading) is largest number within the range.
#### You just said that range and scale are not the same thing, then, that
they are.
It would have been easy to have stated accuracy as +/- 2% within it's
intended "range" ...not "full scale". which would make full scale
irrelevant, but they didn't. Why would that be?
Perhaps Industry Standard 'Reporting' is as full of butt covers as a
lawyers closet.
A covered butt can still toot in tune, [especially if faced off with a
tuning fork before each performance] it just doesn't 'have' to.
The PWT does perform as we apply it better than expected but it's far from
perfect. [it's not 'just' the meter]
CS is a very weird sort of water. The conductivity changes even in the
same batch. The very act of measuring it seems to change it. [OK, call it
stabilization. Will any two batches stabilize the same?]
The PWT might be great for testing salinity. Saline solutions are pretty
stable. CS? Who knows?
Are we mixing our own metaphors? [Absolutely! Measuring apple sauce to
see how many oranges there are.]
I have not been 'happy' with ANY of the methods for measuring PPM
including the various ways that labs do it. I also know it doesn't matter
that much as long as we stay within a nebulous range of common sense.
We're not feeding it into a computer. It doesn't take a furniture maker to
adequately frame a house.
I won't let something like that ruin my day. It's just no big deal..like
an apple to an elephant.
But it does take some explaining to those who want precise numbers and
can't get them.
People expect and demand certainty and tend to get certainty from people
who will give it to them whether or not there really is any. Then they
wonder why so many people say so many different things and why their
results don't exactly match any of the statements.
Not enough butt covers leads to em-bare-ass-ment? {Sure. That's the way
the real weird world of comparisons works}
Does PHD stand for piled high deniability?
The mountain, to the ant vs the elephant, is but a matter of relative time
and awareness. Neither probably gives a hoot, being focused on eating the
apples and oranges found along the way. But an apple to an elephant is a
morsal while it's a mountain of food to an ant. [something worth fighting
over]
Moral to the story:
The CS you like the best is the best CS.
If there's some way to make something different, 'that' may become the
best CS that you like best.
Batch to batch repeatability is more important than person to person
comparison. In that, a Hanna meter does OK and the PWT does that better
than the other Hanna meters no matter what the specs say or how they read.
It would seem that everything having to do with CS is subjectively
relative, CS still does what it does and it's hard to hurt yourself with
it if ANY degree of common sense is employed.
Common sense doesn't rely on specific numbers.
Being 'more right' doesn't make anyone totally wrong.
The world is clearly confused. Why not admit that nothing is what it looks
like?
Ken
It stands to reason, then reason wobbles around its eccentricity.
>
>
>The absolute determination of ppm as silver ions etc. may be
>difficult, but the measurement of conductivity is not. Discrepancies
>between different meters can be overcome by multi-point calibration
>within the expected range.
## The tuning fork. If one was not used, don't even 'think' about an
arguement...then think twice about apples and oranges.
Discrepencies are not entirely due to the instrumentation, however, Hanna
could have stated their specs without mixing them up.
>
>
>A mountain to an ant is what to an elephant?
>
>
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