Hi Mike,
I haven't worried about calibration since the first couple of months
I owned my PWT. It has remained consistent with itself, and the
measurment of uS of an immediately finished batch of CS in my
Silverpuppy never varies more than fraction.
A meter that isn't too far off, that gives consistent readings of
both my DW and the finished CS is more important than that it read an
exactly accurate uS. Hope that makes sense? I can tell immediately if
anything is different in the DW or the CS, and I think that consistency
is what is important.
I believe Ode some years back had a similar experience to what you
described your friend had with two PWTs that gave very different readings.
sol
Mike Monett wrote:
I have a Hanna PWT but the COM100 is next on my
shopping list. I really like the temperature display, and I understand from
David that the probe is a bit smaller than the Hanna which will make it
easier to get readings from a bit of cs in a shot glass prior to sublingual
absorption.
I should also mention that my Hanna arrived several years ago in perfect
calibration, and has held the original calibration extremely well. I have
verified it numerous times with precision measurements using the Faraday
calculation, and it has always agreed within 1uS up to about 15uS. The
readings tend to depart around there due to AgOH formation. So I am
confident my unit is functioning well.
My faith in Hanna plummeted recently when I recommended a friend get one.
She got two, with the calibration solution. When she brought them over to
compare calibration with mine, we discovered that one unit was so far out
of calibration that the adjustment screw could not bring it into
calibration.
The second unit was fine, but it was out of calibration. We discovered her
calibration solution read high, about 96uS. So I recommended she send them
back and get a refund.
It is very difficult to recommend what to do to verify the manufacturer's
products in a case like this. If you can do the Faraday calculation, it can
help up to about 15uS. The salt test is useful, but it takes practise to
judge the readings, and they won't be closer than about 5uS. So it can only
catch gross calibration errors. Diluting a saturated salt solution takes
some skill, and the resulting solution may not be very stable. It can also
become contaminated from the container the solution is stored in.
--
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