From: Ryuji Suzuki (rs@silvergrain.org)
Date: 10/17/03-11:14:20 AM Z
From: Sandy King <sanking@clemson.edu>
Subject: Re: pH meter
Date: Fri, 17 Oct 2003 11:31:52 -0400
> I use a pH meter quite often in my testing of different developers.
> All developers are designed to work best at a certain pH and the
> ability to verify the pH is important because it serves as a check
> that the developer is in good working condition.
I agree with you in most parts. I do check pH of developers at least
once in each batch. Because I formulate my developers and I like to
know batch-to-batch consistency, and also because in my darkroom pH
electrode is always ready to do measurement, I just do. Any decent
developer should use suitable buffering agent for the target pH and in
an sufficient amount of titratable base. This way, the bath pH is very
consistent batch-to-batch even without doing anything special. So,
end users need not worry much, but if they wish to do some sanity
check, pH test strips are very easy, low maintenance and sufficient in
accuracy.
> As to the issue of reliability, I have two small hand held pH meters
> and both have worked fine for at least the past five years. Both are
> made by Oaklon, and one is called the pHTestr 1, the other is called
> the pH Wand. The Wand is more accurate and has a replaceable probe.
> The meters have to be re-calibrated from time to time but otherwise
> seem to have been pretty trouble free over the period of time
> mentione. The Testr cost less than $100, the Wand about $150, and I
> purchased both of them from Bryant Labs (now Bryant Laboratory) in
> Berkeley, CA.
Speaking of Oakton, I have used Oakton Waterproof pH Tester 3+, which
is their latest and high performance pocket pH tester. It's double
junction but gel filled, and this tester failed very quickly and
miserably in darkroom. I communicated with the tech support guy about
the problem and they sent me replacement, etc. but the result is the
same, it failed again. It's not the matter of expectation -- the meter
becomes completely uncalibratable and useless after using with
developers for a few days, maybe a week. I saw same problems with
other manufacturer's products.
Again, my recommendation is not to bother with these, but instead just
go to refillable double junction probes. Some of these probes are
inexpensive, but they are rarely sold as a complete kit (because kits
are designed for convenience for less difficult application areas,
which is the majority of the market, they use gel filled probes) with
display module, so you have to buy the display module
separately. There are several display modules that are relatively
inexpensive. The probe and display modules do not have to be the same
manufacturer, as long as the connection is compatible (it's usually
through a BNC connector), because the electrical interface is the same
except some proprietary ones, which tend not to use BNC connector.
-- Ryuji Suzuki "Reality has always had too many heads." (Bob Dylan, Cold Irons Bound, 1997)
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