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Re: ISFET pH pens and controllers
On Thu, 17 Aug 2000, Dirk wrote:
> About those Ph pens: For the last 20 years I have checked my Ph the chemical way.
> Last X-mas I was in the JLFS ( Japanese Local Fish Store, meaning, no english
> communication only my "beer and fish" japanese). I saw this "Ph-boy II" pen hanging there.
> ( ISFET probe, Ion-Sensitive Field Effect Transistor)
> I thought it would be less hassle than a chemical test and with a pen you can take
> a really quick peak at you Ph morning and evening. Great! ( so far ).
The pH pens are the absolute, rock-bottom low end of the pH meter market
-- the Yugo of pH measuring equipment. They're sold in professional
catalogs for less the $20.00 and sometimes given away as freebee
promotional gifts. They're intended to be used a few times and thrown
The behavior that Dirk described is pretty much what you have to expect
when you buy something at the bottom end of the market. It's unfortunate
that those devices are sold in the hobby without making it clearly obvious
what they are and *are not* good for.
You pay for what you get. As a point of reference, a basic, good quality
professional pH meter (in this case the Hach SensION1) good for fresh
water lists in a year-old catalog for $525 with probe (but no other
accessories, including calibration solutions) and the low-cost replacement
probe costs $120.