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Re: Novel pH sensors (was APD V4 #490)

Hello Charley,

While fiber optics are possibly the technology of the future, the new
ISFET (Ion Sensitive Field Effect Transistor) pH sensors, although
pricey, are already on the market. See http://www.sentronph.com/

They are supposed to be rugged, can be stored dry, cleaned with a tooth
brush, and are supposed to give a stable reading in seconds. The company
even offers probes that can be used with regular (glass electrode) pH



> Date: Mon, 21 Aug 2000 15:01:15 -0600
> From: Charley Bay <Charleyb at Cytomation_com>
> Subject: RE: pH Meters and Electrodes
> There's been a lot of discussion on pH probes and their
> calibration here, but I wanted to point out some advances
> I saw a year ago that looked interesting.
> Apparently you can take an optical fiber and run it into your
> tank, and send a light down the center of the fiber.  A certain
> amount of light will be "refracted" back into the fiber based
> on the pH of the solution.
> When I found this a year ago, I thought it was really cool.
> They also had mounts for other sensors (temp, etc.) and
> all were driven with light in a fiber optic line.
> The efficiency of operation, no-wearing parts, no need for
> calibration, and applicability in hazardous or volatile
> environments are obvious (sometimes you just don't want
> an electrical current inside the gas storage tank.)
> I did a quick web search and couldn't find the source from
> last year, but I did run across a similar type device at
> http://www.topsensors.nl/ooe/phsensor.html
> It's a little expensive and has a halogen lamp that may
> wear out, though (the one I was looking for is just a
> terminated fiber optic wire.)
> FYI, I've seen a lot of other fiber optic measurement
> devices that may be interesting to our hobby, such as
> a fiber optic oxygen monitoring device at
> http://www.instechlabs.com/oxygen.html
> that measures oxygen by coating the end of the
> fiber with a fluorophor captured in a sol-gel, and
> then measuring the fluorescent quenching resulting
> from oxygen binding to the material (a pulsed blue LED
> is used, and we all know LEDs don't wear out.)
> I'm thinking my automated system will be all fiber.
> - --charley
> charleyb at cytomation_com