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