Optical pH sensors

by Steven
(Washington)

One technique to measure pH is to use a fiber optic sensor. Maybe an uncommon pH technique, but I think it's important to know it exists. The development of optical sensors is of great interest because of their possible application in biotechnology, ecology and medicine.


Principle of operation

The main principle of an optical sensor is to measure the color changes of a pH indicator which are trapped in a thin porous glass membrane.

• An optical light source sends a pulse of light via fiber to the pH sensitive membrane. The membrane changes its color (absorbance) in dependence on pH of the measured sample.

• A reflected light pulse is measured by a photodetector. The reflected pulse depends on the absorbance (color) of the membrane. An increase of the absorbance of the membrane (change of pH) will result in a smaller reflected light pulse.


Fiber optic chemical sensors can offer several advantages over traditional sensors as:

• light weight
• small size
• strong immunity to electromagnetic interference
• free from the handling problems associated with pH glass electrodes

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May 13, 2015
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Good
by: cce

Good

Oct 04, 2011
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components of optical ph sensor
by: Anonymous

photodiode
LED (light source)
fluorescence or absorbent dye

May 21, 2010
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Disadvantages
by: Mike

Well, there are a couple of disadvantages that you should also be aware of:

• narrow pH-range
• interferences from ionic strength
• photo bleaching - the optical sensors must be kept in the dark
• signal intensity may decrease with use

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