Appendix 2 The Optical Design - Aanderaa 4330 Operating Manual

Appendix 2 The Optical Design

An illustration of the optical design is given in Figure A 4.
The sensing foil is mounted outside the optical window and is exposed to the surrounding water. The foil
is held in place by a screw fixed plastic plate.
Two light emitting diodes (LEDs) and one photodiode are placed on the inside of the window. A blue-
green LED is used for excitation of the foil. The photodiode is used for sensing the fluorescent light.
Even thought the sensing foil is highly fluorescent parts of the transmitted light will be directly reflected.
The photo diode is equipped with a colour filter that stops light with short wavelengths to minimize the
influence of the reflected light. Further, the blue-green LED is equipped with a filter that stops light with
long wavelengths.
In addition, a red 'reference' LED is included to compensate for potential drift in the electronics of the
transmitter and receiver circuit.
The spectral response of the LEDs and the filter are illustrated in Figure A 5.
Figure A 4 The Optical Design
TD 269 OPERATING MANUAL
OXYGEN OPTODE 4330, 4831, 4835
June 2017
page 48 of 93