Theory Of The Optical Oxygen Measurement; Introduction; Principle; Principle Of The Design Of The Optical Oxygen Sensor - Mettler Toledo InPro 6880 i Série Instructions D'utilisation

InPro 6880 i Series O
10

Theory of the optical Oxygen Measurement

10.1 Introduction

Optical oxygen measurement is a non-invasive
method. No electrochemical reaction occurs during
measurement.

10.2 Principle

In contrast to the aperometric and potentiometric
method the optical measurement is not based on a
chemical reaction and current measurement.
A chromophore in the Sensor is illuminated with blue
light. The chromophore absorbs this energy and is
transferred to a higher energy level. A part of the ener-
gy is transferred as heat. After a short time the chromo-
phore emits a red fluorescence light and returns to its
ground state.
If an Oxygen molecule collides with the chromophore
in its excited state, the energy can be transferred to Oxy-
gen (Dynamic Quenching). In this case, no fluorescen-
ce light is emitted. Oxygen itself can transfer this ener-
gy as heat without light emission.
The emission of fluorescence light is therefore depen-
dent on the Oxygen partial pressure at the chromo-
phore layer.
The emission of fluorescence shows a short time de-
lay to the excitation. This time delay can be measure,
if the excitation light is being modulated. In this case,
the fluorescence shows the same modulation.
The phase shift between excitation and fluorescence
decreases with increasing Oxygen concentration.
The oxygen concentration is calculated and digitally
transfered to the transmitter.
10.3 Principle of the design of the optical oxygen
sensor
Fiber
optic
Temperature
sensor
Cap-
sleeve
O-Ring
© 09/07 Mettler-Toledo AG
Printed in Switzerland
Sensor 12 mm
2
Excitation
LED
Optical Filter
Detector
Reference
LED
Metal body
Glass
Opto-layer with
chromophor
Optical isolation
(black silicone)
Opto-cap
InPro 6880 i
52 206 256
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Sensor
head
Sensor
shaft