RADIOMETER ABL90 FLEX - Calculations; Measuring Sequence; Optical System for Po

ABL90 FLEX reference manual 5. Sensors and optical system
5-29
Measuring principle of the pO
2
sensor
The optical system for pO
2
is based on the ability of O
2
to reduce the intensity
and time constant of the phosphorescence from a phosphorescent dye that is in
contact with the sample.
The optical system for measuring
pO
2
is shown in the following diagram:
The green LED emits light, which is reflected by a dichroic mirror onto the
pO
2
sensor. Due to the phosphorescence, red light is emitted back through the
dichroic mirror and onto a photo detector. The photo detector sends the
electrical signals, proportional to the light intensity, to the analog/digital
converter and the data processing unit. The calculation of the pO
2
is performed.
The pO
2
is calculated on the basis of the Stern-Volmer equation, which describes
the relationship between the phosphorescence intensity/time constant () and
the
pO
2
value in a sample:
0
2
O() k 1p




 


where k and 
0
are constants.
Optical system
for pO
2
Measuring
sequence
Calculations