9
THEORY OF OPERA
TION
THEORY OF OPERATION
The Hanna
HI764113
optical
DO
sensing probe is based on the principle of fluorescence quenching.
The sensing method features an immobilized Pt based luminophore that is excited by the light of a
blue LED and emits a red light. Dissolved oxygen quenches this excitation. When there is no oxygen
present, the lifetime of the signal is the greatest; as oxygen hits the sensing surface, the lifetime
becomes shorter. The intensity and lifetime are inversely proportional to the amount of oxygen present;
as oxygen interacts with the luminophore it reduces the intensity and lifetime of the luminescence. The
lifetime of the luminescence is measured by a photodetector, and is used to calculate the dissolved
oxygen concentration. This is in turn reported by the meter as a % saturation or mg/L reading of
Dissolved Oxygen.
The major components of the probe include a blue LED for excitation, a red LED that is used as a reference
light, and a photodetector. The Smart Cap™ is locked in place on the optical probe and includes the
immobilized O
2
sensitive luminophore with rugged insoluble black oxygen permeable protective layer.
Over time, the sensor’s optical components can age but are compensated for by using the reference
signal to compensate the measuring path. As a result, the sensor provides accurate
DO
measurements
over long periods of time without the need for frequent calibration.
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