Optical oxygen sensors are mainly based on the principle of
luminescence quenching. In contrast to arready existing intensity-based
systems, the measurement of the luminescence lifetime provides certain
advantages, such as insensitivity to photobleaching or leaching of the
dye, or changes in the intensity of excitation light. This facilitates
the use of simple optical systems or optical fibres.
A new family of oxygen-sensitive dyes, the porphyrin-ketones, has been
introduced, which exhibits favorable spectral properties and decay times
in the order of tens and hundreds of microseconds. This allows the use
of simple optoelectronic circuitry and low-cost processing electronics.
An optical oxygen sensor module has been developed with the dimensions
of only 120 x 60 x 30 mm. The prototype is based on the measurement of
the decay time of the luminophore by measuring the phase shift between
the square-wave excitation and the detected square-wave of the emission
coming from the sensor.
The instrument is based on semiconductor devices (light-emitting diodes,
photodiodes) and may be used for the detection of oxygen in gaseous or
liquid samples. The measurement range of the device is from 0 to 200 hPa
oxygen partial pressure with a resolution of < 1 hPa over the whole
measurement range. The overall measurement accuracy of < +/- 1 hPa
has been obtained for periods of 24 h of continuous measurement in a
thermostatted environment. The sensor response times t90 are typically
< 1 s for gases and 0.5 to 5 min for liquid samples.
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