Maintenance
Page 160 Lorrca Maxsis User Manual
Version 5.04 MRN-231-EN
10.3. Oxygen sensor spot protocol
For Oxygenscan option only
Background
In the Oxygenscan, the oxygen level in the sample is measured through the luminescence
quenching of a luminophore spot. When the luminophore spot is illuminated by a green/blue light, it
reacts by returning orange light. When the green/blue light is switched off, there is a decay time of
the returning orange light. The decay time is dependent on the temperature and oxygen level in
contact with the luminophore spot, referred to here as the partial oxygen pressure (pO2) sensor
spot.
The pO2 at sea level is approximately 149.3 mmHg at 37°C. In the Lorrca, a new pO2 sensor spot
will show an equilibrium pO2 of about 149 mmHg. For improved accuracy, each batch of sensor
spots is accompanied by calibration data. The response of the sensor from ambient oxygen to no
oxygen is not all linear along this trajectory and can vary between different production batches of
the sensor spot. The calibration data is the input for the formula to correct for this non-linearity.
Beside this correction, over time, the pO2 measured by the spot will decline due to the influence of
light and mechanical wear, resulting in an inaccurate reading of the real ambient pO2.
Correcting the decline in the pO2 measurement
The pO2 measured by a new sensor spot and the decline in subsequent pO2 measurements are
proportional and can therefore be corrected using a proportional correction factor:
Correction factor=(pO2 of the new sensor spot)/(pO2 measured during self-check)
For example, if the pO2 measured by the new sensor spot is 143 mmHg, and the self-check
measures 135 mmHg, then the correction factor is 1.06.
To then correct pO2 measurements from the Oxygenscan, the pO2 value is multiplied by the
correction factor:
Corrected pO2=(measured pO2 )*(correction factor)
For example, if the Oxygenscan measures the Point of Sickling (PoS) as 31 mmHg, then the
corrected pO2 would be 32.9 mmHg.
We recommend correcting the Oxygenscan pO2 results when the start-up pO2 measures less than
140 mmHg.
Checking and replacing the pO2 spot
The user should perform a pO2 self-test during each start-up of the instrument to check the pO2
measurement before using the Oxygenscan. If the pO2 sensor spot measures an ambient pO2 of
less than 130 mmHg, the wear of the spot is considered too high and should be replaced with a
new one. See Replacement sensor-spot (on page 161).
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