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Beschikbare talen
Beschikbare talen
8.2 Ambient pressure and water depth for dissolved O
The air pressure ratio at the place of measurement is relevant to:
• calculate the oxygen saturation (%sat).
Pure water can achieve 100% saturation in air. On the condition that there are no oxygen-
depleting processes (biological degradation processes, chemical effects) or oxygen-enriching
processes such as excessively strong ventilation or photosynthesis)
• calculate the oxygen concentration (mg/l)
• evaluate the calibration
This is why it is necessary to correct the air pressure by conducting a measurement or, with
more basic devices, using tables or pressure or sea height parameters.
The integrated air pressure sensor constantly measures the ambient pressure for
• air pressure-compensated calculation of the concentration[mg/l] and saturation [%O
• air pressure-compensated calibration
9. Calibration of oxygen sensor
The sensor is prone to aging which means the oxygen sensor must be calibrated on a regular
basis.
For this reason, the device features easy-to-use calibration functions. It is recommended to
calibrate the sensor every 7 days to achieve maximum precision immediately prior to the
measurement.
If the sensor has been stored for one or several days exposed to dry air, the sensor must be
moistened for at least 30 minutes prior to calibration.
Prior to calibration, remove the protective flask and dry the membrane using a soft cloth.
9.1 1-point calibration ('(AL 1-PT')
With 1-point calibration, the sensor is calibrated to the oxygen content of air (20.95 %). There
are basically three different ways of calibration. The sensor must be prepared accordingly:
Air calibration without aid ('Cal Air')
The sensor is exposed to ambient air. Wrap
the sensor in a paper towel or cloth to
protect against any draft. (leave for at least
15 minutes prior to calibration to stabilize
the temperature and allow the membrane
to dry). Depending on the rel. air humidity
[%] and the temperature [°C], a minor
calibration error is tolerated. The cooler the
air, the lower the deviation. Recommended
temperature < 25 °C. Error correction:
see table.
Air calibration for extremely precise measurements ('Cal Air')
The sensor is exposed to air at a rel. air humidity of 100 %.
Proceed as follows: Fill a bottle with some deionized water, close it and shake vigorously for
approx. 3 minutes to produce a water vapor saturation (100% rel. air humidity) in the air at
the top of the bottle. The temperature of the water and the ambient air should be the same.
Open the bottle and insert the sensor so that the membrane is in the air at the top of the bottle.
Caution! Do not immerse the membrane into the water or allow it to get wet. The bottle
SD 310_1 10/2015
20 % 40 % 60 % 80 % 100 %
5 °C 1.007 1.005 1.003 1.002 1.00
10 °C 1.01
1.007 1.005 1.002 1.00
15 °C 1.014 1.01
20 °C 1.019 1.014 1.009 1.005 1.00
25 °C 1.026 1.019 1.013 1.006 1.00
30 °C 1.035 1.026 1.017 1.009 1.00
35 °C 1.047 1.035 1.023 1.012 1.00
40 °C 1.063 1.047 1.031 1.016 1.00
Diff. with air calibration without aid,
O
saturation = display value x correction factor
2
measurement
2
]
2
1.007 1.003 1.00
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