Salinity Correction ('Sal'); Calibration Of Oxygen Sensor; 1-Point Calibration ('(Al 1-Pt') - Lovibond SD 310 Oxi Mode D'emploi

8.1 Salinity correction ('SAL')

With increasing amounts of salt (salinity), the dissolving properties of oxygen in water reduce,
i.e. at the same oxygen partial pressure, less mg of oxygen dissolves in each liter of water.
To calculate the oxygen concentration, the first step is to enter the salinity of the medium
(see 'Device configuration'). The salinity correction is based on fluid media that have an
equivalent chemical composition to sea water. The correction is based on the "International
Oceanographic Tables" (IOT).
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.
SD 310_2 07/2018
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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