for each degree:
Coefficients :
The above request is repeated for the degree of polynomial. At the end of the coefficients data entry, the
sensor selection list appears again.
5.5.3 Simple check of conductivity sensor calibration
The conductivity sensor is usually very accurate. A check of any drift with time or calibration can be
performed by using a Standard Seawater. A worldwide used Standard Seawater for conductivity is the
so-called “Copenhagen Water” which is supplied by I.A.P.S.O. - Standard Seawater Service. The
certified value of Chlorinity is 19.371 ppt, that corresponds to a Practical Salinity of 35.00 ppt. The
temperature value is used in the salinity calculation, as explained in the sensor description paragraph;
nevertheless, since the temperature sensor is much less prone to drift than the conductivity sensor, it is
assumed that any variation, with respect to the certified value, is totally due to the conductivity sensor.
The probe must be carefully rinsed with distilled water, in order to remove any salt residue, and then
dried. These precautions are necessary for not diluting or contaminating the Standard Seawater.
Transfer some Standard Seawater into a beaker provided with a magnetic stirrer and immerse the probe
into it. From the data acquisition functions, check that the value for conductivity and temperature can
be read. The conductivity value is supposed to be coincident or very close to the theoretical one which
can be found in the "STANDARD SEA WATER K15 0,99999 - CONDUCTIVITY VERSUS
TEMPERATURE TABLE". If a considerable difference is present, a calibration procedure must be
performed.
5.5.4 Oxygen sensor calibration
The dissolved oxygen sensor requires most attention of all the OCEAN SEVEN 310 sensors.
maintenance (mostly membrane and electrolyte replacement) should be carried out at least every three
months and assembling/disassembling requires great care. Calibration of the sensor should be carried
out:
❖ after a long period of disuse;
❖ once a day during an extended field survey;
❖ once a month if the probe is installed on a Buoy Profiler or is used in a continuous monitoring.
It is preferable to calibrate the oxygen sensor in a liquid (ideally distilled water) saturated (i.e. in perfect
equilibrium) with ambient air and well stirred to have homogeneous temperature. If possible, check the
oxygen saturation using the Winkler method. However, this procedure is rarely used because of the
difficulties of obtaining a solution homogeneous in temperature and at saturation, particularly on the
field. For this reason, the calibration is usually carried out in air. Once selected the sensor to be
calibrated, the following message appears:
O2sat% sensor calibration
Gently wipe O2 membrane and Temperature sensor
Type <any key>To continue, <ESC>To leave
Before calibration, it is important to be sure that both the oxygen and temperature sensors are perfectly
dry. The oxygen sensor may be dried with a piece of clean towelling taking particular care not to damage
the membrane. Dry the temperature sensor with clean towelling taking care not to touch the sensor or
heat it in any other way above ambient temperature. After drying both sensors, leave them in a well
ventilated atmosphere, far from heat sources and direct sun rays, for at least one minute before
proceeding with calibration. When ready, press any key to continue; the following message appears:
Oxygen calibration in progress
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