idronaut Ocean Seven 304Plus Operator's Manual page 63

APPENDIX A – DISSOLVED OXYGEN SENSOR
Wipe O
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 or direct sun rays, for at least one
minute before proceeding with calibration. When ready, press any key to continue; the following
message appears:
Sensor Current
42.59 nA
"% of last calibration" is given by (new cal/old cal) x 100 and gives a measurement of aging of the
membrane and the electrode. If excessive drift is detected (>2%) the message:
Oxygen error
appears for three seconds, then the display returns to the sensor list and the calibration must be
repeated. If this last message does not appear, it means that calibration has been achieved and the
oxygen calibration continues with the question concerning the atmospheric pressure/stirring effect
compensation coefficient:
Correction coeff. for Barometric pressure and Stirring effect
Coeff. : 1.05 >
The operator must confirm the default coefficient 1.05 or enter a different value (see the below note);
the calibration continues with the confirmation of the Oxygen sensor DC-OFFSET value. This value is
indicated in the document accompanying the CTD and should not be modified unless the sensor is
changed.
DC-OFFSET: -56 >
NOTE REGARDING VARIATIONS IN BAROMETRIC PRESSURE (ALTITUDE) AND THE
SENSOR MEMBRANE COEFFICIENT ALSO CALLED "STIRRING EFFECT"
The correction coefficient different from the nominal one 1.05 is needed for the following reasons:
1)To enter barometric pressure values differing from the 760-mm Hg standard which represents the
nominal B.P. at sea level. For example, if the measurements to be made are carried out in an area
which is at 1.340 meters above sea level, then the nominal local barometric pressure is only 655
mmHg. In this case, the correction coefficient is given by the formula:
Correction Coefficient =
2)To correct (if considerable) the possible differences in readings from the gaseous phase (calibration)
and the liquid measurements due to the oxygen consumption of the sensor during measurements.
3)If both of the above coefficients 1) and 2) are simultaneously requested, then the two relevant
correction coefficients must be multiplied together to obtain the correction coefficient to be entered.
4)To expand the scale of the oxygen sensor readings.
IDRONAUT – Brugherio (MB)
membrane and Temp. sensor
2
%Last cal.
98.9 %
Local nominal B.P.
---------------------------
Standard nominal B.P.
Drift Temp.
0.0 Count 18.216 C
OCEAN SEVEN 304Plus CTD
55
12-2015