Manual revision 005
Section 5: Routine Maintenance and Calibration
SBE 63
34
Sensor Calibration
Each SBE 63 is calibrated individually in a temperature-controlled bath. Bath
temperatures are varied at each of 4 oxygen values, providing a comprehensive
24-point calibration. Two reference sensors in each bath are standardized
against Winkler titrations. Response time tests are conducted on each sensor,
using gas. Salinity and pressure impacts on sensor response are each checked
at two separate points
The SBE 63 calibration coefficients are printed on the Calibration Certificate
supplied with the sensor. These coefficients have also been stored in the
SBE 63, allowing the SBE 63 to directly output dissolved oxygen in ml/l.
When used on a Sea-Bird CTD (SBE 16
plus
V2, 16
plus
-IM V2, 19
plus
V2,
37-SMP-ODO, 37-IMP-ODO, 37-SIP-ODO), dissolved oxygen can be
calculated in other units in post-processing.
The primary mechanism for calibration drift in optical oxygen sensors is the
fouling of the optical window by chemical or biological deposits. Accordingly,
the most important determinant of long-term sensor accuracy is the cleanliness
of the window. We recommend that oxygen sensors be calibrated before and
after deployment, but particularly when the sensor has been exposed to
contamination by oil slicks or biological material.
Another important mechanism for oxygen sensor drift is photobleaching of the
sensor film. Keep the SBE 63 sensor film out of direct sunlight. Also, every
sample that is taken illuminates the film with short wavelength light that
eventually degrades the film. As a rule of thumb, re-calibration of the oxygen
sensor is recommended after 300,000 to500,000 samples.
Note:
See
Appendix I: Functional Description
for details on the calibration equation.
