Manual revision 001
Section 5: Routine Maintenance and Calibration
SBE 39
plus
-IM
79
Sensor Calibration
Sea-Bird sensors are calibrated by subjecting them to known physical
conditions and measuring the sensor responses. Coefficients are then
computed, which may be used with appropriate algorithms to obtain
engineering units. The sensors on the 39
plus
-IM are supplied fully calibrated,
with coefficients printed on the Calibration Certificate (in the manual). These
coefficients have been stored in the 39
plus
-IM’s EEPROM.
We recommend that the 39
plus
-IM be returned to Sea-Bird for calibration.
Temperature Sensor Calibration
The primary source of temperature sensor calibration drift is the aging of the
thermistor element. Sensor drift will usually be a few thousandths of a degree
during the first year, and less in subsequent intervals. Sensor drift is not
substantially dependent upon the environmental conditions of use, and —
unlike platinum or copper elements — the thermistor is insensitive to shock.
Pressure Sensor Calibration
The optional strain-gauge pressure sensor is a mechanical diaphragm type,
with an initial static error band of 0.05%. Consequently, the sensor is capable
of meeting the 39
plus
-IM’s 0.10% error specification with some allowance for
aging and ambient-temperature induced drift.
Pressure sensors show most of their error as a linear offset from zero.
A technique is provided below for making small corrections to the pressure
sensor calibration using the
offset
(
#iiPOffset=
) calibration coefficient term by
comparing 39
plus
-IM pressure output to readings from a barometer.
