Sea-Bird Electronics SBE 38 Manual de usuario descargar pdf (Pagina 101)

Manual revision 006 Section 5: Routine Maintenance and Calibration SBE 19plus V2

101

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 conductivity, temperature, and pressure sensors on the

SBE 19plus V2 are supplied fully calibrated, with coefficients stored in

EEPROM in the 19plus V2 and printed on their respective Calibration

Certificates.

We recommend that the 19plus V2 be returned to Sea-Bird for calibration.

Conductivity Sensor

The conductivity sensor incorporates a fixed precision resistor in parallel with

the cell. When the cell is dry and in air, the sensor’s electrical circuitry outputs

a frequency representative of the fixed resistor. This frequency is recorded on

the Calibration Certificate and should remain stable (within 1 Hz) over time.

The primary mechanism for calibration drift in conductivity sensors is the

fouling of the cell by chemical or biological deposits. Fouling changes the cell

geometry, resulting in a shift in cell constant.

Accordingly, the most important determinant of long-term sensor accuracy is

the cleanliness of the cell. We recommend that the conductivity sensors be

calibrated before and after deployment, but particularly when the cell has been

exposed to contamination by oil slicks or biological material.

Temperature Sensor

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.

Note

After recalibration, Sea-Bird enters

the new calibration coefficients in the

19plus V2 EEPROM, and ships the

instrument back to the user with

Calibration Certificates showing the

new coefficients. We also ship a new

instrument configuration (.con) file,

which includes the new coefficients.

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Sea-Bird Electronics SBE 38 Manual de usuario Pagina 101