Sea-Bird Electronics SBE 38 Manual do Utilizador descarregar pdf (Página 81)

APPLICATION NOTE NO. 31 Revised February 2010

Computing Temperature and Conductivity Slope and Offset Correction

Coefficients from Laboratory Calibrations and Salinity Bottle Samples

Conductivity Sensors

The conductivity sensor slope and offset entries in the configuration (.con or .xmlcon) file in SEASOFT permit the user

to make corrections for sensor drift between calibrations. The correction formula is:

(corrected conductivity) = slope * (computed conductivity) + offset

where :

slope = (true conductivity span) / (instrument reading conductivity span)

offset = (true conductivity - instrument reading conductivity) * slope measured at 0 S/m

For newly calibrated sensors, use slope = 1.0, offset = 0.0.

Sea-Bird conductivity sensors usually drift by changing span (the slope of the calibration curve), and changes are

typically toward lower conductivity readings with time. Any offset error in conductivity (error at 0 S/m) is usually due

to electronics drift, typically less than ±0.0001 S/m per year. Offsets greater than ±0.0002 S/m per year are symptomatic

of sensor malfunction. Therefore, Sea-Bird recommends that conductivity drift corrections be made by assuming

no offset error, unless there is strong evidence to the contrary or a special need.

Example

true conductivity =3.5 S/m

instrument reading conductivity = 3.49965 S/m

slope = 3.5 / 3.49965 = 1.000100

Correcting for Conductivity Drift Based on Pre- and Post-Cruise Laboratory Calibrations

Suppose a conductivity sensor is calibrated (pre-cruise), then immediately used at sea, and then returned for post-cruise

calibration. The pre- and post-cruise calibration data can be used to generate a slope correction for data obtained

between the pre- and post-cruise calibrations.

If α is the conductivity computed from the pre-cruise bath data (temperature and frequency) using post-cruise

calibration coefficients and β is the true conductivity in the pre-cruise bath, then:

postslope =

(postslope is typically < 1.0)

Sea-Bird calculates and prints the value for postslope on the conductivity calibration sheet for all calibrations since

February 1995 (see Appendix I: Example Conductivity Calibration Sheet)

Σ (α

)(β

)

Σ (α

)(α

)

i=1

Sea-Bird Electronics, Inc.

13431 NE 20

Street

Bellevue, WA 98005

Phone: (425) 643-9866

Fax: (425) 643-9954

E-mail: [email protected]

Web: www.seabird.com

1 2 ... 76 77 78 79 80 81 82 83 84 85 86 ... 103 104

Comentários a estes Manuais

Sem comentários

Sea-Bird Electronics SBE 38 Manual do Utilizador Página 81

Comentários a estes Manuais

Manuais e produtos relacionados com Medição, teste e controlo Sea-Bird Electronics SBE 38