Sea-Bird Electronics SBE 45 MicroTSG, Руководство пользователя

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APPLICATION NOTE NO. 10 Revised
March 2008
COMPRESSIBILITY COMPENSATION OF SEA-BIRD CONDUCTIVITY SENSORS
Sea-Bird conductivity sensors provide precise characterization of deep ocean water masses. To achieve the accuracy
of which the sensors are capable, an accounting for the effect of hydrostatic loading (pressure) on the conductivity
cell is necessary. Conductivity calibration certificates show an equation containing the appropriate pressure-
dependent correction term, which has been derived from mechanical principles and confirmed by field observations.
The form of the equation varies somewhat, as shown below:
SBE 4, 9, 9 plus , 16, 19, 21, 25, 26, 26 plus , and 53 BPR
Conductivity (Siemens/meter) = slope + offset ( recommended )
or
Conductivity (Siemens/meter) = slope + offset
SBE 16
plus , 16 plus -IM, 16 plus V2, 16 plus -IM V2, 19 plus , 19 plus V2, 37, 45, 49, and 52-MP
Conductivity (Siemens/meter) = slope + offset
where
•
a, b, c, d, m, and CPcor are the calibration coefficients used for older sensors (prior to January 1995).
Sea-Bird continues to calculate and print these coefficients on the calibration sheets for use with old
software, but recommends use of the g, h, i, j, CTcor, CPcor form of the equation for most accurate results.
•
g, h, i, j, CTcor, and CPcor are the calibration coefficients used for newer sensors.
Note : The SBE 26, 26 plus , and 53 BPR use the SBE 4 conductivity sensor, so both sets of calibration
coefficients are reported on the calibration sheet. SEASOFT for Waves for DOS , which can be used with
the SBE 26 only, only supports use of the a, b, c, d, CTcor, and CPcor coefficients. The current processing
software for these instruments,
SEASOFT for Waves for Windows , only supports use of the g, h, i, j,
CTcor, CPcor coefficients.
•
CPcor is the correction term for pressure effects on conductivity (see below for discussion)
•
slope and offset are correction coefficients used to make corrections for sensor drift between calibrations;
set to 1.0 and 0 respectively on initial calibration by Sea-Bird (see Application Note 31 for details on
calculating slope and offset)
•
f is the instrument frequency (kHz) for all instruments except the SBE 52-MP.
For the SBE 52-MP, f = instrument frequency (kHz) * (1.0 + WBOTC * t)
0.5
/ 1000.00
•
t is the water temperature (
°
C).
•
p is the water pressure (decibars).
Sea-Bird CTD data acquisition, display, and post-processing software
SEASOFT for Waves (for SBE 26, 26 plus , and
53 only) and SEASOFT (for all other instruments) automatically implement these equations.
Sea-Bird Electronics, Inc.
13431 NE 20
th
Street
Bellevue, WA 98005
USA
Phone: (425) 643-9866
Fax: (425) 643-9954
E-mail: seabird@seabird.com
Web: www.seabird.com
g + h f
2
+ i f
3
+ j f
4
1 + [CTcor] t + [CPcor] p
( g + h f
2
+ i f
3
+ j f
4
) / 10
1 + [CTcor] t + [CPcor] p
(a f
m
+ b f
2
+ c + dt ) / 10
1 + [CPcor] p
106