Sea-Bird Electronics SBE 19plusV2 - Page 239

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APPLICATION NOTE NO. 64-2 Revised April 2008
SBE 43 Dissolved Oxygen Sensor Calibration and Data Corrections
using Winkler Titrations
This application note describes methods for adjusting the calibration
coefficients for the SBE 43 Dissolved Oxygen (DO) sensor, and for correcting
long-term moored data either in real-time or during post-processing.
The first method requires numerous Winkler titrated water samples and
corresponding sensor voltages to compute new slope and offset terms for the
sensor calibration. The second method is most applicable for long-term moored
data applications that typically only have a few reference samples and are
temporally affected by bio-fouling of the sensor membrane.
Calibration Adjustment Using Multiple Winkler Water Samples and
Sensor Voltages over a Wide Range of Oxygen Calculations
This method statistically estimates calibration coefficients for calculating dissolved oxygen in milliliters per liter
from SBE 43 output voltage. The technique requires dissolved oxygen concentrations reported in ml/l (determined
from a range of Winkler titrated water samples) and SBE 43 oxygen voltage outputs measured at the times the water
samples were collected. Sea-Bird’s data processing software, SBE Data Processing, is used to produce a data table
suitable for the analysis.
Basic Principal
The equation below, used in Sea-Bird’s software for calculating dissolved oxygen in ml/l from SBE 43 output
voltage, is a form of that given in Owens-Millard (1985):
()
()
1****0.1
),(*),(/
)
*
(
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eqneTCTBTA
STOxsol
t
V
PTtauVoffsetVSoclmlOxygen
K
PE
+++∗
∗
⎭
⎬
⎫
⎩
⎨
⎧
⎟
⎠
⎞
⎜
⎝
⎛
∂
∂
++∗=
Where:
V = SBE 43 output voltage signal (volts)
t
V
∂
∂
= time derivative of SBE 43 output signal (volts/second)
T = CTD temperature (°C)
S = CTD salinity (psu)
P = CTD pressure (dbars)
K = CTD temperature (°K)
tau(T,P) = sensor time constant at temperature and pressure
Oxsol(T,S) = oxygen solubility function (ml/l), which converts oxygen partial pressure (sensor measurement) to
oxygen concentration (Garcia and Gordon, 1992). See Appendix A in Application Note 64 for values at various
temperatures and salinities.
Soc, Voffset, A, B, C, E, and tau20, D1, D2 [terms in calculation of tau (T,P)] are calibration coefficients
Sea-Bird Electronics, Inc.
1808 136th Place NE
Bellevue, WA 98005
USA
Phone: (425) 643-9866
Fax: (425) 643-9954
E-mail: seabird@seabird.com
Web: www.seabird.com
Figure 1. SBE 43
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