Use in Hydrogen Sulfide (H
2
S) Environments
SBE 43 oxygen sensors can be used for hours in hydrogen sulfide rich environments with no ill effects to sensor
elements or signal calibration.
Poisoning of oxygen sensors in hydrogen sulfide environments was a phenomenon common to early sensor designs
that used silver as the cathode element. The SBE 43 uses a noble metal (gold) as the cathode and silver as the anode,
and shows no degradation of signal or calibration when used for profiling in hydrogen sulfide environments. In
particular, a month of intensive hydrographic profiles in the Black Sea using Sea-Bird oxygen sensors has
demonstrated that these sensors can operate repeatedly in the H
2
S rich depths for durations of hours without any
degradation of signal or calibration over that experienced in equivalent profiling work in the open, oxygenated ocean.
We have no laboratory or field evidence of the effect of mooring Sea-Bird oxygen sensors in H
2
S rich environments
for periods of days to months.
Oxygen Algorithm
Sea-Bird uses an algorithm based on that of Owens and Millard (1985) to convert SBE 43 oxygen sensor data to
oxygen concentration. The Sea-Bird algorithm incorporates a term related to the offset voltage produced for zero
oxygen signal. In addition, there is a third-order polynomial that compensates for changes in sensitivity with
temperature and an exponential term that compensates for changes in sensitivity with pressure.
Sea-Bird’s algorithm has the following form:
()
()
)
*
(
32
****0.1
),(*),(/
K
PE
eTCTBTA
STOxsol
t
V
PTtauVoffsetVSoclmlOxygen
+++∗
∗
⎭
⎬
⎫
⎩
⎨
⎧
⎟
⎠
⎞
⎜
⎝
⎛
∂
∂
++∗=
where.....
Description Symbol Definition
Computed Oxygen Dissolved oxygen concentration (ml/l)
T CTD Temperature (ºC)
P CTD Pressure (decibars)
S CTD Salinity (psu)
Measured
Parameters
V SBE 43 temperature-compensated output oxygen signal (volts)
Soc Oxygen signal slope
Voffset Voltage at zero oxygen signal
A, B, C Residual temperature correction factors
E Pressure correction factor
tau20
Sensor time constant tau (T,P) at 20 ºC, 1 atmosphere, 0 PSU;
slope term in calculation of tau(T,P)
D1, D2 Temperature and pressure correction factors in calculation of tau(T,P)
Calibration
Coefficients
H1, H2, H3 Hysteresis correction factors
Oxsol(T,S) Oxygen saturation value after Garcia and Gordon (1992); see Appendix A
δV/δt
Time derivative of SBE 43 output oxygen signal (volts/second)
tau(T,P)
Sensor time constant at temperature and pressure =
tau20 * exp (D1 * P + D2 * [T – 20])
Calculated
Value
K Absolute temperature
Our software requires you to enter Soc, Voffset, A, B, C, E, tau20, D1, D2, H1, H2, and H3 in the configuration
(.con) file; values are taken from the Calibration Sheet provided with the sensor.
Note: H1, H2, and H3 values are available on calibration sheets for SBE 43s calibrated after October 2008.
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