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Ref. No. [UMCES] CBL 2016-010
ACT VS16-01
6
foil time-drift and helps ensure reliable and accurate data. The method consists of simply recalibrating
the DO sensor at two saturation points (0% and 100%) using a Na2SO3 aqueous solution (0%
saturation) and air saturated water (100% saturation). Depending on the application, RINKO sensors
are offered in different models and among them there are:
RINKO AroUSB is an autonomously deployable time data logger with temperature and fast
response optical DO sensor. The instrument has various operating modes, offering flexibility
when carrying out observations. The compact size containing the data logger allows for being
easily integrated on different platforms (e.g. CTDs). Compared to galvanic, clark-cell and optical
DO sensors, RINKO I has the fastest response time (< 1 s with 90% response), allowing for
measurements of dissolved oxygen concentration at high resolution (at sub-meter scale) and
enabling continuous profiling at 0.5 m s
-1
.
RINKO AroW-USB is an autonomously deployable/real time data logger with temperature
and optical DO sensor. The instrument has a mechanical wiper in order to protect the sensing foil
against accumulating bio-fouling, and therefore, allowing for long-term observations without
affecting data quality.
PERFORMANCE EVALUATION TEST PLAN
Laboratory Tests
Laboratory tests of accuracy, precision, response time, and stability were conducted at Moss
Landing Marine Lab. All tests were run under ambient pressure (logged hourly from a barometer at
the laboratory) and involved the comparison of dissolved oxygen concentration reported by the
instrument versus Winkler titration values of water samples taken from the test baths. All tests were
run in thermally controlled tanks at specific temperature, salinity, and DO concentrations. Tanks were
well mixed with four submersible Aquatic Ecosystem Model 5 pumps with flow rates of 25 L/min.
Temperatures were controlled to within approximately 0.2
o
C of set point using Thermo Digital One
Neslab RTE 17 circulating thermostats flowing through closed coils distributed within the tank. Four
RBR temperature loggers were deployed within the tank to verify actual temperature to better than
0.02
o
C. Salinity was varied by addition of commercial salts (Instant Ocean) to Type 1 deionized
water. Salinity was verified at the beginning and end of each test condition by analysis on a calibrated
CTD
.
Dissolved oxygen concentrations were controlled by use of compressed gases of known oxygen
concentration sparging through diffusers within the tank. Tanks were covered with a layer of floating
closed-cell plastic insulation that continuously sealed the water surface and to minimize atmospheric
exchange. If required by the manufacturer, instruments were only calibrated prior to the start of the
first lab test, and then again prior to the stability test which began one month later. The following
series of tests were conducted in the laboratory trials:
Accuracy at various T/S and DO conditions
A series of measurements were conducted under 36 discrete conditions to target 3 temperatures, 3
salinities, and at least 4 DO concentrations as follows:
•
Temperature Conditions: 5, 15, 30
o
C
•
3 Salinity Conditions: 0, 10, 34
•
Dissolved oxygen,(% air saturation): 0% (hypoxic), 20 – 30%, 100% and >120%, (levels were
achieved by mixing pure O
2
and N
2
sources with pure N
2
was used for the 0% O
2
concentration)