In-Situ RDO Sensor for TROLL 9500: Installation, Calibration, and Care (purchased after 09/2008) - Manual (Page 3)

Page 3
After allowing 5 – 10 minutes for temperature stabilization, click the 5.
Run button. Follow the on-screen instructions to complete the 100%
calibration point.
Continue with the 0% Oxygen Calibration for a 2-point calibration or
6.
select Next, then Finish to finalize the calibration.
Preparation for 0% Oxygen Calibration
0% D.O. calibration is performed in an oxygen-depleted solution. Sodium
sulfite (Na
2
SO
3
, see Replacement Parts list) is available from In-Situ Inc.
Bubbled nitrogen may be used; in this case allow plenty of time for the
oxygen to be completely purged from the water.
uNITS aND CalCulaTED MEaSuREMENTS
Four units of measurement are available for DO:
TIP: To change unit preferences: In Win-Situ 4, select
Preferences on the Options menu. In Pocket-Situ, select the
Home site, then tap Setup in the command bar.
• Oxygen concentration in milligrams of oxygen per liter of water (mg/L).
Since a liter of pure water weighs 1000 grams, and a milligram is
1/1000 of a gram, this is equivalent to ppm (parts per million).
• Oxygen concentration in micrograms of oxygen per liter of water (µg/L). This
is equivalent to parts per billion (ppb).
• Oxygen concentration in microMolar (µmol/L) = mg/L x 31.25
• Oxygen saturation in % —100% DO being the maximum (equilibrium)
amount of oxygen that can be dissolved in water at a given atmospheric
pressure, water temperature, and salinity. The percent saturation
output is automatically corrected using the TROLL 9500 instrument's
temperature, conductivity, and barometric pressure values (from a
barometric sensor on vented cable or from a user-entered input). If no
conductivity sensor is present, salinity is assumed to be zero.
uSagE RECOMMENDaTIONS aND CauTIONS
The amount of oxygen that can be dissolved in water decreases at higher
temperatures and with increasing altitude (i.e., as barometric pressure
drops) and salinity. In other words, as water becomes warmer and saltier, it
can hold less DO.
During tests that include the RDO channel, the TROLL 9500 instrument
automatically measures barometric pressure and temperature for
compensation of DO readings.
The barometric pressure value at the time of calibration is stored in the
sensor and will be used to correct DO readings for weather-induced
pressure fluctuations taken at the same relative barometric pressure
as the calibration. However, the large changes in barometric pressure
due to changes in elevation are best accommodated by performing a
recalibration. If you calibrate at sea level, for example, and deploy the
instrument in the mountains, you should perform a recalibration at the
new altitude.
Exposure to direct sunlight can bleach the sensing foil over time but this
effect is minimized with the protection provided by the opaque optical
isolation layer. However, the frequent application of strong blue light (blue
LED during readings) will eventually have a bleaching effect on the foil.
In-Situ recommends sampling intervals of greater than 1 minute for long-
term deployments.
Warning: The RDO sensor is not compatible with organic
solvents.
Salinity
Since the absolute solubility of oxygen is lower in saline waters, it is
advantageous to compensate DO concentration readings (µg/L, mg/L,
µmol/L) to ensure that the sensor accurately reports the concentration of
DO in the presence of significant salinity. This can be accomplished by
storing a salinity value in the sensor before taking measurements. The
compensation algorithm is applied internally before the concentration is
reported. The degree of compensation is minimal at very low salinities, and
but may affect readings by several percent at higher levels.
To store a salinity value in the RDO sensor, connect in Win-Situ 4 or
Pocket-Situ 4, select RDO in the Navigation tree, click
Edit and in the next
screen select "Edit RDO Salinity Value."
Indicators During Calibration
Status • :
NOT TESTED is displayed until you begin the calibration by selecting Run.
UNSTABLE indicates the sensor response does not yet meet the criteria
for a valid calibration point.
NOMINAL indicates the sensor deviation meets early stabilization criteria.
The Accept button becomes available when nominal stability is achieved.
You may accept the early value or wait for complete stability. If you accept
the early value, the calibration point will be designated “USER SET” in the
calibration report.
STABLE is displayed when the readings have stabilized sufficiently to take
a valid calibration point. The calibration proceeds automatically to the next
screen.
Reading:
• The current sensor response in mg/L and degrees Celsius.
Deviation: • Change in sensor response between the last two readings. This
enables you to follow the progress of the stabilization, but deviation from
the previous reading is not necessarily the best indicator of stability as the
software is looking at longer-term trends.
Barometric Pressure
• is shown in your selected unit.
Preparation for 100% Oxygen Calibration
100% DO calibration is performed in water saturated with air. We
recommend a container of clean water aerated with the In-Situ RDO
bubbler cal kit (see Replacement Parts list) or an aquarium pump.
Fill the bubbler cup with clean water. Turn on the pump and regulate
with the pinch valve. Insert the TROLL 9500 instrument into the bubbler,
resting the RDO adapter plate on the rim of the cup. Ensure that the
temperature sensor is submerged at least ½ in, and the RDO sensing
foil is not in the direct path of the bubbles.