User`s manual

Manual revision 016 Section 4: Deploying and Operating FastCAT SBE 49
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Optimizing Data Quality
This section contains guidelines for obtaining the best quality data. Some of
these guidelines may conflict with the goals of a particular application, but you
should be aware of the tradeoffs of data quality vs. mission goals.
Expelling Air from Plumbing for Optimal Pump Operation
Upcast Data
If performing a single vertical profile from above the surface, and wanting
to obtain upcast data, optimal orientation is vertical, sensors-up. This provides
a U-shape to the system plumbing, allowing air to be quickly expelled during a
brief soak period just below the surface, ensuring proper pump operation for
the entire cast. If FastCAT is oriented so that air cannot be easily expelled, the
top 10 meters of data is suspect because the pump may not be operating
properly until the air bubbles are collapsed due to water pressure. This may not
be an issue if performing a deep cast, because air bubbles will collapse long
before upcast begins.
The U-shape and the FastCAT’s good seals, combined with optimal pump
operation, can prevent surface oils and other contaminants from getting into
the plumbing and conductivity cell. These oils and contaminants are the
primary cause of calibration drift in conductivity sensors. Pump operation
to prevent intrusion of surface oils and contaminants follows:
1. On Deployment -
When not in use, store the FastCAT dry (see Section 5: Routine
Maintenance and Calibration). Fill the cell with a 0.1% solution of Triton
1 hour before deployment. Deploy the FastCAT without removing the
Triton solution. As the FastCAT breaks the surface, oils and other
surface contaminants will float on the Triton solution at the intake and
exhaust, preventing contaminants from getting into the plumbing and
conductivity cell. Hold the FastCAT below the surface until the pump
turns on, expelling the Triton solution and drawing in seawater.
2. On Recovery -
Turn off the pump before the FastCAT reaches the surface (if sampling
autonomously, stop sampling to turn off the pump). Water will be held in
the U-shaped plumbing. As the FastCAT breaks the surface, oils and other
surface contaminants will float on the water at the intake and exhaust,
preventing contaminants from getting into the plumbing and conductivity
cell. Turn over the FastCAT when it is on deck, emptying the water from
the conductivity cell and exhaust plumbing, so the oil floating on the
intake and exhaust surfaces does not get into the system.
Pump exhaust
plumbing
and outlet
Sensor
intake