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Section 4: Deploying and Operating SBE 52-MP
Horizontal Orientation, Upcast and/or Downcast Data
If you plan to use the 52-MP to obtain both upcast and downcast data,
mount the 52-MP with a horizontal orientation. Orient the sensors as
described below:
• Deep profiles: Orient the 52-MP with the temperature sting at the same
elevation as the plumbing sensor exhaust. With the intake and exhaust
on the same plane, Bernoulli pressures are equalized, minimizing
acceleration of water in the plumbing. While this orientation does not
provide an upward path to the system plumbing, it provides a neutral
path. The top 0 to up to 30 meters of data of the first downcast only is
suspect, because the pump may not operate properly until the air bubbles
collapse due to water pressure.
• Shallow profiles: If the 52-MP is oriented so that air cannot be easily
expelled, the top 0 to 30 meters of data is suspect, because the pump may
not operate properly until the air bubbles collapse due to water pressure. If
the moored profiler is operating only at shallow depths, it may take days
for the air bubbles to completely dissipate on their own. Therefore, for
shallow profile applications, orient the 52-MP with the temperature sting
slightly below the plumbing exhaust; this orientation provides an
upward path from intake to exhaust, allowing air to be quickly expelled
during a brief soak below the surface, ensuring proper pump operation for
all casts. Although Bernoulli pressures are not equalized for this
orientation, the difference in elevation, and the resulting pressure
differential, is small.
Intake and
exhaust
at same
elevation
Intake
slightly
below
exhaust
Intake
Exhaust
Intake
Exhaust
For Shallow Profiles
For Deep Profiles
Although the 52-MP can obtain downcast data in a horizontal orientation, the
52-MP’s commands were designed for obtaining upcast data. In particular, the
52-MP automatically stops autonomous sampling when the measured pressure
is less than PCUTOFF= (i.e., PCUTOFF= defines the top of the upcast).
If sampling for a downcast, make sure to set PCUTOFF= above the top of
the cast, or the 52-MP will turn off immediately after sampling is started.
Example: You plan to sample on downcast, starting each profile at 5 decibars.
Set PCUTOFF=3 (decibars) to ensure proper operation.
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