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It
may be noted that for best accuracy, trim and list should be
eliminated. When both conditions exist, every effort should be made to
eliminate at least one condition, preferably list. Conditions
of trim and list must be noted and corrections made for their affect on
measurements and/or volumes.
Liquid Level Gauging
Before
commencing level measurement, the manufacturer's specific operating
procedures should be consulted, as well as appropriate vessel
personnel, for operational instruction on the particular system aboard
the vessel. The manufacturer's instruction should always be used to
supplement the following generic guidelines:
-
Confirm
the vessel's automatic gauge system is working. Determine whether the
system calculates volumes automatically, or requires the input of
measurement data to generate calculated volumes.
-
Verify
that measurements are being taken from the reference point specified by
capacity tables.
-
Determine
if tank capacity tables include volumes within vessel lines.
If they do not, so note and record.
-
Read
and record level gauge to the nearest graduation (1/8th-in.,
1-mm, 0.01-ft). See API MPMS Chapters 3.1B and 3.4. If the
system automatically converts gauges to volumes, record them also. It
may be noted that if the cargo is moving because of swells or waves, at
least five measurements should be taken, the highest and lowest
readings dropped, and the remaining three averaged. Such
adverse conditions should be noted on the ullage report.
-
Repeat
step d until all tanks are completed.
Measuring of Small
Quantities/Free Water
Most
automatic tank gauging systems do not have the ability to accurately
measure free water under oil or small amounts of ROB/OBQ, especially if
the surface of the ROB/OBQ cannot be detected due to the trim or
list. With those systems which can perform such measurements,
the sensing devices used must be located so that measurements can be
taken under all conditions of trim. To handle varying trim
configurations, sensors must be located as close to the aft and forward
bulkheads as possible. On vessels which normally operate with
only a single trim condition (aft or forward), the vessel need only
have sensors located in the direction of its normal operational trim
seen on the vessel. For more infor- mation on gauge point location, see
API MPMS Chapters 2.8B, 3.1B, and 3.4.
Automatic Temperature Measurement Procedures
Review
temperature system verification log and record the last calibration
date. Read and record the temperature at each tank, or in the cargo
control room, for all tanks being 'temperatured'. Indicate if
temperatures are automatically averaged for each tank. If so,
report temperatures to the nearest 0.5°F or 0.5°C. If not, temperatures
at each tank level should be recorded to the nearest 0.1°F or 0.1°C and
then the level temperatures of each tank manually-averaged to 0.5
degrees, and so reported.
Sections of text taken from API - MPMS Chapter 17 Marine Measurement
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