Sequoia LISST-SL, Руководство по эксплуатации

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LISST-SL V2.1
User’s Guide
20
4. Collecting
Test Data in a
Lab
Set up a head on the pitot tube as in the last
test. Apply about 10 cm of head.
Turn on the TCB and go directly to MEASURE.
Observe the indicated velocity on the display.
It should be fairly steady. Its magnitude should
also be consistent with the formula:
Velocity (ft/sec) = 8 H fps; H in feet.
Or,
Velocity (m/sec) = 4.43
H m/s; H in
meters
If the numbers show more than 10% variability,
try again. If the variability persists, you may
need to purge air from the pitot tube. This
procedure is described in Appendix B.
This step also serves as a practice run for field tests.
Begin with power switch off at the TCB. It is assumed that
you have just acquired a good background file.
Fill a 1-liter beaker with 1 liter of clean water
and add about 500 mg of coarse sediment (say
20-100 micron). Put the beaker on a magnetic
table and set up a small magnetic stir bar so
that the sediment won’t all settle out. Stir
vigorously.
Connect one water-filled flexible tube (1/4-inch
ID, or 6 mm ID) with a pinch clamp to the
intake of the LISST-SL.
Connect a second tube to the exit of the SL (at
top, behind the 6-pin connector). Send the free
end of this tube to a drain.
Finally, to simulate a dynamic hydraulic head of
10 cm or more, connect a tube to the pitot
intake, fill with water, and raise it. See photo.
Turn on power at the TCB. The pump will start
pumping. Water will recirculate. From the MAIN
MENU press the MEASURE button on the
panel. After several samples, open the pinch
valve to the beaker. The instrument will display
the measured mean grain size, concentration,
and a velocity. These are your test data. With
this method, only 5 to 10 samples will be valid
before air bubbles will be sucked into the inlet
tube to produce erroneous data. Compare the
displayed velocity from a computed value; it is
related to the head H on the pitot tube, as
(2gH)
1/2
where g is 9.81 m/s
2
or 32 ft/s
2.
and H is
in corresponding units.