Sequoia LISST-SL, Руководство по эксплуатации

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LISST-SL V2.1
User’s Guide
2
and immediately begins transmitting data to the TCB. It continues transmitting data
regardless of if the TCB is capturing it or not. In this regard, it is a ‘dumb’ sensor. The –SL
needs the TCB for power. The TCB executes the user commands, e.g. capturing a
background scattering file, or capturing river data.
The sensor is the entire streamlined instrument which enters the water.
At the top of the LISST-SL sensor is the cable attachment point (1), which is hidden in a
streamlined black ‘housing’ that looks like the sail of a submarine. Immediately behind is
the underwater connector (2) to which the cable from the B-reel will be connected [see
Appendix F for connector pin outs]. Note the exit point for the intake flow
– it is behind the
connector (3). Three dots are shown (4), for aligning the nose, the front bulkhead, and the
mid-section of the LISST-SL. A hole on the far side in this image, exactly behind the mark
(4), and on the bulkhead is a static pressure port. Depth of the instrument below water
surface is sensed through 2 small holes on the side of the
bulkhead (‘static port’),
connected to a pressure sensor. The hole at top (8) of the bulkhead is to purge air. If over
years of operation, sediment fills the static ports, you may use the top static port to inject
water and blow out the sediment. The three radial holes in the bulkhead are connected to a
common cavity that is applying the static pressure for the flow velocity and the pressure for
the depth sensor. Temperature is sensed in the water passage, within the instrument. On
the nose is an intake tube (9) on the instrument axis, and above it is the pitot-tube velocity
sensor (5). To prevent large sediment grains from entering the pitot tube, a 35 micron metal
screen is fitted behind the conical opening. Whenever not in use, KEEP THE PITOT TUBE
covered with a pinched tube or a plastic cap provided with the shipment. Not doing so may
dry up the passage to the pitot pressure sensor and introduce bubbles. We will describe
separately how to identify if bubbles are present in the pitot tube and how to remove
bubbles.
This is a time consuming process, so best to keep the pitot tube covered . Note
that the front (6) and rear (7) bulkheads are identified on the photo.
A large fin is provided to stabilize the LISST-SL Sensor and point it into the flow. The
downward fin, as against the upward surfaces on airplanes is chosen so that the fins enter
water first, immediately spinning the instrument and pointing it into the flow. Do not be
alarmed if the LISST-SL sways in the river current
– turbulent eddies in the river cause the
instantaneous flow direction to veer; the instrument follows this instantaneous direction.
1.2 The B-reel
This is an essential system. It has 50m of a strong cable wrapped on a barrel and a handle
to manually operate it as a winch. The B-reel serves a dual purpose: it is used to lower the
LISST-SL sensor from the bridge, and also, it provides electrical connection between the
sensor and the Topside Controller Box (TCB) which houses data scheduling and controlling
electronics. The B-reel cable has a river side end, which splits into a Y. One