SonTek/YSI Argonaut-XR Technical Manual - HydroScientific West

Argonaut Operation Manual Firmware Version 7.9 (May 1, 2001)
SonTek/YSI
radius of 3.5 m). While this provides a remote measurement free from flow interference in most
situations, there is some potential for measurement interference in certain mounting
arrangements. This can be avoided by following some basic precautions in instrument mounting.
Flow interference occurs when one acoustic beam is oriented directly downstream of the mooring
line. If a small cable is used for the mooring line, it will have little effect on the flow pattern and
should not influence Argonaut measurements. However, if a chain or other large line is used, it
can create significant flow distortion that can potentially affect velocity measurements. To avoid
this, we recommend mounting the Argonaut such that no beam tends to align downstream. This
is shown for a simple mounting arrangement in Figure 12.
In a case where the Argonaut MD is mounted off the center of the mooring line, the instrument
will tend to act as a fin and align downstream of the line. If the mooring line has been placed
directly between two acoustic beams, as in Case 1 above, one beam will tend to be located
directly downstream of the mooring line and may see flow interference.
No beam should be pointed directly at the mooring line, which can cause interference with the
acoustic signals. If the mooring line is between two beams, as in Case 2 above, no beams are
oriented towards the mooring line and no beams tend to align downstream, which greatly reduces
the potential for flow interference. We advise keeping all acoustic beams oriented at least 30°
away from the mooring line. An arrangement such as Case 2 (where the closest beam is 40° from
the mooring) works well to avoid measurement interference in all beams.
6.3.2. Argonaut XR
The Argonaut XR is normally mounted on the bottom looking up. The mounting should keep the
instrument securely fixed and not shift with time. The instrument should be as level as is
practical (ideally within 10°). The internal tilt sensor allows the Argonaut XR to adapt its
operation for non-level installations, but large tilt angles can have an adverse effect on near
boundary performance. Installation tilt angles greater than 25° will have a serious impact on
instrument performance.
Figure 12 – Argonaut MD Mounting for “Fin” Effect
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