Sequoia LISST-SL, Руководство по эксплуатации

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LISST-SL V2.1
User’s Guide
31
VIII.
FAQ’s
How do I evaluate the
background measurement?
Upon obtaining a background, the red line shows the
factory background and the blue bars show the current
background. If they are close, well and good.
Increased scattering on the middle rings results from just
one source: dirt or fine scratches on the windows.Try
cleaning the windows a few times. They are acceptable.
If you see increase in the inner-most rings, i.e. rings 1-8
the explanation is more complex. See Appendix D.
In the end, what really matters is that the instrument is
reasonably aligned, and that the background be STABLE.
Try to MEASURE with the clean water that you used for
Background. If the displayed concentration is small
(<5mg/l), you may use the instrument, knowing that that is
the noise floor.
Does the LISST-SL take
into account the irregular
shape of the natural
sediment grains?
Yes. This was published in a study by our scientists (see
Agrawal YC,Whitmire A, Mikkelsen OA, Pottsmith HC
(2008); download from our website:
http://www.sequoiasci.com/library/technical.aspx?Section
Name=library
). Our software that processes raw data files
incorporates irregular particle shape.
Does the LISST-SL require
any calibration?
No. All that is required is that the user makes a
background measurement before a sample is taken. This
is in order to evaluate the state and cleanliness of the
optical system. If this is good (e.g. the current
background measurement is close to the factory
background, see FAQ above) the instrument will deliver
good data.
Drifts in laser power output are taken care of by the data
processing software.
What happens if there are
particle present outside of
the size range covered by
my LISST-SL? This is a more complex question. Very briefly, the
presence of sediment particles outside the size range
covered by the instrument will cause some additional
scattering on the inner- or outermost rings of the ring
detector. In turn, this increased scattering will be
interpreted as particle volume, so that the net effect is to
increase the particle volume in the smallest and/or largest
size classes.
Typically, the effect can be seen if there is a significant
amount of particles outside the size range, so that a rising
tail will appear in the coarse and/or fine end of the size
spectrum.
Does the instrument No. All laser diffraction based instruments measure the