Campbell Scientific OBS-5+ Sediment Concentration Monitor and Pressure Sensor - Manual (Page 29)

OBS-5+ System
FIGURE 7-1. Manual (left) and automatic (right) sediment suspenders
7.1.1 General Guidance
The OBS-5+ uses response curves from the near and far detectors to create
three lookup tables like those shown on FIGURE 4-3 and FIGURE 7-2. The
objective of sediment calibration is to create lookup tables from the sediment
you will monitor. The OBS-5+ can store lookup tables for as many as 14
sediments. The fifteenth table is reserved for auto-saved archives.
To view a calibration table, click button (step 3 in Section 6.2.10,
Surveying), highlight a table number and click on the Activate button; then
click View Active. The calibration data table contains all the information
needed by the OBS-5+ to interpolate SSC values from the detector signals.
From left to right, the column lists: 1) SSC values (g L
–1 ), 2) ND counts, 3) 2 nd
derivatives for ND curve, 4) FD counts, and 5) 2 nd derivatives for FD curve.
During a calibration, the first table, highlighted in red, is created from the
rising limb of the near detector response between zero counts and point “a”
(FIGURE 7-2). The second table, bold blue curve, is used for mid-range SSC
values. It is derived from the descending limb of the far detector curve
between points “a” and “c”. High SSC values are estimated from a third
lookup table, indicated by the bold green line and point “b”, and are derived
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