Campbell Scientific OBS500 Smart Turbidity Meter with ClearSensor Technology - Manual (Page 36)

OBS500 Smart Turbidity Meter with ClearSensor™ Technology
6. Repeat steps 2, 3, 4, and 5 for the other standards.
7. Perform 2 nd -order polynomial regressions on the calibration data to get the
coefficients for converting OBS signals to TU values.
FIGURE 7-7. OBS500 in 500-TU AMCO Clear ® turbidity standard in
100-mm black polyethylene calibration cup
7.5.2 Sediment
There are three basic ways to calibrate an OBS sensor with sediment. These
are described in the following sections. However, only the procedures for dry-
sediment are explained in this manual. Typically, the sensor will record in
turbidity units and the relationship to suspended sediment is calculated in a
spread sheet or database after the data is retrieved to a computer.
7.5.2.1 Dry-Sediment Calibration
Dry-sediment calibration is a calibration performed with sediment that has
been dried, crushed, and turned to powder. This is the easiest calibration to do
because the amount of sediment can be determined accurately with an
electronic balance and the volume of water in which it is suspended can be
accurately measured with volumetric glassware. Of the three methods, dry-
sediment calibration causes the greatest physical and chemical alteration of the
sediment. Alteration of the sediment size as a result of processing can
significantly affect the calibration slope. FIGURE 7-5 shows, for example, that
reducing the grain size by a factor of two during grinding can increase OBS
sensitivity by a factor of two.
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