Campbell Scientific OBS-3A Turbidity and Temperature Monitoring System - Manual (Page 66)

OBS-3A Turbidity and Temperature Monitoring System
10.3 High Sediment Concentrations
At high sediment concentrations, particularly in suspensions of high clay and
silt, the infrared radiation from the emitter can be so strongly attenuated along
the path connecting the emitter, the particle, and the detector, that backscatter
decreases with increasing sediment concentration. For mud, this occurs at
concentrations greater than about 5,000 mg/L. FIGURE 10-3 shows a
calibration in which sediment concentrations exceed 6 g/l cause the output
signal to decrease. It is recommended not to exceed the specified turbidity or
suspended sediment ranges unless calibrations extend over range “A” on
FIGURE 10-3.
0 5 10
Sediment Concentration (g/l)
0
1
2
3
4
5
Signal
(
V
)
A
Signal (V)
15 Sediment Concentration (g/L)
FIGURE 10-3. Response at high sediment concentrations
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