Campbell OBS500, Руководство оператора

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OBS500 Smart Turbidity Meter with ClearSensor
®
Technology
9
5.2 Turbidity Units
Conceptually, turbidity is a numerical expression in turbidity units (TU) of the
optical properties that cause water to appear hazy or cloudy as a result of light
scattering and absorption by suspended matter. Operationally, a TU value is
interpolated from neighboring light-scattering measurements made on
calibration standards such as Formazin, StablCal, or SDVB beads. Turbidity is
caused by suspended and dissolved matter such as sediment, plankton, bacteria,
viruses, and organic and inorganic dyes. In general, as the concentration of
suspended matter in water increases, so will its turbidity; as the concentration
of dissolved, light-absorbing matter increases, turbidity will decrease.
Descriptions of the factors that affect turbidity are given in Section 8 ,
Factors
that Affect Turbidity and Suspended-Sediment Measurements
(p. 32)
. Like all
other optical turbidity monitors, the response depends on the size, composition,
and shape of suspended particles. For this reason, for monitoring
concentrations, the sensor must be calibrated with suspended sediments from
the waters to be monitored . There is no “standard” turbidimeter design or
universal formula for converting TU values to physical units such as mg/l or
ppm. TU values have no intrinsic physical, chemical, or biological
significance. However, empirical correlations between turbidity and
environmental conditions, established through field calibration, can be useful
in water-quality investigations.
The USGS has an excellent chapter (6) on turbidity measurements in their
“National Field Manual for the Collection of Water-Quality Data”:
http://water.usgs.gov/owq/FieldManual/Chapter6/Section6.7_v2.1.pdf
Historically, most turbidity sensor manufacturers and sensor users labeled the
units NTUs, for Nephelometric Turbidity Units. ASTM and the USGS have
come up with the following unit classifications that are applicable to the
OBS500:
Optical Backscatter FBU Formazin Backscatter Unit
Sidescatter FNU Formazin Nephelometric Unit
Ratio Back and Sidescatter FNRU Formazin Nephelometric Ratio Unit
The document “U.S. Geological Survey Implements New Turbidity Data-
Reporting Procedures” details the units:
http://water.usgs.gov/owq/turbidity/TurbidityInfoSheet.pdf
Throughout this manual, the measurements will simply be referred to as
Turbidity Units (TU).