Campbell OBS-3A Especificaciones descargar pdf (Pagina 41)

Section 6. Calibration

x 2 gallons filtered distilled water (purified water from the super market

works fine),

x Hand-drill motor,

x Paint stirrer.

6.2.2 Sediment Preparation

Sediment preparation is a critical factor in calibration quality. It is most

convenient to use dry material because it can be accurately weighed with an

electronic balance. However, this only works well for clean sand because

disaggregation produces a sediment size different than existed in the field. For

example, deep harbors with weak currents often have cohesive (sticky) mud

with high organic-rich flocculation. Disaggregation of the flocs will reduce the

particle size and change the OBS response. Sediment or suspended solids

concentration is the dry weight of sediment divided by the weight of the

sample (expressed in ppm) or by the volume of sample in liters (expressed as

mg/l). Usually the disaggregated particles will be finer than untreated

sediment. When dried sediment is used, verify that field estimates are accurate

by comparing the OBS results with direct samples of suspended matter. (See

Section 9—References: USGS Book 9.)

FIGURE 6.2-1 shows how different methods of disaggregating sediment can

change the relationship between turbidity and the concentration of suspended

material. This occurs because vigorous disaggregation produces more small

particles than less vigorous methods as well as more OBS signal per unit of

mass concentration. The result is higher signal levels for a given

concentration.

10 20 30 40 50

Sediment Concentration (mg/l)

Turbidity (NTU)

Hand Shaking

15-min. Sonic Bath

3-min. Sonic Probe

FIGURE 6.2-1. Effects of Disaggregation

6-5

1 2 ... 36 37 38 39 40 41 42 43 44 45 46 ... 57 58

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Campbell OBS-3A Especificaciones Pagina 41