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2 sediment, Sediment, 1. mixing volumes for formazin standards – Campbell Scientific OBS-3A Turbidity and Temperature Monitoring System User Manual

Page 54

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OBS-3A Turbidity and Temperature Monitoring System

The formula for preparing turbidity standards other than shown in TABLE 7-1
is:

⎥⎦

⎢⎣

+

=

stk

dw

stk

stk

std

V

V

V

T

T

or

⎥⎦

⎢⎣

×

=

std

stk

dw

std

stk

T

T

V

T

V

Where:

T

std

= Turbidity of the standard solution;

T

stk

= Turbidity of the stock solution, usually 4000 NTU;

V

stk

= Cumulative volume of stock solution at each calibration point;

V

dw

= Initial volume.

TABLE 7-1. Mixing Volumes for Formazin

Standards

Formazin Volume

V

stk

(ml)

Solution Turbidity

T

std

(NTU)

12.7 50

32.3 125

66.7 250

143 500

333 1000

1000 2000

7.2 Sediment

The procedure for sediment calibration is more involved than for turbidity. For
a modest charge we will pre-calibrate OBS sensors with sediment provided by
users. Call us for a quotation to perform this service.

The most common cause of errors in OBS data is improper
calibration.

CAUTION

Before proceeding with a sediment calibration, review Section 10, Factors
Affecting OBS Response
, to learn about factors that can influence the quality of
your results. The most difficult part of the procedure is maintaining a stable
sediment concentration while the OBS logs calibration values. This is
straightforward when the material is dry, completely disaggregated mud with
particles smaller than ~20 μm. It becomes more difficult the larger the
sediment gets and special calibration equipment may become necessary (see
Section 11, References).

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