Campbell Scientific OBS-3A Turbidity and Temperature Monitoring System - Manual (Page 54)

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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