Campbell OBS-3+, Instruction Manual

Page: 25 / 54

OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors
NTU value with a 2 nd -order polynomial. This section explains how to do a
turbidity calibration.
0 1000 2000 3000 4000
Turbidity (TU)
0.0
0.2
0.4
0.6
0.8
1.0
N
or
m
al
iz
ed
O
B
S-
3+
R
es
po
ns
e
(O
PV
33
0
VC
SE
L)
FIGURE 8-1. Normalized response of OBS-3+ to AMCO Clear ® turbidity.
The inset shows the response function of an OBS sensor
to high sediment concentrations.
GFS Chemicals manufactures AMCO Clear
®
SDVB turbidity standards that
are used to calibrate an OBS sensor. SDVB standards are made for individual
instruments and standards made for one model of turbidity meter cannot be
used to calibrate a different model. The standard values for calibrating OBSs
are: 125 NTU (GFS Part No. 8428), 250 NTU (GFS Part No. 8429), 500 NTU
(GFS Part No. 8430), 1000 NTU (GFS Part No. 8431), 2000 NTU (GFS Part
No. 8432), and 4000 NTU (GFS Part No. 8433). The standard values and
volumes required for the standard low ranges are given in TABLE 8-1. SDVB
standards have a shelf life of two years provided that they are stored in tightly
sealed containers and evaporation is minimized.
TABLE 8-1. SDVB NTU values for turbidity calibrations
in standard low ranges.
Low Range 1st Std. Value 2nd Std. Value 3rd Std. Value
250 125 (1000 ml) 250 (1000 ml) 1000 (500 ml)
500 250 (1000 ml) 500 (500 ml) 2000 (500 ml)
1000 500 (500 ml) 1000 (500 ml) 4000 (500 ml)
0 20000 40000 60000
SSC (mg/l)
0
1000
2000
3000
4000
Tu
rb
id
ity
(N
TU
)
A B C
15