Campbell OBS501, Operator'S Manual

Page: 34 / 66

OBS501 Smart Turbidity Meter with ClearSensor
®
Technology
24
TABLE 8-3. RS-232 Settings
Bits Per Second 9600
Data Bits 8
Parity None
Stop Bits 1
Flow Control None
8.6 Calibration
8.6.1 Turbidity
Field recalibration is not recommended and usually not needed until the
OBS501 is sent back to Campbell Scientific for the two year service. We
recommend checking the calibration in the field as described below. If a
9-point calibration is needed, the OBS501 should be sent to Campbell
Scientific to perform the calibration.
The normalized response of an OBS501 sensor to SDVB turbidity over the
range from 0 to 4,000 TU is shown in FIGURE
8-2 . As shown on the inset, the
response function is contained within region A, the linear region, of the
universal response curve. However, there is residual nonlinearity that is
removed by calibration and by computation of a TU value with a 2nd-order
polynomial. This section explains how to do a turbidity calibration.
0 1000 2000 3000 4000
Tur bidity (TU)
0.0
0.2
0.4
0.6
0.8
1.0
N
o
rm
a
li
z
e
d
O
B
S
-3
+
R
e
s
p
o
n
s
e
(O
P
V
3
3
0
V
C
S
E
L
)
FIGURE 8-2. Normalized response of OBS501 to AMCO Clear
®
turbidity. The inset shows the response function of a turbidity
sensor to high-sediment concentrations.
0 20000 40000 60000
SSC (mg/l)
0
1000
2000
3000
4000
T
u
rb
id
ity
(N
T
U
)
A B C