OBS501 Smart Turbidity Meter with ClearSensor
®
Technology
29
FIGURE 8-5. Portable Sediment Suspender (left) and OBS beam
orientation in suspender tub (right)
SSC = Wt
s
[V
w
+ Wt
s
/ρ
s
]
–1
, where Wt
s
= total sediment weight in tub in mg,
V
w
= volume of water in liters,
and ρ
s
= sediment density (assume 2.65 10
3
mg
L
–1
)
Procedure
1.
Record and log the clean-water signal as in Step 1, Section
; see FIGURE
Position of OBS501 in clean tap water in big black
(p. 26)
. Use the same value, such as, sidescatter, backscatter, or ratio
throughout the calibration.
2.
Move the OBS501 to the suspender as described in setup.
3.
Weigh 500 ± 10 mg of sediment in a weigh boat and transfer it to the
teacup. Record the weight on the calibration log sheet and add about 10 cc
of water from the suspender tub to the teacup and mix the water and
sediment into a smooth slurry with the teaspoon.
4.
Add the sediment slurry to the tub and rinse the teacup and spoon with tub
water to get all the material into the suspender.
5.
Turn the suspender on and let it run for 10 minutes or until the OBS signal
stabilizes.
6.
Take averages of signals with the computer or datalogger and enter them
on the calibration log sheet.
7.
Calculate the sediment-weight increment as follows: W
i
= 2500 mg
(4000/V
x
), where W
i
= the incremental weight of sediment and V
x
= the
average output signal from step 6. The resulting weight gives the amount
of sediment to add in order to have evenly spaced calibration points.
8.
Add enough additional sediment to get one full increment of sediment, W
i
± 5%. Repeat steps 4, 5, and 6.
9.
Repeat step 8 until five full increments of sediment have been added or
until the OBS signals exceed the output range.
