Campbell Scientific OBS-5+ Sediment Concentration Monitor and Pressure Sensor - Manual (Page 31)

OBS-5+ System
TABLE 7-1. Schedule of Concentrations for Sediment Calibrations
MUD (D
60
< 62 µm) Sand (D
60
> 62 µm)
Low
SSC
(0-5 g/l)
Mid-
range
(5-20 g/l)
High
SSC
(> 20 g/l)
Low
SSC
(0-10 g/l)
Mid-
range
(10-40 g/l)
High
SSC
(> 49 g/l)
0.0 5 25 0.0 12 50
1.0 6 30 2.0 14 60
1.5 7 40 3.0 15 70
2.0 8 50 4.0 20 80
2.5 9 60 5.0 25 90
3.0 10 6.0 30 100
3.5 15 8.0 35 140
4.0 20 10.0 40 160
The operator can control the electronic gain of the detector circuits to optimize
the instrument for his sediment. This can be done with the ND Gain and FD
Gain boxes in the OBS-5+ program during the calibration using the + and –
buttons to toggle gain up or down. The unit automatically scales all calibration
counts to match the selected gain. Set the initial ND and FD gain values to 16,
starting with the third SSC value in TABLE 7-2, adjust the gain to keep the ND
and FD counts in the range of 50,000 to 60,000.
While calibration points can be deleted at any time, never
start a new SSC value until you are satisfied with the
current values and gain setting. CAUTION
The FD counts will peak first at around 2 to 7 g L –1 and the ND will peak
between 5 to 20 g L –1 . Set the water volume and sediment density for your
calibration in cells D1 and E1 (default volume and density are 3.0 l and
2,650 g L
–1 ). Every time sediment is added to the suspender, enter the grams
added to column A and read the current SSC value in column C.
TABLE 7-2. SSC-Calculation Spreadsheet
A
Grams
Added
B
Total
Grams
C
Cs (g/l)
(g/l)
D
Water
Volume (l)
E
Sediment
Density (g/l)
1 0.00 0.00 0.00 3.0 2650
2 1.00 1.00 0.33
2 2.00 3.00 1.00
3 3.00 6.00 2.00
4 4.00 10.00 3.33
23