Turbidity (Ntu) Calibration; Equipment And Materials; Procedure For Turbidity - Campbell OBS-5+ Operator's Manual

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OBS-5+ System

7.2

Turbidity (NTU) Calibration

the FD curve where it starts decay exponentially, also 10 on FIGURE 7-2

9. Points 'b' and 'c' will usually have the same numerical value.

15) Save the table in the EMPTY Table number selected at Step 3.

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Large black, neoprene or polyethylene tub

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100 mm test cylinder (www.deslinc.com, No. TC4)

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AMCO Clear turbidity standards (GFS No. 8429, 8430, and 8431,

www.gfschemicals.com)

1) Put batteries in the OBS-5+ and connect it to a PC with test cable using the

RS-232 plug (FIGURE 6-1).

2) Start the OBS-5+ Utility software; wake the OBS-5+; and click the OBS

Settings button to verify its response.

3) Use the OBS-5+ pull-down menu, select Gain and set ND and FD gain to

2. This is the setting used for the factory calibration.

4) Start the calibration with the button and secure the unit in a big black tub

filled with clean tap water (FIGURE 7-3). The NTU-calibration dialog

will appear.

5) Enter 0.3 in the value box and click the record button to log the clear-water

data point. The unit will take 1,200 measurements in 60 seconds. When

the process is complete, the data appear in the data table and the point will

be plotted on the calibration graph. If you are satisfied with the data,

mount the unit in a 100 mm calibration cup as shown on FIGURE 7-5.

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