Campbell Scientific OBS-5+ Sediment Concentration Monitor and Pressure Sensor - Manual (Page 21)

OBS-5+ System
2) Wave your hand in front of the OBS-5+ sensor; the turbidity and SSC
levels on the top plot will fluctuate as data scrolls across the plot.
3) Blow into the pressure sensor or press your thumb on it to compress air on
the diaphragm (FIGURE 4-1). A small elevation in the pressure signal
will occur (bottom plot).
4) Click Stop and then OBS Settings to view time, serial numbers,
depth corrections, and software versions.
6.2.6 Monitoring Turbidity (NTU)
The OBS-5+ was calibrated and factory-certified using AMCO Clear, U.S.
EPA-approved turbidity standards (
www.gfschemicals.com ). In order to
measure turbidity, the electronic gain of the near detector is set to the
calibration value and the active lookup table is overridden. Consequently, the
unit cannot simultaneously measure SSC (g L
–1 ) and NTU when either g L –1 or
NTU is selected. You must choose one or the other.
6.2.7 Water Density and Barometric Corrections
Instrument depth is estimated from pressure and it is important to set the water
temperature and salinity so the OBS-5+ can correct for water density and
calculate depth correctly. The sensor measures absolute pressure so the
instrument must also correct for barometric pressure. Be sure to do this while
the OBS-5+ is at the surface. Depending on the magnitude of barometric
pressure fluctuations at the site and the desired accuracy, you may want to
correct data for atmospheric effects using barometric pressure simultaneously
recorded at a nearby site.
6.2.8 Sample Statistics
The individual measurements are not recorded in the data flash memory and
you must select the sample statistics that will be recorded. Two types of
statistics can be selected for OBS-5+ measurements.
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