Campbell Scientific OBS-3A Turbidity and Temperature Monitoring System - Manual (Page 60)

OBS-3A Turbidity and Temperature Monitoring System
Power failed due to battery clip corrosion or a broken power wire.
Check for a broken red wire connecting the battery tube and circuit board.
Green powder or tarnish on the battery contact parts indicates salt-water
corrosion. Remove the electronics from the pressure housing. Pull battery-
clip-retainer pin out with needle-nose pliers and slide the clip from its track.
Clean the corroded surfaces of clip and track with a Scotch-brite® pad and
reassemble unit.
OBS or other sensor malfunction.
• Inspect for physical damage such as a broken or bent thermistor, a dirty
conductivity sensor, or an OBS sensor fouled with marine growth.
• Open unit and inspect for broken sensor and communication wires and
loose connectors (FIGURE 8-1).
• Check sensor power by starting OBS-3A Configuration | Survey
Configuration and selecting All Sensors. Green LEDs should illuminate
for installed sensor.
• If the depth sensor reads high and does not change, it may need to be
cleaned (see Section 9.2, Pressure Sensor).
• If the sensors appear to be in working order, the digitizer or
microcontroller may be damaged. Such problems usually require factory
service.
Bright sun near the surface (<2 meters) or black-colored sediments cause
erroneous OBS readings.
Do not survey in shallow water between 10:00 and 14:00 local time and avoid
areas with suspended black mud.
Changing the water temperature in the setup dialog box does not change
the temperature measurement.
This is normal. Temperature inputs only change the water density correction
used to convert pressure to depth.
OBS-3A indicates different NTU values in the field than other
turbidimeters.
Not all turbidity meters read the same! OBS sensors are checked with a Hach
2100N laboratory instrument, using U.S. EPA-approved, formazin turbidity
standards before leaving our factory. Turbidimeters other than the 2100N will
read different NTU values on natural water samples.
OBS-3A indicates different suspended sediment levels in the field than in
the laboratory.
This results from a change in sediment size or color (see Section 10, Factors
Affecting OBS Response). You may have to perform a field calibration with
water samples.
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