Campbell Scientific OBS500 Smart Turbidity Meter with ClearSensor Technology - Manual (Page 50)

OBS500 Smart Turbidity Meter with ClearSensor™ Technology
The following three tests are used to diagnose malfunctions of an OBS500.
1. The Finger-Wave Test is used to determine if an OBS sensor is ‘alive’.
Power the OBS sensor and connect datalogger (see Section 7.2, Device
Configuration Utility). Wave your finger across the sensor window about
20 mm away from it. The datalogger should show the output fluctuating
from a few TU to the full-scale signal. If there are no signal fluctuations
of this order, there is a problem that requires attention.
2. The Shake Test is done to determine if water has leaked inside the
pressure housing. Unplug the cable and gently shake the sensor next to
your ear and listen for sloshing water. This test gives a false negative
result when the amount of water in the housing is large enough to destroy
the circuit but too small to be audible.
3. A Calibration Check is done to verify if a working OBS sensor needs to
be recalibrated. In order to be meaningful, the user must have a criterion
for this test. For example, this criterion might be 5%. The sensor is
placed in calibration standards with the 1 st and 2 nd TU values listed in
FIGURE 7-5 and the datalogger readings are logged. If either reading
differs by more than 5% from ones reported on the factory calibration
certificate, or the user’s own calibration data, the sensor should be
recalibrated. If the first two calibration points fall within the acceptance
criterion, then the third value can be tested. The recommended frequency
for calibration checks is quarterly when an OBS sensor is in regular use.
Otherwise it should be performed prior to use. Calibration checks can be
done in the field.
TABLE 10-1. Troubleshooting Chart.
Fault Cause of Fault Remedy
Fails finger-
wave test
No power, dead battery Replace battery and reconnect
wires.
Plug not fully seated Disconnect and reinsert plug.
Sensor broken Visually inspect for cracks.
Return OBS500 to
manufacturer if cracks are
found.
Electronic failure. Unit
draws less than 11 mA or
more than 40 mA.
Return OBS500 to
manufacturer.
Fails shake
test
Sensor leaked Return OBS500 to
manufacturer.
Fails
calibration
check
Aging of light source
causes it to become
dimmer with time
Recalibrate (see Section 7.5,
Calibration).
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