Campbell OBS-3+, Instruction Manual

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OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors
8. Add enough additional sediment to get one full increment of sediment, Wi
± 5%. Repeat steps 4, 5, and 6.
9. Repeat step 8 until five full increments of sediment have been added or
until the OBS signals exceed the output range.
10. Perform third-order polynomial regressions on the data to get the
coefficients for converting OBS output to SSC.
9. Troubleshooting
Do not use a sensor with a stainless steel housing in
seawater. This will void the warranty and cause
corrosion and leakage.
Do the following tests and see TABLE 9-1 to diagnose an OBS sensor:
1. The Finger-Wave Test is used to determine if an OBS sensor is ‘alive’.
Power the OBS sensor and connect a DMM across the low- or high-range
output leads (see Section 8.1.2, Setup ). Wave your finger across the sensor
window about 20 mm away from it. The DMM should show the output
fluctuating from a few mV 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 1st and 2nd NTU values listed in TABLE
8-1 and the DMM readings are logged. If either reading differs by more
than 5% from ones reported on the factory calibration certificate, or the
user 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.
WARNING
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