Vaisala FD12P - Manual (Page 136)

User's Guide _______________________________________________________________________
136 _____________________________________________________ M210296en-A
Visibility is Constantly Too Low
Usually there is something disturbing in the sample volume. Check
the following:
1. Check the condition of the hoods. If the hoods are slightly
twisted, try to align them as well as possible.
2. Try to find a better direction for the receiver/transmitter optics.
See section Location and Orientation on page 30.
3. There may be an electrical fault. See items in section Visibility
Value is Missing on page 135.
FDP12 Reports Precipitation When
There Is None
When temperatures are below 0 °C, only the optical measurement is
used in precipitation detection. When the temperature is above 0 °C,
the DRD12 detection is used in cross-checking the optical detection
and false detection can only be caused by problems in both
measurements.
1. Check that there are no flashing lights close to the FD12P.
Flashing lights may cause the FD12P to detect peaks in the
optical signal.
2. Check that there are no foreign objects in the sample volume.
Tree branches or any other moving objects in the sample volume
may cause sudden changes in the scatter signal.
3. If a false detection has occurred in a temperature above 0 °C, the
DRD12 does not function correctly. Do the following:
- Clean the DRD12 sensing surfaces thoroughly.
- Check the DRD12 operation.
FD12P Reports Frozen
Precipitation during Rain
The ratio of optical intensity measurement to DRD12 measurement is
too high. Do the following:
1. Check the optical calibration and DRD12 operation.
2. Check the TS temperature sensor operation.