Vaisala FD12P - Manual (Page 135)

Chapter 7 ____________________________________________________________ Troubleshooting
VAISALA _______________________________________________________________________ 135
Visibility Value is Missing
1. The FD12P control electronics is probably working. Check the
following:
- Check the status information with the STA command (see
section STA Command on page 85). If there are active
hardware alarms, visibility values are removed from data
message.
- Check especially
P15, M15, BACKSCATTER and LEDI
. See
section Values for Internal Monitoring on page 137 for the
limits.
2. Go to the FD12P site and do the following:
- Check the cable connector at the control board.
- Check the receiver and transmitter units. Follow the
instructions in section Removing and Replacing on page 126
when removing the units.
- Check that the ribbon cable connector is properly connected.
- Pull out the circuit boards, first of the receiver (loosen the
bolts) and then the transmitter.
- Visually inspect the condition of the electronics.
Visibility Value is Continuously Too
Good
This can be caused by several reasons, some of which are listed
below. Most probably the light path from the transmitter to the
receiver is disturbed.
a. The lenses may be excessively contaminated, which
produces a warning. Clean the lenses (see section
Cleaning on page 118).
b. One of the hoods has been filled with snow, leaves, or
other things, for which a warning is generated. Clean the
hoods.
c. There is condensation on the lens surfaces, which is a sign
of heating failure.
d. An electrical fault has occurred in the transmitter or
receiver. See items in section Visibility Value is Missing
on page 135.