Message Exists But Visibility Value Does Not; Visibility Value Is Continuously Too Good - Vaisala PWD22 User Manual

Chapter 7_____________________________________________________________ Troubleshooting
VAISALA _______________________________________________________________________ 101
Message Exists but Visibility Value
Does Not
1. PWD22 control electronics is probably working.
- Check the status information with the STA command (see
section STA on page 82). If there are any active alarms, the
visibility value does not exist.
- Check especially P12, M12, BACKSCATTER and LEDI.
See section PWD22 Electrical Troubleshooting on page 103
for internal monitoring values of the limits.
2. Go to the PWD22 site.
- Check the cable connectors.
- Check the receiver and transmitter units. Follow the
instructions in section Removing and Replacing on page 94
when removing the units.
- Visually inspect the condition of the electronics.
Visibility Value is Continuously Too
Good
This can be caused by several reasons. Most probably the light path
from the transmitter to the receiver is disturbed.
1. The lenses may be excessively contaminated. A warning has
been received.
- Clean the lenses (see section Cleaning Lenses and Hoods on
page 90).
2. One of the hoods has been filled with snow, leaves, or
something similar. A warning is generated.
- Clean the hoods (see section Cleaning Lenses and Hoods on
page 90).
3. There is condensation on the lens surfaces. This is a sign of
heating failure.
4. There is an electrical fault in the transmitter or receiver.
- Check the status information with the STA command (see
section STA on page 82).
- Go to section Message Exists but Visibility Value Does Not
on page 101.