Cleaning; Cleaning Lenses And Hoods - Vaisala PWD22/52 User Manual

USER'S GUIDE____________________________________________________________________
NOTE
82 __________________________________________________________________ M210543EN-E

Cleaning

It is very important to clean PWD22/52. No specific operations are
necessary before cleaning the sensor, in other words, it is possible to use
the service terminal while cleaning. Some erroneous data may, however,
be generated. Problems from this can often be eliminated by restarting
PWD22/52 after cleaning (by pressing power OFF/ON, for example).

Cleaning Lenses and Hoods

The lenses of the PWD22/52 transmitter and receiver units should be
relatively clean to get reliable results as dirty lenses give too good
visibility values. Cleaning should be done every six months or more
often depending on the conditions (for example, if there are roads
nearby).
The cleaning need is indicated in the hardware alarm field of the data
message (2nd character on the message). Refer to section Message Types
on page 50.
Number 3 = backscatter alarm indicates that the contamination level is
too high and cleaning must be done at once. The measurement values are
not shown in the data message.
Number 4 = backscatter warning indicates that the contamination level
has increased and cleaning must be performed in the near future. The
measurement values are still reliable and shown in the data message.
The complete cleaning procedure is as follows:
1. Moisten a soft, lint-free cloth with isopropyl alcohol and wipe the
lenses. Be careful not to scratch the lens surfaces. Lenses should
dry indicating that the lens heating is functioning.
2. Check that the hoods and lenses are free of condensed water, or ice
and snow deposits.
3. Wipe the dust from the inner and outer surfaces of the hoods.
4. After the optical surfaces are properly cleaned, give the CLEAN
command.
It is not necessary to give the CLEAN command after every cleaning.
Alternatively choose the STA command and check that the Backscatter
CHANGE value of both the receiver and the transmitter is close to zero
(set to zero by the previous CLEAN command).