User's Guide _______________________________________________________________________
92____________________________________________________________________ M210543EN-B
unit (PWC22) or transmitter unit (PWT11) is replaced, both visibility
and contamination measurements need recalibration.
In addition, the Temperature Sensor value should be compared with
air temperature. In daytime TS is higher than the air temperature, in
sunshine, for example, more than five degrees (Celsius) higher.
Visibility Calibration
The calibration is checked and adjusted with the PWA11 calibration
kit. The kit consists of a blocking plate and two opaque glass plates
with known scatter properties. The
ZERO
,
CHEC
, and
CAL
commands are used in the procedure. The calibration procedure
checks two points; zero scatter signal and a very high scatter signal.
The zero signal is obtained using a blocking plate and the high signal
using opaque glass plates.
When visibility measurement is calibrated, visibility should be better
than 500 meters. Calibration is not recommended to be carried out in
heavy rain or in bright sunshine. Bright sunlight on the calibrator
plates will increase noise in the scatter measurement and make the
CHEC
command output less stable. However, light rain does not
matter.
Calibration Check Procedure
Clean the lenses following the instructions in section Cleaning Lenses
and Hoods on page 90 before the calibration check procedure. Also
check the condition of the opaque glass plates and clean them if
necessary.
1.
For blocking the light path, place the blocking plate in the
receiver hood and wait for 30 seconds.
2.
Give the
ZERO
command. PWD22 should answer as follows:
ZERO SIGNAL: OK>
3.
Move the blocking plate.
4.
Install the calibrator plates to the lens hoods. Refer to Figure 21
on page 93.
