Calibration Check Procedure - Vaisala PWD22/52 User Manual

USER'S GUIDE____________________________________________________________________
84 __________________________________________________________________ M210543EN-E
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 82 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. PWD22/52 should answer as follows:
ZERO SIGNAL: OK>
3. Move the blocking plate.
4. Install the calibrator plates to the lens hoods. Refer to Figure 19 on
page 85.
5. Fasten the opaque glass plates to the hoods. Pay attention to the
signal value printed on the plates because it is needed during the
following steps.
6. Move away from the optical path and wait for 30 seconds.
7. Give the CHEC command.
8. After one minute, read the displayed signal.
9. The signal value must be close to the one printed on the plates. If
the difference is less than 5 %, calibration is correct. If not,
continue with the calibration procedure.
10. Terminate the CHEC command by pressing the ESC key.