Vaisala FD12P - Manual (Page 120)

User's Guide _______________________________________________________________________
120 _____________________________________________________ M210296en-A
When the calibrator is used in precipitation, the error will be
proportional to the area of the scatter plates, which are covered by
droplets. Make sure that this area is negligible compared with the total
area. Bright sunlight shining on the calibrator plates will increase
noise in the scatter measurement and make the CHEC command
output less stable. If calibration needs to be carried out in bright
daylight, we recommend that the crossarm be turned so that sunlight
intensity on the calibrator plates is minimized (that is, the plates are
parallel to the sunrays).
Calibration Check Procedure
Clean the lenses before the calibration. Check the cleaning procedure
in section Cleaning Lenses and Hoods on page 118. Check also the
condition of the opaque glass plates and clean them if needed.
To check the calibration, do the following:
1. For blocking the light path, place the blocking plate near either
of the lenses, preferably near the receiver.
2. Wait for 30 seconds.
3. Give the
CHEC
↵ ↵↵ ↵ command. Then wait at least two minutes.
The signal value must be between ± 0.1 Hz. If it is not, there
may be a hardware error. Check the connectors.
4. Remove the blocking plate and terminate the CHEC command
by pressing the ESC key.
To install the calibrator, do the following:
1. The calibrator clamp is permanently installed. If the clamp is not
installed or the old FDA12 calibrator is used, install the
calibrator clamp in the middle of the transducer crossarm. The
correct place is marked by two grooves on the crossarm. Refer
to Figure 31 on page 122. Do not tighten the clamp bolts, the
clamp needs to be adjusted later.
2. Fasten the opaque glass plates to the tie rod. The labels with
signal values should face outwards. Take note of the signal
value printed on the plates because it is needed during the
following steps.
3. Attach the calibrator to the clamp, tighten the rod knob. Position
the calibrator plates by lifting or lowering the tie rod. The
transmitter and receiver should point to the middle of the glass