Chapter 6 _______________________________________________________________Maintenance
VAISALA _______________________________________________________________________ 119
To clean the rain detector, do the following:
1.
Clean the DRD12 rain detector carefully with a soft, lint-free
cloth moistened with a mild detergent. Be careful not to scratch
the surface.
2.
Check that the detector and the windshield are free of ice and
snow deposits.
Calibration
General
The FD12P has been calibrated at the factory. Normally, the FD12P
needs no recalibration as long as the circuit boards are not changed or
there is no call for warnings and alarms. The circuit boards need no
hardware calibration.
A periodic check every year is recommended. The user checks the
visibility calibration using the FDA13 calibration kit. If the check
shows less than a
±
3 % change, recalibration is not recommended as
the change is within the repeatability of the calibration procedure.
If any mechanical damage changes or weakens the optical
measurement path, that is, either the receiver or the transmitter heads
or the crossarm supporting them, recalibration is needed. If the
receiver unit (FDR12), transmitter unit (FDT12B), or the CPU unit
(FD12P) is changed, both visibility and contamination measurements
need recalibration.
Also calibrate the DTS14B Temperature Sensor once a year.
Visibility Calibration
Calibration is checked and adjusted with the FDA13 calibration kit.
The kit consists of a blocking plate and two opaque glass plates with
known scatter properties. The CHEC and CAL commands are used in
the procedure. The calibration procedure checks the zero scatter signal
and the very high scatter signal. The zero signal is obtained using a
blocking plate and the high signal using opaque glass plates.
When the visibility measurement is calibrated, visibility should be
better than 500 m. Calibration is not recommended to be carried out in
heavy rain or in bright sunshine. However, light rain is of no harm.
