Campbell Scientific PWS100 Present Weather Sensor - Manual (Page 102)

Section 9. Maintenance
9-2
It is advisable to use airduster to blow any loose dust and dirt from the lenses
as a first step. Using a lint free lens cloth or lens tissue impregnated with a
small amount of isopropyl alcohol solvent, clean the lens surface by dragging
the cloth across the lens surface being careful not to apply excessive pressure.
Excessive pressure may lead to some types of contaminant scratching the lens
surface. Over time such scratches can lead to reduced sensor accuracy.
Once clean, replace the baffle by carefully slotting it into position, being
careful not to scratch the paint coating or damage any heater element. Lock the
baffle into place using the retaining screw, ensuring that the nylon washer is in
place.
9.3 Calibration
The PWS100 is fully calibrated before leaving the factory. This calibration
covers the mechanical arrangement of the system (including detection volume)
as well as setting laser power and other electronic settings. The system is self
regulating; however, it is recommended that the PWS100 is calibrated every
two years. If the calibration process is unable to bring it into specification, a
warning LED will flash on the PWC100 calibrator. The PWS100 should then
be sent to the factory.
The detection volume is calibrated using the PWC100 calibrator. The particle
analysis is done using the unit with a rotating disc which has an embedded high
precision ball lens. The refractive index of this ball lens is taken into
consideration when calibrating the unit. The disc is rotated at a known speed
which provides a known velocity component to the calibration and the
refraction from the known diameter ball lens to the two detectors provides a
size calibration. Visibility calibration is carried out using the second fixture
which comprises a material with known scatter parameters. Light impenetrable
sensor blocks are used to determine sensor offset and will need to be placed in
the sensor heads when required. The unit will then determine the calibration
factors and indicate if there is any problem with the optical or mechanical
arrangement of the present weather sensor. Laser power can be monitored
using a commercial laser power meter.
Please refer to the PWC100 calibrator manual for further details of operation of
the PWC100 calibrator and the procedure for calibration of the PWS100.