User`s guide

Chapter 4 ______________________________________________________________ Maintenance
VAISALA______________________________________________________________________ 161
Leaf Wetness Sensor
Periodic Maintenance
Leaf Wetness Sensor does not need any regular maintenance. Field
repairs are accomplished by replacing the complete sensor.
Fuel Moisture/Fuel Temperature Sensor
Periodic Maintenance
The sensing element of the sensor is a wooden dowel that exchanges
moisture with its surroundings. In the course of a year, it undergoes
many cycles of soaking up moisture and drying. These processes
eventually cause the structure of the wood to deteriorate. Similarly, dust
and other contaminants become embedded in the surface and they
change the surface properties. When this occurs, the calibration is no
longer valid.
The only way to restore the sensor accuracy is to replace the wooden
dowel, which must be done at the factory.
Your experience will eventually determine how frequently the sensor
needs service. At the beginning, the manufacturer recommends that you
return it to the factory once per year for replacement of the dowel and
calibration.
At most sites, where the sensor is used to assess fire danger, there is a
season when the danger is low. That is usually a good time to replace or
refurbish the sensor.
Present Weather Detector
Periodic Maintenance
Present Weather Detector is designed to operate continuously for
several years without other maintenance than cleaning lenses and DRD
sensing surface (see Figure 116 on page 162). No initial calibration is