Campbell CMP11, Инструкция по эксплуатации

Страница: 28 / 48

CMP6, CMP11, and CMP21 Pyranometers
The silica gel desiccant granules in the drying cartridge should be orange and
opaque. Replace the desiccant granules when they become translucent
(normally after several months). Refill packs of desiccant are shipped with the
pyranometer and can be purchased from Campbell Scientific. The drying
cartridge uses the content of one refill pack. FIGURE 8-2 shows the
replacement process.
When changing the desiccant, ensure that:
•
The surfaces touching the rubber O-ring are clean. Dirt, in combination
with water, can cause corrosion, harming it.
• The rubber O-ring is coated with silicon grease or petroleum jelly. The
grease coating improves the O-ring’s seal.
•
The drying cartridge is tightly threaded into the pyranometer’s body.
FIGURE 8-2. Changing the desiccant
8.1.3 Check Sensor Output
It is also important to check the data returned from the sensor as it will show
the first indication of a fault. When doing this you should be aware of several
expected phenomena that can cause strange measurements. In particular on
clear, windless nights the outer dome temperature of horizontally placed
pyranometers can fall as low as the dew point temperature of the air, due to
infrared radiation exchange with the cold sky. (The effective sky temperature
can be 30 °C lower than the ground temperature, which results in an infrared
emission of –150 W
•
m –2 ). If this happens, dew, glazed frost or hoar frost can
be precipitated on the top of the outer dome and can stay there for several hours
in the morning. An ice cap on the dome is a strong diffuser and can increase
the pyranometer signal by up to 50% in the first hours after sunrise.
18