Campbell CM 21, Инструкция по эксплуатации, Страница: 33 / 65

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5 MAINTENANCE
Once installed the pyranometer needs little maintenance. The outer dome
must be cleaned and inspected regularly, e.g. every morning. On clear
windless nights the outer dome temperature of horizontally placed
pyranometers will decrease, even to the dew point temperature of the air,
due to IR radiation exchange with the cold sky. (The effective sky
temperature can be 30ºC lower than the ground temperature). In that case
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 increases the pyranometer signal drastically
up to 50% in the first hours after sunrise. Hoar frost disappears due to solar
radiation during the morning, but should be wiped of as soon as possible
manually.
Another daily check is to ensure that the instrument is level and that there is
no condensation inside the dome. If there is condensation the silica gel must
be replaced, even when the colour is still blue. Apparently the location
requires very fresh silica gel and a low dew point inside.
It is normal in humid areas to replace the desiccant twice a year.
The exchange interval is affected by humidity, change in air pressure and
the amount of temperature changes.
When the blue silica gel in the drying cartridge is turned pink (normally after
several months), it must be replaced by active material. Pink silica gel can
be activated again in an oven at 130ºC within several hours.
Apart from that it is good to visit the pyranometer (or any other sensor)
regularly to check its condition. (desiccant, dirt on dome, levelling of
instrument and condition of cabling)
Some tips to check when changing the desiccant:
-
Make sure the surfaces of the pyranometer and the
cartridge that touch the rubber ring are clean (corrosion can do a lot
of harm here and dirt, in combination with water, can cause this)
5. MAINTENANCE