Maintenance And Re-Calibration; Daily Maintenance; Monthly Maintenance; Yearly Maintenance - Kipp & Zonen SMP series Instruction Manual

6. Maintenance and re-calibration

.
SMP pyranometers are simple to maintain and do not require any special tools or training. There are no service items requiring
scheduled replacement, only the desiccant of the SMP11 requires changing when needed.

6.1 Daily maintenance

On clear windless nights the outer dome temperature of horizontally placed radiometers will decrease, even to the dew point
temperature of the air, due to infrared radiation exchange with the cold sky. The e ective sky temperature can be 30 °C lower
than the ground temperature.
Depending upon the weather conditions dew, glazed frost or hoar frost can be precipitated on the top of the dome and can stay
there for several hours in the morning. An ice cap on the dome is a strong di user and increases the pyranometer signal drastically,
up to 50 % in the first hours after sunrise. Snow may completely cover the dome.
The frequency of cleaning is highly dependent upon the local weather and environmental conditions, such as dust, airborne
pollutants or salt spray in marine environments. Ideally, the dome of the pyranometer should be cleaned every morning before
sunrise. In all cases the frequency of cleaning can be reduced by the use of a ventilation unit (all SMP's, execpt SMP3), with the
heaters switched on when necessary.
Note Clean the dome using pure alcohol or distilled water and a lint-free cloth. Ensure that no smears or deposits are
left on the dome.

6.2 Monthly maintenance

For the SMP11 only, check the desiccant in the drying cartridge. This is a self-indicating silica-gel. When it requires replacement
the colour changes from orange to clear.
To replace the desiccant unscrew the cartridge from the radiometer housing, if it is tight a 16 mm or 5/8" open-ended wrench /
spanner can be used to loosen it. Remove the cap from the end of the cartridge and safely dispose of the used silica-gel. Refill
with fresh desiccant, and refit the end cap to the cartridge. Make sure that the o-ring seal and its seat in the housing are clean,
grease with Vaseline if it is dry.
Note
Screw in the drying cartridge hand-tight only, to avoid distorting the o-ring seal.
Desiccant refill packs are available from Kipp & Zonen. One pack is su cient for one complete refill.
Check that the pyranometer is level and adjust if necessary.
Check that the sun shield is firmly clipped on.

6.3 Yearly maintenance

Check all the electrical connections. Unscrew the plugs, clean if necessary and then reconnect.
Check cables for damage caused by accident or by rodents.
Check the instrument mountings and any base supports are secure.

6.4 Calibration

An ideal radiometer gives an output that is proportional to the absolute irradiance level. This relationship can be expressed as
a constant ratio called 'sensitivity'. SMP series pyranometers are very stable instruments, but they do change very slightly with
time. This is largely due to exposure of the black detector coating to UV solar radiation. Re-calibration is recommended every
two years. Normally this is carried out at the Kipp & Zonen factory or at an authorised calibration facility.
31