Kipp & Zonen CMA Series Instruction Manual

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Kipp & Zonen CMA Series Instruction Manual Manual pdf 14 page image

CMP/CMA series manualPage 132.6. MaintenanceOnce installed the radiometer needs little maintenance. The outer dome(s) must be cleaned andinspected regularly, ideally every morning. On clear windless nights the outer dome temperature ofhorizontally placed radiometers will decrease, even to the dew point temperature of the air, due toinfrared radiation exchange with the cold sky. (The effective sky temperature can be 30°C lower thanthe ground temperature). In this case dew, glazed frost or hoar frost can be precipitated on the top ofthe outer dome and can stay there for several hours in the morning. An ice cap on the dome is a strongdiffuser 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 aspossible manually.The dome of the pyranometer can be ventilated continuously by a heated blower to keep the domeabove dew point temperature. The need for heating strongly depends upon local climatologicalcircumstances. Generally, heating is advised during cold seasons when frost and dew can be expected.The Kipp & Zonen CV 2 ventilation unit is specially designed for unattended operation under mostweather conditions and has a choice of heating levels.Note that the CMA albedometers and the CMP 3 pyranometer cannot be used with the CV 2 ventilationunit.A periodic check is to ensure that the radiometer is level and that the silica gel desiccant is stillcoloured orange. When the orange silica gel in the drying cartridge is turned completely transparent(normally after several months), it must be replaced by fresh silica gel as supplied in the small refillpacks. The content of one pack is sufficient for one complete refill. At the same time check that theradiometer mounting is secure and that the cable is in good condition.Some tips when changing the dessicant:- Make sure the surfaces of the radiometer and the drying cartridge that touch the rubber o-ring areclean (corrosion can do a lot of harm here and dirt, in combination with water, can cause this);- The rubber o-ring is coated with a silicon grease to improve the seal. If the rubber o-ring looks dryapply some grease to it (Vaseline will also do);- Check that the drying cartridge is tightly threaded into the radiometer body.It is very difficult to make the radiometers hermetically sealed; so, due to pressure differences betweenthe inside and the outside of the instrument, there will always be some exchange of (humid) air.The radiometer sensitivity changes with time and with exposure to radiation. Calibration every twoyears is advised. Further information about Kipp & Zonen recalibration services can be found inAppendix VI.