Zero Offset Type A; Zero Offset Type B; Operating Temperature; Field Of View - Kipp & Zonen SMP series Instruction Manual

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B.7 Zero offset type A
By physical laws any object having a certain temperature will exchange radiation with its surroundings. The domes of upward
facing radiometers will exchange radiation primarily with the relatively cold atmosphere. In general, the atmosphere will be
cooler than the ambient temperature at the Earth's surface. For example, a clear sky can have an e ective temperature up to
50 °C cooler, whereas an overcast sky will have roughly the same temperature as the Earth's surface.
Due to this the pyranometer dome will 'lose' energy to the colder atmosphere by means of radiative transfer. This causes the
dome to become cooler than the rest of the instrument. This temperature di erence between the detector and the instrument
housing will generate a small negative output signal which is commonly called Zero O set Type A. This e ect is reduced by using
an inner dome. This inner dome acts as a 'radiation bu er'.
This o set can be minimized by applying appropriate ventilation of the instrument. The CVF4 ventilation unit can be used with
the SMP's, no ventilation unit is available for the SMP3.
B.8 Zero offset type B
Proportionally to the ambient temperature the instrument temperature varies and causes heat currents inside the instrument.
This will cause an o set commonly called Zero O set Type B. It is quantified as the response in W/m² to a 5 K/hr change in
ambient temperature.
B.9 Operating temperature
The operating temperature range of the radiometer is determined by the physical properties of the individual parts. Within the specified
temperature range Kipp & Zonen radiometers can be operated safely. Outside this temperature range special precautions should be
taken to prevent any physical damage or performance loss of the radiometer. Please contact your Kipp & Zonen representative for
further information regarding operation in unusually harsh temperature conditions.
B.10 Field of view
The field of view is defined as the unobstructed open viewing angle of a radiometer. ISO and WMO require that a pyranometer
for the measurement of global solar radiation has a field of view of 180 ° in all directions (i.e. a hemisphere). The inherent field
of view of the instrument should not be confused with the clear field of view of the installation location.
Cold atmosphere
Thermal exchange between:
A Outer dome and atmosphere
B Inner dome and outer dome
C
Inner dome and detector
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A
B
C