Campbell Scientific Kipp and Zonen CMP-Series Pyranometers - Manual (Page 17)

CMP/CMA series manual
Page 16
4. Pyranometer physical properties
4.1. Spectral range
The spectrum of the solar radiation reaching the Earth’s surface is in the wavelength range between
280 nm and 4000 nm, extending from ultraviolet (UV) to the far infrared (FIR) as shown in Figure 9.
Due to the excellent physical properties of the glass dome and black absorber paint, Kipp & Zonen
CMP/CMA series radiometers are equally sensitive in a wide spectral range. 97-98% of the total
energy will be absorbed by the thermal detector. The CMP 22 pyranometer has a wider spectral range
due to the quartz domes used in its construction.
Figure 9 Solar irradiance spectrum at the Earth’s surface and pyranometer response
4.2. Sensitivity
The radiometer thermopile sensitivity is mainly determined by the physical properties of the detector
itself. The thermoelectric power, thermal conductivity of the junctions and the overall dimensions of the
sensing element are related to its sensitivity.
4.3. Impedance
The radiometer impedance is defined as the total electrical impedance at the radiometer output
connector fitted to the housing. It arises from the electrical resistance in the thermal junctions, wires
and passive electronics within the radiometer.
4.4. Response time
Any measuring device requires a certain time to react to a change in the parameter being measured.
The radiometer requires time to respond to change in the incident radiation. The response time is
normally quoted as the time for the output to reach 95% (sometimes 63%) of the final value following a
step-change in irradiance. It is determined by the physical properties of the thermopile and the
radiometer construction. CMP/CMA series radiometers have a fast response, which makes them
suitable for measuring solar radiation under variable weather conditions.