Campbell Scientific Kipp and Zonen CMP-Series Pyranometers - Manual (Page 25)

CMP/CMA series manual
Page 24
6.3. CMP 21
CMP 21 is a high precision scientific pyranometer based upon the CMP 11 but with individual
optimisation and characterisation and an integrated housing temperature sensor. CMP exceeds the
ISO-9060 specification criteria for an ISO Secondary Standard pyranometer
The special features of the CMP 21 are:
•
Individually optimised and characterised temperature dependence.
•
Individually characterised directional response.
•
Integrated housing temperature sensor.
6.4. CMP 22
CMP 22 is a high precision scientific pyranometer base upon the CMP 21 but with strictly selected
quartz domes which are 4 mm thick. CMP 22 has an extended spectral range to match pyrheliometers
with quartz windows. Because of the high optical quality and higher refractive index of the quartz
domes the directional error is reduced to less than 5 W/m
2
.
The zero offset behaviour is fundamentally improved in two ways:
The zero offset caused by changing instrument temperature is negligible, because of the very well
balanced thermopile construction.
The zero offset due to the difference between sensor and dome temperature (e.g. Far Infrared
Radiation absorption or emission by the outer dome) is minimised using an improved thermal coupling
of sensor and top of dome. Thicker domes, both of 4mm, and the 50% higher thermal conductivity of
quartz, compared to glass, improve this thermal coupling.
CMP 22 features are:
• Negligible thermal gradient zero-offset.
• Lowest zero-offset due to FIR radiation.
• Broadened spectral range 200 – 3600 nm.
• Directional error < 5 W/m 2
.
• Lowest temperature dependency of sensitivity.
Like the CMP 11 and CMP 21 pyranometers, the CMP 22 complies with the specifications for the best
of three classes of pyranometer, ‘High quality’, as defined in the 'Guide to meteorological Instruments
and Methods of Observation', sixth edition, 1996, of the World Meteorological Organisation (*WMO)
Geneva, Switzerland. Most specifications of the CMP 22 are twice as good as required.
* The WMO classification is adapted from the international standard ISO 9060 (1990). Herein ‘high
quality’ class is referred to as ‘secondary standard’.