Kipp&Zonen CNR 4 Net Radiometers - Manual (Page 5)

4
1 GENERAL INFORMATION
The CNR 4 is a 4 component net radiometer that measures the energy balance between incoming short-wave
and long-wave Far Infrared (FIR) radiation versus surface-reflected short-wave and outgoing long-wave radiation.
The CNR 4 net radiometer consists of a pyranometer pair, one facing upward, the other facing downward, and a
pyrgeometer pair in a similar configuration. The pyranometer pair measures the short-wave radiation. And the
pyrgeometer pair measures long-wave radiation. The upper long-wave detector of CNR 4 has a meniscus dome. This
ensures that water droplets role off easily and improves the field of view to nearly 180°, compared with a 150° for a
flat window. All 4 sensors are integrated directly into the instrument body, instead of separate modules
mounted onto the housing. Each sensor is calibrated individually for optimal accuracy.
Two temperature sensors, a Pt-100 and Thermistor, are integrated for compatibility with every data logger. The
temperature sensor is used to provide information to correct the infrared readings for the temperature of the
instrument housing. Care has been taken to place the long-wave sensors close to each other and close to the
temperature sensors. This assures that the temperatures of the measurement surfaces are the same and accurately
known. This improves the quality of the long-wave measurements.
The design is very light in weight and has an integrated sun shield that reduces thermal effects on both long-wave
and short-wave measurements. The cables are yellow with waterproof connectors as used with all our new
radiometers. The mounting rod can be unscrewed for transport, like the CNR 2.
An optional ventilation unit with heater is designed as an extension of the sunshield and can be fitted new to the
CNR 4 or retro-fitted later. The ventilation unit CNF 4 is compact and provides efficient air-flow over the domes and
windows to minimize the formation of dew and reduce the frequency of cleaning. The integrated heater can be used
to melt frost.
The CNR 4 specifications when used with CNF 4 comply with the WMO classification of Good Quality
The Net Radiometer, CNR 4, is intended for the analysis of the radiation balance of Solar and Far Infrared radiation.
The most common application is the measurement of Net (total) Radiation at the earth's surface.
The CNR 4 design is such that both the upward facing and the downward-facing instruments measure the energy
that is received from the whole hemisphere (180 degrees field of view). The output is expressed in Watts per square
meter. The total spectral range that is measured is roughly from 0.3 to 42 micrometers. This spectral range covers
both the Solar Radiation, 0.3 to 3 micrometers, and the Far Infrared radiation, 4.5 to 42 micrometers.
Chapter 1 describes how to operate the CNR 4, giving separate attention to the use of the individual pyranometers
and pyrgeometers. More about the physics of the pyranometer and pyrgeometer can be found in chapter 2.
The CNR 4 radiometers all have individual calibration factors. As opposed to the CNR 1 they are not made equal.
The advantage is that the individual sensitivities are more accurate then when made equal with shunt and series
resistors.
For quality assurance of the measurement data, we recommend the recalibration of the CNR 4 as part of a regular
maintenance schedule every two years. More about calibration can be found in chapter 3.
The CNR 4 is intended for continuous outdoor use. It is weatherproof. The materials used in Pyranometer and
pyrgeometer are robust. Contrary to most competitive instruments, plastic domes are not used. Therefore the CNR
4 requires very low maintenance. For optimal results however, proper care must be taken. More about maintenance
can be found in chapter 4. Chapter 5 can be consulted if a problem with the CNR 4 is suspected; this chapter
addresses trouble shooting.
The general user should read chapter 1 and chapter 4.