User`s guide

User’s Guide ______________________________________________________________________
62 ___________________________________________________________________M210662EN-A
application is the measurement of Net (total) Radiation at the earth's
surface.
The CNR1 sensor consists of two pyranometers, model type CM3, for
measuring solar radiation, and of two pyrgeometers, model type CG3,
for measuring Far Infrared radiation.The properties of CNR1 are mainly
determined by the properties of the individual sensors, both the CM3's
and CG3's. The combination of these sensors offers the advantage of
accuracy, robustness, and the possibility to evaluate the quality of the
measured data.
From a spectral point of view, the CM3 and CG3 are complementary.
Together they cover the full spectral range: The CM3 from 0.3 to
3 microns, and the CG3 from 5 to 50 microns. The gap between these
two produces negligible errors.
CNR1 has several output signals: two voltages for the model type CM
3 pyranometers, two voltages for the model type CG 3 pyrgeometers,
and a 4 wire Pt-100 connection. A heater is incorporated. The heater is
intended to prevent dew and frost deposition at night. Heating generally
improves accuracy but at the same time introduces some measurement
errors. It is not a necessity.The maximum allowable power for the
heater is 50 VA. In case of snow or frost one might also consider heating
at a higher level than the usual 6 VA. Heating at 20 VA will melt snow
in most cases. 20 VA can be reached at 22 Volts. During high power
heating, measurement accuracy cannot be specified. You are advised to
reject measured data readings during this high power heating. If lower
voltage is available, one might consider heating at a lower power. The
6 VA is designed for extreme conditions, 2 VA is sufficient for
moderate conditions. Time needed for reaching a stable instrument
temperature when heating is about 60 minutes.
Generally the accuracy of CNR1 will be higher than that of competitive
Net-Radiometers. The main reason for this is that the solar radiation
measurement performed by the CM3 is accurate, and offers a traceable
calibration. Due to the fact that the Net Solar radiation can be very
intense, 1000 Watts per square metre compared to a typical -100 for the
Net Far Infrared radiation, the accuracy of the solar measurement is
very critical. The CM3 is an instrument that complies with the ISO
second class specifications, and can be relied upon to give an accurate
reading. Wind corrections, as applied by less accurate competitive
instruments are not necessary. The robustness of the materials used
implies that CNR 1 will not suffer from damage inflicted by birds.