CMP6, CMP11, and CMP21 Pyranometers
Nearby AC power lines, electric pumps, or motors can be a
source of electrical noise. If the sensor or datalogger is
located in an electrically noisy environment, the
measurement should be made with the 60 or 50 Hz rejection
integration option as shown in the example programs.
7.3.1.1 Input Range
The output voltage is usually between 5 and 20 mV per 1000 W
•
m
–2
. When
estimating the maximum likely value of sensor output a maximum value of
solar radiation of 1100 W
•
m
–2
can be used for field measurements on a
horizontal surface. Plane of array irradiances can exceed 1500 W
•
m
–2
.
Select the input range as follows:
1. Estimate the maximum expected input voltage by multiplying the
maximum expected irradiance (in W
•
m
–2
) by the calibration factor (in µV /
W
•
m
–2
). Divide the answer by 1000 to give the maximum in millivolt
units.
2. Select the smallest input range which is greater than the maximum
expected input voltage. Normally the 50 mV range for the CR3000,
CR5000, or CR9000(X) and the 25 mV or 250 mV range for the CR6,
CR800, CR850, or CR1000 will be suitable. The exact range will depend
on the sensitivity of your individual sensor and the maximum expected
reading. With some dataloggers an autorange option can be used if
measurement time is not critical.
The parameter code for the input range also specifies the measurement
integration time. The slow or 60 Hz rejection integration gives a more noise-
free reading. The 250 µs integration takes less power and allows for faster
throughput.
7.3.1.2 Multiplier
The multiplier converts the millivolt reading to engineering units. The
sensitivity value supplied by the manufacturer gives the output of the sensor as
µ
V (micro-volts) / W
•
m
–2
. As the datalogger voltage measurement instructions
give a default output in mV, the following equation should be used to calculate
the multiplier to give the readings in W
•
m
–2
:
m = 1000/c
Where,
m = multiplier
c = sensor output in µV / W
•
m
–2
Other units can be used by adjusting the multiplier as shown in TABLE
CAUTION
15
Summary of Contents for CMP11
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