Campbell CMP3-L, Инструкция по эксплуатации

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CMP3-L Pyranometer
Select the input range as follows:
1. Estimate the maximum expected input voltage by multiplying the
maximum expected irradiance (in Wm
-2)
by the calibration factor (in
µV/Wm
-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 CR23X,
CR5000, CR9000 and CR7, and the 25 mV or 250 mV range for the
CR510, CR10X and 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. A fast integration takes less power and allows for faster
throughput.
5.2 Multiplier
The multiplier converts the millivolt reading to engineering units. The
calibration supplied by the manufacturer gives the output of the sensor (c) as
microvolts (V x 10
-6 )
per Wm
-2
. As the datalogger voltage measurement
instructions give a default output in mV, the following equation should be used
to calculate the multiplier (m) to give the readings in Wm
-2
:
m = 1000/c
Other units can be used by adjusting the multiplier as shown in Table 5-1.
TABLE 5-1. Multipliers Required for Flux Density and Total Fluxes
Units Multipliers Output Processing
W m
-2 m Average
MJ m
-2 m*t*0.000001 Total
kJ m
-2
m*
t
*0.001
Total
cal cm
-2 m*t*0.0239*0.001 Total
cal cm
-2
min
-1 m*1.434*0.001 Average
m = calibration factor in Wm
-2
/mV
t = datalogger program execution interval in seconds
5.3 Offset
The offset will normally be fixed at zero as the sensor should output no
significant signal in dark conditions. In practice, because of the nature of
thermopile detector sensors, there will be some offset in dark conditions;
sometimes this offset can give negative light readings. This offset varies with
several factors, e.g. rate of change of sensor temperature, so it cannot be
removed with a fixed offset. Some users may wish to remove small negative
readings by including code after the measurement instructions that sets
negative readings to zero.
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