EPPLEY PSP
2
Table 1. Multipliers and Output Processing
OUTPUT/
UNITS
MULTIPLIERS
PRCSS
kJ m-2
(1/C)*t
(Total)
kW m-2
(1/C)
(Averages)
cal cm-2
(1/C)*t*(0.0239)
(Total)
cal cm-2 min-1
(1/C)*(1.434)
(Averages)
C = (EPPLEY calibration)
t = datalogger program execution
interval in seconds
3. OUTPUT FORMAT CONSIDERATIONS
The largest number that the datalogger can
output is 6999 in low resolution and 99999 in
high resolution (Instruction 78, set resolution). If
the measurement value is totalized, there is
some danger of overranging the output limits,
as shown in the following example.
EXAMPLE
Assume that daily total flux is desired, and the
datalogger scan rate is 1 second. With a
multiplier that converts the readings to units of
kJ m-2 and an average irradiance of .5 kW m-2,
the maximum low resolution output limit will be
exceeded in less than four hours.
Solution #1 - Record average flux density and
later multiply the result by the number of
seconds in the output interval to arrive at total
flux.
Solution #2 - Record total flux using the high
resolution format. The drawback to high
resolution is that it requires 4 bytes of memory
per data point, consuming twice as much
memory as low resolution.
4. CONNECTIONS
Differential and single-ended connections to the
datalogger are shown in Figures 2 and 3,
respectively.
*AG in Figure 2 refers to Analog Ground in the
CR10 which is the same as ground for the 21X
and CR7.
Figure 2. Differential Measurement
Connection
On a differential measurement, the low side of
the signal is jumpered to AG to keep the signal
in common mode range, as shown in Figure 2.
Figure 3. Single-ended Measurement
Connection
*AG in Figure 3 refers to Analog Ground in the
CR10, which is the same as ground for the 21X
and CR7.
5. RESOLUTION
The Eppley PSP outputs approximately 12mV
at 1400 watts meter-2 (solar constant). The
CR10 measures this sensor on the 25mV range
while the 21X and CR7 measure it on the 15mV
range.
An example of the datalogger resolution of the
PSP measurement with a PSP calibration of
8.61 mVw-1m2 is given below:
CR10 differential resolution:
= ±0.00333mV * (1w/m2)/(.00861mV)
= ±0.387w/m2
