Campbell CM 21, Инструкция по эксплуатации

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53
APPENDIX IV PYRANOMETER MEASUREMENT REPORT
Routine measurement of directional error during final inspection.
Mean cosine error of each new CM 21 pyranometer is measured by a simple
routine.
The pyranometer base is placed against the vertical turntable of a
goniometer in the parallel (0,5º) beam of a sun simulator.
Voltage output U(z) is measured for beam incidence (zenith) angles of 0º, 40º,
60º, 70º and 80º coming in over azimuth East (cable pointing to North).
Next the pyranometer output U(-z) is measured for incidence angles of -80º,
-70º, -60º, -40º and 0º for azimuth North. The dark signal is measured at the
beginning of the routine in the middle and at the end. For each beam incident
angle the dark signal is interpolated.
During the CM 21 measurement cycle a check is done on the azimuth error
at 40º and 70º by measuring voltages for azimuth-directions E, N, W and S.
Also at -70º and -40º this azimuth error is measured and the mean of both
azimuth measurements cancels out eventual error in the 0º position.
With the extended procedure at both 40º and -40º and 70º and -70º the specific
cosine error
δ
cos
for 8 azimuth directions (40º E, N, W, S and 70º E, N, W, S)
can be calculated according to formula 1 and verified whether it is within
±
5
W/m
2
.
The applied formula for the relative cosine error is:
U(0º) Pyranometer output voltage for normal incidence
U(z) Pyranometer output voltage for angles (z)
Zero(z) Dark signal for angles (z)
% 100
) ( cos ) (
2
) 0 ( ) 0 (
) (
2
)) ( ) ( (
cos
⋅
⋅






−
° + °
−
− +
=
z z zero
U U
z zero
z U z U
δ
(
formula 3)