Vaisala MAWS201 User's Guide Page 147

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Chapter 5 _______________________________________________________________Maintenance
VAISALA _______________________________________________________________________ 145
Table 28 Calibration Factors
Number of tips C.F.
96.7 to 96.9 0.204 mm/tip
97.0 to 97.4 0.203 mm/tip
97.5 to 97.9 0.202 mm/tip
98.0 to 98.4 0.201 mm/tip
98.5 to 98.9 0.200 mm/tip
99.0 to 99.4 0.199 mm/tip
99.5 to 99.9 0.198 mm/tip
100 to 100.4 0.197 mm/tip
Solar Radiation Sensors
QMS101
The pyranometer is an all weather instrument.
Once installed the pyranometer needs little maintenance. It is
recommended that you clean the detector as part of a regular routine,
using water or alcohol.
Re-calibration is suggested every two years. This can be done in two
ways. The first is to compare with the measurement of a similar sensor
at the same site. Preferably, daily totals of several days should be
compared. Calibration factor could be corrected if results differ by
more than five percent. The second way is to let a re-calibration be
performed at the factory.
If necessary, the sensitivity of the pyranometer can be adjusted. This
can be done by soldering a resistor between the + (white) and - (black)
output wires. In this way the pyranometer is shunted. For the standard
pyranometer, the internal resistance is 47 , and the cable resistance is
0.12 per meter. The cable is 3 meters long. The cable resistance has
to be multiplied by two, for the + and - wire. Total resistance is 47.7
. In order to reduce the sensitivity by a factor of 10, when the full 3
meters of cable is used, a shunt resistor of 5.3 can be made out of a
1 and a 4.3 resistor. The order of magnitude for the sensitivity will
be 10 µV/Wm
-2
.
The general formula for establishing the proper resistor for trimming
by a factor of 10 is [47 + (0.24 × cable length)]/9. The cable length is
in meters and the resistance is in ohms.
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