Kipp&Zonen CFR Calibration Facility - Manual (Page 13)

CFR manual
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There are several procedures for transferring calibration values from a narrow field of view instrument
(pyrheliometer) to a wide field of view instrument (pyranometer). For example the direct component of the
solar radiation can be eliminated temporarily from the pyranometer by shading the whole outer dome of the
instrument with a disk. However, there is no thermal equilibrium with this method and some models of
pyranometer show significant zero-offset drift.
An alternative procedure maintains the test pyranometer in its normal operating condition. This 'component
sum' method involves measuring the direct component of the solar radiation with a pyrheliometer and the
diffuse component with a shaded pyranometer, and adding together the two values to obtain the global
radiation. As, during a clear day, the diffuse radiation is only about 10% of the global radiation, the
sensitivity of the second pyranometer does not need to be known very accurately. Both procedures are
suitable to obtain a working standard pyranometer. This method is extensively described in international
standard ISO 9846.
Transfer from the working standard pyranometer to other pyranometers can be done in sunlight. The
pyranometers must be mounted side by side so that each views the same sky dome. It is desirable to
integrate, or average, the outputs over a period of time and then compute the calibration constants on the
basis of these averages. This reduces the errors due to changing parameters during the day.
Transfer from a working standard pyranometer in the laboratory is only reliable when both pyranometers
are of the same construction and have similar optical characteristics. Kipp & Zonen can recalibrate
pyranometers according to this method.
2.3.3 Spare Parts Specification
This section provides the article numbers for ordering spare parts for the Calibration Facility.
Part
Description Part No.
Lamp Housing : 230 VAC / 50Hz Version 2654116
: 115 VAC / 60Hz Version 2654117
Bulb (115 & 230 VAC) : Philips CDM-T 150 W / 942 2603864
Lamp stabilizer (230 VAC) : MCB Industries , Model 250 VA / 50Hz 2681060
Voltage measurement device : Keithley Instruments, model 2000 4902212