BS 7621:1993

Committees responsible
National foreword
Introduction
Method
1. Scope
2. Normative references
3. Definitions
4. Apparatus
5. Calibration procedure
6. Certificate of calibration
7. Precision and accuracy
Annexes
A. (informative) Calibration devices using artificial
     sources
B. (informative) Interferences and precautions
C. (informative) Computation of daily average solar
     angle
D. (informative) Procedure to determine the ratio of
     the directional response
E. (informative) Bibliography

Specifies two preferred methods for the calibration of field pyranometers using reference pyranometers. Coverage includes definitions, apparatus and calibration procedure. Includes detailed annexes.

1.1 This International Standard specifies two preferred methods for the calibration of field pyranometers using reference pyranometers.

1.2 One method, the outdoor calibration or type I, employs solar radiation as the source, while the other method, the indoor calibration or type II, employs an artificial radiation source.

1.2.1 The outdoor calibration of field pyranometers may be performed with the pyranometer in a horizontal position (i.e. zero tilt) (type la), in a tilted position (type lb), or at normal incidence (type Ic) maintaining the receiver surface perpendicular to the sun’s beam component.

1.2.2 The indoor calibration of field pyranometers may be performed using an integrating sphere with shaded (type IIa) or unshaded (type IIb) lamp(s), or at normal incidence (type IIc) frequently using an optical bench to present the receiver surface perpendicular to the beam of the lamp.

Types IIa and lib correspond to an outdoor calibration under conditions of overcast and sunny sky with large light cloud fields, respectively. Type lie is comparable with the normal incidence calibration of type Ic.

1.3 The methods of calibration specified are traceable to the world radiometric reference (WRR); traceability to the International Pyrheliometric Scale of 1956 is not permitted.

1.4 This International Standard is applicable to most types of field pyranometers regardless of the type of radiation receptor employed. In general, all pyranometers used for long-term monitoring of incident solar irradiance may be calibrated by using the described methods, provided that the reference pyranometer has been calibrated at essentially the same tilt from horizontal as the tilt employed in the calibration.

NOTE 1 Pyranometers used for collector tests should be calibrated using a reference pyrheliometer (see ISO 9846).