ISO 9847-1992 Solar energy calibration of field pyranometers by comparison to a reference pyranometer《太阳能 与标准总日射表比对校准工作总日射表》.pdf

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1、INTERNATIONAL STANDARD IS0 9847 First edition 1992-07-01 Solar energy - Cali bration of field pyranometers by comparison to a reference pyranometer hergie solaire - Etatonnage des pyranom8tres de terrain par comparaison 21 un pyranom6fre de r traceability to the International Pyrheliometric Scale of

2、 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 inci- dent solar irradiance may be calibrated by using the 1) To be published

3、. 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 IS0 9846). 2 Normative referen

4、ces The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publi- cation, the editions indicated were valid. All stan- dards are subject to revision, and parties to agreements based on this International

5、Standard are encouraged to investigate the possibility of ap- plying the most recent editions of the standards in- dicated below. Members of IEC and IS0 maintain registers of currently valid International Standards. IS0 9060:1990, Solar energy - Specification and classification of insfrumenfs for me

6、asuring hemispherical solar and direct solar radiation. IS0 9846:-t), Solar energy - Calibration of a pyranomefer using a reference pyrheliomefer. 3 Definitions For the purposes of this International Standard, the following definitions apply. 3.1 altazimuth mount: A tracking mount capable of rotatio

7、n about orthogonal altitude and azimuth axes: tracking may be manual or by a follow-the-sun servomechanism. (See also IS0 9846.) 3.2 global (solar) irradiance: Hemispherical solar irradiance received by a horizontal plane surface. (See also IS0 9060.) IS0 9847:1992(E) 3.3 integrating sphere hemisphe

8、re: A sphere hemisphere, generally from 1 m to 4 m in diam- eter, provided with a planar segment (usually a horizontal bottom segment) on which to mount pyranometers (to be compared with an artificial light source), the sphere wall of which is coated with a flat, white paint that is as lambertian as

9、 possible to provide uniform illumination. 3.4 pyranometer: Radiometer designed for meas- uring the irradiance on a plane receiver surface which results from the radiant fluxes incident from the hemisphere above within the wavelength range 0.3 pm to 3 pm. (See also IS0 9060.) 3.5 geld pyranometer: P

10、yranometer usually meet- ing second class* specifications or first class speci- fications, designed for field use and (typically) tontintrnrrs exposure. 3.6 reference pyranometer: Well-maintained pyranometer, selected for its stability and quality, used exclusively to calibrate other instruments. 3.

11、7 test pyranometer: Pyranometer being cali- brated, regardless of its classification or its photoreceptor type. 3.8 tilt angle: Angle between the vertical and the pyranometer axis (which is equal to the angle be- tween the horizontal plane and the plane of the de- tector surface). 3.9 calibration fa

12、ctor: Multiplicator, used to derive the global solar irradiance from the measured out- put (voltage). The units are those of the reciprocal value of the responsivity (e.g. watts per square me- tre per microvolt). 4 Apparatus 4.1 Digital electronic readout devfce Any digital microvoltmeter having an

13、accuracy of better than * 0,l % may be employed. Data loggers with print-out shall be capable of a measurement frequency of at least two per minute. A data logger having at least a three-channel capacity may be useful. 4.2 Reference pyranometer The reference pyranometer shall be specially se- lected

14、. tested and maintained as follows. 2) For the classification of pyl anometers, see IS0 9060. 4.2.1 For outdoor calibration (type I) The reference pyranometer for outdoor calibration (type I) should be typically of a higher class (in ac- cordance with the classification given in IS0 9060) than the t

15、est pyranometer, and should exhibit a particularly high long-term stability. The depen- dence of its responsivity on temperature, irradiance, tilt and angles of incidence shall be determined.3) Within 12 months prior to its use for calibrating field pyranometers, the reference pyranometer should it-

16、 self be recalibrated outdoors by comparison to a pyrheliometer (see IS0 9846). This recalibration should be carried out under conditions typical of those in which the field pyranotneter and reference pyranometer will be used. The calibration history of the reference pyranometer should be well docu-

17、 mented. If the measuring conditions during calibration devi- ate strongly from those during the typical use of the held pyranometer (by more than +_ 5 “C and f 15” azimuth angle), a reference pyranometer of the same type that has been calibrated under similar conditions should be used. 4.2.2 For in

18、door calibration (type II) The reference pyranometer for indoor calibration (type II) shall be of the same type as the test pyranometer (to avoid errors that may be caused by the artificial radiation employed; these errors may arise mainly from imperfect homogeneity of the source beam or from an imp

19、erfect match to the solar spectrum). In addition, the pyranometer shall meet the requirements specified in 4.2.1. 4.3 Integrating sphere or hemisphere For type lla or Ilb calibration (see 5.3.1) an inte- grating sphere or hemisphere (see 3.3) is required. Suitable apparatus are described in annex A

20、for in- formation. 4.4 Precision calibration table A precision calibration table is required for all hori- zontal and fixed-angle tilt calibrations. It shall be level at 0” tilt (i.e. horizontal) and shall be able to be tilted over a suitable range of angles from the horizontal with an uncertainty o

21、f less than 0,3”. NOTE 2 The deviation between the tilt angle of the ref- erence pyranometer and that of the field pyranometer should be not more than 0,l” which means that the tilt of the pyranometers has to be finely adjusted. If the cali- bration tables are mechanically and thermally stable it is

22、 necessary to check the tilt only after periods longer than a week. 3) Test methods to determine the dependence of the responsivity of a pyranometer on temperature, irradiance. tilt and angle of incidence will form the subject of a future International Standard. 2 IS0 9847:1992(E) 4.5 Sun-tracking m

23、ount The mount, whether power driven or manually op- erated, shall be capable of maintaining the refer- ence pyranometer and all test pyranometers normal to the sun for the entire test period. The tracking precision shall be such that for all data-taking peri- ods, deviations from the exact normal t

24、o the sun do not exceed a) f 4” where the reference and test pyranometers are mounted on separate trackers: b) + IO” where the reference and test pyrano- meters are mounted on the same tracker. NOTE 3 An altazimuth mount is preferred for pyrano- meters with a responsivity dependent on tile altazimut

25、h angle of the tilteri receiver. The requirements for tracking a pyranometer at normal incidence are less stringent than those for tracking a pytheliometer. For example, the cosine of 4” is 0,997 6, and only an insigniticant uncer- tainty in normal incident calibration will result from a de- viation

26、 of this magnitude. 5 Calibration procedure 5.1 General considerations A number of possible interferences and precautions relating directly to the methods specified in this In- ternational Standard are given for information in annex B. Particular care shall be taken to correct for zero off-sets. The

27、 off-set of signals of the reference and test pyranometers shall be checked, as a minimum, at the start and the end of a measurement series. 5.2 Outdoor calibration (type I) 5.2.1 General (types la, lb and Ic) 5.2.1.1 Mount the reference pyranometer and the test pyranometer outdoors on a common cali

28、bration table for horizontal calibration (type la) and cali- bration at tilt (type lb) and on an altazimuth or sun- pointing mount for normal-incidence calibration (type Ic). Adjust both instruments to a common el- evation facing the equator. Ensure that the azimuth reference marks point in a common

29、 direction. NOTE 4 Convention is to use the electrical connector as the azimuth reference and to point it towards the equator and downwards. 5.2.1.2 Adjust the calibration table to the required tilt (which may be 0”) from the horizontal. 5.2.1.3 Connect the reference and test pyrano- meters to their

30、 respective, or common, digital voltmeter, using proper shielding. Check the instru- ments for electrical continuity, signal polarity, signal strength and stability. Clean the domes of the pyranometers (see 13). Check that the radiant fluxes of the foreground on both instruments are equal at the rel

31、evant tilt angle by transposing the positions of the pyranometers. 5.2.2 Horizontal calibration for meteorological and resource measurements (type la) 5.2.2.1 Stable cloudless sky conditions For stable cloudless sky conditions, simultaneously take instantaneous voltage readings on both instru- ments

32、 for a minimum of fifteen 10 min to 20 min measurement series, each consisting of 21 or more instantaneous readings. Take these measurement series over a 2 day to 3 day period, or over a longer period to cover a larger range of environmental conditions. Obtain data from early morning, through and in

33、cluding solar noon, to late afternoon to ensure that data are taken during the period that the solar elevation angle exceeds 20”. 5.2.2.2 Unstable sky conditions with some cloud For unstable sky conditions, with clouds at a dis- tance from the sun of greater than 30” (see 6.2), simultaneously take i

34、nstantaneous voltage readings on both instruments continuously at from 1 min to 5 min intervals from sunrise to sunset for a mini- mum of 5 days (and for as long as 2 weeks). The length of time should be chosen such that a mini- mum of fifteen series of 21 or more measurements are obtained that repr

35、esent steady radiation span- ning a period from forenoon to afternoon (with sun elevation angle r 20”). Alternatively, take a minimum of fifteen measure- ment series integrated over 1 min to 5 min intervals in such a manner that data are spread over the pe- riod from forenoon to afternoon, including

36、 solar noon. 5.2.2.3 Cloudy sky conditions For cloudy sky conditions take simultaneous readings integrated over more than tiny 1 h intervals on both instruments. Take this hourly data for a minimum of 10 days at different solar elevation an- gles, and different types of cloudiness if the hourly mean of global 100 W.rne2. irradiance is greater than 5.2.3 Calibration at tilt (type lb) Calibration at tilt shall be carried out only under clear sky conditions with clouds at a distance from the sun of greater than 30”. Use as the tilt from 3