A comparison of four different robitzsch pyranometers (actinographs) under high humidity tropical conditions, including standard measurements of total global radiation and their calibrations

Thumbnail Image
Journal Title
Journal ISSN
Volume Title
University of Dar es Salaam
In this thesis four Robitzsch actiongraphs for measuring daily solar radiation are compared, under high humidity tropical conditions prevailing in Tanzania, with Kipp and Eppley (working) sub-standard pyranometers. Descriptionsof the instruments under study and auxiliary equipment are given. The report provides a summary of the procedures for measuring both diffuse and direct solar radiation. It also describes the methods of calibrating the reference instruments using our standard (working) pyrheliometer. Performance of the actinography used under field conditions is reported including some of the possible source of errors common to this type of instruments. Attention is paid to the effects weather regards the frequency of routine servicing of the instruments. Comparisons have shown a consistent ratio of 0.99 ± 0.01 between the two sub-standard pyranometers for the daily averages throughout the experiments. The calibration experiments have revealed a lowering of the calibration constants due to deterioration from outdoor mounting of the standard instrument. The (working) sub-standard pyranometers showed a 5% decrease in sensitivity over one and half years. Early comparisons (before conditioning) of the four robitzesch actinographs, with estimation of sensitivity changes of the sub-standards to be 3% (which had not been determined), showed consistently lower values for the casella, averaging at -3% and not lower than -5%. The puess showed lower and higher values of -1.5% and 2.5%. The Science Associate showed also consistently lower values averaging -2% and not more than -5%. The difference percentages of a too low indicating SIAP were initially very large (>20%) and even after a scale adjustment the errors were so large (>10%). After a corditioning period of three months, the Casella and fuess showed consistently lower sensitivition in respect to the recalibrated sub-standards (i.e real changes in sensitivity incorporated). The Casella showed an average of -4% and the fuess an average of -2.5%. But taking these average values as being due to deterioration from outdoor use, and in this way recalibrating the actinography with the recalibrated standards, largest errors in daily average of Casella and fuess actinographs are +3.5% and -2.5% respectively. The Science Associate would be usable for weekly average routine measurements, but with more inaccuracy risks. In the appendix we report on testing a commercially available commulatively integrating recorder for application in our research on measuring solar energy. The note reports briefly on the recorder, its testing and the use made of it so far. Some other situations in solar radiometry for which we believe these recorders will be very useful are suggested.
Available in print form, East Africana Collection, Dr. Wilbert Chagula Library, Class mark (THS EAF QC912.M2)
Pyranometer,, Calibration, Actinometer
Mabuba, Kabende Ibrahim (1979) A comparison of four different robitzsch pyranometers (actinographs) under high humidity tropical conditions, including standard measurements of total global radiation and their calibrations, Master dissertation, University of Dar es Salaam