Delta-T SPN1 User Manual

Also see for SPN1: Technical note

Delta-T SPN1 User Manual Manual pdf 32 page image

Appendix A: Design and testsummaryThis appendix gives a brief description of how the SPN1 design works and a summaryof the results of the test program. More detailed versions of these are available fromDelta-T.IntroductionMeasurement of Direct and Diffuse components of solar radiation has manyapplications - in modelling the interaction of light with crop canopies, studying theenergy balance of structures, or as a meteorological indicator. Instruments that makethese measurements have generally been expensive and require considerableattention.One common approach has been to have two sensors, one measuring radiation fromthe whole sky, the other measuring the whole sky apart from the sun. The shading isgenerally done using a shade ring, adjusted to match the track of the sun across thesky for that day, or using an occluding disk held on a robot arm. Both of theseapproaches require accurate alignment to the Earth's axis, and regular adjustment.Another well established approach is the Campbell-Stokes recorder, which uses aglass sphere to focus the Direct solar beam onto a recording chart causing a burn,which indicates Direct beam strength.Design objectivesThe aim of the SPN1 design was to measure the Direct and Diffuse components ofincident solar radiation, and provide a measure of sunshine hours, in a sensor thatused no moving parts, and required no specific polar alignment or routine adjustment.The outputs should be compatible with electronic data loggers, and work at anylatitude.How the design evolvedThe prime requirement for this design was to create a system of radiation sensorsand a shading pattern such that wherever the sun is in the sky:• at least one sensor was always exposed to the full solar beam• at least one was always completely shaded• all sensors receive equal amounts of Diffuse light from the rest of the skyhemisphere.32 z Appendix A: Design and test summary SPN1 User Manual v1.0