(111)Measurements were made through

(111)Measurements were made throughout the year, so data covering an almost complete range of atmospheric conditions in Harare were used to derive the calibration coefficients.. The average empirical first and second order quadratic calibrationcoefficients of 6.40 and 0.0034 respectively were obtained [6].So the empirical function for this system as applied to solar radiation monitoring is
I = 6.40D + 0.0034D
(112)where I is the calculated global irradiance and D is the digital data value recorded by the acquisition system.
(113)A typical calibration graph is shown in Fig.4. In order to examine the correctness of the fit, the data acquisition system readings were recorded against corresponding Eppley pyranometer readings and (1) used to estimate the radiation.Fig. 5 shows how well the DAS fit compares with the data from the Eppley pyranometer.
(114)artly cloudy days, relatively wide scatters were obtained.This is mainly due to the difference in response times of the two instruments, with the Eppley PSP pyranometer less able to respond quickly to rapid changes in irradiance levels.The data acquisition system takes about 2 ms to do 20 A/D conversions compared to a response time of about 1 s for the Eppley.So the
applied to monitor solar radiation.It has been successfully interfaced to a computer for initial setup of the system and for data retrieval.