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![]() Eppley Normal Incident Pyrheliometer (NIP) ![]() ![]() ![]() ![]() Specifications ![]()
![]() Accuracy ![]() The NIP is calibrated against an absolute cavity radiometer. Absolute accuracy of calibration is on the order of ±2%, while the relative accuracy is about ±1%. The figure below shows a 5-year comparison of an Eppley NIP against an Absolute Cavity Radiometer [F. Vignola and Ibraham Reda, "Responsivity of an Eppley NIP as a Function of Time and Temperature", Proceedings of the 1998 Annual Conference American Solar Energy Society, 517-522, 14 Jun 1998]. Note that there is no detectable trend in the change of the responsivity over the 5-year period. ![]() ![]() Field performance ![]() For a short period of time, the windows of the NIP were sealed with a sealant that cracked over time and allowed moisture to enter the tube. Moisture would condense on the inside of the window. Fig. 20, in the chapter entitled Use of Chart Records in Data Analysis, of our Pacific Northwest Solar Radiation Data book, presents an example of how this problem can affect the data. ![]() ![]() ![]() © 202, UO Solar Radiation Monitoring Laboratory. ![]() ![]()
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