Since Johnson's experimental observations of thermal noise in 1927, and Nyquist's explanation of the phenomenon shortly afterwards in 1928, thermal noise has attracted interest as a means of measuring temperature. The independence of the thermal noise from the material nature of the sensor makes it particularly attractive for metrological applications. However, the noise signals are extremely small and some ingenuity is required to make accurate measurements. This paper reviews the foundations of Johnson noise thermometry and the various techniques that have been employed to measure temperature via Johnson noise. Emphasis is placed on key developments in noise thermometers for metrological applications. The review includes the current activities of teams involved in noise thermometry research.
This paper describes the traceability chain for photovoltaic devices and the measurement methods employed to perform the various transfer steps. The measurement uncertainties are analysed in detail based on the accreditation of the European Solar Test Installation (ESTI) for the calibration of photovoltaic devices. The various contributions to the overall uncertainty are critically analysed for various traceability chain options. A major contribution is the uncertainty in the calibration of the primary reference device. The overall measurement uncertainty is reduced using the ESTI reference cell set compared to the traceability from the world photovoltaic scale. For the maximum power of photovoltaic modules, the expanded combined uncertainty is reduced from ±2.6% to below ±2%. Recommendations are made on the scope for further reduction of uncertainty and for the best calibration strategy for various PV technologies.
Multijunction photovoltaic (PV) thin-film modules are becoming more and more important on the market, due to their low cost and improved module efficiency now well above 10%. The spectral response (SR) measurement of multijunction thin-film cells presents additional challenges with respect to the SR measurement procedure for single-junction devices. Several works have appeared in the last 15 years in the PV literature, describing certain measurement artefacts that typically appear when measuring the SR of multijunction cells without applying an appropriate voltage bias to the entire cell. In this paper, the authors revise the theoretical description of SR measurements on multijunction devices, show how to detect the possible origin of measurement artefacts from the dark SR and show why bias voltage sometimes is not enough to avoid such artefacts or why it is not even necessary. An experimental confirmation of the theoretical approach is finally given.
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