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This paper proposes a simple capacitor clamped current-sharing circuit including linear and loop types according to the connection of capacitors for multistring light-emitting diodes (LEDs). The proposed circuit employs interleaved turn-on switches and multicapacitor charge conservation to solve the current imbalance problem caused by voltage drop tolerance and the negative temperature coefficient of LEDs. The operating principle and parameter design of the topologies are analyzed in detail. Based on this analysis, a three-string current-sharing topology has been validated by experiments. Experimental waveforms show that the proposed circuit does not only have good effect on current sharing while the effect is not affected by individual LED short but also has the advantages of low voltage stress, nonmagnetic components, ease of integration, and simple control. [ABSTRACT FROM PUBLISHER]

An improved error analysis of an existing capacitance scaling system for supporting measurements of higher valued (10 nF to 100 μF) ceramic-dielectric four-terminal-pair (4TP) capacitance standards over the 100-Hz to 100-kHz frequency range is described. The capacitance scaling system uses a commercial impedance (inductance-capacitance-resistance) meter and a single-decade inductive voltage divider as an impedance comparator. Four-terminal-pair capacitors in decade (10: 1) steps from 10 nF to 100 F are measured. The system's 10:1 scaling error is determined using 100-pF and 1-nF air-dielectric 4TP capacitance standards with known capacitance and loss characteristics over frequency. This paper discusses the significant reductions in measurement uncertainty that were attained through the use of improved calibration standards and measurement method refinements. Details of the uncertainty analysis for a 10-nF capacitor (in the 100-Hz to 10-kHz frequency range) and verification data are presented. [ABSTRACT FROM AUTHOR]

This paper presents a portable electrical instrument that measures the complex impedance of a parallel-plate capacitor with a sample of peanut kernels between its plates. A novel method of measuring the capacitance and phase angle of a parallel-plate system is described. The measured values were used in an empirical equation to estimate the moisture content (mc) of the sample. The estimated values were in good agreement with the mc values that are obtained by a standard air-oven method. This method can be used to estimate the mc in other types of nuts and grain by calibrating the instrument with samples of these materials with known mc values. This instrument would be useful in grain industries for quick and nondestructive mc measurement. [ABSTRACT FROM AUTHOR]

This paper describes frequency dependence measurements of fused-silica capacitance standards from 200 to 2000 Hz, using a 1-pF cross-capacitor as the reference. The measured frequency dependence of fused-silica capacitors was found to vary significantly, ranging from a change of less than 0.2 μF/F for one standard to a change of 0.8 μF/F for another over the frequency range. Increasing capacitances with decreasing frequency from 1592 Hz for all tested fused-silica capacitors indicates that dielectric relaxation due to dielectric bulk and/or interfacial defects is the dominant source of frequency dependence. The relative combined standard uncertainty at 200 Hz (the largest in the frequency range) is 0.07 μF/F, which is smaller by about a factor of three than the uncertainty reported previously from the National Institute of Standards and Technology (NIST). [ABSTRACT FROM AUTHOR]

An assessment was made of estimating the moisture content (mc) of single peanut pods (in-shell peanuts) by measuring the complex impedance of a parallel-plate capacitor with a single pod between the plates. Capacitance (C), phase angle (θ) and/or dissipation factor (D) were measured at 1.0 and 5.0 MHz, and the measured values at these two frequencies were used in a derived empirical equation to calculate the mc. Previous research had determined that the mc of single and small samples of shelled peanuts (kernels) could be determined by similar measurements at 1 and 4.5 MHz. In this paper, the mc of the pods tested was between 5% and 25%. The predicted mc of the pods was within 1% of the standard air-oven values for about 85% of the single pods. [ABSTRACT FROM AUTHOR]