Search

Signal theory methods and a time dependent quantum mechanical analysis were used to determine the mechanism by which noise transfer takes place in an Rb-cell frequency standard.

We present a capacitance build-up method suitable for the determination of the measurement error of a capacitance meter. The method requires only a small number of uncalibrated base capacitors, to be connected in parallel in various combinations, and a single calibrated capacitor, which provides measurement traceability. The outcome of the method is both the determination of the meter error and the calibration of all the base capacitors; it can therefore be also considered a capacitance scaling method. The method’s equations, cast in matrix form, express estimates and uncertainties for all the quantities of interest. As an example of application, a commercial $\mathit {LCR}$ meter is calibrated in the ranges of (100–1000) pF and (1–10) nF at 1.6 and 10 kHz, with an accuracy at the level of a few parts in 106. The calibration is validated by comparison with an ultrahigh accuracy capacitance bridge. [ABSTRACT FROM AUTHOR]

High accuracy impedance measurements are performed with coaxial transformer bridges, whose conventional design allows the comparison of like impedances—pure resistors or capacitors. Here, we present a current comparator bridge suited for the measurement of impedances of arbitrary magnitudes and phase angles. The bridge has three arms, to connect the impedance under measurement and two calibrated standards. The bridge is digitally assisted and its operation is based on a polyphase digital sine wave synthesizer. To allow the measurement of midimpedance to low-impedance magnitudes, the bridge network and the balancing procedure are designed to approximate the four terminal-pair definition of the three impedance standards. The bridge has been extensively tested with conventional impedance standards and custom designed phase standards. The relative base accuracy is in the 10−5 to 10−6 range at kilohertz frequency. [ABSTRACT FROM AUTHOR]

The four-terminal-pair (4TP) definition of impedance standards allows reaching ultimate accuracy in impedance metrology. In general, the 4TP definition requires dedicated circuitry to be included in the bridge network and the attainment of auxiliary bridge balances during the measurement. A careful choice of the network topology allows the bridge to be self-compensating: the 4TP definition is in large part achieved by the behavior of the network itself without any adjustment. The additional circuitry required for impedance definition can therefore be simpler, the balancing procedure becomes easier, and a more robust 4TP can be achieved. This paper analyzes a current comparator bridge network with a topology featuring self-compensation. A digitally assisted test bridge has been implemented; test measurements on ac resistance comparison in the 25–100- $\Omega $ range at kilohertz frequencies are reported. [ABSTRACT FROM AUTHOR]

This paper describes the realization of a two-terminal-pair digital impedance bridge and the test measurements performed with it. The bridge, with a very simple architecture, is based on a commercial two-channel digital signal synthesizer and a synchronous detector. The bridge can perform comparisons between the impedances having arbitrary phase and magnitude ratio. The bridge balance is achieved automatically in less than 1 min. R – C comparisons with calibrated standards, at kilohertz frequencies and 100- \textk\Omega magnitude level, give ratio errors of the order of 10^-6 , with potential for further improvements. [ABSTRACT FROM PUBLISHER]

We present here the concept of three-arm current comparator impedance bridge, which allows one to perform comparisons among three unlike impedances. Its purpose is the calibration of impedances having arbitrary phase angles against calibrated nearly pure impedances. An analysis of the bridge optimal setting and proper operation is presented. To test the concept, a two-terminal-pair digitally assisted bridge has been realized; preliminary measurements of an air-core inductor and of an $RC$ network versus decadic resistance and capacitance standards, at kilohertz frequency, have been performed. The bridge measurements are compatible with previous knowledge of the standard values with relative deviations of parts in 10^{-5} . [ABSTRACT FROM PUBLISHER]

It has already been reported that 1/f noise in graphene can be dominated by fluctuations of charge carrier mobility. We show here that the increasing damage induced by oxygen plasma on graphene samples result in two trends: at low doses, the magnitude of the 1/f noise increases with the dose; and at high doses, it decreases with the dose. This behaviour is interpreted in the framework of 1/f noise generated by carrier mobility fluctuations where the concentration of mobility fluctuation centers and the mean free path of the carriers are competing factors. [ABSTRACT FROM AUTHOR]