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Instrumentation and Measurement, IEEE Transactions on

Issue 6 • Date Dec 1993

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Displaying Results 1 - 10 of 10
  • Microwave noise measurement errors caused by frequency discrepancies and nonzero bandwidth

    Page(s): 983 - 989
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (488 KB)  

    We develop analytical expressions for two frequency-related errors encountered in noise parameter measurements of devices with high-reflection coefficients such as GaAs FET's and HEMT's. The first error is caused by a discrepancy between the measurement frequency of the noise-measuring receiver and the frequency of the reflection coefficient-measuring apparatus. The second is caused by variation of the noise power spectral density across the bandwidth of the noise-measuring receiver. A noise power measurement on a cooled GaAs FET is presented as a demonstration, in which the noise power level exhibits narrow peaks which rise about 10 dB above the general level at regular frequency intervals. It is shown that the severity of both of the frequency-related errors is related to the shape of these peaks. Simple expressions are derived which allow the severity of these two types of errors to be estimated when values are available for the reflection coefficient magnitudes and transmission line lengths in a system. Expressions are also derived which give the variation with frequency of the measured noise power and also of the two error terms, if the noise parameters of the device under test are also available. This analysis accounts successfully for the main features of the experimental noise power observation View full abstract»

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  • Simultaneous measurement of material characteristics of layered structures by a single acoustic interrogation

    Page(s): 976 - 982
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    Conventionally, ultrasonic techniques extract material features from the echo return which consists of impulse signals convolved with the transfer function of the medium being investigated. In most cases, only a single parameter such as the boundary reflection coefficient, acoustic impedance, or velocity of propagation is used for material identification. For a more complex medium, however, it is desirable to utilize as many parameters as possible from a single trace of echo return to characterize material such that a higher precision of identification can be achieved. The advantage of our approach is that the information obtained is based solely on the echo return from the successive acoustic interfaces without using the signature of the incident pulse which is rather difficult to capture experimentally. An additional feature of this method is that it works rather well even in a noisy environment View full abstract»

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  • Accurate digital time-of-flight measurement using self-interference

    Page(s): 990 - 994
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (316 KB)  

    Most ultrasonic distance measurements are based on the determination of the time of flight. This paper presents a novel way for the measurement of the time of flight, based on the detection of the envelope zero in an ultrasonic wave. A particular wave form is produced by supplying two pulse trains subsequently to an acoustic transducer. Distance information is retrieved from the zero, so a fully digital measurement is possible, reducing signal-processing time and resulting in a fast and accurate distance measurement View full abstract»

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  • An indirect test method for the characterization of variable reluctance motors

    Page(s): 1020 - 1025
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    The determination of the characteristics of the variable reluctance motors (both in static and dynamic conditions) represents a quite critical point, due to the heavy nonlinearity of the motor magnetic paths, to the high distortion of the supply voltage from the converter, and to the high level of saturation of the magnetic paths in normal working conditions. This creates a great difficulty in the accurate measurement of the motor magnetic characteristics (saturation curves or flux linkage versus current curves) and consequently in the determination of the mechanical characteristics (static torque versus current and static torque versus rotor position) which are directly related to the saturation curves. The paper proposes an original digital method that, starting from the measurement of the flux linkage in the motor magnetic paths, determines the saturation curves, evaluates the coenergy versus current curves and then the motor torque characteristics in static conditions. It is then shown how the availability of a fast and accurate method for the measurement of the flux linkage allows the determination of the electromagnetic torque in dynamic conditions, too View full abstract»

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  • Simultaneous measurements of RF electric and magnetic near fields-theoretical considerations

    Page(s): 1001 - 1008
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (516 KB)  

    Theoretical considerations for the design of an isotropic combined electric and magnetic radio-frequency field probe are presented. The probe is intended for simultaneous measurements of hazardous electric and magnetic fields under near-field conditions in the frequency range from 10 MHz to 300 MHz. The probe consists of six dipoles and six loops placed on all six sides of a small cube, thus providing a well defined electrical center due to the symmetry. Other significant advantages are improvement of the isotropicity, reduction of the detection errors associated with asymmetrical waveforms, and reduction of the electric field coupling to the magnetic field sensors. Theoretical findings are in agreement with the measured results of a constructed experimental probe View full abstract»

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  • Simple circuits for generating high-voltage staircase waveforms

    Page(s): 1026 - 1031
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (380 KB)  

    Two novel circuits are described which provide simple generation of high-voltage staircase waveforms for driving electro-optical (EO) loads. The circuits use power MOSFET's in what is essentially a switching mode. For applications which require high-voltage step-type waveforms, this technique offers substantial power savings and improved time-domain response over drive circuits that use a linear amplifier approach. Waveform characteristics can be controlled at a low voltage point, allowing flexible and accurate operation View full abstract»

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  • A new method of measurement of the different types of noise altering the output signal of oscillators

    Page(s): 968 - 975
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (524 KB)  

    Oscillator noise is generally modeled by a power law spectral density. Thus it is possible to characterize different noise sources, each of them corresponding to a particular power law. The measurement of the contribution of these sources is necessary to know their origin and to remedy these causes in order to improve oscillator performance. Usually, an estimation of the different types of noise present in a signal is obtained by using a variance. However, the sensitivity of these variances differs for each type of noise and then limits this method. On the other hand, the use of several variances, each of them more sensitive to one type of noise, permits one to notably improve the measurement accuracy. The method suggested here uses as many different variances as there are types of noise to measure. The improvement of measurement accuracy of the noise coefficient is discussed in this paper View full abstract»

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  • Experimental optimization of the probe for eddy-current displacement transducer

    Page(s): 995 - 1000
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    The experimental optimization of the coil for an eddy-current displacement transducer probe is presented in the paper. The coil geometry is optimized for the special design of the transducer as a meter of the real part of the probe's impedance. Measurement of the transducer's transfer function has been performed with several samples of ring-shaped coils, as well as with the flat, pancake-shaped coil and with the single-layered cylindrical coil. For the sake of comparison, measurement with the ferrite-cored coil has been included too. The measurement results clearly indicate that the optimal coil geometry is a ring with a uniform and very small cross section of the winding View full abstract»

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  • RF attenuation measurement system with 1-kHz voltage ratio standard

    Page(s): 1014 - 1019
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (424 KB)  

    A homodyne system for measuring attenuation at 10 GHz and 30 MHz is constructed and evaluated. The radio frequency (RF) attenuation is converted to 1-kHz attenuation, and the 1-kHz attenuation is measured by an inductive voltage divider built in a 1-kHz receiver. A 1-kHz voltage ratio standard (VRS) is proposed to check the accuracy of the 1-kHz receiver for maintaining long-term accuracy. The differences between the VRS and the 1 kHz receiver are smaller than 0.0003 dB for 0-40 dB. A precision piston attenuator of 30 MHz agrees with the system within 0.0018 dB for 0-30 dB. The change in measured values at an interval of one year are less than 0.001 dB. The results demonstrate that this system can be expected to reliably maintain high accuracy View full abstract»

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  • Voltage ratio technique used with the national RF standard attenuation measuring equipment at the PTB

    Page(s): 1009 - 1013
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB)  

    With a new measuring system, the attenuation range of the national RF standard attenuation measuring equipment at the Physikalisch-Technische Bundesanstalt (PTB), Germany, has been extended to 60 db in the waveguide bands R 220 and R 320. Most of the system is automated to shorten the calibration and measurement time. The total uncertainty of measurement is estimated to be 0.0027 dB per 10 dB attenuation View full abstract»

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Papers are sought that address innovative solutions to the development and use of electrical and electronic instruments and equipment to measure, monitor and/or record physical phenomena for the purpose of advancing measurement science, methods, functionality and applications.

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