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  • 1
    Electronic Resource
    Electronic Resource
    Computer-aided data-acquisition system for thermal gradient mapping and calibrations of high-temperature cavities (1989)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 673-682 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have designed, built, and tested a robust, thermocouple-based furnace calibration system having automated data acquisition and processing. The system can be used to produce maps of the thermal fields and gradients inside high-temperature cavities. The apparatus consisted of nine type K thermocouples mounted in a ceramic frame, an analog-to-digital interface board, a computer, NBS traceable calibration instrumentation, and software coded specially for the data acquisition and reduction. The absolute accuracy of the system was ±1.3 °C up to 300 °C, providing that the thermocouples had not previously been exposed to temperatures higher than that. The resolution of its gradient sensing ability was ±0.02 °C mm−1. We present details of its construction and operation, a front-to-back error analysis, and results of its use with a box furnace operated between 50 and 1200 °C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140382
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  • 2
    Electronic Resource
    Electronic Resource
    Interrupt-driven digital controller for a magnetic suspension system (1989)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 456-466 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The hardware interrupt structure of an MS-DOSTM -based personal computer was used to enable real-time, keyboard manipulation of the control parameters of a stable, vertical magnetic suspension without halting its operation. The positions of objects suspended with this system were measured to be stable to within ±15 μm of a reference position. Stable suspensions were achieved at sampling rates as low as 45 Hz, although the system was typically operated at sampling rates of 1.0–2.0 kHz. The dynamics of the suspension were explored for several different values of proportional, integral, and derivative gains, and the system's transient response and steady-state behavior were characterized. We present here the data resulting from those studies, as well as measurements of the suspension's drift, empirically determined values of its second-order transfer function parameters, a discussion of the suspension's foreground/background capabilities, a description of its algorithm, and details of its electromechanical construction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140399
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  • 3
    Electronic Resource
    Electronic Resource
    Small-signal recovery and analysis with a novel, phase-locked digital filter (1989)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 3762-3768 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new technique for recovering small signals from large background disturbances is described. The technique combines the narrow-band sensitivity of synchronous detection via lock-in amplifier with the waveform-recovery capabilities of boxcar averaging. However, unlike a boxcar averager, this technique operates in real time. A digital filter-based realization of this technique phase-locks to a reference signal at frequencies up to 500 Hz. It samples input at a rate of 256 kHz with 12-bit precision, recovers the complete synchronous and asynchronous components of the input signal, and reconstructs them with a precision of 12 bits. This allows for either the extraction of or deletion from the original signal of phase-lockable waveforms. We describe here the design and performance of this instrument and present the results of its use in a signal-recovery problem made difficult by the presence of power-line noise.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140487
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  • 4
    Electronic Resource
    Electronic Resource
    Magnetically suspended centrifuge for studies of nonlinear phenomena in stratified fluids: Developmental aspects (1989)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 3293-3300 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Design studies of a novel magnetically suspended centrifuge suggest that such a device would be useful for investigating the nonlinear dynamics of interfacial waves in a rotating two-phase liquid. In its final form, the apparatus would use magnetic bearings, a directly-driven rotor, precision temperature control, and vibration isolation. The mechanical noise in the magnetic suspension coil of a preliminary apparatus was measured to be 3-μm rms in a 5-kHz bandwidth. However, these vibrations were attenuated by an active differentiator to the point where there was no observable oscillation in a 183-gram suspended test mass.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140568
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  • 5
    Electronic Resource
    Electronic Resource
    Precision limits of lifetime estimation algorithms as determined by Monte Carlo simulation: A comparison of theory and experiment (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1310-1315 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The estimation of exponential decay lifetimes is important in many areas of physics, but often difficult if the waveform produced by some particular process (say, fluorescence decay) is noisy. We have used a simulation technique which makes it possible to model accurately two common waveform analysis methods. Results from actual experiments can be compared with those produced by the simulation in order to investigate the nature of the measurement system's precision limits and thereby effect a reduction of the measurement error. Specifically, an algorithm calculating decay lifetime from two data points exhibited a one-sigma error of 4% when the measurement signal-to-noise ratio was 40:1, compared with a 0.1% error of a least-squared error algorithm under similar conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139715
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  • 6
    Electronic Resource
    Electronic Resource
    Using the fast Fourier transform to determine the period of a physical oscillator with precision (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 778-782 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Measuring the period of torsion pendulums with precision has long been a formidable challenge in gravitation experiments, particularly those measuring the Newtonian gravitational constant G. An alternative method to fitting the position signal of the pendulum to a sine wave is the use of the power spectrum generated by the fast Fourier transform (FFT) as the source of information from which the period of oscillation can be determined. There are, however, known limitations to the use of a FFT to measure the period of a physical oscillator with precision. These limitations include two effects due to the finiteness of the duration of the sinusoidal data record and one effect due to the uncertainty of the starting phase of the oscillator relative to the window imposed by this duration. We have done a phenomenological study of the FFT using a desktop computer to imitate a precision oscillator having the physical characteristics of a finite damping constant and drift in the zero potential-energy position. Also, we have taken extensive data with a torsion pendulum, and analyzed them in this way. These studies show that for a real oscillator, such as the classical torsion pendulum, the FFT is a useful tool for determining the period of oscillation with the precision usually associated with larger, more complex, fitting algorithms. With good signal-to-noise ratio and under conditions appropriate to a torsion pendulum, the FFT method can measure the frequency or period to five parts in 106 or better.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139828
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  • 7
    Electronic Resource
    Electronic Resource
    Improved magnetic suspension densimeter for biochemical reactions (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 307-313 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An improved version of our magnetic suspension densimeter has been developed for use with samples of aqueous systems as small as 100 μl. The instrument's sensitivity to a change in density of the solution under test (measured as a voltage shift) is 0.1 mV≈4.5×10−6 g ml−1, with a base-line drift less than 9 μV/h. The nonlinearity of the densimeter's response is less than 5 ppm over its calibration range. In this paper, we describe the new magnetic suspension circuit, discuss the precision limits of the instrument, and present the results of measurements made on a tetracarboxylate sequestering agent known as BAPTA which we use as a calcium-ion indicator.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140246
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  • 8
    Electronic Resource
    Electronic Resource
    Precision limits of waveform recovery and analysis in a signal processing oscilloscope (1987)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 58 (1987), S. 1245-1250 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The precision limits of a waveform processing oscilloscope have been investigated for the situation where the instrument is used to recover a repetitive exponential signal from high levels of noise. In these studies, the oscilloscope was programmed to sample the signal, average it, and then calculate its exponential decay time constant. The measurement errors in the resulting time constants were found to decrease with continued averaging, but not without limit. In fact, we found that there was an optimum number of samples needed to minimize the error for any particular value of the signal-to-noise ratio at the input to the oscilloscope. We present here our empirically determined values of those optima, an intercomparison of them with the results of a theoretical model, and a description of the measurement system developed for this work.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139447
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  • 9
    Electronic Resource
    Electronic Resource
    Digital controller for a magnetic suspension system (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 1616-1626 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An active magnetic suspension system controlled digitally by a microprocessor has been built and operated in our laboratories. The control algorithm has integral, proportional, and derivative feedback loops. The remainder of the system including the sensor, power amplifier, and suspension coils, is of standard design. This developmental system has been used successfully to suspend small steel spheres and small rotors up to 190 g in weight, and shows promise of having wide application.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138540
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  • 10
    Electronic Resource
    Electronic Resource
    Precision limits of lock-in amplifiers below unity signal-to-noise ratios (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 268-270 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An investigation of noise-related performance limits of commercial-grade lock-in amplifiers has been carried out. The dependence of the output measurement error on the input signal-to-noise ratio was established in each case and measurements of noise-related gain variations were made.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138927
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