The Experts below are selected from a list of 27 Experts worldwide ranked by ideXlab platform

Peter W. Rodgers - One of the best experts on this subject based on the ideXlab platform.

  • Frequency limits for seismometers as determined from signal-to-noise ratios. Part 1. The electromagnetic seismometer
    Bulletin of the Seismological Society of America, 1992
    Co-Authors: Peter W. Rodgers
    Abstract:

    The range of frequencies that a seismometer can record is nominally set by the corner frequencies of its amplitude frequency response. In recording pre-event noise in very quiet seismic sites, the internally generated self-noise of the seismometer can put further limits on the range of frequencies that can be recorded. Some examples of such low seismic noise sites are Lajitas, Texas; Deep Springs, California; and Karkaralinsk, U.S.S.R. In such sites, the seismometer self-noise can be large enough to degrade the signal-to-noise ratio (SNR) of the recorded pre-event data. The widely used low seismic noise model (LNM) (due to Peterson, 1982; Peterson and Hutt, 1982; Peterson and Tilgner, 1985; Peterson and Hutt, 1989) is used as representative of the input ground motion acceleration power density spectrum (pds) at such very low noise sites. This study determines the range of frequencies for which the SNR of an electromagnetic seismometer exceeds 3 db (a factor of 2 in power and 1.414 in amplitude). In order to do this, an analytic expression is developed for the SNR of a generalized electromagnetic seismometer. The signal pds using Peterson's LNM as an input is developed for an electromagnetic seismometer. Suspension noise is modeled following Usher (1973). In order to determine the electronically caused component of the self-noise, noise properties are compared among three commonly used Amplifiers. The advantages and disadvantages of the inverting and noninverting configurations in terms of their SNR are discussed. In most cases, the noninverting configuration is to be preferred as it avoids the use of the large gain setting resistances required in the inverting configuration to avoid loading the seismometer output. A noise model is developed for a typical low noise operational Amplifier (Precision Monolithics OP-27). This noise model is used to numerically compute the SNRs for the three electromagnetic seismometers used as examples. The degradation in SNR caused by large gain setting resistances is shown. Numerical examples are given using the Mark Products L-4C and L-22D and the Teledyne Geotech GS-13 electromagnetic seismometers. For each of the example seismometers, the calculated range of frequencies for which their SNR exceeds 3 db is as follows: the GS-13, 0.078 to 56.1 Hz; the L-4C, 0.113 to 7.2 Hz; and the L-22D, 0.175 to 0.6 Hz. For the GS-13, the calculated lower and upper frequencies at which the SNR is 3 db are 0.078 and 56.1 Hz. This compares with the values 0.073 and 59 Hz measured in the noise tests on the vertical GS-13. Expressions for the total noise voltage referred to the input of an operational Amplifier are developed in Appendix A. It is shown that in the inverting configuration, although no noise current flows in the input resistor, the noise current appears in the expression for the total noise voltage as if it did. In Appendix B, it is shown that any noise current flowing through an electromagnetic seismometer having a generator greater than several hundred V/m/sec generates a back emf that adds significantly to the noise of the system. This implies that system noise tests that substitute a resistor at the noninverting input of the preAmplifier or clamp the seismometer mass will tend to underestimate the system noise.

Gu Dong-hua - One of the best experts on this subject based on the ideXlab platform.

  • Design of single-phase electrieal parameter measuring instrument based on STC12C5410AD MCU
    Journal of Zhengzhou University of Light Industry, 2010
    Co-Authors: Gu Dong-hua
    Abstract:

    The single phase AC parameters instrument was designed based on STC12C5410AD using high Precision electric meter IC CS5463 as its measurement core.Combined with sampling,zero-crossing comparison circuit,the measurement frequency and phase difference of timer in MCU were utilized;combined with sampling,Amplifier,Precision rectification and filter circuit,utilizing the A/D converter in CS5463 and the effective value of voltage,current is measured through instantaneous sampling method,and the apparent power,active power and reactive power are worked out.Every measurement value is displayed by 12864LCD at last.

George Erdi - One of the best experts on this subject based on the ideXlab platform.

Zhang Ling - One of the best experts on this subject based on the ideXlab platform.

  • Study of Differential Capacitance Small Displacement Sensor
    Instrument Technique and Sensor, 2009
    Co-Authors: Zhang Ling
    Abstract:

    A displacement sensor using differential capacitors was presented.The sensor can measure the small displacement.The mechanical frame and signal processing circuit were designed.The sensor circuit was composed of sinusoidal excitation circuit,converting bridge,Amplifier,Precision rectifier and low-pass filter.The operation principle of the sensor was analyzed.The signal processing circuit parameters were calculated.The sensor is of simple construction,convenient and low cost.Experimental results show that the measurable linear range of the displacement sensor is 0 mm to 0.6 mm.

Gong Yi-jian - One of the best experts on this subject based on the ideXlab platform.

  • Design for High Precision Miniature PWM Temperature Controller
    Optics & Optoelectronic Technology, 2004
    Co-Authors: Gong Yi-jian
    Abstract:

    Based on the analysis to the thermoelectric cooler driving principle and its characteristics, This paper proposes a design for a high Precision miniaturized PWM temperature controller circuit. The circuit mainly is applied on a 320X240 UFPA (Uncooled Focal Plane Arrays) infrared detector, it can increase the accuracy by restricting the local temperature of crucial sense organ to a narrow range. Appropriate applications for this approach include fiber optic laser module, photon Amplifier, Precision miniaturized black body and high-performance crystal-oscillator.