1,063 research outputs found

    Performance of Several Low‐Cost Accelerometers

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    Several groups are implementing low-cost host-operated systems of strong-motion accelerographs to support the somewhat divergent needs of seismologists and earthquake engineers. The Advanced National Seismic System Technical Implementation Committee (ANSS TIC, 2002), managed by the U.S. Geological Survey (USGS) in cooperation with other network operators, is exploring the efficacy of such systems if used in ANSS networks. To this end, ANSS convened a working group to explore available Class C strong-motion accelerometers (defined later), and to consider operational and quality control issues, and the means of annotating, storing, and using such data in ANSS networks. The working group members are largely coincident with our author list, and this report informs instrument-performance matters in the working group’s report to ANSS. Present examples of operational networks of such devices are the Community Seismic Network (CSN; csn.caltech.edu), operated by the California Institute of Technology, and Quake-Catcher Network (QCN; Cochran et al., 2009; qcn.stanford.edu; November 2013), jointly operated by Stanford University and the USGS. Several similar efforts are in development at other institutions. The overarching goals of such efforts are to add spatial density to existing Class-A and Class-B (see next paragraph) networks at low cost, and to include many additional people so they become invested in the issues of earthquakes, their measurement, and the damage they cause

    Dynamic Pressure Sensing for the Flight Test Data System

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    This thesis describes the design, assembly, and test of the FTDS-K, a new device in the Boundary Layer Data System (BLDS) family of flight data acquisition systems. The FTDS-K provides high-frequency, high-gain data acquisition capability for up to two pressure sensors and an additional three low-frequency pressure sensors. Development of the FTDS-K was separated into a core module, specialized analog subsystem, and practical testing of the FTDS-K in a flow measurement mission. The core module combines an nRF52840-based microcontroller module, switching regulator, microSD card, real-time clock, temperature sensor, and trio of pressure sensors to provide the same capabilities as previous-generation BLDS-P devices. An expansion header is included in the core module to allow additional functionality to be added via daughter boards. An analog signal chain comprised of two-stage amplification and fourth-order active antialiasing filters was implemented as a daughter board to provide an AC-coupled end-to-end gain of 7,500 and a DC-coupled end-to-end gain of 50. This arrangement was tested in a wind tunnel to demonstrate that sensors with a full-scale range of 103 kPa can be used to reliably discriminate between laminar and turbulent flows based on pressure fluctuation differences on the order of tens of Pa. A combination of wind-off correction and band-filtering was used to reduce the effect of inherent and induced electrical noise, while two-sensor correlation was tested and shown to be effective at removing certain types of noise. Total power consumption for the FTDS-K in a representative mission is 208 mW, which translates to an operational endurance of 9 hours with 2 AAA LiFeS2 cells at -40°C

    Alternative Methods for Non-Linearity Estimation in High-Resolution Analog-to-Digital Converters

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    The evaluation of the linearity performance of a high resolution Analog-to- Digital Converter (ADC) by the Standard Histogram method is an outstanding challenge due to the requirement of high purity of the input signal and the high number of output data that must be acquired to obtain an acceptable accuracy on the estimation. These requirements become major application drawbacks when the measures have to be performed multiple times within long test flows and for many parts, and under an industrial environment that seeks to reduce costs and lead times as is the case in the New Space sector. This thesis introduces two alternative methods that succeed in relaxing the two previous requirements for the estimation of the Integral Nonlinearity (INL) parameter in ADCs. The methods have been evaluated by estimating the Integral Non-Linearity pattern by simulation using realistic high-resolution ADC models and experimentally by applying them to real high performance ADCs. First, the challenge of applying the Standard Histogram method for the evaluation of static parameters in high resolution ADCs and how the drawbacks are accentuated in the New Space industry is analysed, being a highly expensive method for an industrial environment where cost and lead time reduction is demanded. Several alternative methods to the Standard Histogram for estimating Integral Nonlinearity in high resolution ADCs are reviewed and studied. As the number of existing works in the literature is very large and addressing all of them is a challenge in itself, only those most relevant to the development of this thesis have been included. Methods based on spectral processing to reduce the number of data acquired for the linearity test and methods based on a double histogram to be able to use generators that do not meet the the purity requirement against the ADC to be tested are further analysed. Two novel contributions are presented in this work for the estimation of the Integral Nonlinearity in ADCs, as possible alternatives to the Standard Histogram method. The first method, referred to as SSA (Simple Spectral Approach), seeks to reduce the number of output data that need to be acquired and focuses on INL estimation using an algorithm based on processing the spectrum of the output signal when a sinusoidal input stimulus is used. This type of approach requires a much smaller number of samples than the Standard Histogram method, although the estimation accuracy will depend on how smooth or abrupt the ADC nonlinearity pattern is. In general, this algorithm cannot be used to perform a calibration of the ADC nonlinearity error, but it can be applied to find out between which limits it lies and what its approximate shape is. The second method, named SDH (Simplified Double Histogram)aims to estimate the Non-Linearity of the ADC using a poor linearity generator. The approach uses two histograms constructed from the two set of output data in response to two identical input signals except for a dc offset between them. Using a simple adder model, an extended approach named ESDH (Extended Simplified Double Histogram) addresses and corrects for possible time drifts during the two data acquisitions, so that it can be successfully applied in a non-stationary test environment. According to the experimental results obtained, the proposed algorithm achieves high estimation accuracy. Both contributions have been successfully tested in high-resolution ADCs with both simulated and real laboratory experiments, the latter using a commercial ADC with 14-bit resolution and 65Msps sampling rate (AD6644 from Analog Devices).La medida de la característica de linealidad de un convertidor analógicodigital (ADC) de alta resolución mediante el método estándar del Histograma constituye un gran desafío debido los requisitos de alta pureza de la señal de entrada y del elevado número de datos de salida que deben adquirirse para obtener una precisión aceptable en la estimación. Estos requisitos encuentran importantes inconvenientes para su aplicación cuando las medidas deben realizarse dentro de largos flujos de pruebas, múltiples veces y en un gran número de piezas, y todo bajo un entorno industrial que busca reducir costes y plazos de entrega como es el caso del sector del Nuevo Espacio. Esta tesis introduce dos métodos alternativos que consiguen relajar los dos requisitos anteriores para la estimación de los parámetros de no linealidad en los ADCs. Los métodos se han evaluado estimando el patrón de No Linealidad Integral (INL) mediante simulación utilizando modelos realistas de ADC de alta resolución y experimentalmente aplicándolos en ADCs reales. Inicialmente se analiza el reto que supone la aplicación del método estándar del Histograma para la evaluación de los parámetros estáticos en ADCs de alta resolución y cómo sus inconvenientes se acentúan en la industria del Nuevo Espacio, siendo un método altamente costoso para un entorno industrial donde se exige la reducción de costes y plazos de entrega. Se estudian métodos alternativos al Histograma estándar para la estimación de la No Linealidad Integral en ADCs de alta resolución. Como el número de trabajos es muy amplio y abordarlos todos es ya en sí un desafío, se han incluido aquellos más relevantes para el desarrollo de esta tesis. Se analizan especialmente los métodos basados en el procesamiento espectral para reducir el número de datos que necesitan ser adquiridos y los métodos basados en un doble histograma para poder utilizar generadores que no cumplen el requisito de precisión frente al ADC a medir. En este trabajo se presentan dos novedosas aportaciones para la estimación de la No Linealidad Integral en ADCs, como posibles alternativas al método estándar del Histograma. El primer método, denominado SSA (Simple Spectral Approach), busca reducir el número de datos de salida que es necesario adquirir y se centra en la estimación de la INL mediante un algoritmo basado en el procesamiento del espectro de la señal de salida cuando se utiliza un estímulo de entrada sinusoidal. Este tipo de enfoque requiere un número mucho menor de muestras que el método estándar del Histograma, aunque la precisión de la estimación dependerá de lo suave o abrupto que sea el patrón de no-linealidad del ADC a medir. En general, este algoritmo no puede utilizarse para realizar una calibración del error de no linealidad del ADC, pero puede aplicarse para averiguar entre qué límites se encuentra y cuál es su forma aproximada. El segundo método, denominado SDH (Simplified Double Histogram) tiene como objetivo estimar la no linealidad del ADC utilizando un generador de baja pureza. El algoritmo utiliza dos histogramas, construidos a partir de dos conjuntos de datos de salida en respuesta a dos señales de entrada idénticas, excepto por un desplazamiento constante entre ellas. Utilizando un modelo simple de sumador, un enfoque ampliado denominado ESDH (Extended Simplified Double Histogram) aborda y corrige las posibles derivas temporales durante las dos adquisiciones de datos, de modo que puede aplicarse con éxito en un entorno de prueba no estacionario. De acuerdo con los resultados experimentales obtenidos, el algoritmo propuesto alcanza una alta precisión de estimación. Ambas contribuciones han sido probadas en ADCs de alta resolución con experimentos tanto simulados como reales en laboratorio, estos últimos utilizando un ADC comercial con una resolución de 14 bits y una tasa de muestreo de 65Msps (AD6644 de Analog Devices)

    A method for characterization of vibration testing setups

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