Introduction to Modern Instrumentation

Introduction to Modern Instrumentation For Hydraulics and Environmental Sciences, 2014

Natural hazards and anthropic activities threaten the quality of the environment surrounding the human being, risking life and health. Among the different actions that must be taken to control the quality of the environment, the gathering of field data is a basic one. In order to obtain the needed data for environmental research, a great variety of new instruments based on electronics is used by professionals and researchers. Sometimes, the potentials and limitations of this new instrumentation remain somewhat unknown to the possible users. In order to better utilize modern instruments it is very important to understand how they work, avoiding misinterpretation of results. All instrument operators must gain proper insight into the working principles of their tools, because this internal view permits them to judge whether the instrument is appropriately selected and adequately functioning. Frequently, manufacturers have a tendency to show the great performances of their products without advising their customers that some characteristics are mutually exclusive. Car manufacturers usually show the maximum velocity that a model can reach and also the minimum fuel consumption. It is obvious for the buyer that both performances are mutually exclusive, but it is not so clear for buyers of measuring instruments. This book attempts to make clear some performances that are not easy to understand to those uninitiated in the utilization of electronic instruments. Technological changes that have occurred in the last few decades are not yet reflected in academic literature and courses; this material is the result of a course prepared with the purpose of reducing this shortage. The content of this book is intended for students of hydrology, hydraulics, oceanography, meteorology and environmental sciences. Most of the new instruments presented in the book are based on electronics, special physics principles and signal processing; therefore, basic concepts on these subjects are introduced in the first chapters (Chapters 1 to 3) with the hope that they serve as a complete, yet easy-to-digest beginning. Because of this review of concepts it is not necessary that the reader have previous information on electronics, electricity or particular physical principles to understand the topics developed later. Those readers with a solid understanding of these subjects could skip these chapters; however they are included because some students could find them as a useful synthesis. Chapter 4 is completely dedicated to the description of transducers and sensors frequently used in environmental sciences. It is described how electrical devices are modified by external parameters in order to become sensors. Also an introduction to oscillators is presented because they are used in most instruments. In the next chapters all the information presented here is recurrently referred to as needed to explain operating principles of instruments. VIII Preface Chapters 1 to 4 are bitter pills that could discourage readers interested in the description of specific instruments. Perhaps, those readers trying this book from the beginning could abandon it before arriving at the most interesting chapters. Therefore, they could read directly Chapters 5 to 11, going back as they feel that they need the knowledge of the previous chapters. We intended to make clear all the references to the previous subjects needed to understand each one of the issues developed in the later chapters. Chapter 5 contributes to the understanding of modern instrumentation to measure flow in industrial and field conditions. Traditional mechanical meters are avoided to focus the attention on electronic ones, such as vortex, electromagnetic, acoustic, thermal, and Coriolis flowmeters. Special attention is dedicated to acoustic Doppler current profilers and acoustic Doppler velocimeters. Chapter 6 deals with two great subjects; the first is devoted to instruments for measuring dynamic and quasi static levels in liquids, mainly water. Methods to measure waves at sea and in the laboratory are explained, as well as instruments to measure slow changes such as tides or piezometric heads for hydrologic applications. The second subject includes groundwater measurement methods with emphasis on very low velocity flowmeters which measure velocity from inside a single borehole. Most of them are relatively new methods and some are based on operating principles described in the previous chapter. Seepage meters used to measure submarine groundwater discharge are also presented. Chapter 7 presents methods and instruments for measuring rain, wind and solar radiation. Even though the attention is centered on new methods, some traditional methods are described not only because they are still in use, and it is not yet clear if the new technologies will definitely replace them, but also because describing them permits their limitations and drawbacks to be better understood. Methods to measure solar radiation are described from radiation detectors to complete instruments for total radiation and radiation spectrum measurements. Chapter 8 is a long chapter where we have tried to include most remote measuring systems useful for environmental studies. It begins with a technique called DTS (Distributed Temperature Sensing) that has the particularity of being remote, but where the electromagnetic wave propagates inside a fibre optic. The chapter follows with atmosphere wind profilers using acoustic and electromagnetic waves. Radio acoustic sounding systems used to get atmospheric temperature profiles are explained in detail as well as weather radar. Methods for ocean surface currents monitoring are also introduced. The chapter ends with ground penetrating radars. Chapter 9 is an introduction to digital transmission and storage of information. This subject has been reduced to applications where information collected by field instruments has to be conveyed to a central station where it is processed and stored. Some insight into networks of instruments is developed; we think this information will help readers to select which method to use to transport information from field to office, by means of such diverse communication media as fibre optic, digital telephony, Preface IX GSM (Global System for Mobile communications), satellite communications and private radio frequency links. Chapter 10 is devoted to satellite-based remote sensing. Introductory concepts such as image resolution and instrument’s scanning geometry are developed before describing how passive instruments estimate some meteorological parameters. Active instruments are presented in general, but the on-board data processing is emphasized due to its importance in the quality of the measurements. Hence, concepts like Synthetic Aperture Radar (SAR) and Chirp Radar are developed in detail. Scatterometers, altimeters and Lidar are described as applications of the on-board instruments to environmental sciences. Chapter 11 attempts to transfer some experiences in field measuring to the readers. A pair of case studies is included to encourage students to perform tests on the instruments before using them. In this chapter we try to condense our ideas, most of them already expressed throughout the book, about the attitude a researcher should have with modern instruments before and after a measuring field work. As can be inferred from the foregoing description the book aims to provide students with the necessary tools to adequately select and use instruments for environmental monitoring. Several examples are introduced to advise future professionals and researchers on how to measure properly, so as to make sure that the data recorded by the instruments actually represents the parameters they intend to know. With this purpose, instruments are explained in detail so that their measuring limitations are recognized. Within the entire work it is underlined how spatial and temporal scales, inherent to the instruments, condition the collection of data. Informal language and qualitative explanations are used, but enough mathematical fundamentals are given to allow the reader to reach a good quantitative knowledge. It is clear from the title of the book that it is a basic tool to introduce students to modern instrumentation; it is not intended for formed researchers with specific interests. However, general ideas on some measuring methods and on data acquisition concepts could be useful to them before buying an instrument or selecting a measuring method. Those readers interested in applying some particular method or instrument described in this book should consider these explanations just as an introduction to the subject; they will need to dig deeper in the specific bibliography before putting hands on

Instrumentation Science & Technology, 1998

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This third edition of Sensors and Transducers has been thoroughly revised to take account of the ever-increasing role of these components and of improvements in design. New tables of properties and illustrations have also been added. The topic of switches and switching actions has also been added because so many types of sensor are intended ultimately to provide a switching action. Ian Sinclair because he didn't really understand it. The text should prove useful to anyone who encounters sensors and transducers, whether from the point of view of speci¢cation, design, servicing, or education. I am most grateful to RS Components for much useful and well-organized information, and to Bernard Watson, of BSP Professional Books, for advice and encouragement.

users.evtek.fi

ABSTRACT

In this work the significance of treating a set of measurements as a time series is being explored. Time Series Analysis (TSA) techniques, part of the Exploratory Data Analysis (EDA) approach, can provide much insight regarding the stochastic correlations that are induced on the outcome of an experiment by the measurement system and can provide criteria for the limited use of the classical variance in metrology. Specifically, techniques such as the Lag Plots, Autocorrelation Function, Power Spectral Density and Allan Variance are used to analyze series of sequential measurements, collected at equal time intervals from an electromechanical transducer. These techniques are used in conjunction with power law models of stochastic noise in order to characterize time or frequency regimes for which the usually assumed white noise model is adequate for the description of the measurement system response. However, through the detection of colored noise, usually referred to as flicker noise, which is expected to appear in almost all electronic devices, a lower threshold of measurement uncertainty for this particular system is obtained and the white noise model is no longer accurate.

Robotics Automation and Control, 2008

IEEE Transactions on Instrumentation and Measurement, 2013

Bulletin of the Seismological Society of America, 2008

Using three different short-period electromagnetic sensors with resonance frequencies of 1 Hz (Mark L4C-3D), 2 Hz (Mark L-22D), and 4.5 Hz (I/O SM-6), coupled with three digital acquisition system, the portable data acquisition system (PDAS) Teledyne Geotech, the refraction technology (REFTEK) 72A, and the Earth Data Logger PR6-24 (EDL), the effect of the seismic instruments on the horizontal-to-vertical spectral ratio (H/V) using seismic noise for frequencies less than 1 Hz has been evaluated. For all possible sensors-acquisition system pairs, the background seismic signal and instrumental self-noise power spectral densities have been calculated and compared. The results obtained when coupling the short-period sensors with different acquisition systems show that the performance of the considered instruments at frequencies < 1 Hz strongly depends upon the sensor-acquisition system combination and the gain used, with the best performance obtained for sensors with the lowest resonance frequency. For all acquisition systems, it was possible to retrieve correctly the H/V peak down to 0.1-0.2 Hz by using a high gain and a 1-Hz sensor. In contrast, biased H/V spectral ratios were retrieved when low-gain values were considered. Particular care is required when using 4.5-Hz sensors, because they may not even allow the fundamental resonance frequency peak to be reproduced.

A new acoustical measurement technique has been developed ,that provides a solution for the conflicting requirements of anechoic spectral measurements in the presence of a reverberant environment. This technique, called time delay spectrometry, recognizes that a system-forcing function linearly relating frequency with time provides spatial discrimination of signals of variable pal0h_lengthwhen perceived by a frequency-tracking spectrum analyzer.

2018

The basic elements of a noise measuring system are a microphone, an amplifier, a signal processor and a readout or monitoring unit. The simplest practical realization of such a system is the portable sound level meter. The microphones are the standard acoustical transducer for all sound and noise measurement. Different types of microphones are available; each has its own advantage and disadvantage. This paper attempts to compile the information on different types of microphones available, its characteristics, calibration methods and relevant standards. This paper also discusses the secondary free field calibration procedure as per IEC 61094 part 8 -2012 and highlight the contribution of various uncertainty factors affecting calibration.

IEEE Transactions on Instrumentation and Measurement, 2000

The paper presents a spectral method for robust and accurate real-time frequency estimation when a square wave affected by impulsive noise is considered. The method, tailored for signals coming from typical resonant sensors (frequency from 2 kHz to 22 kHz), has been implemented and tested using a floatingpoint digital signal Pprocessor (DSP) and a 16-bit analog-to-digital converter (ADC). It has been observed that there is a greater immunity to glitches with respect to the classic solution based on Constant Elapsed Time, while resolution (10 6 ) and measuring time (10 ms), are close to the ones of traditional high-cost laboratory instrumentation.

SEG Technical Program Expanded Abstracts 2016, 2016

Broadband seismic data acquisition requires a wide spectrum down to the very low frequencies (< 1Hz) for both the source and the receivers. Significant progress has been made on broadband data acquisition and processing, but the low frequency sensitivity of the land geophone to particle velocity remains an issue. The geophone output to particle velocity decays toward the low frequencies relative to displacement. A similar decay occurs in accelerometers due to particle acceleration. (Poggiagliolmi et al., 2015). In this paper comparisons of field measurements were made using two low frequency geophones and a new particle displacement sensor. This comparison has demonstrated that the sensitivity of the geophones decreases toward the low frequencies, while the response of the displacement sensor remains essentially flat down to less than 1Hz.

EAGE Workshop on Broadband Seismic, 2015

Since geophones and accelerometers sense respectively particle velocity and particle acceleration, they both lack sensitivity at the low frequencies relative to their performance at the high frequencies. Whereas displacement sensors have a broad response especially at the very low frequencies. A field comparison of a displacement sensor and a 5 Hz geophone demonstrated that the response of the displacement sensor is essentially flat at low frequencies, while the geophone attenuates low frequencies below and above resonance.