CHAPTER ONE INTRODUCTION TO INSTRUMENTATION

Elektronika ir Elektrotechnika, 2014

As the effects of global warming are spreading all over the planet, the activities on monitoring the environment are getting on importance and are becoming the focus of many projects, in particular those targeting development of smart cities and smart societies in general. Development of technology is enabling implementation of low-cost environment monitoring systems that can be installed across the cities utilizing the existing city infrastructure (for example attached to lampposts or installed on public transport vehicles) or even carried around by individuals contributing to crowd sourced based monitoring solutions. However, even though the costs are significantly lower than just a few years ago, it is still prohibitive to deploy such systems on a very large scale. This paper presents a possible approach towards significant reduction of the number of measurement points as well as the number of required sensors while still providing reliable estimations of environment parameters across an area. The approach is based on the mathematical statistics methods. It is shown that the proposed solution works well in the areas with stable and slowly-changing weather conditions, i.e. in cases when there are no sudden climate changes.

This document examines the significance of several performance parameters in instrumentation and their corresponding relationships. In-depth analyses are provided for static sensitivity, scale readability, accuracy, bias, precision, reliability, maintainability, and error analysis. The performance qualities of instruments have a significant impact on their accuracy, reliability, and utility. Understanding their interdependencies and significance enables academics and practitioners to make well-informed decisions, process data efficiently, and provide meaningful measurement outputs.

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

quantities. The term has its origins in the art and science of scientific instrument-making Instrumentation involves both measurement and control functions. In technology, the development and use of precise measuring equipment. Although the sensory organs of the human body can be extremely sensitive and responsive, modern science and technology rely on the development of much more precise measuring and analytical tools for studying, monitoring, or controlling all kinds of phenomena. Instrumentation is the essential process control in industry. In industrial control a wide number of variables temperature, move, level, pressure, and distance can be sensed together. All of these can be interdependent factors in one processing need a sophisticated microprocessor system for total control. Instrumentation is the science of automated measurement and control. Instruments are used to measure and control the condition of process streams as they pass through a Plant. Principles of Instrumentation  Accessibility (operator's posture and patient positioning).  Visibility, illumination, and retraction.  Selection of proper instrument.  Condition of instruments (sharpness).  Maintaining a clean field.  Instrument stabilization.  Instrument activation. Instrument Instrument is a device or mechanism used to determine the present value of a quantity under observation Instruments are used to measure and control process variables such as: Temperature; Flow; Level; Pressure; Quality. The instrument used for measuring the physical and electrical quantities is known as the measuring instrument. Measurement Measurement is the process of determining the amount, degree, capacity by comparison (direct or indirect) with the accepted standards of the system units being used. The term measurement means the comparison between the two quantities of the same unit. Classification of Measuring Instruments The instrument used for measuring the physical and electrical quantities is known as the measuring instrument. The term measurement means the comparison between the two quantities of the same unit. The magnitude of one of the quantity is unknown, and it is compared with the predefined value. The result of the comparison obtained regarding numerical value. Active and Passive Instruments Diligence, Determination, and Discipline are Keys to Excellent Success Instruments are divided into active or passive ones according to whether the instrument output is entirely produced by the quantity being measured or whether the quantity being measured simply modulates the magnitude of some external power source. This is illustrated by examples. Passive Instrument An example of a passive instrument is the pressure-measuring device shown in Figure below. The pressure of the fluid is translated into a movement of a pointer against a scale. The energy expended in moving the pointer is derived entirely from the change in pressure measured: there are no other energy inputs to the system. Active Instrument An example of an active instrument is a float-type petrol tank level indicator as sketched in Figure below. Here, the change in petrol level moves a potentiometer arm, and the output signal consists of a proportion of the external voltage source applied across the two ends of the potentiometer. The energy in the output signal comes from the external power source: the primary transducer float system is merely modulating the value of the voltage from this external power source. In active instruments, the external power source is usually in electrical form, but in some cases, it can be other forms of energy such as a pneumatic or hydraulic one. One very important difference between active and passive instruments is the level of measurement resolution that can be obtained. With the simple pressure gauge shown, the amount of movement made by the pointer for a particular pressure change is closely defined by the nature of the instrument. Diligence, Determination, and Discipline are Keys to Excellent Success Comparison between Active and Passive Instruments While it is possible to increase measurement resolution by making the pointer longer, such that the pointer tip moves through a longer arc, the scope for such improvement is clearly restricted by the practical limit of how long the pointer can conveniently be. In an active instrument, however, adjustment of the magnitude of the external energy input allows much greater control over measurement resolution. While the scope for improving measurement resolution is much greater incidentally, it is not infinite because of limitations placed on the magnitude of the external energy input, in consideration of heating effects and for safety reasons. In terms of cost, passive instruments are normally of a more simple construction than active ones and are therefore cheaper to manufacture. Therefore, choice between active and passive instruments for a particular application involves carefully balancing the measurement resolution requirements against cost. Difference between Active and Passive Instruments Diligence, Determination, and Discipline are Keys to Excellent Success Types of Measuring Instrument The measuring instrument categorised into three types;  Electrical Instrument  Electronic Instrument  Mechanical Instrument The mechanical instrument uses for measuring the physical quantities. This instrument is suitable for measuring the static and stable condition because the instrument is unable to give the response to the dynamic condition. The electronic instrument has quick response time. The instrument provides the quick response as compared to the electrical and mechanical instrument. The electrical instrument is used for measuring electrical quantities likes current, voltage, power, etc. The ammeter, voltmeter, wattmeter are the examples of the electrical measuring instrument. The ammeter measures the current in amps; voltmeter measures voltage and Wattmeter are used for measuring the power. The classification of the electric instruments depends on the methods of representing the output reading. The response time of the electronic instrument is very high as compared to the electrical and mechanical device. Diligence, Determination, and Discipline are Keys to Excellent Success GENERAL CHARACTERISTICS OF MEASURING INSTRUMENTS The subject of performance criteria assumes major proportions when one is paced with the choice from commercially available ones of measuring instruments that would be most suited to a particular measurement task often, two performance characteristics come into consideration-the static and dynamic characteristics. The static characteristics define the performance yardstick for the measurement of such quantities which are constant, or vary only quite slowly the dynamic characteristic define the comparison between system input and system output for measured quantities that vary rapidly. It has been discovered in practice that the characteristics of one group sometimes influence that of the other. CLASSIFICATION OF INSTRUMENTS Instruments are broadly classified into three types such as indicating, recording and controlling instruments. These are given in the subsections below: INDICATING INSTRUMENTS These safer to the instruments in which the value of the measurand is indicated visually but not at all recorded. The instruments may be analogue or digital display types. a) Analogue Display Indication on this instrument is by means of a mechanical pointer. The final amplification is provided by the length of the pointer from its pivot to the scale friction may possibly develop at the errors very likely when this type of measuring instrument is used. Example of analogue display devices are bourdon tube pressure gauge, oscilloscopes moving coil meters, Huggen berger extensometer, scale and galvanometer in which an electrical signal is transmitted to mechanical movement of the pointer etc. Diligence, Determination, and Discipline are Keys to Excellent Success b) Digital Display This type of indicating instruments such that the final value of the measurement is expressed in numbers. Example are digital voltmeters and ammeters, digital voltmeters and ammeters, digital frequency, meters, digital thermometer etc. RECORDING INSTRUMENTS The operation of these instruments involves recording output of measurement on a chart, digital computer or data logger. Examples are D'Arsonval galvanometer (which has similar electro-mechanical movement as in analogue display out having the pointer replaced with a writing arm) pen recorders, Yt recorders, X-Y plotters, ultra violet light recorders. Also commonly used in the performance of instrumentation tasks is the Magnetic Tape Recorders. CONTROLLING INSTRUMENTS These instruments function in line with a fixed program. For instance, when a computer is programmed to perform a specific control function, it cease to be a generalpurpose device but it is dedicated instead to the control of a single piece of equipment, such an instrument is called controlling instrument or controller Robot arms, for example, work according to specified programs while there are certain instruments which execute these computer programs, these are controlling instruments or controllers. Different Types of Electrical Instrument Absolute Instrument The absolute instrument gives the value of measures quantities regarding the physical constant. The physical constant means the angle of deflection, degree and meter constant. The mathematical calculation requires for knowing the value of a physical constant. The tangent galvanometer is the examples of the absolute instruments. In tangent galvanometer, the magnitude of current passes through the coil determines by the tangent of the angle of deflection of their coil, the horizontal component of the earth magnetic field, radius and the number of turns of wire used. The most common applications of this type of instrument are found in laboratories....