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1. 52 V Smie ko K Kov VIRTUAL INSTRUMENTATION AND DISTRIBUTED MEASUREMENT SYSTEMS SENSORS SERIAL INSTRUMENTS GP IB VXI INSTRUMENTS INSTRUMENTS PROCES Fig 4 Structure of the PC based instrumentation hardware 3 1 Computer and Display The computer and the display are the heart of virtual instrument systems These systems are typically based on a personal computer or workstation with a high resolution monitor a keyboard and a mouse It is impor tant for the chosen computer to meet the system require ments specified by the instrumentation software packages Rapid technological advancements of PC technology have greatly enhanced virtual instrumentation Moving from DOS to Windows gave to PC users the graphi cal user interface and made 32 bit software available for building virtual instruments The advances in processor performance supplied the power needed to bring new ap plications within the scope of virtual instrumentation Faster bus architectures such as PCI have eliminated the traditional data transfer bottleneck of older buses ISA The future of virtual instrumentation is tightly coupled with PC technology 3 2 Software If the computer is the heart of the virtual instrument systems the software is their brain The software uniquely defines the functionality and personality of the virtual instrument system Most software is designed to run on industry standard operating systems on per
2. PIURI V A Simulation Tool for Virtual Laboratory Experiments in a WWW Environment Proc IEEE Conf on Instrumentation and Measurement Technology St Paul Minnesota USA 18 21 May 1998 1 102 107 SCPI Standard Commands for Programmable Instruments ver sion 1991 0 May 1991 ni com dvi SMIESKO V KOVAC K KAZICKA R VXLbus as a Tool for Dynamic Testing Proc Int Conf CATE 93 Brno 1993 283 287 ANSI IEEE Std 488 1 1987 IEEE Standard Digital Interface for Programmable Instrumentation ANSI IEEE Std 488 2 1987 IEEE Standard Codes Formats Protocols and Common Commands SMIESKO V Some Properties of VXI System in Relation to HP IB Proceedings Precise Measurement in Army Brno 1991 68 71 VXI bus System Specification Revision 1 3 Tektronix ONDRASOVA I SMIESKO V SETNICKA V Contri bution to the Efficiency of GPIB Instrumentation In Measure ment Science Review Vol 1 No 1 2001 59 62 HELSEL R Visual Programming for PH VEE Prentice Hall PTR 1997 14 15 16 17 18 19 20 21 22 23 24 HP VEE for Windows User Manual Hewlett Packard Corp 1993 25 LabWindows CVI User Manual National Instr Corp Austin 1994 26 Test Point Demo System Keithley Instruments 1992 27 EREN H NICHOLS W J WONGSO I Towards an Internet Based Virtual Wire Environment with Virtual Instru mentation IEEE Instrumentation and Measurement Confer ence Bud
3. One note is worth to be repeated Virtual instrumentation never eliminates the instrument hardware completely To measure the real world there will always be some sort of measurement hardware sensor transducer and conditioning circuit but the physical form factor of this instrumentation may continue to evolve 4 DISTRIBUTED MEASUREMENT SYSTEMS The present trend in interconnected measurement sys tems is to extend the area covered by the interconnected systems in the geographical scale This sets a further limit Journal of ELECTRICAL ENGINEERING VOL 55 NO 1 2 2004 TERMINAL TERMINAL TERMINAL 1 2 3 CONTROLLER VXI v LNAWNYLSNI S LNANNUYLSNI Fig 8 Block diagram of distributed measurement system based on LAN DATA SOCKET CONTROLL INTERNET EXPLORER Fig 9 The architecture of a distributed system based on Internet to the use of such systems As in the case of large and com plex plants a structured networked measurement system can be adopted by scaling its use to the geographical area The geographical process to be monitored and controlled is partitioned into cells that can be dealt with by a sin gle processing unit or a group of locally connected units Geographically distributed units are connected by a geo graphical computer network into a distributed measure ment system In this case communication delays usually cannot be neglected This is even more relevant if the traf fic in the co
4. due to their low price and high flexibility obtained from the associated software VXI bus In the late eighties the VME eXtension for Instrumentation VXI standard allowed communication among units with transfer over 20 Mbytes second be tween VXI systems VXI instruments are installed in a rack and are controlled by and communicate directly with a VXI computer These VXI instruments do not have buttons or switches for direct local control and do not have local display typical in traditional instruments It is an open system instrument architecture that com bines many of the advantages of GPIB and computer backplane buses VXIbus instruments are plug in mod ules that are inserted into specially designed card cages 54 V Smie ko K Kov VIRTUAL INSTRUMENTATION AND DISTRIBUTED MEASUREMENT SYSTEMS GPIB To another Controller GPIB Fl instrument Co VXI Mainframe INST INST INST f CPU 1 2 Sere 3 Fig 5 A VXIbus system controlled by GPIB VXI Mainframe PC INST INST RAM INST INST 1 2 wae 3 4 Fig 7 A VXIbus system controlled by an embedded VXIbus computer inserted into the mainframe known as mainframes Mainframes include power sup plies air cooling equipment and backplane communica tion for the modules The VXIbus is unique in that it combines a computer backplane based on the VME bus for high speed communication and offers a quality EMC environment that allows high
5. 2 ans 3 Fig 6 A VXIbus system controlled over a high speed MXIbus cable conversions to VXIbus are simple and fast bringing MXIbus performance within a factor of 2 or so of na tive VXIbus speeds The advantage of MXIbus is that it allows the use of off the shelf computers to commu nicate with VXIbus instruments at a speed consider ably higher than GPIB A disadvantage is that the MXIbus cable can be thick and unwieldy and there is some loss of data transfer bandwidth due to the con version Figure 6 shows an example VXIbus system using MXIbus c The third way is to insert powerful VXIbus computers directly into the VXIbus mainframe VXIbus comput ers tend to be repackaged versions of industry standard personal computers and workstations that run indus try standard operating systems and software The ad vantage of this technique is that it preserves the full communications performance of VXIbus The disad vantage is that the choice of VXIbus computers will always be a subset of the choice of standard industry computers VXIbus computer technology will typically lag behind the performance of the industry as a whole offer fewer alternative configurations and be priced at a premium due to its lower volume Figure 7 shows an example VXIbus system using an embedded computer 3 4 Instrument Hardware The preceding subsection on interfaces also touches on the attributes found in each of the respective instrument hardware products
6. as C and Java can be used with off the shelf development tools to implement the embedded network node applications and the web based applications respectively Internet based TCP IP protocols Ethernet technology and or DataSockets can be used to design the networking infrastructure Fig 9 DataSocket is a software technology for Windows that makes sharing all measurements across a network remote Web and FTP sites as easy as writing information to a file It uses URLs to address data by the same way we use URL in a Web browser to specify Web pages DataSocket included with any software tool is ideal when someone wishes to complete control over the distribution of the measurement but does not want to learn the intricacies of the TCP IP data transfer protocols In all types of networked and distributed measurement systems presented above real time operation and con straints are critical issues to be considered during system design to ensure the correct system operation With distributed measurement system one can take re mote measurements distribute a program s execution or publish measurement data over the Internet The evolved hardware and software technologies provide users with the tools they need for easy building of a powerful dis tributed system By publishing your measurement or automation ap plication over the Internet real time data can be viewed by users on remote computers With application develop ment environments Web
7. level tool software Currently the most popular way of programming is based on the high level tool software With easy to use in tegrated development tools design engineers can quickly create configure and display measurements in a user friendly form during product design and verification The most known popular tools are as follows e LabVIEW Laboratory Virtual Instrument Engineer ing Workbench is a highly productive graphical pro gramming language for building data acquisition and in strumentation systems To specify the system function ality one intuitively assembles block diagrams a nat ural design notation for engineers Its tight integration with measurement hardware facilities rapid development of data acquisition analysis and presentation of solutions e LabWindows CVI C for Virtual Instrumentation is a Windows based interactive ANSI C programming environment designed for building virtual instrumenta tion applications It delivers a drag and drop editor for building user interfaces a complete ANSI C environment for building test program logic and a collection of auto mated code generation tools as well as utilities for build ing automated test systems and monitoring applications of laboratory experiments The main power of CVI lies in the set of libraries e HP VEE Hewlett Packard s Visual Engineering En vironment allows graphical programming for instru mentation applications It is a kin
8. servers are available so you can publish a user interface to the Internet Without any ad ditional programming you can publish your front panel as a Web page so users across the Internet can view these panels running within any standard Web browser Applications have one or more measurement nodes physically separated from the computer that is con trolling them and collecting data Remote measure ment applications often require high speed streaming of data and several clients connected to a single measure ment For streaming measurement data across a network DataSocket provides you with an easy to use interface Using DataSocket you can easily stream any kind of mea surement data across a local area network or the Inter net to several client programs Both Web servers and DataSocket provide a simple and convenient way to pub lish your measurement data 5 CONCLUSIONS Virtual instrumentation is fuelled by ever advancing computer technology and it offers the power of creating and defining someone s own system based on an open framework The combination of computer performance graphical software and modular instrumentation has led 56 to the emergence of virtual instruments which are sub stantially different from their physical ancestors Virtual instruments are manifested in different forms ranging from graphical instrument panels to complete instrument systems Modular instrumentation building blocks are be coming more prevalen
9. Journal of ELECTRICAL ENGINEERING VOL 55 NO 1 2 2004 50 56 REVIEWS LETTERS REPORTS VIRTUAL INSTRUMENTATION AND DISTRIBUTED MEASUREMENT SYSTEMS Viktor Smie ko Karol Kov The development and use of programmable measurement systems have been widely explored The possibility of modifying the measurement procedure simply by changing the algorithm executed by the computer based architecture without replacing the hardware components makes the experimental activity easier Virtual measurement systems have been introduced to simplify the design implementation and use of programmable measurement systems by adopting a visual interface Networking has also been introduced successfully in measurement to interconnect different instruments and data processing sites into a distributed measurement system DMS Industries that develop and use DMS are migrating away from proprietary hardware and software platforms in favour of open systems and standardized approaches Keywords virtual instrumentation distributed measurement system remote and networked measurement intercon nect buses 1 INTRODUCTION For many years electronic instruments have been easily identified products Although they ranged in size and functionality they all tended to be box shaped objects with a control panel and a display Stand alone electronic instruments are very powerful expensive and designed to perform one or more specific tasks defined by the v
10. apest Hungary May 21 23 2001 817 820 JASENEK J Sensors with Distributed Parameters on the Basis of POTDR Journal of Electr Eng 53 No 9 s 2002 101 106 Presented at XVI th International Conference EMFM Bratislava Sept 11 13 2002 KAZICKA R ONDRASOVA I SMIESKO V Improving the AT amp MS Parameters J Electrical Engineering 46 No 7 1995 261 264 ONDRASOVA I SETNICKA V SMIESKO V Auto mated Instrumentation Application In 12 P International Sci entific Conference Radioelektronika 2002 Bratislava Slovak Republic 14 16 May 2002 182 185 Received 17 October 2003 28 29 Viktor SmieSko Prof Ing CSc was born in Zlatovce Czechoslovakia in 1948 He graduated with honors in 1970 and received the CSc PhD degree at the Faculty of Elec trical Engineering Slovak Technical University Currently is Full Professor for Instrumentation at the Faculty of Electrical Engineering and Information Technology Slovak University of Technology His research interests are in the areas of auto mated instrumentation and electromagnetic compatibility Karol Kov Doc Ing CSc was born in Bratislava Slo vakia on June 9 1952 He received the Ing MSc degree with honors in 1976 and the CSc PhD degree in electrical engi neering from the Faculty of Electrical Engineering of the Slo vak Technical University Bratislava Since 1976 he has been with the Department of Measurement of the Faculty
11. ate of 1 Mbytes s and typical data transfers are between 100 and 250 Kbytes s It depends on the response of the mea sured subject PC bus With the rapid acceptance of the IBM per sonal computer in test and measurement applications there has been a corresponding growth of plug in instru mentation cards that are inserted into spare slots How ever high accuracy instruments require significant cir cuit board space to achieve their intended precision Be cause of the limited printed circuit board space and close proximity to sources of electromagnetic interference PC bus instruments tend to be of lower performance than GPIB instruments but also of lower cost Many are simple ADCs DACs and digital I O cards PC bus instrumen tation is best suited for creating small inexpensive acqui sition systems where the performance is not of paramount importance Since these cards plug directly into the com puter backplane and contain no embedded command in terpreter as found in GPIB instruments personal com puter plug in cards are nearly always delivered with driver software so that they can be operated from a personal computer This software may or may not be compati ble with other virtual instrument software packages so it is recommended to check with the vendors beforehand Most data acquisition boards are multifunctional ie they accept both analogue and digital signals These plug in data acquisition boards gain wider and wider acceptance
12. ation amp Measurement Magazine Vol 2 1999 14 19 5 SMIESKO V KUKUGA P Measurement on the Threshold of the Third Millennium J Electrical Engineering 52 No 7 8 2001 240 243 6 TRUCHARD J Future of Virtual Instrumentation NI Week 2002 7 DES JARDIN L Virtual Instruments and the Role of Soft ware Electronic Instrument Handboock McGraw Hill 1995 44 1 44 14 8 GALWAS B A RAK R J Virtual Laboratory a Fu ture Part of the New Web Based Model of Undergraduate Engi neering Studies Developed by Warsaw University of Technology Joint IMEKO TC 1 amp XXXIV MKM Conference 2002 Wroclaw 8 12 September 2002 9 McCONNELL E The Future of Virtual Instrumentation Sen sors July 1997 237 240 EPPLER B A Beginners Guide to SCPI Addison Wesley Publishing Company Inc 1999 BERTOCCO M FERRARIS F OFFELLI C PARVIS M A Client Server Architecture for Distributed Measurement Systems IEEE Transactions on Instrumentation and Measure ment 47 No 5 1998 1143 1148 LEE K B SCHNEEMAN R D Internet Based Distributed Measurement System and Control Application IEEE Instru mentation amp Measurement Magazine June 1999 23 27 V Smie ko K Kov VIRTUAL INSTRUMENTATION AND DISTRIBUTED MEASUREMENT SYSTEMS 13 TAN K K SOH C Y Instrumentation on the Internet Engineering Science and Education Journal IEE 10 No 2 2001 61 67 FERRERO A
13. d of Visual Engineering Environment an iconic programming language for solv ing engineering problems It also provides an opportunity to gather analyze and display data without conventional text based programming e TestPoint is a Windows based object oriented soft ware package that contains extensive GPIB instrument and DAQ board support It contains a novel state of the art user interface that is easy to use Objects called stocks are selected and dragged with a mouse to a work Journal of ELECTRICAL ENGINEERING VOL 55 NO 1 2 2004 area panel Logic flow is easily established with a point and drag action list TestPoint takes advantage of every Microsoft Windows features e Measurement Studio is a measurement tool for data acquisition analysis visualization and Internet connec tivity This development tool helps you build your test system by integrating into your existing Microsoft com piler Measurement Studio provides a collection of con trols and classes designed for building virtual instrumen tation systems inside Visual Basic or Visual C With Measurement Studio you can configure plug in data ac quisition boards GPIB instruments and serial devices from property pages without writing any code With user interface components you can configure real time 2D and 3D graphs knobs meters gauges dials tanks ther mometers binary switches and LEDs With powerful In ternet components you can share
14. endor However the user generally cannot extend or customize them The knobs and buttons on the instrument the built in circuitry and the functions available to the user all of these are specific to the nature of the instrument In addition special technology and costly components must be developed to build these instruments making them very expensive and hard to adapt Widespread adoption of the PC over the past twenty years has given rise to a new way for scientists and engi neers to measure and automate the world around them One major development resulting from the ubiquity of the PC is the concept of virtual instrumentation A virtual instrument consists of an industry standard computer or workstation equipped with off the shelf application soft ware cost effective hardware such as plug in boards and driver software which together perform the functions of traditional instruments Today virtual instrumentation is coming of age with engineers and scientists using virtual instruments in literally hundreds of thousands of appli cations around the globe resulting in faster application development higher quality products and lower costs Virtual instruments represent a fundamental shift from traditional hardware centred instrumentation sys tems towards software centred systems that exploit the computing power productivity display and connectivity capabilities of popular desktop computers and worksta tions Although PC and in
15. f analysis of measurement signals and presentation of data The concept of virtual instrument is frequently used in industrial measurement practice but not always with precisely the same meaning For some people virtual in struments are based on standard computers and repre sent systems for storage processing and presentation of Department of Measurement Slovak University of Technology Ilkovi ova 3 812 19 Bratislava Slovakia ISSN 1335 3632 2004 FEI STU Journal of ELECTRICAL ENGINEERING VOL 55 NO 1 2 2004 PROGRAM DEVICE DRIVER INSTRUMENTATION BUS BUS DEVICE 1 ee EE DEVICE 2 DEVICE n PROCESS Fig 1 Conceptual model of early computerized instrumentation ACQUISITION AND INSTRUMENT CONTROL SIGNALS PROCESSING OR ANALYSIS PRESENTATION Fig 2 The diagram of measurement process DATA PROCESSING DATA PRESENTATION Fig 3 The general conception of virtual instrument measurement data For others a virtual instrument is a computer equipped with software for a variety of uses in cluding drivers for various peripherals as well as analogue to digital and digital to analogue converters representing an alternative to expensive conventional instruments with analogue displays and electronics Both views are more or less correct Acquisition of data by a computer can be achieved in various ways and for this reason the under standing of the architecture of the measuring inst
16. ing computer technologies 3 3 Interconnect Buses Four types of interconnect buses dominate the indus try the serial connection serial port the GPIB the PC bus and VXI bus Serial port Serial communication based on RS 232 standard is the simplest way of using a computer in mea surement applications and control of instruments Serial communication is readily available via the serial port of any PC and it is limited in data transmission rate and dis tance up to 19 2 Kbytes sec recently 115 Kbytes sec 53 and 15 m and it allows only one device to be connected to a PC GPIB It was the first industry standard bus for connect ing computers with instrumentation A major advantage of GPIB is that the interface can be embedded on the rear of a standard instrument This allows dual use of the instrument as a stand alone manual instrument or as a computer controlled instrument Because of this fea ture there are a wide variety of high performance GPIB instruments to choose from The GPIB offers a flexible cable that connects a GPIB interface card in the com puter to up to 15 instruments over a distance of up to twenty meters The interface card comes with software that allows transmission of commands to an instrument and reading of results Each GPIB instrument comes with a documented list of commands for initiating each func tion Typically there is no additional software delivered with the instrument GPIB has a maximum data r
17. live measurement data among applications via the Internet SCPI Standard commands for programmable instruments SCPI is not a software tool as are former systems but it is an effective aid enabling easy standardised control of programmable instruments SCPI decreases development time and increases a readability of test programs SCPI provides an easy understandable command set guaran tees a well defined instrument behaviour under all condi tions which prevents unexpected instrument behaviour Although IEEE 488 2 is used as basis of SCPI it defines programming commands that we can use with any type of hardware or communication link It has an open struc ture The SCPI Consortium continues in adding com mands and functionality to the SCPI standard Real time and embedded control has been long the domain of specialised programs Advances in industry standard technologies including more reliable operating systems more powerful processors and computer based real time engineering tools are introducing new levels of control and determinism to virtual instrumentation This presents new opportunities for scientists to take on in creasingly sophisticated real time and embedded develop ment Software scales across development on the PC into development in real time and embedded applications Sci entists and engineers can move into new application areas without a steep learning curve because the software itself evolves to incorporate emerg
18. mputer network is not negligible due to the number of computers connected and the amount of com munications especially if a public computer network is used to realise the interconnections among the measuring processing units It seems that in the near future local network LAN can be considered as a kind of measurement bus from the viewpoint of measurement and control systems A typical example of such a system including various virtual instruments is presented in Fig 8 It can be considered as a first step to a wider Internet based technology In the last few years a surprisingly rapid growth of fast and reliable communication networks has allowed an easy interchange of information and commands between com puters both connected to local networks and connected to faraway site of wide area networks WAN such as the Internet Thus network services and programmable instrumentation now permit the development of measure ment laboratories distributed on a wide geographical area and simultaneously available to several users variously lo cated in the territory Common Internet based software can be used to pro vide easy data migration between various communication 55 pathways Multi computer processing systems are effec tive in creating complex systems by overcoming limita tions of a single computer concerned with the overall com puting power or the number of signals to be acquired and processed Standard software languages such
19. odules or instruments al controlled module is plug in DAQ board a2 controlled instrument is based on GP IB board a3 controlled instrument is connected via serial port a4 controlled instrument is VXI board or system b Graphical front panel with no physical instruments at all connected to the computer Instead the computer acquires and analyses the data from files or from other computers on a network or it may even calculate its data mathematically to simulate a physical process or event rather than acquiring actual real world data To the PC connections according to point a the fol lowing process measuring devices are attached Sensors GP IB instruments Serial instruments VXI instruments This structure is a result of international standardization allowing more freedom in using boards and instruments from various manufactures The main representative features of virtual instru ments describing their functionality are following Enhancing traditional instrument functionality with computers Opening the architecture of instruments Widespread recognition and adoption of virtual instru ment software development frameworks 3 BASIC COMPONENTS OF VIRTUAL INSTRUMENTS The basic components of all virtual instruments in clude a computer and a display the virtual instrument software a bus structure that connects the computer with the instrument hardware and the instrument hard ware
20. of Elec trical Engineering and Information Technology Slovak Uni versity of Technology now as Associate professor for Electric Measurement His research interests are in the area of com puter modelling and measurement of ESD pulse processes
21. performance instrumenta tion similar to that found in GPIB As a result much more compact measuring systems can be built There are three ways to communicate between the computer and the VXI bus instruments a The first method is by using GPIB In this case a GPIB to VXIbus converter module is plugged into the VXIbus mainframe and a standard interface cable con nects it and the GPIB interface card in the computer The advantages and disadvantages of this technique are very similar to a pure GPIB design This system tends to be easy to program but data speeds are lim ited to GPIB speeds However because the internal data speeds within the VXIbus mainframe can exceed 10 Mbytes s often a high speed application is solved by local high speed acquisition and processing occur ring within the mainframe and high level results trans fer to the computer over GPIB Figure 5 shows an ex ample of VXIbus system using GPIB b The second technique is to use a higher speed inter connect bus between the VXIbus mainframe and the computer The most common implementation of this is a high speed flexible cable interface known as MXIbus As in GPIB an MXIbus interface card and software are installed on the computer and a cable attaches it to an MXIbus to VXIbus converter module in the VXIbus mainframe MXIbus is essentially an implementation of the VXIbus on a flexible cable This means that the VXI Mainframe INST INST RAM INST CPU 1
22. rument becomes important A virtual instrument can be defined as an integration of sensors by a PC equipped with specific data acquisi tion hardware and software to permit measurement data acquisition processing and display A virtual instrument can replace the traditional front panel equipped with buttons and display by a virtual front panel on a PC monitor Virtual instruments are a 51 means of integration of the display control and central ization of complex measurement systems Industrial instrumentation applications however re quire high rates long distances and multi vendor in strument connectivity based on open industrial network protocols In order to construct a virtual instrument it is nec essary to combine the hardware and software elements which should perform data acquisition and control data processing and data presentation in a different way to take maximum advantage of the PC It seems that in the future the restrictions of instruments will move more and more from hardware Such a general conception of virtual instrumentation is presented in Fig 3 The vendor of virtual instrument can use the serial communication based on RS 232 standard or the parallel communication based on GPIB standard known also as HP IB IEEE 488 1 2 or IEC 625 1 2 PC bus or VXI bus VME eXtension for Instrumentation The main categories of virtual instruments a Graphical front panel on the computer screen to con trol the m
23. sonal com puters and workstations Software implemented can be divided into several levels which can be described in a hierarchical order Register level software Register level software requires the knowledge of inner register structure of the device DAQ board RS 232 in strument GP IB instrument or VXI module for entering the bit combination taken from the instruction manual in order to program measurement functions of the de vice It is the hardest way in programming The resulting program is strongly hardware dependent and it is rarely executable on systems with different hardware Driver level software One of the most important components in measure ment systems today is the device driver software Device drivers perform the actual communication and control of the instrument hardware in the system They provide a medium level easy to use programming model that en ables complete access to complex measurement capabili ties of the instrument In the past programmers spent a significant amount of time writing this software from scratch for each instru ment of the system Today instrument drivers are deliv ered as modular off the shelf components to be used in application programs Several leading companies formed in 1988 the Interchangeable Virtual Instrument IVT Foundation The IVI Foundation was formed to establish formal standards for instrument drivers and to address the limitations of the former approaches High
24. t in the industry and are allow ing users to develop capabilities unattainable using tra ditional instrument architectures Despite these changes however the measurement paradigm remains unaltered This might be the proper platform for the new develop ment The trend in virtual instrumentation increasingly inte grates the measurement systems into more complex moni toring and control systems distributed over different pos sibly geographically distant locations The remote in strumentation control is becoming popular since the net works have become reliable and world wide and almost every new instrument embeds programmable capabilities The past has shown that unless proper standards are available diversification due to ad hoc solutions will slow the progress in the field Thus it seems a proper chal lenge for the future to start thinking of standardization of virtual instrumentation and distributed measurement systems REFERENCES 1 CRISTALDI L FERRERO A PIURI V Programmable Instruments Virtual Instruments and Distributed Measure ment Systems IEEE Instrumentation amp Measurement Maga zine Sep 1999 20 27 2 BAICAN R NESCULESCU D Applied Virtual Instrumen tation WIT Press Boston 2000 3 GOLDBERG H What is Virtual Instrumentation IEEE Instrumentation amp Measurement Magazine December 2000 10 13 4 SPOEDLER H J W Virtual Instruments and Virtual En vironments IEEE Instrument
25. tegrated circuit technologies expe rienced significant advances in the past two decades it is the software that makes possible building virtual instru ments on this foundation Engineers and scientists are no longer limited by traditional fixed function instruments Now they can build measurement and automation sys tems that suit exactly their specific needs 2 THE CONCEPTION OF VIRTUAL INSTRUMENT Usually instrumentation manufacturers provide spe cific functions to given architecture and fixed interfaces for measuring devices and thus limit the application do main of these devices In actual use much time is required for adjusting the measuring range and for saving and doc umenting the results The advent of microprocessors in the measurement and instrumentation fields produced rapid modifications of measuring device technology soon followed by the appearance of computer based measurement techniques Conceptual model of early computerized instrumentation is given in Fig 1 A single user controls the system which runs exclu sively on a piece of hardware There is a single control structure which is formed by the combination of the user and the program that controls the multiple devices at tached to the instrumentation bus The main challenges are the device coupling and the programming models The measurement consists of three parts as shown in Fig 2 acquisition of measurement data or signals conditioning and processing o

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