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Methodology for teaching measuring systems
Measurement Vol. 18, No. 4, pp. 237 244, 1996
PII: S0263-2241 (96)00063-2
ELSEVIER
Copyright©1996 Elsevier Science Ltd Printed in The Netherlands. Allrightsreserved 0263-2241/96 $15.00 +0.~)
Methodology for teaching measuring systems Wieslaw Winiecki Warsaw University of Technology, Institute of Radioelectronics, Nowowiejska 15/19, 00-665 Warsaw Poland
Abstract In this paper, a system approach to electrical measurement teaching is presented. This approach enables one to integrate different fields of measurements and different measurement courses. "Measuring Systems" is proposed as a main measurement course for students of Electronics Faculties. A multi-function laboratory stand for teaching measuring systems is proposed to train basic abilities in measuring system design. The stand consists of an IBM PC with an IEEE-488 (IEC-625) interface board, a bus tester, HP 33120A function generator, HP 34401A multimeter with IEEE-488 and RS-232 interface, and - - optionally - - a measurement plug-in card and a device with a VXI interface. Students are taught how to remote control, in a unifying way, various measuring devices with various interfaces, using simple IEEE-488 software and advanced software (LabWindows/CVI, HP VEE). The laboratory stand enables students to learn practical aspects of the design of measuring systems, teaching them the system approach to measurements. Copyright © 1996 Elsevier Science Ltd
Keywords: Measuring systems; Education
basic measurement instruments, elementary error analysis) and fundamentals of computer aided measurements. This paper is concerned with teaching automation of measurements. A course "Measuring Systems" (including lectures and laboratory exercises) is proposed as a main measurement course. It is based on a system approach to electrical measurement [1, 2]. This paper presents the essential idea of this approach, short characteristics of the course and a multifunction laboratory stand that supports teaching measuring systems.
1. Introduction Traditional developments in measurement science and technology consist mainly of increasing the accuracy and speed of measuring methods and instruments, but over the last decade traditional metrology has been changed by integration with information science, especially with computer techniques. This implied adding a new course, usually named "Measuring Systems" to higher engineering education. Usually these courses were just added and offered after basic measurement courses without their reconstruction. On the other hand, an explosion of technology has generated many new physical, chemical and biological sensors, m a n y new measuring instruments and measurement methods. Which part of this knowledge should be presented for students? And in what way? In the situation of fast changing technology, measurement education ought to cover: fundamentals of measurement techniques (measurement methods of basic electrical quantities, operation of
2. System approach to measurements A measurement can be considered as a procedure of getting desired information from a signal, called the measurement signal, and presenting it in a useful form, called the result of the measurement [ 3 ]. Any measurement signal can be characterised by its physical nature and the features of the 237
238
w. Winiecki
mathematical model assumed for its analysis. Any measurement may be considered as a sequence of elementary operations which consist of transforming such features of a signal as its physical nature, the set of values of the signal, the set of time values and the way of coding this information. Consequently, any measuring system can be considered as a set of functional blocks performing these elementary operations, operating as a whole, organised in order to accomplish the desired processing of measurement signal [ 1,4]. Any electrical measuring system can be composed of the basic blocks presented in Fig. 1 [1,2]. The essential idea of the system approach to electrical measurements is uniform treatment of measuring problems and/or instruments, which can be considered as special cases of a system whose functions are performed via signal processing [ 1]. The same approach can be applied to the growing number of measurement methods, corresponding measuring instruments and systems, using the same terminology. In this situation, different measurements can be treated as the same problem, which enables us to unify a hardware of measuring systems. Differences between various measuring systems amount only to the application of different sensors. A system for measuring various physical quantities can be presented by the same functional block diagram (Fig. 2). The functional block diagram of a measuring system can be independent of the technology that is applied to realise the system (Fig. 3). As we can see from Fig. 3, an intelligent sensor (smart sensor) and an instrument have the same functional structure as a measuring system based on an IBM PC (with a data acquisition plug-in card or with an external voltmeter). Thus, they can be treated, analysed and designed as a system. This approach can be also applied to each functional block, at any level of multilevel decomposition. Various blocks in general, are themselves subsystems composed of subsystems and elements. They employ a diversity of technologies [4]. In all these cases, independently of the applied technology, the designing of such a system includes: decomposition of the measurement task into functional blocks, analysis of the time and accuracy requirements for each block and synthesis of a
system using the blocks. Multilevel decomposition has to lead to getting the set of elementary functional blocks that can be made or that can be chosen (taken) from the thesaurus of ready to use blocks. Time and accuracy analysis consists in distribution of the signal transformation errors and delays between all functional blocks in such way that satisfies the total time and accuracy requirements for the measuring system. The analysis must take account of technological limitations. Synthesis covers connecting all the blocks into the measuring system (or subsystem) according to the chosen configuration and chosen interface (standard or non-standard), and also ensuring their control and communication (data flow). Is the uniform treatment of such measuring systems reasonable? Substantial advances towards the automation of engineering design of instrumentation, based on the application of new approaches arising from progress in computing, leads to integration of individual design tools into environments (for example LabWindows, LabView, HP VEE, TestPoint etc.). Design of measuring systems using these environments consists of creating virtual instruments/systems, by choosing icons from libraries, that represent real elements/blocks/ instruments and linking them into the system using a mouse. The same, graphical method of design is applied to create a program for the system; we can use graphical symbols of operations or extended menu. Thus, these new tools for computer aided design of measuring systems use functional blocks as a basis for design. System approach seems to be a natural basis for integration of different measurement cases. Such an approach would be helpful in teaching measurement and measuring instrumentation.
3. Group of courses related to basis measurement knowledge Which part of the basis of measurement knowledge do we have to choose for creating a new study program? Common blocks for all students of the Electronic Faculty should contain interdisciplinary elements in the program, reducing highly specialised topics which dominated over the pro-
239
W. Winiecki
CONVERSION OF PHYSICAL NATURE OF MEASUREMENT SIGNAL (e g. sensors, transdusers of linear and non-linear quantities, )
CONVERSION OF NUMBER INTO VOLTAGE (e g. D/A voltage converters, signal generators,
CONVERSION OF VOLTAGE OF MEASUREMENT SIGNALS INTO NUMBER ( e g AID voltage converters, voltmeters, )
:=.===============::==:::. ==:.t =
CONVERSION OF SUPPORT OF MEASUREMENT SIGNAL INTO NUMBER (eg time/frequency counters, )
t
~
~
CONVERSION OF NUMBER INTO TIME/FREQUENCY ( e g programmable time/frequency generators
/
CONVERSION OF DATA (eg. signal processors,
)
CONVERSION OF WAY OF CODING INFORMATION (e g interfaces)
I
) analog sygnals
~ digital information signals
~
~CONTROL
~|
digital organization signals COORDINATION OF MEASUREMENT OPERATIONS IN TIME AND SPACE (e g personal computers, ) Fig. 1. T h e f u n c t i o n a l blocks o f measuring systems.
SIGNAL GENERATORS
I
MEASURING SIGNALS
SENSORS
C
DATA ACQUISITION
DATA USER PROCESSING INTERFACE
ROL
Fig. 2, Functional diagram of a system for measuring various physical quantities.
R
)
240
W. Winiecki
a) IBM PC
SENSOR
IEEE*488 VOL1METERINTERFACE
IEEE-488 IEEE-488/uP-bus INTERFACEINTERFACE DSPcard
USER INTERFACE l
°°l°°
U S E R
I I C
(31-
MICROPROCESSOR
b) IBM PC
SENSOR
DATAACQUISITION card
DSPcard
U/D
D/D
USER INTERFACE l
u
H n
li,
1
CONTROL MICROPROCESSOR
U S E R
c) SMART SENSOR or INSTRUIVENT
SENSOR
USER : INTERFACE
VOLTAGE/DIGITAL converter
i
(DSP)
S E
CONTROL
R
MICROCONTROLER Fig. 3. Block diagrams of measuring systems -- examples of realisations using various technology. grammes realised in the last years. It should contain 4 groups of subjects: • Fundamentals of measurement techniques (measurement methods of basic electrical quantities, operation of basic measurement instruments, error elementary analysis); • Fundamentals of system approach to measurement;
• Basic standards in computer aided measurements; • Analysis of measured results. The first subject can be treated as an introductory course in the first semester. The next three subjects can be joined and included into one, main, measurement course named "Measuring Systems". This course integrates measurements of various
W. Winiecki
physical quantities and enables one to approach measurements in a unifying way. The course is based on the system approach to measurement, presented in the previous section of this paper. Uniform treatment of all measuring tools (smart sensors, microcontroller-based measuring units, measuring plug-in cards, measuring modules, instruments, computer-cased systems) as special cases of a measuring system is the starting point of the course. Based on the functional specifications of a system, the course concentrates on these problems that are common for different measurements. Basic problems concerning measurement technique, dependent on the present state of the art, are presented (functional blocks, system configurations, measurement buses, organisation and communication in a system, methods of data transmission). Decomposition of the measurement task and synthesis of a system using functional blocks is described. Specific problems of measurement automation are considered. Main interface standards (in particular the IEEE-488 standard) and software tools are described, indicating the physical, technological and economical limitations of presented solutions. Relations and connections between the software and hardware are shown. The course produces students with a general knowledge of automation measurement techniques and with the practical ability to design measuring systems based on IEEE-488 (IEC-625) interface. Furthermore, the methodology of experimental technique (designing a measurement experiment, its technical realisation and analysis of its results) is described. The course gives a framework of measurement problems, that can be described in detail in specialised courses. Thanks to such an approach, a set of specialist courses, which are offered for students of higher semesters, contains a natural extension of the problems outlined in the main measurement course, including samples of the realisation of systems and/or instruments.
4. Main idea of the measuring systems laboratory Knowledge presented in lectures is verified in a laboratory. Which practical abilities of the design
241
of measuring systems have to be taught in a student laboratory and in what way? Exercises can be divided into 2 groups: (a) basic exercises - - which enable us to examine the practical abilities for automation of measurements, (b) advanced exercises - - which present examples of experimentation techniques in various fields of electronics. The basic exercises should present typical problems of the automation of measurements, such as setting up a measuring system using functional blocks (interface problems, interface standards), communication between system devices (data transfer problems), and specific CAD tools for desig'fing a measuring system. A starting point in the group of basic exercises is uniform treatment of all measuring tools. A measuring system can be considered as a set of functional blocks (realised in various technologies) that perform a measurement task. Basic exercises should enable students to: • learn basic interface standards which are used in measuring systems, • design the configuration of a measuring system based on a PC as a system controller, • set a system using typical functional blocks, • design software for the configured system using simple software tools as well as advanced, integrated tools, • train and service the system using typical service tools. Basic exercises should be based on the software and hardware standards that are the most frequently used in the world. At present these are: (a) hardware standards: • PC-based controller with IEEE-488 (IEC-625) i~terface board (National Instruments, Hewlett-Packardt or RS-232 interface; • instruments with IEEE-488 (IEC-625) or RS-232 interface and VXI devices; • data acquisition plug-in cards: (b) software standards: • standard controller software based on popular programming languages, such as C, Pascal, Basic, supported by communication commands enabling us to send or receive
242
W. Winiecki
data to or from devices (e.g. National Instruments [5], Hewlett-Packard [6]); • IEEE-488.2/IEC-625.2 standard commands [7]; • SCPI standard commands [8]; • interactive environments [9], (e.g. LabWindows [10, 11], LabView [11], HP VEE [12]), that simplify development of systems to perform data acquisition, analysis, and presentation, • DSP software (e.g. Matlab). In designing a multi-function laboratory stand, all the above requirements should be taken into account.
5. General characterisation of multi-function laboratory stand
The multi-function laboratory stand for teaching measuring system is proposed to train basic abilities in measuring system design (Fig. 4). The stand consists of: • IBM PC with IEEE-488 interface board GPIBPCIIA (and NI-488.2 software), • HP 33120A function generator with IEEE-488.2 and RS-232 interfaces, • HP 34401A multimeter with IEEE-488 and RS-232 interfaces, programmed with SCPI commands,
IEEE-488-bus tester [13], LabWindows/CVI software environment, HP VEE software environment, Matlab (DSP software), and - - optionally - - measurement plug-in card and a device with VXI interface. The stand enables us to perform 6 laboratory exercises: (1) simulation of a measuring system, (2) control of an instrument via IEEE-488 bus using a simple tester without a computer, (3) control of an instrument via IEEE-488 interface using the National Instruments Basic or C language and SCPI commands, (4) control of instruments with IEEE-488 interface, RS-232 interface or - - optionally - - a measurement plug-in card and VXI device and using the LabWindows/CVI software environment, (5) DSP in measuring systems using LabWindows/CVI software environment or Matlab, (6) graphical designing of virtual instruments and measuring systems using HP VEE software environment. A group of 8 laboratory stands is placed permanently in the laboratory of "Measuring Systems"; it enables students to perform various exercises at the same time (each student may perform one of the six exercises). Students are taught how to • • • • •
Mea,,
plug.
Fig. 4. The block diagram of the multi-function laboratory stand.
W. Winiecki
perform remote control, in a unified way, using various measuring devices with various interfaces. These basic exercises enable students successively to learn how to simulate a measuring system, to control an instrument through the IEEE-488 bus using a tester and analysing all states of the IEEE-488 bus, to control measuring devices using C language and SCPI commands, to control a measuring system using LabWindows and H P VEE software environments. The experience acquired during one exercise is useful in the next one. For the first exercise only the PC is needed. Students have to simulate a measuring system. Simulation involves choosing a group of devices from a library, configuring them into a system and programming it using a set of simple instructions, where the IEEE-488 commands are included. As a result of the simulation, the states of all IEEE-488-bus lines are visualised during the work of the system. In the second exercise the multimeter and the tester are in use. The students' task consists of performing basic IEEE-488 procedures (i.e. Data Transfer, Serial Polling) using the bus tester, that enable us to set separately and watch the state of each of the IEEE-488-bus lines. Students have to send appropriate programming data and the trigger command to the multimeter and receive the measuring results from it using only the bus tester. The third exercise needs the multimeter and the tester (as in the second exercise) plus the PC, the generator and the interface board. Students need to configure a measuring system and design a program for the PC in C language using a set of National Instrument instructions (NI-488.2 software) to perform a set of measurements. In the fourth exercise the LabWindows/CVI Base Package, a measurement plug-in card and a VXI device are added to the equipment used in the third exercise. The students' task is the same as in the previous exercise, but the design tools are more advanced. They have to design a graphical panel and a program for the configured system using CAD tools that are available in the LabWindows/CVI Base Package. The instruments can be controlled via the IEEE-488 or RS-232 interface and via a microprocessor bus (plug-in cards).
243
The measurement data acquired in the fourth exercise are processed in the fifth exercise, when the Advanced Package of LabWindows/CVI or Matlab is available. Students get familiar with the Analysis Library and try to apply some of its functions to process the measurement data. Graphical designing of virtual instruments and programming of a measuring system using H P VEE is the subject of the last basic exercise. The task is the same as in the fourth exercise. Advanced exercises that present examples of experimentation technique in various fields of technology are performed using specialised stands.
6. Conclusion In this paper a new, systematic approach to electrical measurement education is presented. This approach enables one to integrate different fields of measurement. "Measuring systems" is proposed as a main, basic measurement course for students of Electronics Faculties. Based on a functional specification of a system and/or an instrument, it concentrates on these problems, which are common for different measurements. The course provides a framework of measurement problems that can be described in detail in specialised courses. The multi-function laboratory stand for teaching the measuring system is proposed for training basic abilities in the automation of measurements. The stand enables students to learn practical abilities for the designing of measuring systems (how to set a system using various blocks, how to perform remote control of various measuring devices with various interfaces, how to use simple and advanced software tools for designing a measuring system) teaching them the system approach to measurement. A set of various measuring devices grouped in one stand enables us to know various aspects of the automation of measurements.
References [-1 ] A. Barwicz, System approach to electrical measurement, in: Proc. IEEE Instrumentation and Measurement Technology Conf., Irvine, California, 1993, pp. 397-402.
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[2] W. Winiecki and K. Adamowicz, System approach to electrical measurement teaching, in: Proc. X I I I IMEKO World Congress, Torino, 1994, Vol. 1, pp. 29-33. [3] A. Barwicz, A system approach to electric measurement helps in understanding the measurement methods, IEEE Transactions on Instrumentation and Measurement 4 (1985) 525-528. [4] L. Finkelstein and A. Finkelstein, Advances in the automation of instrument systems design, in: Proc. X I I IMEKO World Congress, Peking, 1991, pp. 1293-1297. [5] IEEE-488 Interface Board Model GPIB-PC2, User Manual, National Instruments, 1994. [6] HP-85, User Manual, Hewlett-Packard, 1986. [7] IEEE Standard codes, formats, protocols and common commands for use with IEEE Std. 488.1-1987, IEEE Std.
[8] [9]
[10] [11] [12] [13]
488.2-1987, The Institute of Electrical and Electronics Engineers, Inc., New York, 1987. Standard commands for programmable instruments, The SCPI Consortium Publishers, La Mesa, CA, 1989. W. Winiecki, T. Galas, T. Szafranski and M. Wisniewski, CAD tools for measuring system design - - review of programs, Pomiary, Automatyka i Kontrola 5 (1995) 127-132 (in Polish). LabWindows, User Manual, National Instruments, 1992. NI IEEE-488 and VXIbus Control, Data Acquisition, and Analysis, Catalog, National Instruments, 1994. HP VEE 2.0 Visual Engineering Environment, User Manual, Hewlett-Packard, 1994. R. Leoniak and W. Winiecki, IEC-625 tester, in: Proc. VIH K K M Conf., Warsaw, 1995, pp. 305-306 (in Polish).
PII: S0263-2241 (96)00063-2
ELSEVIER
Copyright©1996 Elsevier Science Ltd Printed in The Netherlands. Allrightsreserved 0263-2241/96 $15.00 +0.~)
Methodology for teaching measuring systems Wieslaw Winiecki Warsaw University of Technology, Institute of Radioelectronics, Nowowiejska 15/19, 00-665 Warsaw Poland
Abstract In this paper, a system approach to electrical measurement teaching is presented. This approach enables one to integrate different fields of measurements and different measurement courses. "Measuring Systems" is proposed as a main measurement course for students of Electronics Faculties. A multi-function laboratory stand for teaching measuring systems is proposed to train basic abilities in measuring system design. The stand consists of an IBM PC with an IEEE-488 (IEC-625) interface board, a bus tester, HP 33120A function generator, HP 34401A multimeter with IEEE-488 and RS-232 interface, and - - optionally - - a measurement plug-in card and a device with a VXI interface. Students are taught how to remote control, in a unifying way, various measuring devices with various interfaces, using simple IEEE-488 software and advanced software (LabWindows/CVI, HP VEE). The laboratory stand enables students to learn practical aspects of the design of measuring systems, teaching them the system approach to measurements. Copyright © 1996 Elsevier Science Ltd
Keywords: Measuring systems; Education
basic measurement instruments, elementary error analysis) and fundamentals of computer aided measurements. This paper is concerned with teaching automation of measurements. A course "Measuring Systems" (including lectures and laboratory exercises) is proposed as a main measurement course. It is based on a system approach to electrical measurement [1, 2]. This paper presents the essential idea of this approach, short characteristics of the course and a multifunction laboratory stand that supports teaching measuring systems.
1. Introduction Traditional developments in measurement science and technology consist mainly of increasing the accuracy and speed of measuring methods and instruments, but over the last decade traditional metrology has been changed by integration with information science, especially with computer techniques. This implied adding a new course, usually named "Measuring Systems" to higher engineering education. Usually these courses were just added and offered after basic measurement courses without their reconstruction. On the other hand, an explosion of technology has generated many new physical, chemical and biological sensors, m a n y new measuring instruments and measurement methods. Which part of this knowledge should be presented for students? And in what way? In the situation of fast changing technology, measurement education ought to cover: fundamentals of measurement techniques (measurement methods of basic electrical quantities, operation of
2. System approach to measurements A measurement can be considered as a procedure of getting desired information from a signal, called the measurement signal, and presenting it in a useful form, called the result of the measurement [ 3 ]. Any measurement signal can be characterised by its physical nature and the features of the 237
238
w. Winiecki
mathematical model assumed for its analysis. Any measurement may be considered as a sequence of elementary operations which consist of transforming such features of a signal as its physical nature, the set of values of the signal, the set of time values and the way of coding this information. Consequently, any measuring system can be considered as a set of functional blocks performing these elementary operations, operating as a whole, organised in order to accomplish the desired processing of measurement signal [ 1,4]. Any electrical measuring system can be composed of the basic blocks presented in Fig. 1 [1,2]. The essential idea of the system approach to electrical measurements is uniform treatment of measuring problems and/or instruments, which can be considered as special cases of a system whose functions are performed via signal processing [ 1]. The same approach can be applied to the growing number of measurement methods, corresponding measuring instruments and systems, using the same terminology. In this situation, different measurements can be treated as the same problem, which enables us to unify a hardware of measuring systems. Differences between various measuring systems amount only to the application of different sensors. A system for measuring various physical quantities can be presented by the same functional block diagram (Fig. 2). The functional block diagram of a measuring system can be independent of the technology that is applied to realise the system (Fig. 3). As we can see from Fig. 3, an intelligent sensor (smart sensor) and an instrument have the same functional structure as a measuring system based on an IBM PC (with a data acquisition plug-in card or with an external voltmeter). Thus, they can be treated, analysed and designed as a system. This approach can be also applied to each functional block, at any level of multilevel decomposition. Various blocks in general, are themselves subsystems composed of subsystems and elements. They employ a diversity of technologies [4]. In all these cases, independently of the applied technology, the designing of such a system includes: decomposition of the measurement task into functional blocks, analysis of the time and accuracy requirements for each block and synthesis of a
system using the blocks. Multilevel decomposition has to lead to getting the set of elementary functional blocks that can be made or that can be chosen (taken) from the thesaurus of ready to use blocks. Time and accuracy analysis consists in distribution of the signal transformation errors and delays between all functional blocks in such way that satisfies the total time and accuracy requirements for the measuring system. The analysis must take account of technological limitations. Synthesis covers connecting all the blocks into the measuring system (or subsystem) according to the chosen configuration and chosen interface (standard or non-standard), and also ensuring their control and communication (data flow). Is the uniform treatment of such measuring systems reasonable? Substantial advances towards the automation of engineering design of instrumentation, based on the application of new approaches arising from progress in computing, leads to integration of individual design tools into environments (for example LabWindows, LabView, HP VEE, TestPoint etc.). Design of measuring systems using these environments consists of creating virtual instruments/systems, by choosing icons from libraries, that represent real elements/blocks/ instruments and linking them into the system using a mouse. The same, graphical method of design is applied to create a program for the system; we can use graphical symbols of operations or extended menu. Thus, these new tools for computer aided design of measuring systems use functional blocks as a basis for design. System approach seems to be a natural basis for integration of different measurement cases. Such an approach would be helpful in teaching measurement and measuring instrumentation.
3. Group of courses related to basis measurement knowledge Which part of the basis of measurement knowledge do we have to choose for creating a new study program? Common blocks for all students of the Electronic Faculty should contain interdisciplinary elements in the program, reducing highly specialised topics which dominated over the pro-
239
W. Winiecki
CONVERSION OF PHYSICAL NATURE OF MEASUREMENT SIGNAL (e g. sensors, transdusers of linear and non-linear quantities, )
CONVERSION OF NUMBER INTO VOLTAGE (e g. D/A voltage converters, signal generators,
CONVERSION OF VOLTAGE OF MEASUREMENT SIGNALS INTO NUMBER ( e g AID voltage converters, voltmeters, )
:=.===============::==:::. ==:.t =
CONVERSION OF SUPPORT OF MEASUREMENT SIGNAL INTO NUMBER (eg time/frequency counters, )
t
~
~
CONVERSION OF NUMBER INTO TIME/FREQUENCY ( e g programmable time/frequency generators
/
CONVERSION OF DATA (eg. signal processors,
)
CONVERSION OF WAY OF CODING INFORMATION (e g interfaces)
I
) analog sygnals
~ digital information signals
~
~CONTROL
~|
digital organization signals COORDINATION OF MEASUREMENT OPERATIONS IN TIME AND SPACE (e g personal computers, ) Fig. 1. T h e f u n c t i o n a l blocks o f measuring systems.
SIGNAL GENERATORS
I
MEASURING SIGNALS
SENSORS
C
DATA ACQUISITION
DATA USER PROCESSING INTERFACE
ROL
Fig. 2, Functional diagram of a system for measuring various physical quantities.
R
)
240
W. Winiecki
a) IBM PC
SENSOR
IEEE*488 VOL1METERINTERFACE
IEEE-488 IEEE-488/uP-bus INTERFACEINTERFACE DSPcard
USER INTERFACE l
°°l°°
U S E R
I I C
(31-
MICROPROCESSOR
b) IBM PC
SENSOR
DATAACQUISITION card
DSPcard
U/D
D/D
USER INTERFACE l
u
H n
li,
1
CONTROL MICROPROCESSOR
U S E R
c) SMART SENSOR or INSTRUIVENT
SENSOR
USER : INTERFACE
VOLTAGE/DIGITAL converter
i
(DSP)
S E
CONTROL
R
MICROCONTROLER Fig. 3. Block diagrams of measuring systems -- examples of realisations using various technology. grammes realised in the last years. It should contain 4 groups of subjects: • Fundamentals of measurement techniques (measurement methods of basic electrical quantities, operation of basic measurement instruments, error elementary analysis); • Fundamentals of system approach to measurement;
• Basic standards in computer aided measurements; • Analysis of measured results. The first subject can be treated as an introductory course in the first semester. The next three subjects can be joined and included into one, main, measurement course named "Measuring Systems". This course integrates measurements of various
W. Winiecki
physical quantities and enables one to approach measurements in a unifying way. The course is based on the system approach to measurement, presented in the previous section of this paper. Uniform treatment of all measuring tools (smart sensors, microcontroller-based measuring units, measuring plug-in cards, measuring modules, instruments, computer-cased systems) as special cases of a measuring system is the starting point of the course. Based on the functional specifications of a system, the course concentrates on these problems that are common for different measurements. Basic problems concerning measurement technique, dependent on the present state of the art, are presented (functional blocks, system configurations, measurement buses, organisation and communication in a system, methods of data transmission). Decomposition of the measurement task and synthesis of a system using functional blocks is described. Specific problems of measurement automation are considered. Main interface standards (in particular the IEEE-488 standard) and software tools are described, indicating the physical, technological and economical limitations of presented solutions. Relations and connections between the software and hardware are shown. The course produces students with a general knowledge of automation measurement techniques and with the practical ability to design measuring systems based on IEEE-488 (IEC-625) interface. Furthermore, the methodology of experimental technique (designing a measurement experiment, its technical realisation and analysis of its results) is described. The course gives a framework of measurement problems, that can be described in detail in specialised courses. Thanks to such an approach, a set of specialist courses, which are offered for students of higher semesters, contains a natural extension of the problems outlined in the main measurement course, including samples of the realisation of systems and/or instruments.
4. Main idea of the measuring systems laboratory Knowledge presented in lectures is verified in a laboratory. Which practical abilities of the design
241
of measuring systems have to be taught in a student laboratory and in what way? Exercises can be divided into 2 groups: (a) basic exercises - - which enable us to examine the practical abilities for automation of measurements, (b) advanced exercises - - which present examples of experimentation techniques in various fields of electronics. The basic exercises should present typical problems of the automation of measurements, such as setting up a measuring system using functional blocks (interface problems, interface standards), communication between system devices (data transfer problems), and specific CAD tools for desig'fing a measuring system. A starting point in the group of basic exercises is uniform treatment of all measuring tools. A measuring system can be considered as a set of functional blocks (realised in various technologies) that perform a measurement task. Basic exercises should enable students to: • learn basic interface standards which are used in measuring systems, • design the configuration of a measuring system based on a PC as a system controller, • set a system using typical functional blocks, • design software for the configured system using simple software tools as well as advanced, integrated tools, • train and service the system using typical service tools. Basic exercises should be based on the software and hardware standards that are the most frequently used in the world. At present these are: (a) hardware standards: • PC-based controller with IEEE-488 (IEC-625) i~terface board (National Instruments, Hewlett-Packardt or RS-232 interface; • instruments with IEEE-488 (IEC-625) or RS-232 interface and VXI devices; • data acquisition plug-in cards: (b) software standards: • standard controller software based on popular programming languages, such as C, Pascal, Basic, supported by communication commands enabling us to send or receive
242
W. Winiecki
data to or from devices (e.g. National Instruments [5], Hewlett-Packard [6]); • IEEE-488.2/IEC-625.2 standard commands [7]; • SCPI standard commands [8]; • interactive environments [9], (e.g. LabWindows [10, 11], LabView [11], HP VEE [12]), that simplify development of systems to perform data acquisition, analysis, and presentation, • DSP software (e.g. Matlab). In designing a multi-function laboratory stand, all the above requirements should be taken into account.
5. General characterisation of multi-function laboratory stand
The multi-function laboratory stand for teaching measuring system is proposed to train basic abilities in measuring system design (Fig. 4). The stand consists of: • IBM PC with IEEE-488 interface board GPIBPCIIA (and NI-488.2 software), • HP 33120A function generator with IEEE-488.2 and RS-232 interfaces, • HP 34401A multimeter with IEEE-488 and RS-232 interfaces, programmed with SCPI commands,
IEEE-488-bus tester [13], LabWindows/CVI software environment, HP VEE software environment, Matlab (DSP software), and - - optionally - - measurement plug-in card and a device with VXI interface. The stand enables us to perform 6 laboratory exercises: (1) simulation of a measuring system, (2) control of an instrument via IEEE-488 bus using a simple tester without a computer, (3) control of an instrument via IEEE-488 interface using the National Instruments Basic or C language and SCPI commands, (4) control of instruments with IEEE-488 interface, RS-232 interface or - - optionally - - a measurement plug-in card and VXI device and using the LabWindows/CVI software environment, (5) DSP in measuring systems using LabWindows/CVI software environment or Matlab, (6) graphical designing of virtual instruments and measuring systems using HP VEE software environment. A group of 8 laboratory stands is placed permanently in the laboratory of "Measuring Systems"; it enables students to perform various exercises at the same time (each student may perform one of the six exercises). Students are taught how to • • • • •
Mea,,
plug.
Fig. 4. The block diagram of the multi-function laboratory stand.
W. Winiecki
perform remote control, in a unified way, using various measuring devices with various interfaces. These basic exercises enable students successively to learn how to simulate a measuring system, to control an instrument through the IEEE-488 bus using a tester and analysing all states of the IEEE-488 bus, to control measuring devices using C language and SCPI commands, to control a measuring system using LabWindows and H P VEE software environments. The experience acquired during one exercise is useful in the next one. For the first exercise only the PC is needed. Students have to simulate a measuring system. Simulation involves choosing a group of devices from a library, configuring them into a system and programming it using a set of simple instructions, where the IEEE-488 commands are included. As a result of the simulation, the states of all IEEE-488-bus lines are visualised during the work of the system. In the second exercise the multimeter and the tester are in use. The students' task consists of performing basic IEEE-488 procedures (i.e. Data Transfer, Serial Polling) using the bus tester, that enable us to set separately and watch the state of each of the IEEE-488-bus lines. Students have to send appropriate programming data and the trigger command to the multimeter and receive the measuring results from it using only the bus tester. The third exercise needs the multimeter and the tester (as in the second exercise) plus the PC, the generator and the interface board. Students need to configure a measuring system and design a program for the PC in C language using a set of National Instrument instructions (NI-488.2 software) to perform a set of measurements. In the fourth exercise the LabWindows/CVI Base Package, a measurement plug-in card and a VXI device are added to the equipment used in the third exercise. The students' task is the same as in the previous exercise, but the design tools are more advanced. They have to design a graphical panel and a program for the configured system using CAD tools that are available in the LabWindows/CVI Base Package. The instruments can be controlled via the IEEE-488 or RS-232 interface and via a microprocessor bus (plug-in cards).
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The measurement data acquired in the fourth exercise are processed in the fifth exercise, when the Advanced Package of LabWindows/CVI or Matlab is available. Students get familiar with the Analysis Library and try to apply some of its functions to process the measurement data. Graphical designing of virtual instruments and programming of a measuring system using H P VEE is the subject of the last basic exercise. The task is the same as in the fourth exercise. Advanced exercises that present examples of experimentation technique in various fields of technology are performed using specialised stands.
6. Conclusion In this paper a new, systematic approach to electrical measurement education is presented. This approach enables one to integrate different fields of measurement. "Measuring systems" is proposed as a main, basic measurement course for students of Electronics Faculties. Based on a functional specification of a system and/or an instrument, it concentrates on these problems, which are common for different measurements. The course provides a framework of measurement problems that can be described in detail in specialised courses. The multi-function laboratory stand for teaching the measuring system is proposed for training basic abilities in the automation of measurements. The stand enables students to learn practical abilities for the designing of measuring systems (how to set a system using various blocks, how to perform remote control of various measuring devices with various interfaces, how to use simple and advanced software tools for designing a measuring system) teaching them the system approach to measurement. A set of various measuring devices grouped in one stand enables us to know various aspects of the automation of measurements.
References [-1 ] A. Barwicz, System approach to electrical measurement, in: Proc. IEEE Instrumentation and Measurement Technology Conf., Irvine, California, 1993, pp. 397-402.
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[2] W. Winiecki and K. Adamowicz, System approach to electrical measurement teaching, in: Proc. X I I I IMEKO World Congress, Torino, 1994, Vol. 1, pp. 29-33. [3] A. Barwicz, A system approach to electric measurement helps in understanding the measurement methods, IEEE Transactions on Instrumentation and Measurement 4 (1985) 525-528. [4] L. Finkelstein and A. Finkelstein, Advances in the automation of instrument systems design, in: Proc. X I I IMEKO World Congress, Peking, 1991, pp. 1293-1297. [5] IEEE-488 Interface Board Model GPIB-PC2, User Manual, National Instruments, 1994. [6] HP-85, User Manual, Hewlett-Packard, 1986. [7] IEEE Standard codes, formats, protocols and common commands for use with IEEE Std. 488.1-1987, IEEE Std.
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488.2-1987, The Institute of Electrical and Electronics Engineers, Inc., New York, 1987. Standard commands for programmable instruments, The SCPI Consortium Publishers, La Mesa, CA, 1989. W. Winiecki, T. Galas, T. Szafranski and M. Wisniewski, CAD tools for measuring system design - - review of programs, Pomiary, Automatyka i Kontrola 5 (1995) 127-132 (in Polish). LabWindows, User Manual, National Instruments, 1992. NI IEEE-488 and VXIbus Control, Data Acquisition, and Analysis, Catalog, National Instruments, 1994. HP VEE 2.0 Visual Engineering Environment, User Manual, Hewlett-Packard, 1994. R. Leoniak and W. Winiecki, IEC-625 tester, in: Proc. VIH K K M Conf., Warsaw, 1995, pp. 305-306 (in Polish).