Overview of a course on electronic instrumentation ... - IEEE Xplore

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IEEE TRANSACTIONS ON EDUCATION, VOL. 45, NO. 4, NOVEMBER 2002

Overview of a Course on Electronic Instrumentation Design for Senior Undergraduate and Graduate Students Ram M. Narayanan, Fellow, IEEE

Abstract—A course on Electronic Instrumentation has recently been developed at the University of Nebraska, which specifically emphasizes design aspects. The objective of the course is to expose senior undergraduate and graduate students to electronic as well as nonelectronic concepts concerned with instrumentation design and development. Topics covered include basic analog and digital circuits, filters and oscillators, linear and switching power supplies, low-noise techniques, signal processing, phase-locked loops (PLLs), transducers, grounding and shielding, thermal analysis, vibration analysis, electronic packaging, wiring and cabling, and engineering ergonomics. The course is intended to enable students to succeed as entry-level engineers in industry. Index Terms—Design, electronic instrumentation.

I. INTRODUCTION

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T IS GENERALLY accepted that a course on electronic instrumentation must cover both the basic principles of electrical and electronic circuits used in these instruments and the nonelectronic concepts required in their development and manufacture. Examples include thermal and vibration analysis of electronic equipment, electronic packaging, human factors, and engineering ergonomics. The process of engineering generally consists of the following sequential activities [1]: 1) conceive; 2) experiment; 3) design; 4) build; 5) test; 6) improve. The aspect of design is crucial. Design involves the meeting of specifications, ease of manufacture, simplicity of usage by the average user, the meeting of the established budget, and tolerance to changing external environmental factors. All factors must be considered to arrive at an optimum solution [2]. The necessary skills to engage in good design practices are, therefore, essential ingredients of any course on electronic instrumentation. A basic exposure to nonelectronic concepts will enable electrical and electronic engineering graduates to incorporate these ideas into their design, thereby making them more productive when they enter industry. It has been suggested that Manuscript received April 11, 2001; revised February 18, 2002. The author is with the Department of Electrical Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588-0511 USA (e-mail: [email protected]). Digital Object Identifier 10.1109/TE.2002.804394

imparting essential instrumentation and measurement (I&M) knowledge must produce engineers who are simultaneously all three of the following: generalists; specialists; and practitioners [3]. The standard pedagogical practice is to combine instruction in both I&M in courses on instrumentation. The emphasis in such courses is on measurement techniques using electronic instrumentation rather than the actual design of the instrument or the equipment. It is believed that although the “instrumentation” part of I&M has reached maturity, the “measurement” part of I&M is constantly evolving, and thus merits greater attention [4]. Few courses exist specifically for the sole purpose of educating students on factors involved in designing and building quality electronic instruments and equipment. Courses that cover essential nonelectrical topics are virtually nonexistent. II. COURSE OUTLINE AND DESCRIPTION In order to provide a unified understanding of all aspects of instrumentation design and construction, a course on Electronic Instrumentation was developed at the University of Nebraska. The course, ELEC 400/800, covers a mix of electronic and nonelectronic design concepts considered essential for entry-level engineering graduates. This elective course is primarily targeted toward senior undergraduate and graduate students in electrical engineering (EE), and graduate students in computer engineering, mechanical engineering, physics, and chemistry. In order to ensure that the non-EE students have the necessary background to succeed in this course, endorsement by their advisors or evidence of prior coursework or interest in electronics is required. The goal of the course is to provide students with an overview of components, specifications, and methods used in the design of electronic instrumentation. Applications of analog and digital devices to electronic instrumentation are studied. Topics include transducers, mechanical and solid-state switches, data-acquisition systems, phase-locked loops (PLLs), and modulation techniques. Special topics, such as grounding and shielding, thermal analysis, vibration analysis, electronic packaging, and human factors issues, are also addressed. Demonstrations with working circuits and systems are used to illuminate theoretical concepts, primarily in conjunction with the two-semester capstone Senior Design project sequence (ELEC 494 and ELEC 495). The Accreditation Board for Engineering & Technology (ABET) Category Content of the course is estimated as 1.5 credits (50%) of

0018-9359/02$17.00 © 2002 IEEE

NARAYANAN: ELECTRONIC INSTRUMENTATION DESIGN COURSE FOR SENIOR UNDERGRAD/GRAD STUDENTS

engineering science, and 1.5 credits (50%) of engineering design. The text by Horowitz and Hill [5] is used for the first two thirds of the course. Two other texts, one edited by Coombs [6] and the other authored by Fowler [7], are used as additional general references. Specialized references are used for specific electronic and nonelectronic topics, and these are listed in [8]–[16]. The course is organized into three sections of approximately equal duration. The three sections cover Basic Electronic Concepts (14 h), Advanced Electronic Concepts (14 h), and Special Topics (13 h), with an examination scheduled after each section has been taught.

A. Basic Electronic Concepts This section is primarily designed to review fundamental circuit concepts needed for designing basic building blocks in instrument design. Material covered in this section encompasses topics from sophomore and junior courses in circuits and their applications. Although the amount of coverage of basic concepts might appear excessive, the author has found from experience that the lack of retention of the fundamental concepts and the opportunity to reinforce these once again justify the coverage of the relevant material. The following topics are covered. 1) Foundations for instrument design (one class): Kirchhoff’s voltage and current laws, signal representation, passive components, passive filters and resonant circuits, and diode circuits. 2) Bipolar junction transistor (BJT) circuits (two classes): BJT characteristics, switches, amplifiers (common emitter, common base, and emitter follower), current sources and mirrors, push–pull configurations, bootstrapping, high-frequency models, and differential amplifiers. 3) Field-effect transistor (FET) circuits (two classes): Junction field-effect transistor (JFET ) and metal–oxide–semiconductor field-effect transistor (MOSFET) characteristics, current sources, amplifiers (common source, common gate, and source follower), FET switches, and switch circuits (multiplexers and sample-and-hold). 4) Operational amplifier circuits (three classes): Ideal operational amplifier characteristics, inverting and noninverting feedback configurations, current sources, differential amplifiers, logarithmic amplifiers, integrators, differentiators, comparators, Schmitt triggers, peak detectors, and instrumentation amplifiers. 5) Filters and oscillators (three classes): Gyrators, active filters, design of various filter types (e.g., Butterworth, Chebyshev, and Bessel), state variable filters, relaxation oscillators, oscillator noise, and design of inductance–capacitance (LC) oscillators (primarily Colpitts, Clapp, and crystal oscillators). 6) Power supplies (three classes): Fundamental regulator concepts, coarse regulator circuits, Zener diode regulators, regulation specifications, design of linear power supplies, switching power supply design, including both forward-mode and flyback-mode configurations.

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B. Advanced Electronic Concepts This section builds upon the material covered in the previous section and introduces relatively advanced level topics useful in a wide range of instrument designs. Much of the material in this section may have been covered in greater detail in courses at the junior and senior levels. The following topics are covered. 1) Low-noise techniques (three classes): Study of different types of noise (e.g., Johnson, shot, and flicker noise), signal-to-noise ratio (SNR), noise figure and temperature, noise models of BJTs and FETs, noise in differential and feedback amplifiers, noise parameter measurements, and bandwidth limiting techniques to combat excessive noise. 2) Digital circuits (three classes): Logic states, noise immunity, number codes, logic gates, transistor–transistor logic/complementary metal–oxide–semiconductor (TTL/CMOS) comparison, combinational circuits, and sequential circuits. 3) Analog-to-digital (A/D) and digital-to-analog (D/A) converters (two classes): Discussion of basic converter errors, D/A converter circuits (e.g., scaled resistors in summing junction, R-2R ladders), and A/D conversion techniques (e.g., parallel and flash encoders, successive approximation circuits, and single-slope A/D converters). 4) PLLs and applications (two classes): PLL basics, phase-detector configurations, voltage-controlled oscillators (VCOs), frequency multipliers, loop-gain calculations, and PLL applications (e.g., FM detection, AM detection, LC oscillators). 5) Transducers (two classes): Transducer basics; temperature measurements using thermocouples and thermistors; light-level measurements using photodiodes, phototransistors, and photomultiplier tubes (PMTs); displacement measurements using linear variable-differential transformers (LVDTs) and capacitive transducers; and frequency measurements. 6) Signal-processing techniques (two classes): Bandwidthnarrowing techniques, signal averaging and integration, and lock-in detection. C. Special Topics This section is primarily nonelectronic in nature and introduces students to certain essential concepts and ideas for the first time in their careers. Thus, these topics are expected to be generally unfamiliar to students. The following topics are covered. 1) Grounding and shielding techniques (three classes): Capacitive and inductive crosstalk, electromagnetic (EM) coupling and interference, cable wiring and harnessing considerations, differential-mode radiation, common-mode radiation, grounding considerations (e.g., equipotential ground plane concept, single-point grounding, and multipoint grounding), shielding theory and techniques, and shielding effectiveness computations. 2) Thermal analysis of circuits and subsystems (three classes): Cooling fundamentals, thermal resistance, heat conduction through materials and interfaces, fin

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efficiency, radiation, natural convection, and heat-sink calculations. 3) Vibration analysis of boards and subsystems (three classes): Vibration modes, vibration of simple electronic systems (e.g., cantilevered aluminum beams and transformers mounted on an aluminum bracket), transmissibility factor, dynamic displacement during resonance, printed circuit board (PCB) vibration considerations, and design of PCBs for vibration environments. 4) Electronic packaging and enclosure design (two classes): Basic structural design methodologies (e.g., rack-and-panel structures, equipment enclosures, and structural frames), chassis design factors, electronic assemblies, functional grouping considerations (e.g., serial-type circuits, series-parallel circuits, and parallel circuits), assembly design considerations (e.g., hinged chassis and fixed subchassis), wiring and cabling considerations, wiring procedures, cable routing, cable forms and wire harnesses, and safety considerations (e.g., safety grounds, shields, guards, and interlock switches). 5) Human factors and engineering ergonomics (two classes): Illumination considerations, control-display relationships, display considerations (with respect to optimal visual zones), color coding of indicator lamps, controls (e.g., switches, levers, and thumbwheel switches), control size and displacement criteria, labeling considerations (e.g., size and viewing distance), and maintainability considerations (e.g., access to internal modules, cables and connectors, chassis layout, and location of test points). III. EXAMPLES OF HOMEWORK AND TEST PROBLEMS Typical examples of sample homework and test problems are provided in this section. These examples are intended to provide an indication of the range and depth of material covered in the course. A. Amplifier Noise Figure Problem Statement: A 2N5087 transistor is used as an amplifier in the circuit shown in Fig. 1(a). Determine the noise figure of the entire amplifier configuration at 300 K when driven by a generator of 1-k source impedance. The frequency of operation is 1 kHz. Solution: First, the collector current is calculated. Using this value of collector current, the input-noise voltage density and the input-noise current density are read from the appropriate plots for the selected transistor. Taking into account the effect of the bias resistors (as referred to the input side), the input-noise voltage and current densities for the entire amplifier circuit are computed next. These values are then used to calculate the amplifier noise figure at room temperature. The result is 1.766 or 2.47 dB. B. Crosstalk Interference Problem Statement: Signal routing in an electronic assembly is accomplished using two-wire conductors of 0.75-mm radius spaced 10 mm apart. Two such lines, somehow brought in close

proximity, run parallel 3 cm apart for a significant length, as indicated in Fig. 1(b). The source circuit consists of a 10-V rms, 100-MHz generator, driving a 50- load. The load resistances in both circuits are 50 . Determine the total ac voltage induced on the receptor circuit. Solution: The total voltage induced on the receptor circuit is the phasor sum of the voltages induced because of capacitive and inductive crosstalk separately. The capacitive crosstalk is first calculated using the self-capacitance of each circuit and the mutual capacitance between the two circuits computed from the geometry. The result is 0.39 V. The inductive crosstalk is then calculated using the self-inductance of each circuit and the mutual inductance between the circuits, again from the geometry. 0.2 V. Thus, the total ac voltage This value is calculated as 0.2 V, which has an induced on the receptor circuit is rms value of 0.438 V. C. Thermal Resistance of Heat Sink Problem Statement: A heat sink made of aluminum is used to cool a power amplifier. Its cross section is shown in Fig. 1(c). The heat sink is 101.6 mm deep and is mounted with its fins vertical. The maximum allowable base-plate temperature is 80 C. If the power amplifier operates at a maximum ambient temperature of 20 C at an altitude of 3000 m above mean sea level, determine the maximum heat transferred by the heat sink by radiation and natural convection. Solution: The total heat transferred by the heat sink is the sum of the heat transferred by radiation and natural convection, with appropriate correction for the fin efficiency. The heat transferred by radiation is calculated first by taking into account the surface emissivity, the reduction factor as a result of close fin spacing for all surfaces, the surface area of each surface type, and the temperatures of the surface and the surroundings. A value of 21.9 W is computed for the heat transferred by radiation. The heat transferred by natural convection is calculated next by taking into account the surface geometry and orientation, the altitude, the total surface area, and the temperature difference between the surface and the surroundings. A value of 33.3 W is computed for the heat transferred by natural convection. Thus, the total heat transferred by radiation and natural convection (assuming a fin efficiency of 100%) is computed as 55.2 W. The fin efficiency is calculated as 0.98 for the fin geometry in the problem. Thus, the actual heat transferred is 54.1 W. D. PCB Vibration Analysis Problem Statement: A PCB of size 25 cm 10 cm is 1.6 mm thick. It is fixed firmly on all four edges. The total mass of components uniformly distributed over its surface area is 600 gm. The components are primarily leadless ceramic chip carriers (LCCCs) of approximately 3.5 cm length. Determine the maximum allowable externally induced acceleration (in g units) to keep the components from being damaged 1 g 981 cm/s . Solution: First, the PCB plate stiffness factor is calculated using the PCB material’s modulus of elasticity and the PCB thickness. Next, the natural frequency of vibration of the PCB is calculated from its dimensions, component density per unit area, the plate stiffness factor, and the manner in which the PCB is


(a)

(b)

(c) Fig. 1.

Supporting figures for problems described in the text. (a) Noisy amplifier circuit. (b) Crosstalk circuit and geometry. (c) Heat-sink geometry.

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(a)

(c) Fig. 2.

(b)

(d)

Photographs of laboratory equipment used for testing. (a) Network/spectrum analyzer. (b) Logic analyzer. (c) Digitizing oscilloscope. (d) A/D trainer pad.

fixed. The natural frequency of vibration yields the acceleration transmissibility factor. The total allowable PCB displacement under dynamic load conditions is then computed from the PCB dimensions, the type of components mounted on the PCB, and the weight distribution factor. By equating the total allowable displacement to the maximum displacement under dynamic load conditions, it is found that the PCB can withstand 3 g of externally induced vibration without damaging the components mounted on it. IV. CONCLUSION The course on Electronic Instrumentation, as described was successfully developed and taught to 80 students over five consecutive fall semesters. The author defines success by steadily increasing enrollments over the last five years and also by positive student evaluations. Although the material on the electronic concepts (covered in Sections II-A and II-B) were generally familiar to the students, the nonelectronic concepts (covered in Section II-C), even though unfamiliar, were greeted with enthusiasm. In addition to exposing students to a broad range of concepts and techniques essential for designing better electronic instruments, the course also provided students the opportunity to submit a number of design reports, rather than homework problems, through the semester. These reports were

expected to be professionally prepared, demonstrate a knowledge of design concepts, and explore worst-case scenarios and tradeoff analyses. Informal communication with some of the early students of the course, currently in industry, revealed that the course material was found to be extremely relevant in their new jobs and well-appreciated by their supervisors. Active consideration is being given to adding a one-credit laboratory course that can be taken either independently or in parallel with ELEC 400/800. Photographs of the equipment available in the Design Laboratory to carry out circuit and subsystem testing are shown in Fig. 2. The author is aware that the overall course material covered within a one-semester duration may appear to be excessive and demanding. However, it is emphasized that much of the material, including the special topics, are covered in breadth rather than in depth, mostly within two or three class periods. REFERENCES [1] W. H. Roadstrum, Excellence in Engineering. New York: Wiley, 1967. [2] Lord Hinton of Bankside, Engineers and Engineering, London, U.K.: Oxford Univ. Press, 1970. [3] J. L. Schmalzel, “I and M education for the new millenium: A U.S. perspective,” IEEE Instrum. Meas. Mag., vol. 2, pp. 31–36, Mar. 1999. [4] T. Laopoulos, “Teaching instrumentation and measurement in the complex systems era,” IEEE Instrum. Meas. Mag., vol. 2, pp. 28–30, Mar. 1999.


[5] P. Horowitz and W. Hill, The Art of Electronics. New York: Cambridge Univ. Press, 1989. [6] C. F. Coombs, Ed., Electronic Instrument Handbook. New York: McGraw-Hill, 1995. [7] K. R. Fowler, Electronic Instrument Design: Architecting the Life Cycle. New York: Oxford Univ. Press, 1996. [8] R. W. Rhea, Oscillator Design and Computer Simulation. Englewood Cliffs, NJ: Prentice-Hall, 1990. [9] J. D. Lenk, Simplified Design of Linear Power Supplies. Boston, MA: Butterworth-Heinemann, 1994. [10] M. Brown, Practical Switching Power Supply Design. San Diego, CA: Academic, 1990. [11] C. S. Walker, Capacitance, Inductance and Crosstalk Analysis. Norwood, MA: Artech House, 1990. [12] J. L. N. Violette, D. R. J. White, and M. F. Violette, Electromagnetic Compatibility. New York: Van Nostrand, 1987. [13] A. W. Scott, Cooling of Electronic Equipment. New York: Wiley, 1974. [14] D. S. Steinberg, Vibration Analysis for Electronic Equipment. New York: Wiley, 1988. [15] G. Shiers, Design and Construction of Electronic Equipment. Englewood Cliffs, NJ: Prentice-Hall, 1966. [16] B. S. Matisoff, Handbook of Electronics Packaging Design and Engineering. New York: Van Nostrand, 1982.

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Ram M. Narayanan (S’84–M’88–SM’91–F’01) received the B.Tech. degree from the Indian Institute of Technology, Madras, India, in 1976, and the Ph.D. degree from the University of Massachusetts, Amherst, in 1988, both in electrical engineering. From 1976 to 1983, he was a Research and Development Engineer at Bharat Electronics, Ltd., Ghaziabad, India, where he designed and developed microwave troposcatter communications equipment. From 1983 to 1988, he was a Graduate Research Assistant at the University of Massachusetts. In 1988, he joined the Electrical Engineering Department, University of Nebraska, Lincoln, where he is currently a Professor. He has more than 50 journal publications and more than 100 conference presentations to his credit. His areas of research interests include radar and laser remote sensing, image characterization and analysis, and wireless antennas. Dr. Narayanan served as the General Chairman of the 1996 International Geoscience and Remote Sensing Symposium (IGARSS’96) held in Lincoln, NB. He served as a Member of the Administrative Committee of the IEEE Geoscience and Remote Sensing Society from 1995 to 2000. He now serves as the Scientific Advisor to the joint National Aeronautics and Space Administration/Department of Transportation (NASA/DoT) Program in Remote Sensing.