REPORT FOR ANALYTICAL
CHEMISTS
Electronics and Instrumentation in Chemical Research H. V. Malmstadt and C. G. Enke The characteristics and operation of basic electronic circuits and their inte gration with other components to form chemical instruments can be learned r a p i d l y in a specialized l a b o r a t o r y course by those w h o a l r e a d y know the principles of spectrochemical a n d electrochemical measurements.
Τ AST SUMMER 12 research chem ists, each representing an indus trial or governmental chemistry laboratory, most with Ph.D. de grees and out of school 2 to 10 years or more, came to the University of Illinois for a special 3-weck course —an experimental course providing laboratory experience with elec tronic circuits and other instrumen tal devices especially useful to chemists. Significantly, the course was presented in the Chemistry De partment and taught by chemists from a chemist's point of view. The course itself is not new. It has evolved slowly at the Univer sity of Illinois over a period of about 10 years. It has existed since 1957 in its present form as a onesemester, one full afternoon per week laboratory course. The 1960 summer course was the first at tempt to present the same material in only 3 weeks, 15 working days. I t was given exclusively for chem ists already out of school, and the participants were required to know in advance the principles of spec trochemical and electrochemical methods of analysis. As might be expected, several of those who en rolled were experts in the applica tion of various methods. The individual reasons of these men for taking part in the summer course varied somewhat but in gen eral they were the same. The pri mary reason seemed to be the realization by both participants and their supervisors that the sci entist who would make the most of electronic instruments and measure
ments must be prepared to design his own instrumentation—or at least to know circuits of existing equipment, how to modify instru ments to accommodate new prob lems, and how to communicate with electronics engineers. These same considerations along with other rea sons provided the incentive several years ago to develop a specialized electronics and instrumentation course for our own chemistry grad uate students. The
Need
I t is discouraging to see research students waste weeks and even months of valuable time because of improper use of perfectly good tools or use of an inadequate tool. In too many instances considerable re search time goes down the drain only because the student does not know how to devise and connect a simple voltage divider, change the value of a condenser, or recognize and eliminate electrical noise. Comments from various research directors point out similar prob lems: how the accumulation of analytical data for a half year was useless because it was discovered that the measurement device was affecting the system under test; how a research project was side tracked after a large expenditure of time and money because commer cial equipment was inadequate to make necessary measurements— even though it might have taken only a few days to modify an exist ing instrument sitting unused in the same laboratory.
These problems and many others indicate an inability to make the most of the many instrumental de velopments which are multiplying so rapidly. Obviously it is desir able to fill the apparent void in the chemist's training so that the qual ity and quantity of his research may increase. Since the end of World War II, courses referred to as "Instrumental Analysis" have become widespread in colleges and universities, as both upper level undergraduate and graduate courses. In most basic principles of spectrochemical and electrochemical methods are emphasized. Laboratory experi ments are generally designed to il lustrate primary applications of
Figure 1 . containing posts
Modular metal chassis parts fitted with metal
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REPORT FOR ANALYTICAL CHEMISTS
methods and operation of the equipment. I n such a course the student learns how physical and chemical phenomena can be transduced into electrical signals and how the readings on a recorder, meter, lights, and dials are related to the chemical system being investigated. We have been enthusiastic for many years about the fine job these courses are doing at the University of Illinois in giving the student a good perspective of methods and operational experience with modern chemical instruments. Electronic circuits which augment, compare, integrate, separate, read out, or control transduced .signals are usually left undiscussed in a functionally ideal "black box." Some attempts have been made, as indicated by recent instrumental analysis books, to provide familiarity with specific circuits. However, we have found it difficult and often
DR. H. V. MALMSTADT Dr. Howard V. Malmstadt is an associate professor of chemistry at the University of Illinois. He was born in Marinette, Wisconsin, in 1922. He received his B.S. degree from the University of Wisconsin in 1943. Upon graduation he attended naval electronics and radar schools at Princeton, MIT, Bell Labs, and Pearl Harbor. From 1944 to 1946 he was radar officer for a division of destroyers in the Pacific, and upon returning to the States was supervisor for the Department of Electronics Fundamentals at the Naval Radar School on Treasure Island, California.
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confusing and inefficient to integrate significant experiments on circuits into the present instrumental course. After much thought and experimentation with lectures, special seminars, and laboratory sections, it was concluded t h a t the most effective and efficient way of overcoming the "electronics barrier" for chemists was with a specially designed laboratory course. The usual instrumental analysis course is considered a prerequisite for the circuits course. Specialized C o u r s e in Electronics and I n s t r u m e n t a t i o n
Unfortunately most chemistry students do not have time to t a k e all the important chemistry courses. Therefore, any new courses must be added with caution and require a minimum of time, which was set at one full afternoon per week for one semester.
After his war service he returned to the University of Wisconsin for graduate work and received an M.S. degree in 1948 and Ph.D. degree in chemistry in 1950. The following year he remained at Wisconsin as a post-doctoral research associate. He joined the faculty of the University of Illinois as an instructor in 1 9 5 1 , and became an assistant professor in 1954 and associate professor in 1957. He was a Guggenheim Fellow in 1960 during which time he studied and visited in European Universities. His major areas of research are in emission and absorption spectrochemical methods, precision null-point potentiometry, automatic derivative spectrophotometr y , potentiometric, amperometric, turbidimetric, and high frequency titrations, coulometry, and automation of analytical methods. He is the author or co-author of 50 technical publications. He was a recent president of the University of Illinois ACS section, and is faculty adviser for the chemical honorary Phi Lambda Upsilon. Dr. Christie G. Enke, an instructor in analytical chemistry at Princeton University, received his
The main objective was ambitious: to provide the chemist with a firm understanding of how, when, and where modern electronics, instrumentation, and automation can serve his needs by providing measurements a n d / o r control for chemical systems in research, development, or production. I t was considered possible to fulfill this objective by teaching (1) characteristics, design, construction, testing, and use of basic electronic components found in instruments used in chemical laboratories; 12) methods of combining basic electronic and mechanical components to perform important measurements and control chemical systems; and (3) important considerations in choosing equipment for chemical measurements and control and some possible modifications of commercial equipment for specific purposes and multiple applications.
DR. C. G. ENKE Ph.D. from the University of Illinois in 1959. While at Illinois he worked as a teaching assistant under Professor Malmstadt during the development of the electronics and instrumentation course. He taught the course during the summer of 1960 and has continued to take part in developing the experiments and writing the textual material. Dr. Enke was born in Minneapolis, Minnesota, in 1933 and received the B.S. degree from Principia College in 1955. He is a member of the A.C.S., Electrochemical Society, Bunsen-Gesellschaft, Sigma Xi, and Phi Lambda Upsilon.
Difficulties
Immediately we ran into three major difficulties. First, the backgrounds of graduate students varied tremendously. True, they all had courses in instrumental analysis, but some could not recognize a resistor or condenser and others had many years of electronics experience as radio hams or radar technicians during their military service. Second, it was difficult to make suitable reading assignments. The material we thought most important was generally buried with much unimportant material, and none of. it helped tie together various laboratory experiments with chemical problems. Third, available methods for connecting, testing, and changing circuits consumed so much time that it was impossible to complete experiments. Solutions t o the
Difficulties
Because of widely varying aptitudes and electronics backgrounds of the students, a lecture pitched at any level is almost sure to miss the mark for a good part of the class. Therefore, reading assignments, problems, and a brief discussion period were usually used instead of lectures. The readings tend to level backgrounds of the students; the discussion period, which precedes the laboratory, leads directly into the laboratory experiment. Considerable individual instruction is given, because there are one professor and one experienced graduate assistant attending the needs of the six students in each section. Advanced, alternative experiments are suggested for each laboratory, so that the student with a good electronics background can always work with circuits new to him. Reading assignments which have the proper balance between theory and application are difficult to find, but several of the Army and Navy technical manuals and electronics textbooks are fairly suitable. The discussion session is often relied on to bring out uses of a particular circuit in chemical instrumentation. Where appropriate readings cannot be found, lectures are given. During the last four laboratory periods of the course, informal lectures are given in component selection, noise
Figure 2.
Circuit parts with spring clip connectors
and grounding, logic, and the form and function of the complete instrument. In many cases material has been written by the authors for the reading assignment. It is hoped that soon all of the assigned reading will be written from the chemist's point of view and published in a single book for easy reference. In the spring semester of 1957 we devised and tested several circuit construction systems involving soldering, clips, banana connectors or spade leads, and binding posts. All systems had shortcomings either because time was wasted in constructing circuits or the circuit characteristics were not as good as when wired conventionally. Finally a breadboarding scheme was devised by the authors, which has subsequently proved to be completely satisfactory. It speeded construction and testing of circuits and enabled experiments to be completed in the desired time. • Figure 3. A two-stage amplifier wired with spring clip-binding post system Figure 4. Modular chassis on a laboratory desk which is completely outfitted with test equipment
REPORT FOR A N A L Y T I C A L CHEMISTS
side of a double chassis with these parts mounted. The inside posts of each terminal strip are connected to the adjacent banana sockets. Parts which would be ordinarily soldered to the posts are clipped to them instead. All resistors, condensers, connecting wires, and special parts have spring clips soldered at their lead ends.
N e w System of C i r c u i t W i r i n g
Connections are made to 1 / 8 inch-diameter posts with spring wire clips. All parts which are mechanically fastened to the modular metal chassis (tube sockets, potentiometers, tie points, banana jacks, and the connector to the power supply) are fitted with the posts. Figure 1 shows the under-
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Figure 2 shows an assortment of parts with the spring clips attached. Insulating sleeving is used to cover the lead wire. In the case of the resistors and condensers, the color of the insulating sleeving corresponds to the multiplier color of the color code. This aids in identifying components and learning the color code. A potentiometer with its posts, a transistor, and a miniature pulse transformer are also pictured in Figure 2. When the parts are clipped into place, they assume the same positions as in a conventionally wired and soldered chassis. A two-stage a.c. amplifier using a nine-pin miniature duo-triode tube is shown wired in Figure 3. The wiring is neat and uncluttered, parts are easily identified, and substitutions are easy to make. Four points in the circuit, usually the input and output connections, are connected to the banana jacks. The gain, noise, and frequency response characteristics of the amplifier shown were virtually identical to those of a similar amplifier which was wired and soldered in the conventional manner. Students can clip together a circuit in about one third the time required to solder that same circuit on a conventional breadboard. Spring clips shown in Figures 2 and 3 are not the ones first used. Original clips, shaped more like a hairpin, made excellent contact, but spread with use and twisted around on the post. Further, they would not support weight of larger condensers when the chassis was inverted. Brief experience with loop clips shown in Figures 2 and 3 has
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ANALYTICAL CHEMISTRY
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Figure 5. Arrangement of laboratory desks and individual test equipment
REPORT FOR A N A L Y T I C A L
shown that all these problems have been overcome, with some improve ment in quality of the contact. The
Equipment
When the wired chassis is in verted, it very much resembles a conventionally wired chassis. Con trols are on the front panel, tubes are upright, the power connector is at the rear, important points in the circuit are available on top of the chassis, and components are out of sight and shielded by the aluminum chassis. An upright chassis is shown in Figure 4 along with a completely outfitted laboratory desk. There are six such desks ar ranged three in a row, back to back as shown in Figure δ. Desks are ordinary office desks with an equip ment cupboard on top. The front door of the cupboard hinges down to provide a working surface on the desk top. Each desk contains a large as sortment of resistors, condensers, and clip leads, tools, potentiometers and tube sockets, connecting cables, chassis and panels, unregulated power supply, regulated power sup ply, vacuum tube voltmeter, oscil loscope, audio generator, multim eter, audio generator, resistance decade box, capacitance decade box, and a variety of components for special experiments. All equip ment and chassis are connected to gether with stackable banana leads. Special signals and power can be supplied to a panel at each of the desks through a panel at either end of the row of desks.
S'S
CHEMISTS
demonstrates errors of measurement due to circuit loading, frequency re sponse, and other characteristics of the measurement device, and serves as an introduction to the wiring system. II. D.C. Power Supplies. Recti fication and filtering are key points of this experiment. The unregu lated power supply is modified to demonstrate half-wave rectifica tion. Various filters are wired and their regulating and filtering char acteristics determined. III. Amplification. A triode, pentode, and transistor are wired as one-stage amplifiers. All three amplifier configurations are investi gated. Effects of various compo nents on characteristics of the amplifier and deviations from the ideal linear amplifier are observed. IV. Amplifiers. A two-stage a.c. amplifier is wired using soldered connections. This acquaints the student with soldering technique and allows use of the amplifier in subsequent experiments. Noise, gain, frequency response, and maxi mum undistorted output are meas ured. V. Oscillators. A Colpitis oscil lator circuit is wired. Frequency is compared with theoretical value, and effects of loading are deter mined. Necessary conditions of feedback and loop gain are stressed. Wiring of a simple gated-sweep generator illustrates generation of a ramp function.
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The Experiments Experiments performed in the laboratory have been modified and rearranged several times and are still being refined. In every experi ment emphasis has been placed on the characteristics and practical use of the circuit. The following experiments were performed during the most recent offering of the course: I. Electrical Measurements. The current meter is used for basic elec trical measurements. The multim eter, vacuum tube voltmeter, and oscilloscope are used to measure various signals. The experiment
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Figure 6. Servo motor coupled to a ten-turn potentiometer and dial
Circle No. 69 on Readers' Service Card VOL.
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REPORT
Figure 7 . Chopper, amplifier, and potentiometer drive system for servo equipment
VI. Comparison Measurements. E m p h a s i s is placed on increased ac curacy of measurements in which the unknown is compared with a standard. Using a W h e a t s t o n c bridge, various d.c. null detectors are tested. A chopper and meter arc added to the amplifier con structed in experiment I V to m a k e a very sensitive d.c. null detector. Characteristics of an a.c. bridge and use of an oscilloscope as an a.c. null detector are also demonstrated. VII. Servomechanisms. A V a r ian recorder driver-amplifier and pen-drive motor have been wired p e r m a n e n t l y on a chassis. As shown in Figure 6, the servomotor is belt- and gear-coupled to a po tentiometer and a 10-turn Helipot dial. Any potentiometer with a quarter-inch shaft m a y be driven by the servomotor a t a n y one of three speeds. Each desk is equipped with one of these servos. A d.c. error signal is converted to a.c. with a chopper. T h e amplifier built in experiment I V amplifies the error signal to feed to the driver amplifier. This servo system has been used as an indicating poten tiometer, for current and voltage control, and for integration. C h a r acteristics of noise, dead zone, speed, and damping as functions of phase and sensitivity are easily demonstrated with this unit. Fig ure 7 shows the chopper, amplifier, and potentiometer drive m e c h a n ism. VIII. Regulated Power Supply. A power supply regulator circuit is used to illustrate the principles of electronic feedback control. The regulator controls output of the u n regulated power supply used in ex periment I I . Line and load regula tion and o u t p u t noise arc deter mined.
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REPORT FOR ANALYTICAL CHEMISTS IX. Analog Circuits. Philbrick operational amplifiers illustrate the many applications of operational amplifiers in electrical measurement and control. T h e d.c. level of the operational amplifier is stabilized with a chopper amplifier u s ing t h e a.c. amplifier built in experiment IV. T h e stabilized operational amplifier is used to add voltages, integrate a voltage with r e -
spect to time, a n d provide a constant current. Other applications are pointed out. X. Wave Shaping. T h e effect of resistance-capacitance circuits on various wave shapes is determined. In addition, diode circuits are used to perform the functions of clipping and clamping. XI. Binary Circuits. T h e wave forms a t various points in a bistable
binary circuit are observed. A transistor astable multivibrator is wired and its characteristics are determined. A monostable multivibrator is wired and used to control the gated sweep circuit which was wired in experiment V. X I I - X V . Projects. Four labor a t o r y periods are spent on special projects of t h e student's choice. I n some cases useful components such as pulse or sweep generators or decade counters are built, using soldered connections a n d permanent construction. I t is hoped t h a t as more a n d more electronic components are constructed and more optical and mechanical components become available, it will be possible to p u t together rather complex chemical instruments during this phase of the course. T h e experience of putting together a combination of circuits which have not been pretested proves to be an exciting experience for even our most a d vanced students.
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ANALYTICAL CHEMISTRY
Our students in the regular semester course tell us t h a t they have gained a working ability and understanding of circuits t h a t help them considerably in their research. Success of the 3-week summer course is probably best indicated by the inquiries already received asking about next summer's course— even though the course has not y e t been announced. One research director recently wrote t h a t his organization was so impressed with the benefits received b y its m a n t h a t it would like to send one or two more men to the course next summer. Reports from other companies with participants last summer have been equally compliment a r y and encouraging. We feel t h a t we have a sound and effective system for presenting electronics and instrumentation to chemists. W e know there are still some bugs in the course, b u t we are now building on a firm foundation. We see dozens of ways of improving reading material, experiments, and components used to construct more complex a n d interesting chemical instruments for the projects.
