C. G. Enke S. R. Crouch
-
F. J. Holler
Department of Chemistry Michigan State University East Lansing, Mich. 48824
H. V. Malmstadt
J. P. Avery
Pacific and Asia Christian University
Department of Chemistry University of lilinois Urbana, 111. 61801
Box YWAM
Kailua-Kona, Hawaii 96740
Instrumentation
Department of Chemistry University of Kentucky Lexington, Ky. 40506
Electronics,Instrumentation, and Microcomputers Principlesand Practicefor the MicrocircuitAge
Tiny and inexpensive integrated circuits now perform many functions that required full racks of equipment only a few years ago. The miniaturization and economies thus introduced have revolutionized the types of scientific instruments available commercially, the form and structure of instruments, and the modes of instrument maintenance and repair. It would seem likely that the suhject of scientific instrumentation, i.e., the body of knowledge and experience that supports the effective use and design of instruments, would also he profoundly affected. There are, in fact, several reasons why this should he so. First, the basic building blocks of electronic circuits have changed; a single integrated circuit (IC) now performs functions that earlier required dozens or thousands of transistors and other discrete components to achieve. Thus understanding of the functions or processes performed by ICs is now more relevant than comprehension of transistor characteristics or discrete circuit design. Second, ICs perform functions on data encoded in all three domainsanalog, time, and digital-and provide all possible conversions among these domains. Many recent domain conversion ICs utilize all three domains. The resulting mixture of domains used in most modern instruments makes the
earlier division of electronics into analog and digital less useful on the systems level. Third, ICs are incredibly inexpensive; the cost of the circuit board, connectors, power supply, and case usually exceeds the cost of the
ICs in an instrument by many times. This inversion of the economic factors from those of discrete device electronics has profoundly affected instrument design and maintenance practices, which suggests that a review of
14 13 12 I I IO 9 8
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1 2 3 4 5 6 7
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I
Figure 1. Integrated circuit The most popular package fw the integrated Circuit Chip is the dual in-line package (DIP) ShOwn hwe. The metal conlact ''legs" are on 0.1-in. centers in huo rows 0.3 in. apart. These me connected to the chip by finegold wires. The actual IC occupies a very tiny fraction of the total package velum. For mmt ICs, the packaging is also the majority of the cost
ANALYTICAL CHEMISTRY, VOL. 54, NO. 2. FEBRUARY 1982
367A
experiments and equipment for learning and design laboratories is in order. Fourth, large-scale integrated (LSI) circuits perform sophisticated operations such as analog multiplication, phase-lock detection, digital computation, active filtering, and correlation, to name just a few. These once-exotic techniques are no longer too expensive to be used in common instrumentation; therefore, their underlying principles are increasingly important. Fifth, the microcomputer has not only entered the scientific laboratory, but elements of microcomputer technology are being used in all kinds of instruments, from elegant spectrometers to pH meters. Computer operations and applications, along with digital data processing and control, are now an important part of the science of instrumentation. The nature and consequences of the impact of microcircuits on the principles and practice of chemical instrumentation are thus profound. Electronics is still an important tool, but the subject of instrumentation should no longer focus on electronic devices and circuits. The increased importance of understanding advanced data processing and control operations is fortunately counterbalanced by the decreased need to know the details of discrete level circuit design. Thus ICs allow and encourage a shift away from the “devices first” approach of traditional electronics presentations to a more “top-down” or function-centered conceptualization of modern instrumentation. Arguments for such a new perspective on electronics and scientific instrumentation are presented here along with a description of a learning system that demonstrates its practicality. The Functional Nature of Microcircuits
All the basic electronic circuit devices can be fabricated on the surface of a silicon chip and interconnected with vapor-deposited conducting paths to produce the amazingly powerful, compact, and inexpensive devices we call microcircuits or ICs. We rarely see the chips themselves, except in pictures. As shown in Figure 1,they are buried in a plastic or ceramic case that supports the chip and its connections. The first microcircuits were very expensive. I t was the rapidly growing consumer market that motivated progress on the technological “learning curve” and enabled the introduction of automated mass production. Even today, the first ICs of a given type are very expensive, but the price drops rapidly as the production quantities go into the thousands and millions. For economy then, the circuits that are integrated must be gen368A
erally useful; ie., they must accomplish a commonly desired function. As a result, we now have an extensive “library” of generally useful functions available in inexpensive IC form. At first, only very basic functions were produced in IC form-logic gates, flip-flops, and crude operational amplifiers-but that was a momentous beginning. Today, as a result of the increased sophistication of electronic products and improvements in IC technology, the level of circuit complexity available in IC form is astounding. Examples of small-scale integration (SSI), medium-scale integration (MSI), and large-scale integration (LSI) are shown in Figure 2. In these examples, and in all ICs, the IC is named for the operation that it performs. The package provides connections for the data input(s), the data output(s), and the power supply. Intermediate points in the circuit are not available unless contact is needed to some supporting component. The base diagram (pinout) does not indicate the circuit of an IC, but rather gives only the symbol for the operation performed. For SSI devices, a “circuit diagram” of the chip is sometimes given in data sheets provided by the manufacturer, but this is oftenjust an incomplete transistor circuit that is similar in design concept to the IC. For an MSI or LSI device, the only diagram provided is a functional or block diagram that shows the IC as a combination of SSI (or MSI) level functions. From a practical standpoint, then, the normal user cannot study the circuitry of an IC or even analyze how its function is achieved in terms of its circuit design. However, to appreciate the use of ICs in instrumentation, it is important to understand the nature of the functions performed and the performance limitations (appropriate signal levels, output limits, sources of inaccuracy, etc.). Furthermore, to implement an IC in a new or custom application, the practical considerations for its effective use (power requirements, loading, etc.) are also important. The pedagogical argument for the need to study the equivalent transistor circuit of an IC in order to understand and/or apply its function is reminiscent of early descriptions of transistor characteristics that began with the analogous behavior of vacuum tubes. Today, the functional building blocks of electronics are neither vacuum tubes nor transistors, but undissectable functional level integrated circuits. This has led to the classification of electronics circuits (combinations of ICs) by their function, i.e., the type of operation(s) performed. Starting at the high level of the operation performed, an application can then be
ANALYTICAL CHEMISTRY, VOL. 54, NO. 2, FEBRUARY 1982
explored to whatever level of detail is necessary. An example of this “top-down” approach to electronics is the operation of taking the integral of a signal. At the highest level, integration can be understood as a mathematical operation performed on the encoded quantity. On the level of the principles of electronic operations, digital integration with a counter involves a different set of principles from those for analog integration with a capacitor and operational amplifier. Finally, on the circuit level, the limitations of a particular analog integrator will depend on the electrical characteristics of the specific integrating capacitor and operational amplifier used. By contrast, the organization of traditional electronics books has often been based on the classification of devices according to their structure and characteristics. This forces one to enter the subject at the device level and work up through circuits to operations. If one is to develop a structure based on the operation performed, a useful classification scheme for the operations is required. Fortunately, there is one-the concept of data domains based on the ways in which data are encoded and transformed in electronic systems ( I ) . Digital, Analog, and Time Domain Microcircuits Information in an electronic instrument is encoded as some characteristic of an electrical signal. For example, the voltage from a photocell in a flame photometer is related to, and can be interpreted in terms of, the concentration of Na in the sample as illustrated in Figure 3. Each of the different ways data can be encoded is a data domain. A transformation from one domain to another occurs whenever there is a change in the characteristic by which the data are encoded. (There is always an associated change in the units of the encoding characteristic.) This provides a useful classification scheme because the number of domains by which data can be electrically encoded is limited. These domains fall into three categories: analog, time, and digital. Data in the analog domains are represented by the magnitude of one of four electrical quantities: charge, current, voltage, or power. The output signal of a pH electrode (voltage magnitude) or of a flame ionization detector (current magnitude) are examples of signals encoded in the analog domains. In the time domain, the information is encoded in the t i m e relationship of the signal variations, not in the amplitudes of the variations. For example, the rate of occurrence of pulses generated by a Geiger tube is related to the
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f
Small is better in LC, too. Tiny sample loops make short columns work better. Short,efficient HPLCcolumns packed with3-pm particles are beginning to appear on the scene. As you might guess, these small columns require small samples. In fact, if you want to get good resolution, you must often inject samples smaller than 5 microliters. And that's where Rheodyne lends a helping hand. Our new 7410 injector has precision sample loops of 0.5 pl, 1 pl, 2 pl and 5 pl.The four loop sizes help you cope with the inevitable trade-off between resolution and sensitivity. For higher resolution,a smaller loop. For higher sensitivity, a larger loop. The 10 to 1 range in loop size lets you approximate the optimum. The sample loops are so small they fit inside the injector, but-we hasten to add-they're still easy to interchange. In operation, loops are completely filled,
so you may inject repeatable sample volumes. And. for automatic operation, you can get the injector with a pneumatic actuator and a position-sensing switch. For more information on our Model 7410 injector contact Rheodyne, Inc..PO. Box996. Cotati, Calif0rl.i. 94928, USA. Phone (707) 664-9050.
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ANALYTICAL CKMISTRY. VOL. 54, NO. 2, FEBRUARY 1982
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inputs
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Flgure 2. Small-, medium, and largkscale integration The equivalent circuit 01 one 01 the four gates in a ~ ~ 7 4 Schonky ~ ~ 0TTL 0 NAND gate (an SSI device) is phorn in (a). Because the circuit exists on a slnple chlp. memodr of constructionand interwnneCtionare often used that cannot be representedexactly by C I ~ C Y ~ 01 I S intercmnecteddiscrete companents. The C t C U k of MSi devices w h as the magnihlde wmparata shown in (b) are not given; a ConneCtiM)scheme lw SSI gates that wwld perform Me equivalent flncticn is given. The pin diagam only idsntilie~ the input and owut connectim. F a LSI devices w h as the dual slope anal~todigitsl COnVeRBr ( A m ) ShQWn In IC). Me circuh is a cmbinatim 01MSI level functims. mi* circuit also demonmas ~m wmmm mixtured analoe. digital. and time dwnain operations in Um same IC. me pinout of the lntenil 7106 ADC IC, which also includes me readout driver circuits, is shown as an example. ReprinW horn Relerence 2. wilh permissim
370A
ANALYTICAL CHEMISTRY. VOL. 54. NO. 2. FEBRUARY 1982
l a k i n g Advantage of Low-Cost
Ftotmflux from
Microcircuits
F’hob n flux from ,No otonns
Mete1 indiiatlon
No concentmtion
Flgure 3. Data domains for a simple flame photometer
..-
The bold isbeis indicate the dala domains in the measvemnt process. ..m, photoCeii, and VOkmeter are imerdomain converters. The flame converls fhe concamations of Na and other sample species into related phaton fluxes. The finer selects the photm.enccded intormation relatedto fhe Na concarmation.me photocell con”& this data lo the voltage domain, *id, is converted by fhe vohmeter to me position of the paimer on the scab
level of radiation, The encoding quantity is the frequency of the pulses rather than their charge or current amplitude. Pulse-width and phase angle are additional examples of time domains. Digital domain information is contained in two-level signals (HI/ LO) that encode a specific integer. Thus, digital data are actually in numerical form. Since the desired result of a measurement is a number related to the measured quantity, measurements have alwaya been digital; the digitizing step used to he done manually. Many modem instruments use signals encoded in all three categories of data domains. The signals from input transducers (devices that convert chemical or physical quantities into related electrical signals) are often in an analog domain. One or more interdomain conversion ICs, such as analog-to-digital converters, convert this information to the domain of the output display. Signal-processing ICs, such as amplifiers or integrators, perform intradomain operations on the data. Thus, a very useful description of an instrument can then he made in terms of the interdomain conversions and intradomain processes that i t incorporates. Furthermore, all circuits and devices can he categorized according to the operation or transformation they perform. The data domains concept reduces the tens of thousands of electronic devices available today to a manageable number of categories and provides a high-level language for the description and analysis of complex instrumentation systems. There are many advantages to the early introduction of data domains in
the study of the electronics of instrumentation. It establishes at the outaet the relationship between digital and analog electronic techniques and allows the full range of modern measurement techniques to be introduced and used throughout the study. The outline of a text (2) and a lab experiment book (3) that follow this plan is given in Table 1. The order of topics is not a violent departure from recent practice, but the data operations or. ientation and top-down flavor are evident in several places. The basic foundation of data transformations among all three domains is completed relatively early, while all the important analog, time, and digital test instruments are introduced and conceptually explained. As the subject unfolds, techniques that involve mixed data domains like logic-controlled analog switches, monostable RC timers, and dual-slope ADCs fit in comfortably. The device-level topics of transistor amplifiers and logic families may be studied if desired, hut they are not prerequisite to later topics. On the other hand, it is very important to introduce the microcomputer, its involvement in modern “intelligent” instruments, and the elegant data-processing techniques that the microcomputer can provide. 4 corresponding laboratory follows the same outline. In fact, the order of topics was developed first in the teachingfiearning laboratory; only from its success there did the parallel text evolve. It is our experience that a topical sequence that works well in the lab can be an interesting and pedagogically sound basis for a text, but that many rationally organized texu do not support an effective laboratory.
The integrated circuit revolution has dramatically altered the economics of electronic system design. The I C costs in a system are now so low that they constitute less than 10?6 of the total system cost. In the period between 1959 and 1977 the per function cost of electronic circuits declined by a factor of 200 OOO ( 4 ) . As costs continue to fall, it is clear that IC costs will soon become a negligible fraction of total system cost. Unfortunately, there has been no similar revolution in connectors, packaging costs, mechanical components, power supplies, and other system components that support the electronic circuitry. Thus as IC prices have fallen, support component costs have assumed a larger and larger fraction of total hardware costs. A similar trend has ocurred in the reliability of electronic systems. As ICs have become more and more reliable, their failure rates have assumed a smaller and smaller fraction of total system failures, and the blame for instrument “down-time’’ has shifted toward mechanical components, power supplies, etc. Impact of Microcircuits in the Laboratory. The changing economics are having an increasing effect on scientific instrumentation in the research and teaching laboratories. The revolution in microcircuits has been accompanied by their incorporation into virtually every type of scientific instrument from balances to Fourier transform NMR spectrometers. Purchasers of scientific instruments are finding much more power and convenience available a t the same or lower costs than in the past. At the same time, the electronic functions performed on scientific data are becoming more and more hidden from the user, making it imperative that we study these operations and functions to ascertain their effects-desired and otherwise. Scientists who design instruments to perform “state-of-the-art” experiments need to take advantage of the capabilities and characteristics of the latest generation of electronics devices and transducers. The teachinghearning laboratory has thus assumed a central position for understanding the principles of the advanced measurement and control concepts now being used in laboratory instruments. A Laboratory Breadboarding Frame. T o he economical, it is necessary that a teachingfiearning lahoratory take advantage of inexpensive, high-volume circuits and test equipment developed for other (commercial) uses and that i t minimize the use of specialized (and thus low-volume) teaching equipment. Therefore, we
ANALYTICAL CHEMISTRY, VOL. 54. NO. 2, FEBRUARY 1982 * 371 A
with Nicolet's GC-IR. W e have optimjzed our FI-IX sys- in real time. The example presented tems to serve as bigblyspeciflc here is an auto and intelligent detectors for WS sophlstlclted w-fe~~ ~-caplllarygas~Utes. The Nicolet graphs. This combination of state-o the-art IR with state-of-the-art GC gives rapid soluuons to complex k Nkolets d chemical problems. The Nicolet GC-IR system is easy to use while shows a series of IR providing fully automated analysis real time as the CC run proceeds. capabiliues. This allows you to observe absorbOur newly designed GC-IR interance peaks during elution. In face has been optimally designed to photo, the spectral data are accommodate the small elution voland displayed at one second intervals. umes characterisuc of capillary GC Each spectrum is the sum o#four System versatility allows for the use of flexible fused silica WCOT columns as well as packed columns, SCOT columns, and WCOT columns. A makeup gas option is included for use mth WCOT columns to maintain their characteristic high resolution. EEicient linking of the GC column witt the infrared light pipe provides zeri dead volume, thus maintaining GC resolution. The versatility of the GC IR interface allows the user to Derform state-of-the-art chromato&aphy for solving any problem. A new&optimfzed iqfrared deecror
tbe lolo nanogram range. These instrument features, combined with an integrated GC-IR software package, provide truly exceptional analytical performance coupled with rapid and convenient experimental automation. Resu)esfrornanAutomatedGC IR Bun. From injection of sample to positive identificauon of compounds, the entire analysis can be fully automated. Once you've inje sample, rhe analysis prom information is plotted and
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Conclusion: N b l e t ' s GC-
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DIPENZOIHIOPHEWE 1 1656 HSJ 4889 IHlOXANTHENE I666 BSJ 286 1518 PROPANE. 1,3-DIIODO-. 287 131 52 BENZENESULFONIL CHLORlDl 289 YSGR 123 ETHANE. I,2-DIBRONO-. 291 E2E 5lb7 FLUORENE 278
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'Lutomatlc searrh wdlng. co-added IR spectra corresponding to each,GC peak in the peak table is searched against a vapor-phase data base. Ihe names of the "best hits" are listed, each with its Wtswesser notation and a numerical indicator of the closeness of the match. L.
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Table 1. Outline of Text, "Electronics and Instrumentation for Scientists" and Lab Book, "Experiments In Electronics, Instrumentation and Microcomputers" Chapter
N.rn
t
"Electrically Encoded Information"
Data domains. analog and digital meters
2
"Periodic Waveforms and the Oscilloscope"
Information in ac signals, reactance, ac meters, oscilloscope
3
"Power Supplies"
4
"Input Transducers and Measurement Systems"
5
"Operational Amplifiers and Servo Systems"
Rectification, filtering, regulation, batteries Measurement principles. gating. counting, time domain measurements, transducers %NO system concepts, follower, summer, integrator
6
"Programmable Analog Switching"
Switch types, response to transients, RC timers, analog sampling
7
"Solid-state Switches and Amplifiers"
Transistors, switching devicas, amplifier circuits
8
"Linear and Nonlinear Op Amp Applications"
Waveshaping, oscillators, active filters am modulation, lock-in amplifier
9
"Frequency, Time. and the Integrating DVM'
Universal counter, Schmin trigger, integrating DVMS. fin modulation
11
"Logic Gates, Flip-Flops. and Counters" "Digital b v i c e s and Signals''
12
"Microcomputers"
13
"DACs, ADCs, and Digital 110'
Gates, latches. flip-flops, counters. shin registers Logic families, output types, digital signal techniques Structure, numerical operations. memory, 110. peripherals, languages Ports, clocks, converters. systems
14
"Optimized Measurement and Control Systems"
to
have developed an efficient, practical, and inexpensive experimental patchwiring system that supports the experiments listed in Table 1. The patchwiring system uses commercially available solderless wire sockets called "breadboards" for wiring and testing the functions and systems being studied. T h e breadboard frame shown in Figure 4 connects readily to an inexpensive open frame power supply a n d supports five interchangeable hreadboard sockets o f the "SK-IO" type (E& 1. Instruments). T h i s frame can be easily constructed from readily available componenw (5).
374A
T*il IOPiS.
Signal-to-noise enhancement, rate measurements, control, optimization
M o d u l a r i t y is provided o n the level of the solderless breadboard socket. Power is provided t o t h e breadboard sockets through their connection t o the frame. T h i s same connector provides easy connection o f the hreadboard circuiw t o external signal sources such as function generatnrs a n d M external test instruments such a~ multimeters, oscilloscopes, a n d frequency meters. T h i s same arrangement allows the interconnection o f signals among the various breadboard circuits so t h a t complete systems can be neatly developed. Three categories of prearranged breadboard sockets (called "job
ANALYTICAL CHEMISTRY. VOL 54. NO. 2, FEBRUARY 1982
Lab t)xp+tlmenls
Breadboarding techniques. voltage, resistance and current measurements wil DMM, voltage divider and current splitter, loading errors Oscilloscope and function generator operations, low-pass and high-pass filters. ac measurements with the DMM Characteristics of diodes and transformers, rectifiers, filters, and regulators Frequency and period measurements, basic digital devices, counting. transducers Comparison measurements, op amp followers, current-tevoltage converters, inverters, summers, integrators and differentiators, op amp characteristics Transient RC response, RC timers. relays and solid-state analog switching, programmable gain amplifier, and digitalto-analog converter Bipolar junction and field-effect transistor characteristics, SCRs and TRIACs, switching speed, transistor amplifiers IDifference and instrumentation amplifiers, waveshaping. analog multiplier, active filters, tuned amplifiers and osciilators. lock-in amplifier Sounters, timers and frequency meters. charge-to-count, voltage-to-frequency, and dual slope converters, phase-locked loop q i c gates, latches, flip-flops, counters, counter gating. shin-registers .ogic families, open collector and tristate gates, digital signal conditioning ~ASICprogramming. execution time and speed. BASIC-machine language interfacc interrupts 10 ports. timers, DAC and ADC interfacing, sample-and-hold, data logger IUoise-reduction techniques, quantizing noise, multichannel averager and analyzer. boxcar integrator. Fourier 'ansfwms. aliasing, smoothing boards") are used in t h e system: 1) prewired boards t h a t p e r f o r m specific unaltered functions, such as logic level indication o r reference voltage generation; 2) IC j o b boards t h a t are loaded w i t h ICs a n d components, but have o n l y t h e power connections p r e w i r e d a n d 3) u t i l i t y j o b boards t h a t have o n l y power connections t o t h e power buses. T y p i c a l j o b boards f r o m categories 1a n d 2 are shown in Figure 5. T h e prewired j o b boards (such as t h e reference j o b board in Figure 5 ) are patchw i r e d once b y t h e instructor a n d n o t altered. Since h i g h function ICs are used, wiring is simple, a n d t h e resulting function boards are m u c h less
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ANALYTICAL CMMISTRY.
vm.
54, NO. 2. FEBRUARY 1982
3 7 5 ~
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Figure 4. Breadboarding frame In conjunction wilh an external power supply. me frame provider +5 V. *15 Y. and commn connections to as many as five breadboard cads plugged into its connectorr.Input and output from the cards we via live BNC ConneCtOrS and live pairs of banana jacks that allow ready connection 01 function generalws, oscilloscopes. digital multimeters. and other lest inshuments to the ICs on the cards. PC board tabs On each card mate with a FC board Smket on the interconnectionmother board to allow bussed signal and pawer Connections
........ ................ ............ .n--.
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Figure 5. Operational amplifier job board and reference job board The op amp job board (top) Contains three dual BlFET op amps. an adjustable ollsel op amp. a generalpurpose op amp. a Comparator, lour analog switches. and 10 precision resistors for op amp bpplicb lions. The referencejob board (bonom) Contains a crystal Oscillator and switch-selectable frequency divider. a voltage reference source that provides tour fixed voltages (t10 V. - 10 V. 1 V. -1 V) and two continuously variable voltages ( + l o to -10 V and +1 to - 1 V). a noise generator. and a dual BlFET ap amp lor summing signals with random noise
+
expensive than special-purpose printed circuit boards would be. With the preloaded IC job boards, students do all the patchwiring (except power connections) of inputs and outputs and interconnections of ICs. This saves student time and avoids damage to IC leads by insertion and removal. Prewiring power and common connections is more efficient and prevents mistakes that cause the IC to perform the “fuse” function. Minimizing the complexity of connections focuses attention on the functions rather than the wiring. Utility job boards are used for special “single-use’’ ICs, for awkward components (photocells, thermistors, and other transducers), and for special advanced projects. Altogether, 13job boards are used a t present in the system as shown in Table 11.For economy, some of the more advanced job boards, which are used only infrequently, can be shared among stations or reconfigured when new functions are needed. Seven job boards are needed frequently. A Complete Laboratory Station. A complete laboratory station consists of the breadboarding frame with its power supply and job boards, commercially available test equipment, and a microcomputer. All of this equipment, except for the breadboard frame (which must be assembled by the user) is standard hardware, available from competitive suppliers. A dual trace oscilloscope, a 3Y-digit digital multimeter, and a function generator (sine, square, triangle) are the standard test equipment. In addition a counterttimerlfrequency meter and a digital panel meter are constructed for each station from inexpensive evaluations kits (Intersil, Inc.). A complete lab station is pictured in Figure 6. The cost of each station, with careful purchasing, can he just over a thousand dollars (not including the microcomputer and the characteristic curve tracer mentioned below). The microcomputer is used for experiments in programming, interfacing, and data acquisition and processing. Since it is possible to avoid having all students do these experiments at the same time, a single microcomputer can serve a group of four or five stations. A microcomputer that satisfies the needs of the laboratory experiments is the AIM-65 computer available from Rockwell International. Its built-in printer, display, standard keyboard, and BASIC interpreter, as well as its user I10 port, give it all the essential functions at low cost. A characteristic curve tracer provides those who would like to learn the details of semiconductor device characteristics with an efficient way to obtain characteristic curves. One unit can be shared by many experimenters.
(continued on page 382 A )
ANALYTICAL CHEMISTRY. VOL. 54. NO. 2, FEBRUARY 1982
377A
What Is New In
If you answer"Yes"to these Htl
Zeeman Flame and Flameless A - A Spectrophotometer is your answer. Arc. y o u tired of rcLplacing a n d ali minx burners a n d furnaccxs w h c n you s w i t k back and forth from flame to flamdess? Are you tired of replacing, aligning a n d payin for burnt-out 112 lamps? Vkuld v o u like to cut the preparation time for high solid s a m c s such as blood, urine a n d oil by a s m u c a\ 80%? Does your baseline drift? Is i t noisy? Are o u using organic solvents? Couib vou use flame detection limits two t o five times better than you're n o w ge t t i n g? Would y o u like the flexibility of flame microsampling?
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K' ,,:
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Do you need com uterization for fast, easy programming angcomplete data processing? . For free literature or a demonstration on how Hitachi's Polarized Zeeman Flame and Flameless AA Spectrophotometercan solve all these problems for you, cqll or write Hitachi Scientific Instruments, 460 East Middlefield Road, Mountain View, California 94043.(415)969-1100.
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keep Sargent-Welch ahead in Infrared Sargent-Welch keep one step ahead in infrared. Yet again. The Series 3 led the way with ratio recording IR spectrophotometers. Then the recenlly introduced Series 3-080 Data Control Console brouoht new ~,~~ oower - and simplicity - to the IR speclroscopisl. Now Sargent-Welch has produced a new system that wili help identify unknown spectra more quickly and accurately lhan ever before. It is called the Library Search System. It consists of ~~
v
~~~
~
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sorted under applications headings, eg General Spectra. Coatings, etc, It allows you also to build up your own specialist library. The success of Library Search resuits laraelv from the innovative spectrum endoding aigorithms which are unique to Sargent-Welch. The algorithms neatiy allow compensalion for wavenumber shift or % transmission errors or ,
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We're instrumentalin your laboratory!
Flgure 6. Complete laboratory station The mmMne lsborpMv station ~imnd coo~kt4of an ~cIIk6cone. a IunctiOn rrmerator. e dhital multlmer. t h breadkwdlngfrm. a dlgiEBl panel meter.
Table 11.
Job Boards c-
N8nn
1.
Relermce
2.
Binary switch and Indicator
3. @amp 4. Basicgates 5. Flip-flop 6. Counter
7.
MSIgates
8. Advanced
getes Signal condltlonlng IO. Advanced analog circuits 11. power supply 9.
12.
Interface
13.
utlllty
and denrlp(lon
Rewired circuns: precision time base. noise generator, voltage reference sowce Rewired clrclrits: eight logic level debounced switches. two momentary debounced switches. 10 LED indicetws ICs: eight op amps, one comparator, one quad analog switch, two resistw arrays. ICs: basic l nlogic gates (seven ICs) ICs: flip-flops and 4-bit shifl register (six ICs) ICs and prewired display: two decade counters. latch and l-decade display ICs: magnnude comparator. adder. decoder, multiplexer. arithmetic logic unit ICs: CMOS gate, trisiate buffer. Schmin trigger buffer1 drlver. open collector NAND, LS NAND ICs: op amp, comparator, timer. mnostabie munivibrators, driver, relay. photoFET ICs: multiplier. active fiier. phaselocked Imp, op amps, lamp ICs and components: regulator. power diodes, zener diodes. liner components ICs: DAC. ADC, sampleaMold, monostable multivibrator. ribbon cable from computer 110 port Empty
Several inexpensive curve tracers that utilize an external XY oscilloscope are available commercially, some in kit form. N~~ instrumentation p,qore man
Electronics The microcircuit revolution necessitates a change in the teachinghearning laboratory. Because modern circuits come in fully functional IC packages, it is less important for the “normal” user to learn about semiconductor device physics, construction of amplifiera. amplifier biasing techniques, and several other topics that were impor-
tant with discrete transistors. (These topics are still of importance for those working with high-frequency electronics and high-power systems). It is our belief that the IC revolution should prompt two changes. First, there should be an emDhasis on the basic principles of measurement and control concepts, including voltage dividers, loading errors, RC filters and time constants, feedback control, null comparison measurements, etc. Because of the new microcircuits, these important principles need not be boring or taught without reference to their applications. The modern operational
*%?I ANALYTICAL CHEMiSTRY. VDL. 54, NO. 2. FEBRUARY 1982
amplifier, with its nearly ideal characteristics, provides an excellent vehicle with which to develop measurement and control concepts. Loading errors are dramatically and readily demonstrated with modern 31/2-digitmultimeten. Integrated circuit timers of the 555 variety provide a fascinating tool for learning about capacitor charging and discharging curves, RC time constants, and level comparison. The power supply regulator, the operational amplifier, and the phase-lock loop ideally illustrate the principles of feedback and its many applications in measurement and control. Integratedcircuit active filters superbly demonstrate the frequency response of RC circuits, the characteristics of resonant circuits, etc. These are but a few examples of the way in which highfunction ICs use and demonstrate basic processes and allow us to focus on the principles rather than the implementation. Second, the microcomputer and high-function ICs give us an exceptional opportunity for studying in a practical manner advanced instrumentation concepts, including signalto-noise enhancement as in Figure I, digital control as in Figure 8,correlation techniques, Fourier transformation methods, sampling and aliasing, and many other topics. Thus there is an increasingly strong need for an instrumentation course to include some statistics, linear systems analysis, control theory, noise and fluctuation phenomena, and computer science as in Figure 9. In our experience, these advanced instrumentation concepts need not be couched in mystique or advanced mathematics, and their omission leaves the student without the knowledge needed to properly operate a computerized data acquisition system as in Figure 10, or even a digital oscilloscope as in Figure 11.These important concepts and principles will (continued on page 386 A )
SARGENT-WELCI
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mplete titration curve Burets in four sizes can interchanged in seconds 0 All controls may be operated from a remote location 0 La e digital displays of pH or mV an mL of titrant clelivery 0 Can be rack m u on the lab bench To all this. add speed important, a high deg complete line of accessories including pH stat, recorders, and a constant temperature cell Send for our complete brochure or ask your nearest Sargent-Welch branch for a demonstration
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Palladiummagnified120 times
A five-Dart series Presented bv Chemical Abstracts Service
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Physical and Analytical Chemistry Chemical Abstracts Service has been reporting new findings from the world’s chemistry and chemical engineering literature since 1907. On our 75th anniversary, we salute a few of the many significant contributions to physical and analytical chemistry during the past 75 years. Abstracts are representative of the scientists’ work. 0
Marie Curie
Chandrasekhara Raman 0 Peter Debye
0
Discovery of Radium and Polonium CA2:230 CA4:1422
(1908) (1910)
Light Diffusion; Raman Effect
CA22:722 CA22:2311
(1928) (1928)
Dipole Moments and X-ray Diffraction
CA23:1789 CA24:4213 CA28:1922’ CA29:51411
(1929) (1930) (1934) (1935)
CA41:6128h CA65:19281 e
(1947) (1966)
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Harold C. Urey
Discovery of Deuterium
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Shin’lchiro Tomonaga
Basic Principles of Quantum Electrodynamics
For color reprints of all five photomicrographs used in this series, send $2.00 (postage and handling) to: Keys to Chemistry, Chemical Abstracts Service, Accounting Dept. CIP, P.O. Box 3012, Columbus, Ohio 43210 U S A . (Make checks payable to Chemical Abstracts Service.)
Llght Fuel Oil
Citric Acid
CHEMICAL ABSTRACTS
Triphenylmethane
KEY T O THE WORLD’S CHEMICAL LITERATURE
CAS ONLINE The Chemical Substance Search and Display System From Chemical Abstracts Service
0 1982 by the American ChemicalSociety
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Detergent
ANALYTICAL CHEMISTRY, VOL. 54, NO. 2, FEBRUARY 1982
Chemical Abstracts Service IS a division of the American Chemical Society.
SARGENT-WELCH SCIENTIFIC COMPANY, land. Dallas. Denver, D
I Signal I"
I Trigger I"
-
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~-
Flaure 7. Cornouter boxcar intearator ~
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A pogrammabletimer 1s used IOgenerate a variaoie delay between the trigger sigrai and the acqLisition of me sample. Thro-gh program c m o i a SPBC lid n-moet of -.es can 08 taken ai a n y given delay. tne delay can be scanned at the desiredrate. and the lime increment between poan18can ne varied. Repinted from Reference2. with permission
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lure 8. Dc motor controller with oosition encoder 3 mota speed and dirmion are contmiledby the CPU Ihrough the DAC. Clockwise (CW) rotations
- --
8se the canter to incremenl, and CwntercIOCkwise(CCW) &lions redme the cwnt. F a clockwise $ion. the LO HI Idark iiaMI. bl-r at the 0 FF occurs when 0 io HI. 60 Q is HI Imunt UDI. For counter&ckwise rotailon. 0 is LO (dark)when the LO HI lrigpr O C C U ~ , . M Q is LO and the counter revetses. The ending wheel JhOwn prodmes'two counts p r mtstion. The positin of whatever the mota is driving can be read horn the m m e r mntents wimin half a revolUtion of the mota shatt. ReprintedI r a n Retwence 2. wim permissfon
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Flgure 9. The structure of a basic digital computer Th+ cenbal processing uni acquiresand executes the instructions.The p w a m is *Wed in a section of rnemw reserved for that purpose. The CPU supwises COmrnuniCaIm along the shared date bur by using the address bus to specify the source or destination of the data. The program cwnter suppliesthe 86686s 01 the insbuctionto be executed. The conbol bus containsdata dirBCtion. timing. and special wntml signals. Reprinted fmm Reference 2, with permission
386A
ANALYTICAL CHEMISTRY, VOL. 54, NO. 2, FEBRUARY 1982
Data bus Addressbus Control bus
COPYRIGHT 1982.0FISHERSCIENTIFIC COMPANY
The NewAtomScan 2000 From Jmll-Ash. Feature for Feature, It's the Perfect Match for Today's Professional Chemist. At last,there's a sequential
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590 LINCOLN STREET WALTHAM, MA 02254 You're invited to see the AtomScan 2000 at Jarrell-Ash booths 401-413 a t the Pittsburgh ConfereFce. For more information, circle RSC #161. For a sales representative to call, circle RSC #162. 'bducuvely Coupled*rgon F7ruma.a Uademark of lamll&h
MUX
EN
Gain
Amp in prwmmming
EXT cap
Sample-and-hold
EN1 EN2 EN3
Digital out
Lord
Address in
strobe
-
Figure 10. Data acquisition system
mi6 hybri data acquisition system (Date1mAS-16) is also avalbble in an em&nnel dineremial input system (HDAS8). A HI LO Wansitm at Strobe ink tiales acquinilion and cmersim. Total acquisition and cmersion time is -20 ps. which glves a thraghput rate 01 50 kHz. Reprinted horn Relerence 2. with pmissh
Analog input
for computer. ete.
I
Figure 11. Block diagram of a digital storage oscilloscope
The amlog input s i w l is dgitizad and stwed in a nolwtate memay at a rate determined by me time base settings. The m e m w cmtent is then read out In wde, m (he y DAC fa on the CRT OT (mslowly) fw (he external recadsr autpn.The reahut can be repeated indefinitely. The x-axis dellecticm signal is obtained by amb -skm 01 the mhmoly addreop. Dam a q M t h in the dbltal oscillosmpe is synchonized wlth me input sQgnsl wavelam by using the s i m 10 -01 the memay address ccxnter. If me canter is runningmntinuousiy before b i w and poceedr 1 8 sW n a hdl munt alter the W l w . me memory will COntain a pewgger podm 01 the waveform. This vnique ability m b w anm me went canbe vw usalul. Repinted from Reference 2. with pmmisim
maser
remain relevant through many generations of electronic devices. There is indeed much more to modern instrumentation than electronics.
A Framework for t h e Future As we have seen, the invention of the transistor and ita evolution into integrated circuits have had a pro-
found effect on scientific instruments and thus on our work as scientists. As new techniques and capabilities are introduced into a discioline. its framework must be expanded to accommodate them. This exoansion is only suc. cessful until the old framework becomes too cumbersome and inefficient. Then a new structure, one that ~~~~~~~
~
takes advantage of unifying concepts on a higher level, takes its place. This is the way science traditionally responds to the geometrically increasing generation of new information and techniques. It is our premise that for the area of electronics in scientific instrumentation, the time for a new framework has come-a framework
(continued on page 393 A ) 388A
ANALYTICAL CHEMISTRY, VOL. 54. NO. 2. FEBRUARY 1982
COPYRIGHT 1981.0FISHER SCIENTIFIC COMPANY
THE FRIENDLY FORCE IN ELEMENTAL ANALYSIS
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runs periodic QC and limit checks, even Plus the unique Spectrum ShifterTM simplifiesmethods development by scanning across each wavelennth oosition.And it automatitally coGecis for background noise. What's best is the ICAP-9000 does all this and more at the mere tovch of a button. Forget which button to touch? Hit HELP for a complete onscreen instruction manual any time. No need to memorize commands. CIRCLE 164 ON READER SERVICE CARD
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ANALYTICAL CHEMISTRY, VOL.. 54, NO. 2, FEBRUARY 1982
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that can accommodate not only the dramatic advances in the recent past but can also provide a structure for future developments. In the teachinghearning laboratory, we must plan for the continued rapid introduction of new and higher level ICs. There is no sign that the technology has reached a plateau in this area. Therefore the experimental equipment should be flexible. Experimenter’s systems in which the hardware is committed to present-day devices (such as special-function circuit boards) encourage the use of these devices long after they are no longer the best choice. This is one of the reasons that all of the job boards in the experimenter’s system describkd above are “soft-wired.” When a better, cheaper, or easier-to-use IC becomes available for any function, the system can be easily altered to accommodate it. Thus the lab can remain current with no loss in hardware investment and with no dependency on a teaching equipment manufacturer. In the research laboratory, the adoption of a data-centered concept of the electronic parts of our instruments can help to restore or even enhance
C. G. Enke
S. R. Crouch C. G. Enke is a professor of chemistry at Michigan State Uniuersity, East Lansing, Mich. He obtained a BS degree from Principia College in 1955 and a PhD in chemistry from the Uniuersity of Illinois in 1959. Enke’s research interests include analytical instrumentation, mass spectroscopy, electroanalytical chemistry, applications of spectroscopic instrumentation, and mini- and microcomputers in chemical research. Stanley R. Crouch is a professor of chemistry a t Michigan State Uniuersity, East Lansing, Mich. He attended Stanford Uniuersity from 1958 to 1963 and receiued BS and MS degrees in chemistry. He receiued his PhD in 1967 from the Uniuersity of Illinois. Crouch’s research interests are in the areas of flame and nonflame AEI AAIAFspectrometry, analytical laser spectroscopy, emission spectrometry in sparks, arcs, and plasmas, molecu-
the rapport we once had with chemical systems under investigation. Many scientists now have a kind of lovehate relationship with their advanced instruments: They love their enhanced capabilities but are anxious about an increasing remoteness from the system being studied. As more data-processing and interpretation features are added to instruments, the loss of a “feeling” for the system and a personal involvement in the measurement processes could increase. Thus the very tools that provide increasingly powerful insights into nature are, for some scientists, becoming a barrier between them and their subjects. Trying to learn all the current electronic techniques and then trying to keep up with the flood of new devices is not an attractive alternative. The higherlevel nature of the data-centered approach can avoid this dilemma. The principles of data encoding, transformation, and processing will not be made obsolete by a new technology for their implementation. Indeed, the focus on data operations serves as a very effective way of categorizing and interpreting the functions of all new devices as well as a means of analyzing
H. Malmstadt
I
and explaining the latest instrumentation. All this ran be done without getting inco the detail level of electronic devices. From the higher level of data operations, technology is providing increasingly powerful and inexpensive tools to perform these functions. In this way, the focus stays appropriately on the science, hut the science now includes the principles of the data manipulations used in modern measurement systems.
References (1) Enke, C. G.Anol. Chem. 1971.43, 69-80 A.
(2) Malmstadt, H. V.;Enke, C. G.;Crouch,
S.R. “Electronics and Instrumentation for Scientists”; BenjaminICummings: Menla Park, Calif., 1981. (3) Holler, J. F.;Avery, J. P.; Crouch, S.R.; Enke, C. G. “Experiments in Electronics, Instrumentation, and M i c r w m puters”; BenjaminICummings:Menlo Park, Calif. 1981. (4) Blakeslee, T. R.“Digital Design with Standard MSI and LSI,” 2nd ed.; New York John Wiley & Sons, 1979. ( 5 ) The experiment book, Reference3 above. gives the construction details and parts needed. For information on the copyrighted printed circuit tab and frame boards, write Printed Circuits, P.O. Box 27315, Lansing, Mich. 48909.
F.J . Holler
lar absorption and fluorescence spectrometry, fast kinetics, reaction-rate methods of analysis, heteropolymolybdate chemistry, signal-to-noise ratio theory, theory of analytical measurements, theory and applications of photon counting in spectrascopy, automation of chemical measurements, and clinical analytical chemistry. Howard Malmstadt is professor emeritus of the Uniuersity of Illinois and uice-president of academic affairs a t Pacific and Asia Christian Uniuersity in Hawaii. He receiued his PhD in chemistry from the Uniuersity of Wisconsin in 1950, and for ouer 30 years has been inuolued in teaching and research in applied spectroscopy, analytical chemistry, and electronics and instrumentation for scientists. His recent research includes clinicall analytical automation and chemical methodologies, and he is helping to
J. P. Auery
deuelop a new type of uniuersity. F. James Holler is assistant professor of chemistry a t the Uniuersity of Kentucky. He receiued his PhD in analytical chemistry from Michigan State University in 1977. His research interests include theory and practice of reaction-rate methods of analysis, applications of stopped-flow techniques, conductometry, applications of computers to analytical chemistry, and chemical instrumentation. James P. Auery is an assistant professor of chemistry a t the Uniuersity of Illinois. He receiued his BS a t Michigan State Uniuersity and his PhD from the Uniuersity of Illinois. His research interests include computerbased instrumental systems, especially for reaction-rate methods of analysis,electrochemistry, spectrophotometry, and the deuelopment of systems and languages for the automation of analytical measurements.
ANALYTICAL CHEMISTRY, VOL. 54, NO. 2, FEBRUARY 1982
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