edited by JAMES P. B~RK Arizona State University. Tempe. AZ 85281
An Integrated Workstation for the Freshman Laboratory John R. Amend. Ronald P. Furstenau, Reed A. Howald, B N C ~E. Ivey, and Kathleen A. Tucker Montana State University, Bozeman, MT 59717 The recent availability of high-performance, low-cost personal computers makes possible a significant increase in quality of iemning, cost-effectiveness;and time utilization in science teaching in colleges and secondary schools. For about the price of two good pH meters, a student laboratory station may be equipped with a personal computer and a research-quality laboratory data acquisition interface that will provide all of the instrumental data acquisition and analysis required in most chemistry and physics courses. The potential for increased student involvement in experimental science is large. The Role of Computers In Chemistry Labs Computers have had a role in chemistry instruction for more than 20 years. From the time terminal access to a mainframe hecame affordable, computers have been used for tutorials, for drills, and for diamostic quizzes, as well as t in personal for record keeping and grading. ~ & e n progress computing has made computing power equivalent to a mainframe of several years ago an affordable component of a student laboratory workstation. Two vears aeo our denartment was in the uniaue oosition of haviig s t u d k t funds available t o purchase c o m p h r s a t the same time we had some state funds for Iaboratorv e a u b ment. Our freshman labs serve about 1500 studengwiih 60 lab stations. Faced with the prohibitive cost of purchasing 60 p H meters, 60 calorimeters, 60 Geiger counters, etc., we decided to design and construct 60 integrated laboratory data acquisition workstations, built around 512 K IBMcompatible personal computers. Our total cost was less than havedecreased to the ~ 1 5 6 0 p ew~rkstation;computercosts r point that the workstationdescribed in thisaniclecan today be assembled for less than $1200. The Role of the Integrated Laboratory Workstallon: Activity in an instructional laboratory can be divided into three categories: individual student work. demonstration. and experikentation (Table 1). There is a component corn: mon to all of these tasks; they all involve recall, presentation, and/or processing of information. Sometimes this role is served by a printed page that provides the instruction set and data for student analysis. Sometimes i t is provided by a pocket calculator, graph paper, and a pencil. Sometimes i t is provided by electronic circuits which perform a specific function, such as converting a voltage from a pH electrode to a meaningful number on a display. A personal computer, however, can perform all of these information management tasks rauidlv and cost-effectivelv. ~ltho&h-weand others are working on cnmputerapplications in all three areas listed in Table 1, this article will deal specifically with Montana State University's effort in student data acquisition and analysis.
Figure I. Recent decline in the cost of personal cmputers makes highperformance data acquisition workstations affordablefor lower division labs. Optional presentation of information in large graphic numbers makes the workstation a versatile demonstration device as well.
Table 1. lnlorrnallon Proceulng Tasks Involved In Laboratory Instructlon-A Personal Cornouter Can Perlorrn All of These Tasks Rapldly and Cost Effectively Individual Student W a k Tutorials Drlil exercises Diagnostic Quizzes Keeping student performancer e d s Demonstration Simuiation of experiments Wo difficult,expensive or dangerous f a students to perform Laboratory Experimemation Experiment Chesign Data acquisition Analysis of student data
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Hardware for Data Acqulsltlon The role of a laboratory instrument is simple: to interact with a physical or chemical quantity of interest, and to transfer information concerning this quantity to a student or scientist. All laboratory instruments use the same structural design to accomplish this task. A measurement-specific detector interacts with the auantitv of interest.. nroducine" a small electrical signal related to tl;e magnitude of this quantity. This signal, usually analngue, is conditioned by simple
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Instrument S y s t a m
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Table 2.
Performance Speclltcatlons for the MSU Lab Interface
Accuracy: Programming: MBBSmmeW F~nction8: Temperature pH Voltage Current
Counts Time
13 bit. 1 paR in 8192 Menudrive", for ease of use by nonprogrammers. -20 to 150°C, resolution 0.01 OC at20°C 2-12 pH. resolution 0.02 pH units i 2 . 5 V, resolution 0.6 mV Four ranges, from i 2 . 5 microamperesto i 2.5 mA Resolution 6 X A TWOrwisters, one of 65.535 and one of 4 X l o 9 Four timers, 10Oms time base, ranges to 298 days.
Figure 2. Laboratory instruments all have the same structural design. A personal computer w n pmvidethe generic components of this system (dotted box);separate measwememspecific detectors, signal conditioning, and infwmation processing algorithms are required f w each type of measurement
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Figure 3. A personal computer is me wmrai component in a student works& tion that will Dertorm all of the tasks outlined in Tabie 1.
amplifier circuits and passed on t o a data processor, which performs algehraic operations on the signal, ultimately producing a meaningful number, which is presented to the ohserver on a readout device. Twocomponents of this instrument are measurement specific-(1) the detector and its signal conditioner and (2) the algorithm performed by the data processor. The data processor, readout, and power supply are generic components of all instrument systems Wig. jj. Stand-alone instruments such as pH meters, Geiger counters, electronic thermometers, and photometric devices use special-purpose electronic circuits to perform the required algebraic operations. The algorithms performed by these circuits, however, can be easily implemented in software with a oersonal com~uter.Given a~orooriatesoftware, a personal cbmputer can provide most ofthecomponents of instrumentation system, as well as the display and storage components of the other tasks outlined in Table 1(Fig. 3.) The MSU Laboratory Interface
The decision t o commit our available funds t o integrated student laboratory workstations placed some design constraints on the data aquisition component of our system. (1) The workstation must make all of the electronic measurements required in lower division student laboratories. (21 If possible, it must make these measurements with research precision. (3) It must make them easily, so that studentsand faculty concentrate on chemistry rather than computer programming. (41 It must he able to participate in simulated experiments, giving students control of the system and providing time base information for real-time experiment simu334
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Figure 4. The MSU lab interface provldes signal procissing for many detect m , highresolution analogue-todigital conversion, switches tor operator Conhol of 'he experiment, a high-accuracy quartz time bash and high-current logic-level outputs for experimental control.
lations. (5) I t must be expandable a t low cost, to provide for additional functions not envisioned at the moment. (6)I t must not be romputerspecific.~lthoughourlaboratori~sare equipped with IBM-compatible computers, Apple 11 compute& are used hy our physics ~ e ~ & t m e anntd are in student laboratories throughout the country. Laboratory experiments in chemistry and physics involve precise measurement of a relatively small number of quantities: temperature, light, voltage, current, high-impedance voltage measurements such as pH and ion-specific electrodes. counts (from a Geieer counter). and time. We designed an interface that would support the detectors required to make these measurements. Information from the interface is transferred t o a personal computer for mathematical processing, presentation, and storage. Performance specifications for the interface are presented in Table 2. The accuracy required ruled out game port access to the computer. A block diagram of the MSU Lab Interface is presented in Figure 4. Besides the analogue, counting, and timing functions outlined ahove, the interface provides switch and photogate inputs, and logic-level 200-mA outputs for computer control of experimental devices. A nine-pin "D" connector on the back of the interface orovides nower (+5. f12 V) and three programmable logic l&es for control o~externalmultiplexers, instrumentation amplifiers, and accessories yet to
Figure 6. The Experiment Builder is a menudriven. English language programming system for developmentof data acquisition programs. The IBM version Is illustrated in this photograph. Figure 5. The MSU laboratory interface.
he designed. The standard version of the interface (Fig. 5) nrovides excentional versatilitv for unver division and reiearch labs. second versionmainta% the accuracy and scooe of measurement of the larger version, but has only one net bieach type of analogue anddigital input and costiless. T o provide hiph-speed, low-cost data transfer hetween the host computer &d the interface, an inexpensive computerspecific card carrying a parallel port was developed for both IBM-compatible and Apple I1 computers. Although the two families of computers run different versions of the software, the lab interface itself is not computer specific.
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Software for Data Acqulsnlon and Analysls Versatile and user-friendly software is the key to successful use of computers in student laboratories. Data acquisition and analysis software should be transparent to the student. who should he concentrating on chemistry. Developmental software should permit a faculty member t o concentrate on experiment design rather than computer programming. Our data acquisition and analysis software consists of five parts: (1) A D ~ i v e rprogram, which provides an initial menu and which
ties together the rest of the software package. The Driver promam is the entrv wint to the data acauisition and analvsis kftware. .~~~Its sme&menu allows the user fo select whether hk or she wishes t o calibrate a sensor. design an experiment. perform an experiment, or analyre and graph the experimental data. (2) A menu-driven Calibration program for calibration of temperature sensors, pH electrodes, and voltage. (3) An Experiment Builder program, which enahles nonprogrammers to design and write data scquisition programs for easy-tounderstand English-language menus. (4) A Runner . oroeram. which will operate the interface to collect .. data, using either preprog~ammedexperiment packages or userdesigned experiments.The runner program lim rheexperimant directory; selection of the desired experiment is done with a moving highlight. (61 An easy-to-us?Spreodrheel program, which will perform repetitive calculations and quickly prepare graphs of experimental dam. Studentsew learn to use the spreadsheet in ahout 5 min. ~
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The program was written in C language to provide tight program structure, easy access t o screen attributes, and fast' program execution. The Experiment Bullder The Experiment Builder Program provides a menu-driven list from which one selects commands to build a simple program listing. A short program that will read temperature,
Flgure 7. A temperature plot produced by the program illustrated in Figure 6. (Currentversions of the software truncate the small temperaturedisplay totwo decimal places.) presenting the latest value on the screen, is illustrated in Figure 6. Submenus appear in windows when most of the 14 commands are selected-the screen photo shows the selection of input devices from which one may "read and print"-read a signal from a detector or a value from a switch or the keyboard, and place this value on the screen or on an output device. Data may also be read and sent to a column of the spreadsheet. Data Acqulsltlon Figure 7 shows the screen image viewed by the student as the temperature measurement experiment detailed in Figure 6 is performed. The graph plots for 30 s, showing the temperature sensor's approach to equilibrium as i t is held in hand, and then replaced in 17 'C liquid. Data Analysls A spreadsheet is an extremely convenient environment for reoetitive calculations. The MSU soreadsheet consists of three data acqusition columns in which acquired data are olaced bv the interface. or bv manual data entrv, - . and three calculated columns that may be an assigned function of any data column or any other calculated column. Mathematical functions available are +, -, ', 1, exponentiation, square root, lop, In, derivative, and mean and standard deviation for a coium-n. Figure 8 shows data from a colorimetry experiment which cons~stsof manually entered concentration data (column A) and the corresponding acquired photocurrent, in milliamoerea. from the-~hotoresistkelieht detector (column B). he spreadsheet and graphingpackage enable students to look for relationships. The calculated columns (D, E, and F) Volume 67
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Figure 8. A Spreadsheet provides a clear, easy-to-use environment for repetltive calculations. The MSU spreadsheet is one dimensional-the data In Mlumns 0.E, and F can be defined as a function of the data in any other column. Once a column is defined, the same celculation is performed for all mws of Me spreadsheet.
FI~UIB 9 GTapns are a good way la look tor exper mental relatlonshlps. The ease w In v h c h tne spreaosneet pertorms ca cdal onr and p msgraphsfrees time for stboents to thmk abos the mplcatlono al ma r expermenla results.
illustrate a three-step data analysis procedure. Column D shows computation of the transmission factor (all light values divided by the zero concentration light value, 1.855 mA). A plot of this data against concentration produces a curve. Column E computes the inverse of column D; a plot of this column vs. concentration also produces a curve. Column F is plot of this data (column F) the log of column E, log (~/T).A vs. concentration (column A) is shown in Figure 9. The straight line relationship between concentration and absorbance [log (l/T)] is recognized as Beer's law. The linear regression shown at the top of the screen is the slope-intercept form of the equation for the line, and is recognized as y (absorbance) = path length * molar absorptivity constant * concentration a small zero concentration offset. A small negative deviation from Beer's law is observable a t high concentration values. The red LED light source is not monochromatic.
ing this data faster and a t less cost than a chart recorder. The second implication is educational. Students learn best what thev experience. and experience is more profitable if it isexplora~or~rather than "proving" what the instructor has told them is true. Exploration, in teaching as in research, is time consuming. Computer acquisition of many data points inashort rime, and rapid spreadsheet calculation and graphing, can free student time from pencils and calculators without removing them from the experimental process. This time saved becomes available for exnloration and rhinkine. Our students now spend more timk thinking and talk& about their data and graphs than they spend collecting the data.
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Conclusion There are two major implications of this work. The first is economic. A personal computer, a programmable data acquisition interface, and a handful of inexpensive detectors can replace manv laboratow instruments, a t a cost eaual to that of two or thiee of the instruments. he combination of computer and interface will also serve as a hieh-speed data logger, accumulating many samples per second and present-
Acknowledgment A project of this size involves the efforts of many people. The experiment builder software and spreadsheet involved the efforts of Kathy Tucker, Bruce Ivey, Glenn Howald, Andy Cohen, and Jim Fait. Allan Overcast was invaluable in circuit debug and checking of assembled units. Pat Hermansou provided administrative hack up and, with the help of Anita Armold, Elaine Howald, Dora Anderson, Joan Johnson. and Peeev Tombre. built circuit hoards and assembled theinterfac&sed in o"r laboratories. Our thanks also go to the more than 30 teachine assistants and 1500 students who participated in field test& of the program this past year.
Iterations II: Computing in the Journal of Chemical Education Iterations 11, a collection of 46 articles that appeared in the Computer Series between 1981 and 1986,has been carefully selected by the editors, Russell Batt and John W. Moore, to bring up to date the collection of computer applications that appeared in its predecessor volume Iterations. In addition to covering all aspects of instructional computing from introductory to graduate level, Iterations I1 provides an annotated bibliography of all computer-related articles that have appeared in the Journal from 1981 to 1986. 1987 paperback, 160 pp; US. $16.50; foreign $17.50 (postpaid). Send prepaid orders to Subscriptions and Book Order Department, Journal of Chemical Education, 20th and Northampton Streets, Easton, PA 18042.
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