STUDIES ON WAVES AND OSCILLATIONS WITH DATA ACQUISITION SYSTEMS * B. LOGOFĂTU, M. MUNTEANU, M. LOGOFĂTU ODL CREDIS Department, University of Bucharest, Romania E-mail: logofatu@credis.ro, mariusmc@credis.ro Received December 21, 2004 Usage of Information and Communication Technology for teaching science and technology has increased significantly in the last years and has proved to be an efficient tool for teaching, practical activities and research. Commonly pedagogical uses of ICT fall into two apparently distinct categories that may be classified as virtual laboratory and real laboratory applications. In a virtual laboratory, computers are used to simulate or animate specific phenomena and students are, normally, engage in hands-on activities, which are directed towards increasing their understanding and insight of the principles, involved. Such educational materials are often integrated within interactive documents for web-based learning (elearning). However, the importance of traditional laboratory teaching involving practical experimentation and hands-on work ( real laboratory ) has not decreased because of the use of computerized simulation experiments. Computers equipped with data acquisition and control systems have had the effect of increasing the level of experimental activity in science laboratories at both high school and university. Supported by a variety of sensors and actuators, these systems have been shown to be pedagogically effective, particularly where higher-level learning skills are concerned. As a user of the data acquisition system, one is interested in measuring and analyzing physical phenomena. The purpose of any data acquisition system is to provide the tools and resources necessary to do so. A data acquisition system is a collection of software and hardware that is connected to the physical world. A typical data acquisition system consists of these components: Data acquisition hardware, sensors and actuators (transducers), signal conditioning hardware, the computer and software. In this paper, we will present some of our works in didactics and research at ODL Department CREDIS of University of Bucharest. In Applied Sciences and Information Technology laboratory we implemented a series of practical activities (experiments) focused on mechanics, electricity, electronics, waves and oscillations and so on. Key words: virtual instrumentation, LabVIEW, data acquisition systems. * Paper presented at the 5 th International Balkan Workshop on Applied Physics, 5 7 July 2004, Constanţa, Romania. Rom. Journ. Phys., Vol. 51, Nos. 1 2, P. 13 19, Bucharest, 2006
14 B. Logofatu, M. Munteanu, M. Logofatu 2 INTRODUCTION In these days, when Physics curricula is constantly reduced for high schools in Romania the objectives of physics teachers are more difficult to be obtained. At the university level, physics laboratories are still equipped with old instruments and apparatus inappropriate for high quality practical activities. For study of waves and oscillations (electrical, mechanical or electromechanical ones) one must use proper equipment in order to obtain good results. As available choices in studying oscillations, one can use traditional equipment or modern tools that use all the power of computers. Taking into account the fact that traditional equipment has many disadvantages (the functionality given by producer, limited range of usage, limited performance in terms of flexibility and time, high costs, etc), at ODL Department CREDIS of University of Bucharest, we decided to use modern technologies in laboratory. These new technologies are based on using data acquisition systems in order to experiment and research. An data acquisition system, although it seems to be some very specialized equipment, assures more opportunities than traditional apparatus and the range of experiments that can be done with one such system is extremely large. In the simplest way, a data acquisition system can be defined as a group of hardware and software components (Fig. 1) that use virtual instruments for acquire, analyze and present data. Data Acquisition Board Experiment Computer Sensors Traducers Cable Terminal bloc Fig. 1 Data acquisition system. The virtual instruments (the software component of data acquisition system) give another important aspect. Graphical programming language LabVIEW is the software used for virtual instruments, and it can be used as a simulation tool or as a tool for creating virtual instruments. More than that, LabVIEW already contains a set of software created instruments (oscilloscopes with one or two channels, waveform generator, spectrum analyzer, digital multimeter and other) (Fig. 2a).
3 Studies on waves and oscillations 15 The user interface of these instruments is identical with the ones of real equipments and the difference is given by the way the user interacts with the machine. In place of using hands to manipulate the knobs and/or sliders, one uses the mouse to perform these tasks. EXPERIMENTAL SETUP The data acquisition system used in our experiments consist in: DAQPad 6020E - data acquisition board, LabVIEW 6.1 virtual instruments, FD4E signal generator, Capacitors, coils, resistors, etc. The DAQPad-6020E is a USB-compatible multifunction analog, digital, and timing I/O device for USB-compatible computers. This board features a 12-bit analog to digital converter (ADC) with eight differential/16 single-ended inputs, two 12-bit DACs with voltage outputs, eight lines of TTL-compatible digital I/O, and two 24-bit counter/timers for timing I/O. The DAQPad-6020E has no DIP switches, jumpers, or potentiometers and is easily configured and calibrated using software. The DAQPad-6020E uses the National Instruments DAQ-STC systemtiming controller for time-related functions. The DAQ-STC makes possible such applications as buffered pulse generation, equivalent time sampling, and seamlessly changing the sampling rate. The DAQ-STC consists of three timing groups that control analog input, analog output, and general-purpose counter/timer functions. These groups include a total of seven 24-bit and three 16-bit counters and a maximum timing resolution of 50 ns. The I/O connector for the DAQPad-6020E has 68 pins that you can connect to 68-pin accessories with the SH6868 shielded cable or the R6868 ribbon cable. You can connect your device to 50-pin signal conditioning modules and terminal blocks using the SH6850 shielded cable or R6850 ribbon cable. In order to easy, the usage of data acquisition board the driver software (NI Measurement and Automation Explorer) allows configuration of virtual channels. One of the major advantages offered by LabVIEW consists in the possibility to create your own instruments or even to modify the built-in instruments. This is one of the most important differences between virtual and traditional instruments: in the case of virtual instruments the user can adapt the instrument to suit better to his/her needs, adding new features and of course new functionality (Fig. 2b). At any moment and with some knowledge and programming skills anyone can modify the virtual instrument, because in terms of flexibility and time required to setup the experimental apparatus, data acquisition systems exceeds the traditional equipment.
16 B. Logofatu, M. Munteanu, M. Logofatu 4 a) 2 Channel Oscilloscope offered in LabVIEW b) 2 Channel Oscilloscope customized Fig. 2 Virtual instruments. For our experiments, we customized the software created instruments that are included in LabVIEW in order to add some new features: More tools for analyzing acquired data, Export of experimental data for further analyzing and processing (experimental data is saved in a spreadsheet format) (Fig. 3a), Possibility to save the image of the scope in order to analyzed it later on [Figure 3 b)]. a) Experimental data exported in Ms EXCEL b) Experimental data displayed by scope. Fig. 3 Data acquisition system. EXPERIMENTAL DATA Experimental data acquired from our experiments are presented as follows.
5 Studies on waves and oscillations 17 ELECTRICAL OSCILLATIONS Study of electrical oscillations is based on RLC circuits. In first experiment, a simple oscillator is constructed using an inductor L and a capacitor C connected in parallel. The inductor receives a square signal from FD4E signal generator (frequencies used were in 10-50 Hz domain). The resistance in the LC circuit will dissipate the energy. The variation of voltage across the capacitor is shown in the following figures. We experimented with resistors of 750Ω and 6,2kΩ, inductors with 15mH and 3Ω resistance and capacitors with 6.8µF (Fig. 4). Fig. 4 Experimental data for R= 753Ω, C=6.8µF, H=15mH, ν=10hz. In this experiment (Fig. 5), there are one capacitor and two inductors that will be used in various combinations to create LC circuits oscillating at various frequencies. Fig. 5 Experimental data for R= 756Ω, C=6.8µF, H=30mH, ν=10hz.
18 B. Logofatu, M. Munteanu, M. Logofatu 6 Using this system one can easily see that the LC circuit resembles a massspring system. Initially, the electrical energy from the capacitor is transferred into the magnetic energy of the inductor. When the electrical energy of the capacitor becomes zero, the process is reversed. The magnetic energy from the inductor is transferred into the electrical energy of the capacitor. Electromagnetic oscillation occurs when energy is transferring between the capacitor and the inductor. MECHANICAL OSCILLATIONS For mechanical oscillations studies we used an inductor and a spring that have magnets attached on one end. Oscillating magnets generates some current in inductor that can be shown on oscilloscope. These simple experimental setups allow a qualitative analysis of mechanical oscillations and some results can be viewed in Fig. 6 (a, b). a) Harmonic oscillation with one inductor b) Harmonic oscillations with two inductors Fig. 6 Experimental data for mechanical oscillations Although the motion is not too interesting, the error-free motion is quite difficult to obtain. We ignore first sets of data and took into account the data after the system is stabilized in some way (only vertical oscillations without rotation or translation). CONCLUSIONS Virtual instrumentation and data acquisition systems are probably the best solution to use in experimenting physics. As one can see, the same experimental equipment can be used in for experiments in electricity, mechanics and electronics and so on. Without any major modifications, anyone can adapt the data acquisition system to fit best to their needs. Creating or modifying existing virtual instruments assures the appropriate tools to acquire, analyze and present the experimental data.
7 Studies on waves and oscillations 19 Using the power of computers we can focus on experimenting not on acquire data or try to fix inherent errors. In fact, experiments based on data acquisition systems are less prone to errors than the ones done by traditional instruments. REFERENCES 1. R. Lincke, I. Bűll, Ath. Truţia, V. Bogatu, B. Logofătu, "PC based oscilloscope", International Semiconductor Conference, 11 14 oct. 1995, Sinaia, Romania. 2. L. Arsenoiu, T. Savu, A. Szuder, Bazele programarii în LabVIEW, Ed. Printech, Bucuresti, 1999. 3. B. Logofătu, M. Munteanu, M. Logofătu, Instrumentaţie virtuală la Departamentul ID CREDIS al Universităţii Bucureşti, Colocviul Naţional de Fizică Învăţământul şi Cercetarea Ştiinţifică (26 28 septembrie 2003), Bucureşti, România.