Measuring Voltage and Time Quantities of a Signal Through a Virtual Oscilloscope

AASCIT Journal of Physics 2017; 3(2): 5-12 http://www.aascit.org/journal/physics ISSN: 2381-1358 (Print); ISSN: 2381-1366 (Online) Measuring Voltage and Time Quantities of a Signal Through a G. Tektas *, C. Celiktas Department of Physics, Faculty of Science, Ege University, Izmir, Turkey Email address gozdetektas@hotmail.com (G. Tektas) * Corresponding author Keywords LabVIEW Software,, Digitizer Received: April 29, 2017 Accepted: May 31, 2017 Published: August 8, 2017 Citation G. Tektas, C. Celiktas. Measuring Voltage and Time Quantities of a Signal Through a Virtual Oscilloscope. AASCIT Journal of Physics. Vol. 3, No. 2, 2017, pp. 5-12. Abstract A virtual oscilloscope which is a type of the virtual instrument was designed by using LabVIEW software. Some voltage and time quantities such as amplitude, maximum voltage, minimum voltage, rise time, fall time and frequency were measured through a signal supplied by a function generator. Measurements were performed by different functions of the software. The same measurements were also acquired by GW Instek 2204 and 3504 model oscilloscopes (real oscilloscope). Signal shapes and measurement results obtained from the virtual oscilloscope and the real oscilloscope were compared with each other. It was deduced from the obtained results that the designed virtual oscilloscope could be used to display the signal shape and to measure its voltage and time quantities with high precision. 1. Introduction Virtual instrumentation is an auxiliary method for the modern laboratories. A virtual instrument consists of a computer, software and modular hardware. They are combined and configured to emulate the function of traditional (real) hardware instrumentation. Because their functionality is software defined by user, virtual instruments are extremely flexible, powerful and cost effective [1]. Figure 1. (a) Front panel, control palette, (b) block diagram and function palette [3, 4].

6 G. Tektas and C. Celiktas: Measuring Voltage and Time Quantities of a Signal Through a LabVIEW (Laboratory Virtual Instrument Engineering Workbench) is a graphical programming environment for research labs and academia [2]. It is a software used to design a virtual instrument. Graphical block diagrams are used for programming in LabVIEW called G programming. These diagrams are designed to facilitate data collection and analysis [2]. LabVIEW consists of two window named as front panel and block diagram. Front panel is the user interface of the instrument. It has a control palette which is taken part of controls such as knobs or buttons and indicators. Block diagram is a window that the code is written for the instrument. It has a function palette. Controls and indicators used in the front panel are appeared in the block diagram. A code is formed by making connections between these functions, controls and indicators used in the block diagram and the front panel. Front panel, block diagram and their palettes can be seen in Figure 1. Hardware part of the virtual instrument consists of some electronics such as data acquisition (DAQ) devices, digitizers and various devices for instrument control. Some of them are directly connected to the computer s internal bus through a plug-in slot, and they are external i.e. they are connected to the computer via serial, GPIB (General Purpose Interface Bus) or Ethernet ports [5]. Digital Signal Processing (DSP) is used in all engineering areas in order to replace real analog systems and to design measurement and test systems with an easy configuration and user-friendly interface. DSP systems are commonly constituted by the virtual instrumentation technique in LabVIEW environment. It is possible to improve a particular system by this approach when new algorithms, drivers or devices are availed [6]. Shape, time and voltage quantities of a signal such as amplitude, maximum voltage, minimum voltage, rise time, fall time and signal frequency can easily be determined by an oscilloscope. Amplitude is the height of a pulse in terms of volt from its starting baseline to maximum value [7]. Maximum and minimum voltages are the values of positive and negative peak in the scope, respectively [8]. Their units are volt (V). Rise time is the time it takes for the pulse to rise from 10 to 90% of its full amplitude. Fall time is the time it takes for the pulse to fall from 90 to 10% of its full amplitude in terms of second (s) [7]. Frequency is the number of signal per unit time, which its unit is Hertz (Hz). An oscilloscope has control buttons as volt/div., time/div. and trigger level. Each division in vertical and horizontal axis of the scope can be adjusted by these controls. The signal displayed on the screen can be stabilized by using the trigger level control. Sample rate (or sampling rate) and record length are other important parameters as well. Sample rate is a measure how often an oscilloscope samples the signal. Record length is the number of points in a complete waveform record [9]. A virtual oscilloscope can be designed by LabVIEW software. Processes in a real oscilloscope can be performed by the virtual oscilloscope also. Main difference between the real and the virtual ones is that the processes in the virtual one were carried out through software functions. A virtual oscilloscope was designed by Khanna et al. by using an USB (Universal Serial Bus) 6008 DAQ device [10]. Guili and Quancun designed a virtual oscilloscope based on GPIB interface and SCPI (Standard Commands for Programmable Instruments) [11]. A multifunctional virtual oscilloscope was developed by Gong and Zhou using LabVIEW software and USB 6210 type DAQ card [12]. A virtual oscilloscope was also designed by Jiang and Yuan using LabVIEW and PCI-6024E type DAQ card [13]. ShengLi et al. designed a virtual oscilloscope based on LabVIEW programme and a DAQ card via EZ-USBFX2 series USB controller [14]. As far as we browsed, we have experienced that no more works have been published about the virtual oscilloscopes with fast digitizers. So, we decided to study on virtual oscilloscope which composed of a 100 MS/s digitizer and a computer code written by the Authors in LabVIEW medium. In the present study, the signals in sinus, triangle and square shapes supplied from a function generator were displayed by the designed virtual and the real oscilloscopes. Voltage and time measurement quantities of the signals were obtained from both type oscilloscopes. Signal shapes and the obtained results were compared with those of two real oscilloscopes for all signal types. Yet, the comparison only for the sinus signal was given here for the sake of simplicity. 2. Materials and Methods A Sweep Function Generator (Brand name: Hung Chang) as a signal source, 3504 and 2204 model oscilloscopes (Brand name: GW Instek) were used in this study. A 5133 model (Brand name: National Instruments, NI) 100 MS/s Bus-Powered USB Oscilloscope/USB Digitizer (shortly 5133) was utilized for the data acquisition. It is a device which digitizes its input signal. It was used here to acquire data from the signal generator to the virtual oscilloscope. A GPIB cable was utilized to start and stop the real oscilloscopes by the developed code. Driver functions of the used real oscilloscopes were employed in the code in order that their controls were performed from the virtual oscilloscope via GPIB. An UPS (Uninterrupted power supply) was operated to prevent the fluctuations of the signal from the generator. Circuit scheme for the measurements is shown in Figure 2.

AASCIT Journal of Physics 2017; 3(2): 5-12 7 Figure 2. Circuit scheme for the measurements. As can be seen in the block diagram, the generator output was connected simultaneously both to the 5133 and to a real oscilloscope, and the signals were displayed in both oscilloscopes. Characteristic quantities for a signal such as amplitude, maximum voltage, minimum voltage, rise time, fall time and frequency of the signal were measured from both oscilloscopes. In the virtual one, the quantities were obtained through software functions ( amplitude and level, array max-min, transition measurements, pulse measurement and NI-Scope read measurement ) for determining the quantities above. Amplitude and level and array max-min functions were used to measure amplitude, maximum voltage and minimum voltage, respectively. In order to measure rise time and fall time quantities, transition measurements function was employed. Pulse measurement function was used to measure the signal frequency. All quantities above were obtained using NI-Scope read measurement function as well. These all functions are presented in the library of LabVIEW. The virtual oscilloscope was run by the developed code in the LabVIEW medium. In this oscilloscope, time/div., volt/div., trigger level, sample rate and record length controls were developed by using the software functions to adjust the signal shape and the measurement quantities. Driver function of the digitizer was used to acquire the data to the virtual oscilloscope. Screen view of the front panel and the block diagram of the designed virtual oscilloscope can be seen in Figures 3 and 4, respectively. Figure 3. Front panel of the virtual oscilloscope.

8 G. Tektas and C. Celiktas: Measuring Voltage and Time Quantities of a Signal Through a Figure 4. Block diagram of the virtual oscilloscope. As a characteristic feature, 3504 and 2204 model real oscilloscopes have a sampling rate of 4 GS/s with the frequency (bandwidth) of 500 MHz and a sampling rate of 1 GS/s with the bandwidth of 200 MHz, respectively. They have four input channels [8, 15]. Sampling rate, bandwidth and the number of channels of the designed virtual oscilloscope are determined by depending on the characteristics of 5133 type digitizer, leading to a sampling rate of 100 MS/s and bandwidth of 50 MHz with two input channels [16]. Record lengths of 3504 and 2204 model oscilloscopes, and the virtual oscilloscope were chosen as 25,000 samples. Different sample rates of the real oscilloscopes were set for the same time/div. settings so that the signal shapes in their screens were in compatible with each other. Sample rate of the virtual oscilloscope was kept the same with those of the 3504 model oscilloscope since 3504 s sample rate was higher than that of the 2204 model oscilloscope. The reason why this was that the higher sample rate was the better signal measurement performance in an oscilloscope [17]. For this reason, the results from the virtual oscilloscope were mostly compared with those of 3504. Time/div., volt/div. and trigger level (160 mv) adjustments of all oscilloscopes were adjusted to the same value to keep the stability of the measurement sensitivities in all oscilloscopes. Amplitude, maximum voltage, minimum voltage, rise time, fall time and signal frequency were obtained using two different methods in order to find out the effect of amplitude and frequency change to the measurement results: 1. Different amplitude and constant signal frequency, 2. Different signal frequency and constant amplitude. The processes followed by these methods are explained below. 2.1. Different Amplitude and Constant Signal Frequency Amplitudes of the signals were varied while signal frequency was remained stable. In this method, frequency of the signal was kept steady on about 38 khz. Time/div. settings of the oscilloscopes were set to 25 µs. The amplitude of the signal from the generator was gradually increased from 1.5 to 29 V. Volt/div. settings for all oscilloscopes were adjusted to 500 mv, 1, 2 and 5 V, respectively to be able to display the signal shapes perfectly. 2.2. Different Signal Frequency and Constant Amplitude Signal frequency was changed, and amplitude of the signal was remained constant with the optimum Volt/div. settings. Frequency of the signal was varied from 6 Hz to 100 khz from the generator. Time/div. settings of all oscilloscopes were adjusted to 25 and 250 µs, 2.5, 25 and 50 ms, respectively. Maximum time/div. setting was adjusted to 50 ms since the signals could not be displayed on the 3504 model oscilloscope screen over this time/div. level. Sample rate of the real oscilloscope was 100 MS/s for the time/div. adjustment of 25 µs/div. Due to the fact that it was the 5133 s maximum sample rate value, the minimum time/div. setting was adjusted to 25 µs. 3. Results Results have been given into two parts. They were obtained through; 1. Sinus signal with different amplitude and constant frequency and 2. Sinus signal with different frequency and constant amplitude. Shapes, amplitude, maximum voltage, minimum voltage, rise time, fall time and frequency of the sinus signals obtained from all oscilloscopes were compared with each other after they were stopped. The comparisons have been given in the following figures and tables. The values at second and third columns of the tables were obtained from automatic

AASCIT Journal of Physics 2017; 3(2): 5-12 9 measurement indicators on the screens of the real oscilloscopes. The results in fourth columns named as Waveform measurement of these tables were determined by using amplitude and level, array max-min, transition measurement and pulse measurement functions of LabVIEW programme. The results obtained through NI-Scope read measurement function are given at fifth columns named as Scope function. Amplitude, maximum voltage, minimum voltage, rise time and fall time quantities are indicated as V amp, V max, V min, T rise, T fall, respectively in these tables. 3.1. Sinus Signal with Different Amplitude and Constant Frequency Time/div. settings of the oscilloscopes were adjusted to 25 µs. Sinus signal shapes displayed from the 3504 model real oscilloscope and the virtual oscilloscope for the volt/div. settings of 500 mv and 2 V are shown in Figure 5 for the shape comparison. The results obtained from the real and virtual oscilloscopes for the volt/div. settings of 500 mv, 1, 2, 5 V were compared with each other in Tables 1-4, respectively. Figure 5. Comparison of the sinus signal shapes in (a) the 3504 and (b) the virtual oscilloscope. Table 1. Results from the real and virtual oscilloscopes for 500 mv/div. V amp (V) 3.16 3.04 3.14 3.06 V max (V) 1.74 1.84 1.79 1.77 V min (V) -1.42-1.34-1.34-1.34 T rise (µs) 8.224 7.682 8.182 8.192 T fall (µs) 8.044 7.472 8.052 8.002 Frequency (khz) 37.45 37.40 37.44 37.47 Table 2. Results from the real and virtual oscilloscopes for 1 V/div. V amp (V) 5.96 5.60 5.90 5.74 V max (V) 3.16 3.24 3.17 3.17 V min (V) -2.80-2.72-2.73-2.73 T rise (µs) 8.112 7.500 7.930 7.900 T fall (µs) 8.032 7.300 7.700 7.740 Frequency (khz) 37.44 37.43 37.49 37.43

10 G. Tektas and C. Celiktas: Measuring Voltage and Time Quantities of a Signal Through a Table 3. Results from the real and virtual oscilloscopes for 2 V/div. V amp (V) 11.20 11.00 11.42 11.11 V max (V) 5.84 6.16 5.96 5.96 V min (V) -5.44-5.44-5.46-5.46 T rise (µs) 7.968 7.668 8.098 8.118 T fall (µs) 7.848 7.464 7.938 7.928 Frequency (khz) 37.44 37.44 37.440 37.450 Table 4. Results from the real and virtual oscilloscopes for 5 V/div. V amp (V) 29.00 27.2 28.84 28.27 V max (V) 14.80 15.4 14.74 14.74 V min (V) -14.20-14.0-14.09-14.09 T rise (µs) 8.010 7.183 8.042 8.022 T fall (µs) 7.880 7.170 7.872 7.754 Frequency (khz) 37.38 37.65 37.420 37.440 3.2. Sinus Signal with Different Frequency and Constant Amplitude Volt/div. settings of the oscilloscopes were adjusted to 1 V. Sinus signal shapes displayed from the 3504 model real oscilloscope and the virtual oscilloscope for the time/div. settings of 2.5 and 50 ms are shown in Figure 6 for the shape comparison. The results obtained for the time/div. settings of 25 and 250 µs, 2.5, 25 and 50 ms are given in Tables 5-9, respectively. Figure 6. Comparison of the sinus signal shapes in (a) the 3504 and (b) the virtual oscilloscope.

AASCIT Journal of Physics 2017; 3(2): 5-12 11 Table 5. Results from the real and virtual oscilloscopes for 25 µs/div. V amp (V) 5.60 5.44 5.65 5.49 V max (V) 2.92 3.04 3.00 3.00 V min (V) -2.68-2.64-2.65-2.65 T rise (µs) 3.020 2.870 3.012 3.022 T fall (µs) 2.940 2.828 2.982 2.982 Frequency (khz) 100.4 100.4 100.4 100.7 Table 6. Results from the real and virtual oscilloscopes for 250 µs/div. V amp (V) 5.60 5.44 5.61 5.49 V max (V) 2.96 3.08 3.00 3.00 V min (V) -2.64-2.60-2.61-2.61 T rise (µs) 148.4 140.5 146.64 148.62 T fall (µs) 147.2 139.0 144.34 148.30 Frequency (khz) 2.040 2.038 2.043 2.040 Table 7. Results from the real and virtual oscilloscopes for 2.5 ms/div. V amp (V) 5.60 5.44 5.65 5.49 V max (V) 2.96 3.08 3.04 3.04 V min (V) -2.64-2.60-2.61-2.61 T rise (µs) 504.0 487.2 500.2 502.4 T fall (µs) 502.0 494.2 500.4 504.2 Frequency (Hz) 593.50 583.20 592.77 593.12 Table 8. Results from the real and virtual oscilloscopes for 25 ms/div. V amp (V) 5.60 5.44 5.65 5.49 V max (V) 2.96 3.04 3.04 3.04 V min (V) -2.64-2.56-2.61-2.61 T rise (ms) 9.950 9.462 9.862 9.852 T fall (ms) 9.900 9.144 9.852 9.802 Frequency (Hz) 29.98 30.10 30.021 30.08 Table 9. Results from the real and virtual oscilloscopes for 50 ms/div. V amp (V) 5.60 5.44 5.61 5.49 V max (V) 2.96 3.08 3.04 3.04 V min (V) -2.64-2.56-2.57-2.61 T rise (ms) 47.32 46.14 46.59 46.404 T fall (ms) 46.90 45.40 46.05 46.404 Frequency (Hz) 6.324 6.169 6.339 6.34 4. Discussion A virtual oscilloscope composed of 5133 model digitizer for the data acquisition different from the works in references [10-14] was designed by developing a code in LabVIEW medium. Additionally, NI-Scope functions were used here to acquire the data to the virtual oscilloscope different from them for the best accordance with the real oscilloscopes. The virtual oscilloscope has an advantage with respect to the real oscilloscope in that user can easily develop it according to user s implementation purpose. The signals in sinus, square and triangle shapes supplied from a function generator were displayed in the real oscilloscopes and the developed virtual oscilloscope. Amplitude and time measurements of the signals were obtained via LabVIEW software functions. Amplitude and level, array max-min, transition measurements, pulse measurement and NI-Scope read measurement functions were used in the developed code to specify which function is the most capable for measuring the signal characteristics. Amplitude, maximum voltage, minimum voltage, rise time, fall time and frequency of the input signals were acquired from the different model (Gw Instek 2204 and 3504) real

12 G. Tektas and C. Celiktas: Measuring Voltage and Time Quantities of a Signal Through a oscilloscopes and the developed virtual oscilloscope. Obtained results were compared with each other. As can be seen in the Tables, differences in the obtained results were observed between 2204 and 3504 model real oscilloscopes. The reason for these is that the 3504 has high sample rate than 2204. If the signal is accurately reconstructed for a sufficiently high sample rate, more accurate measurements will be obtained [9, 17]. These differences between the results from both real oscilloscopes make the result differences between the real oscilloscopes and the virtual oscilloscope normal. In addition, data processing is performed by microprocessor in a real oscilloscope whereas it is done by software functions in the virtual one. When amplitudes obtained by using amplitude and level and NI-Scope read measurement functions were compared with those of the real ones, it was observed that amplitudes obtained via amplitude and level function were quite compatible with those of 3504. Maximum and minimum voltages from the array max-min and the NI-Scope read measurement functions were generally the same as each other. Rise time, fall time and signal frequency obtained through transition measurements and pulse measurement functions were also compatible with those of 3504. The results obtained from 3504 were taken in consideration for comparison because of the fact that sample rates of 3504 and the virtual oscilloscope were the same with each other. As can be seen in Figure 5 and 6, it was observed that the signal shapes in the virtual oscilloscope were quite compatible with those of the real oscilloscope for different time/div. and volt/div. settings. These shows that the developed virtual oscilloscope was quite successful in display the signal shapes. For the data acquired from the 5133 type digitizer, sample rate of the designed virtual oscilloscope was remained 100 MS/s leading to analyze the signals up to 100 MS/s due to 5133 s capability. In the present study, signals in sinus, square and triangle shapes were used to compare the measurement results and signal shapes from the real and virtual oscilloscopes. It was seen that the signal shapes in both type oscilloscopes were quite compatible with each other. Amplitude, maximum voltage, minimum voltage, rise time, fall time and frequency of the signals obtained from the virtual oscilloscope using waveform measurement functions ( amplitude and level, array max-min, transition measurements and pulse measurement ) were more compatible with those of 3504 than the results obtained using NI-Scope read measurement ( scope function ) in the virtual oscilloscope. It is suggested that waveform measurement functions should be used for the measurement of signal characteristics for a virtual oscilloscope. Hence, it can be concluded that the designed virtual oscilloscope could be used as the real oscilloscope with high precision for acquiring and processing the signals from the radiation detectors. Acknowledgements This work was supported by Scientific Research Foundation of Ege University under project numbers 14 FEN 026 and 14 FEN 052. References [1] J. Travis, J. Kring, LabVIEW for Everyone: Graphical Programming Made Easy and Fun, 3 rd ed., Prentice Hall, USA, (2006). [2] J. Jerome, Virtual Instrumentation Using LabVIEW, (2010). 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