Recording of Coincidence Signals in a Software Medium

Transcription

1 Science Journal of Circuits, Systems and Signal Processing 2018; 7(1): doi: /j.cssp ISSN: (Print); ISSN: (Online) Recording of Coincidence Signals in a Software Medium Gozde Tektas *, Cuneyt Celiktas Department of Physics, Faculty of Science, Ege University, Izmir, Turkey address: gozdetektas@hotmail.com (G. Tektas), cceliktas@yahoo.com (C. Celiktas) * Corresponding author To cite this article: Gozde Tektas, Cuneyt Celiktas. Recording of Coincidence Signals in a Software Medium. Science Journal of Circuits, Systems and Signal Processing. Vol. 7, No. 1, 2018, pp doi: /j.cssp Received: December 1, 2017; Accepted: December 12, 2017; Published: January 11, 2018 Abstract: A virtual coincidence unit, a virtual counter and a virtual timer were developed via a software in this study. Different frequency signals supplied from a function generator were sent to a real coincidence unit. The same signals were transmitted to the virtual coincidence unit via a digitizer. Output signals of the real and virtual coincidence units were counted by real and the virtual counters. Count periods were set through real and virtual timers. For different count periods, coincidence counts obtained from the virtual counter were compared with those of the real one. It was seen that obtained results were highly compatible with each other for low frequency (25 55 Hz) signals. Keywords: LabVIEW, Virtual Coincidence Unit, Coincidence Processing 1. Introduction A real instrument is designed to collect data from an environment or a unit under test, and to display information to a user based on the collected data. Such the instrument may employ a transducer to sense changes in a physical parameter and to convert the sensed information into electrical signals [1]. In recent years, the rapid development of computers accelerates the changes in the instruments for measuring, testing and automation. One of the most important outcomes is the creation of the concept of virtual instruments [2]. A virtual instrument (VI) is defined as a computer equipped with user-friendly application software, hardware and driver software that together perform the functions of a real instrument. With virtual instrumentation, engineers and scientists reduce development time, design higher quality products, and lower their design costs. Virtual instruments are defined by user while real instruments have fixed vendordefined functionality [1]. A virtual instrument consists of software and hardware [1]. The hardware allows that data acquired from the real instrument are processed and analyzed or that the real instruments are controlled via the virtual instrument. There is different hardware as digitizer, DAQ (Data Acquisition) device. Digitizer converts analog data from the real instruments to digital data which are processed by a computer. The software provides a means of controlling the instrument, collecting data from the hardware, processing the data, and then displaying, analyzing, and recording the data [3]. Digital signal processing (DSP) is used in all engineering areas to replace conventional analog systems and to build measurement and test system [4]. LabVIEW (Laboratory Virtual Instrument Engineering Workbench) is a software used to design the VI. LabVIEW can be used to acquired data from the instruments, process data, analyze data and control the instruments [5]. Processes in a real instrument are performed by using functions of the software in the VI. The VI designed via the software consists of front panel and block diagram as indicated in Figures 1 and 2. Controls palette indicated in Figure 1 contains the controls and indicators. The functions and constants are selected from functions palette shown in Figure 2 [6]. The front panel is like a user interface of the real instrument. Control buttons and indicators of the VI are taken part in this panel. A code for the VI is developed in block diagram. It is written by making a connection between the used functions, controls and indicators.

2 Science Journal of Circuits, Systems and Signal Processing 2018; 7(1): Figure 1. Front panel and controls palette [7]. Figure 2. Block diagram and functions palette [8]. An extremely important technique in nuclear and particle physics is the electronic determination of coincident events. The basic technique in the coincidence measurement is to convert the analog signal from the signal source into a logic signal and then to send these pulses to coincidence module [9]. If two signals are coincident with each other, output of a real coincidence unit is a logic signal. An example for coincidence output is shown in Figure 3. The coincidence unit designed in the present study via the software is called as a virtual coincidence unit.

3 30 Gozde Tektas and Cuneyt Celiktas: Recording of Coincidence Signals in a Software Medium frequencies and amplitudes. When the literature was browsed, it was found no studies about developing of the virtual coincidence unit and comparing of the real and virtual coincidence counts. In this study, the virtual coincidence unit was developed via LabVIEW and tested whether the virtual one was compatible with the real coincidence unit. 2. Material and Methods Figure 3. Coincidence output of two signals [9]. A counter counts the incoming pulses within a specific count period. This period can be adjusted by using a timer. For this purpose, a virtual timer and a counter were developed to operate the virtual coincidence unit. An oscilloscope is used to display the signals versus time. A virtual oscilloscope was also designed by the software in the introduced study. The signals acquired from the hardware were displayed in its scope. A function generator is used to supply different signal shapes. It is also possible to provide the signals in different In this study, a virtual coincidence unit was designed by writing a code in LabVIEW environment. When both input signals of the virtual unit were in coincidence with each other, an output signal was produced. In a real coincidence unit (Ortec 418A), the output signal is a logic signal of 5 V [10]. So, amplitudes of the output signals from the virtual coincidence unit were adjusted so as to be the same as those of the real one. In order to count the output signals in a specific time interval, another code was also written. Threshold Detector vi. function of Signal Operation group of LabVIEW was used to design a virtual counter. Coincidence counts were acquired through this function. Figure 4. Front panel and block diagram of the virtual coincidence unit. Figure 5. Circuit scheme for the coincidence counts.

4 Science Journal of Circuits, Systems and Signal Processing 2018; 7(1): Using Elapsed Time function from Timing programming group of LabVIEW, the virtual timer was developed, and the count period was set via this Elapsed Time icon. As stated above, besides, a virtual oscilloscope was developed to display and examine the coincidence output signals like a real oscilloscope. The signals were displayed on a Graph indicator of the program. Time and amplitude axis values of this indicator were set so as to be same as with the real one. A view of front panel and block diagram of the code for the virtual coincidence unit is given in Figure 4. A function generator (Thurlby Thandar TG230), universal coincidence (Ortec 418A), counter (Ortec 775), timer (Ortec 719), USB-5133 digitizer and the developed code were used in this study. Circuit scheme for counts are shown in Figure 5. As can be seen in the scheme, output of function generator was split and connected to two inputs of the real universal coincidence unit and the Thus, same signals were sent to the real and the virtual coincidence units at the same time. Output signals of the real and virtual coincidence units were sent to the real and the virtual counters as well. Virtual and real timers, additionally, were used to set the count time in the counters. NI-SCOPE function (driver function of the digitizer) was utilized to read the data acquired from the digitizer. Frequencies of sinus signals supplied from the function generator were set to 25, 35, 45 and 55 Hz, respectively. Amplitudes of the input signals of the real coincidence unit must be minimum 2V to process its input signals [10]. And also, since the nuclear instrumentation modules deal with the signals of max. 10 V, amplitudes of the signals in our scope were chosen as 10 V. Sample rate (the rate at which data are sampled) of the digitizer was automatically changed according to the signal frequency through the developed code. Discrimination levels of the counters were adjusted to 0.1 V to ignore the electronic noise. Count periods were set to 10, 40, 100, 400, 1,000 and 4,000 s. Each coincidence counts were repeated three times for each count period. Relative errors were calculated for the measurements by using the following equation. In equation 1, absolute error is the difference between real and virtual values [11]. 3. Results Relative error (%) = x100 (1) Real and virtual coincidence output signals were displayed on real and developed virtual oscilloscopes. These are compared in Figure 6. Output signals obtained from the real and the virtual coincidence units were counted for the timing interval of 10, 40, 100, 400, 1,000 and 4,000 s. Comparisons of the average counts for the signals of 25, 35, 45 and 55 Hz are given in Tables 1-4, respectively. Table 1. Obtained counts for the signals of 25 Hz ,451 2, ,784 9, ,000 24,429 24, ,000 97,747 97, Table 2. Obtained counts for the signals of 35 Hz ,375 1, ,436 3, ,748 13, ,000 34,371 34, , , , Table 3. Obtained counts for the signals of 45 Hz ,776 1, ,441 4, ,762 17, ,000 44,410 44, , , ,

5 32 Gozde Tektas and Cuneyt Celiktas: Recording of Coincidence Signals in a Software Medium Table 4. Obtained counts for the signals of 55 Hz ,167 2, ,418 5, ,675 21, ,000 54,192 54, , , , Figure 6. Screen shots of the (a) real coincidence output signals in the real oscilloscope and (b) virtual coincidence output signals in the virtual oscilloscope. 4. Discussion A code was developed for a virtual coincidence unit and for counting its output signals in LabVIEW medium. The counts from real and virtual coincidence units were compared with each other. In this study, lower frequency signals (25 55 Hz) were used to test whether the virtual coincidence unit was operated instead of the real one. As can be seen in Figure 6, coincidence output signals were highly in compatible with each other. As can be seen in the Tables above, counts of output signals from the virtual coincidence unit were highly in compatible with the real ones. For 400 s and lower time intervals, the virtual coincidence counts were generally higher than the real ones. In the higher count periods, they were generally lower than the real ones. Timing (timer) functions of LabVIEW use operating system timer. If the timer functions are used to control a loop, it can be expected differences in the time intervals between each iteration of the loop [12]. Because of these differences, the number of iteration of the loop used in the developed code was not changed proportional to the count period. So, counts from the virtual one were higher or lower than the real coincidence counts. High frequency signals require high sample rate values. It was seen in the developed code that when the sample rate was increased, the number of iteration was also increased. As the count period enlarged, the number of iteration increased too. But this increase was not enough for each count period. For this reason, the developed code did not give good performance at the high frequency signals. As stated above, the reason of this, LabVIEW timer functions use the operating system timers. So, the time resolution of these timers depends on the operating system. Since we used the LabVIEW timer functions (in other words, windows operating system timer) in our work, we recorded differences in the time interval between each iteration of the loop. Additionally, the speed of the CPU of the computer was effective on this time interval between each iteration. 5. Conclusion It was concluded that the developed virtual coincidence unit can be used as a real one, for the real and virtual coincidence units were compatible with each other. Acknowledgements This work was supported by Scientific Research Foundation of Ege University under project No. 14 FEN 052. References [1] J. Jerome, Virtual Instrumentation Using LabVIEW, PHI Learning Private Limited, [2] T. St. Georgiev and G. N. Krastev, Virtual System for Generating Analog and Digital Signals, ICEST, [3] M. Tooley, PC Based Instrumentation and Control, Elsevier Butterworth Heinemann, [4] S. Folea, LabVIEW-Practical Applications and Solutions, Eds. InTech., 2011.

6 Science Journal of Circuits, Systems and Signal Processing 2018; 7(1): [5] R. W. Larsen, LabVIEW for Engineers, Prentice Hall, [6] Accessed: 06/12/2017. [7] Accessed: 06/12/2017. [8] Accessed: 06/12/2017. [10] Accessed: 06/12/2017. [11] er/201/jan-11.pdf. Accessed: 06/12/2017. [12] 7A8B003A72D8. Accessed: 06/12/2017. [9] R. W. Leo, Techniques for Nuclear and Particle Physics Experiments, Springer-Verlag, Berlin Heidelberg, 1987.