S.4.2 Low cost sensor for measuring keraunic index and lightning density in the Amazon Region

13/03/2014
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S.4.2 Low cost sensor for measuring keraunic index and lightning density in the Amazon Region

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Low cost sensor for measuring keraunic index and lightning density in the Amazon Region Adonis Ferreira Raiol Leal UNIVERSIDADE FEDERAL DO PARÁ Belém, Brasil adonisleal1@hotmail.com Brígida Ramati Pereira da Rocha SIPAM Belém, Brasil brigida.rocha@sipam.gov.br Abstract—The keraunic index indicates the number of thunderstorm days per year in a given region. The registration can be obtained from organizations responsible for the monitoring the national territory for the incidence of lightning. This index is used by Brazilian standards to assist in the design of systems for lightning protection (SPDA) NBR-5419. It is essential for risk analysis involving lightning. Another important parameter is the lightning density (lightning per square kilometer/year). To establish a good mapping of keraunic index and lightning density in the Amazon Region it is necessary a great number of sensors. In order to measure lightning automatically we propose a prototype sensor for measuring the keraunic index autonomously. The sensor will measure the amount of lightning in a particular region during the interval of one year, and determine how many days of the year lightning occurred. Basically the prototype consists of a loop antenna with resonant frequency centered at 10kHz, to capture the peak of the electromagnetic signal emitted by lightning, an flat plate antenna to measure the variation of the electric field, amplifiers with programmable gain, a system of analog filtering to eliminate possible unwanted noise, an counter days to determine the days of the occurrence of lightning, and a counter for the lightning. Most of these systems are implemented internally to PSoC (Programmable System-on-Chip) , which is the microcontroller with analog and digital modules, reconfigurable, thus the system as a whole will be more immune to interference because the the sub systems will be encapsulated within the PSOC. The system will be developed to work autonomously within one year, so it will be possible to acquire data of the keraunic index of the coverage area of the sensor, and the implementation of more sensors that can be used to generate isokeraunic maps for the region. Keywords: keraunic index, lightning density, loop antenna, flat plate antenna, PSoC. I. INTRODUCTION The objective of this paper is to present a project for a lightning detector prototype for estimate the lightning density and keraunic índex similar to CIGRE 10KHz lightning counter and it has as main characteristc the low cost and simple and objective interface. II. THE PROJECT The prototype is basically constituted of two antennas, a loop and a flat plate one. The signals from these antennas are connected to an electronic circuit, which are connected mainly in a PsoC device, specifically the CY8C27443-24PI type [1]. Antena Loop To tune the antenna in the aimed frequency of 10Khz, it was used a resonant capacitor in parallel, with an antenna output. To calculate what the capacitance necessary to tune this frequency, the equations 1 and 2 (below) were used [2] [3] ‫ܮ‬ఓு = ‫ܰ1ܭ‬ଶ ‫ܣ‬ ቂ‫݊ܮ‬ ቀ ௄ଶ ஺ே ሺேାଵሻ஻ ቁ + ‫3ܭ‬ + ቀ ௄ସሺேାଵሻ஻ ஺ே ቁቃ (1) Where: ‫ܮ‬ఓு is the loop inductance in micro henrys. A is the length of one of the sides of the loop in centimeters (cm) B is the space between each loop in centimeters (cm) N is the number of the turns in the loop K1, K2, K3 and K4 are factors that vary according to the antenna geometry. ‫ܥ‬௣ி = ଵ ௫ଵ଴భఴ ସగమ௙మ ௅ഋಹ (2) First the loop inductance was calculated, and with this result we calculated the capacitor’s resonance according to the aimed frequency. For the frequency of 10KHz it was calculated that a capacitor of 1,418749 μF, however since there is no commercial capacitors within this range, we adopted a 1μF capacitor, which would produce a resonant antenna around 12KHz, which comply to the needs of this project. Amplifiers The amplifiers used are placed internally to the PSoC. The gain of this amplifier can be programed according to the array of the resistors in the feeding input and can vary between 0.062 and 48. In the first stage of the amplifier it was used a gain of 48 in the input of the loop antenna; and in the second stage a gain of 4, implemented through a development interface called "PSoC designer”. Filter Both amplifiers and filters were designed using analogic blocs inside the PSoC. The implemented filter had a bandpass switch in a central frequency of 10Khz and a bandwidth of 14KHz. Comparator The function of the comparator in the prototype is to generate a pulse for the counting algorithm when a lightning occur. It will continuously analyze the output signal in the second stage of the amplification, and when this signal trepass a certain threshold, its output will go to a high logic level, that is a output pulse of +5V. LCD In the LCD display will present 3 data: NR which corresponds to the number of lightning detected, DR which are the density of lightning for the region installed sensor and IC which is the IC keraunic index. Costs The costs for the development of prototypes were divided in three groups: outlay with materials, intellectual development and tests. The cost for the production in large scale/mass production is below US$ 1.000,00 which meets the regional needs. Algorithms. Basically, three algorithm in C languages were implemented in the PSoC microprocessor, the first is a counter which will increase the variable “number of lightning” each time the comparator treshold is trespassed. The second algorithm will calculate the lightning density for the region of installation of the antenna and the third will count the keraunic index. III. TESTS AND RESULTS The test occurred on 01/16/2014, in the interval between 1800h and 1930h (local time). In this test the antenna was installed indoors (in a shelter). In order to validate and compare the obtained results, we used data from the STARNET network (Sferics Timing And Ranging NETwork) available in [4], where it is available in real time the location of lightning, as well as the time distribution in intervals of 15 minutes. In figure 1 it can be seen some examples of lightning detected during a storm. Fig. 1. Example of lightning detected during a storm. To determine the area of scope of the sensor it was carried out the following methodology during a thunderstorm. 1- The prototype was reset, at the same time an image of a localization of a lightning in the surroundings of the installation of the sensor using the STARNET network. 2- Then, the prototype was left in operation during 15 min, which is the same time for the actualization of the STARNET network. 3- After these 15min period a new image was acquired with the localization of the lightning, from the same region that was analyzed previously and it was verified the number of lightning detected by the prototype.. 4- With this information it was identified the lighnings that occurred in this time interval, which ones were identified by the sensor and which were not. 5- The region of the scope for the sensor was defined by the location of the furthest lightning detected and the nearest lightning not detected by the sensor. CONCLUSION The tests for the prototype showed to be very satisfactory. The scope area was estimated in approximately 104Km, and the low cost of production make it viable to be installed in a large number in the amazon region where this type of system is scarce. Despite the advantages of this system it is still necessary to perfect it, especially regarding the development of a more advanced energy module, with a more advanced battery bank to supply power when eventual power outages. Acknowledgment . References [1] http://www.cypress.com/?id=1370 [2] Carr, Joseph J. (1994). "Small Loop Antennas for MW, AM BCB, LF and VLF Reception - Part 1." Elektor Electronics (UK), June1994, pp. 58 - 63.8 [3] Carr, Joseph J. (1994). "Small Loop Antennas for MW, AM BCB, LF and VLF Reception - Part 2." Elektor Electronics (UK), July/August 1994, pp. 104 - 109. [4] http://www.zeus.iag.usp.br/zeus_google_v3/