A Real Time Velocity Measurement System for Small ... - IEEE Xplore

A Real Time Velocity Measurement System for Small Flyers Using Multiple Detectors Amarendra Goap

CSIR- Central Scientific Instruments Organisation Sector-30C Chandigarh-160030, India [email protected]

Deepa Srivastava

CSIR- Central Scientific Instruments Organisation Sector-30C Chandigarh-160030, India

Abstract—World has seen many casualties in bomb explosions from enemies and the terrorists; and defense services across the globe are working on more effective explosives. To develop techniques for analyzing the effectiveness and impact of explosives for attack as well as for defense strategies have become a necessity. Velocity measurement of bomb fragments after explosion is one such technique. However high accuracy results with minimal human interaction at ground zero is required. We propose a technique for monitoring the velocity of small flyers in real time with the help of Laser diodes and Photo detectors. We propose to have two laser source and photodiode optical screen combinations for collecting the flyer passing instances. The collected data will be processed at local level in a low cost Raspberry Pi and uploaded on web for real time access and analysis using web services. Keywords—Laser; Optical Screens;Photodetectors

I INTRODUCTION Several projectile speed measurement methods have been already developed such as Velocity Interferometer System [1], Laser Doppler Velocimetry (LDV) [2] etc. The major missing aspect in already developed techniques is real time monitoring[3] and analysis of result. Laser based projectile speed measurement system is appropriate for small caliber flyers but such systems comprised of prism based assembly having multiple reflection between them [4], which may leads to a space between reflections where target object remains undetectable. Doppler radar is a well known prominent technique to measure the velocity of large objects with high precision. An antenna transmits a continuous radio signal which is aligned to the bullet path. Due to the Doppler Effect frequency shifted pulses bounced off from the bullet. Doppler radar is required to focus on the object manually, and it cannot be operated efficiently without human involvement unless the object is extremely certain to cross the path of system [4, 5]. Optical barrier based technique is one more valuable method for velocity measurement of flyer object [5] but it is not convenient for

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smallcaliber flyers. Particle Image Velocimetry (PIV) is another technique of velocity measurement [6]. Since the incident takes place speedily and time exposures should be little [5], ultra high speed camera is one of the necessary requirements but use of this technique is limited by its high cost. Multiple laser sources and detectors based technique is more beneficial for estimation of speed of small flyers. Basically one has to measure the time elapsed of the projectile passing through space between the screens which can be done using detection unit [7-9] and Data Acquisition unit [10,11]. For real time monitoring of high speed small flyers, a detection unit is required which can sense a very small variation of the order of tens of mV in the detector output. Detection unit is capable to detect target even when flyer size is of the order of a micro-meter. To measure the Time difference precisely an high speed Op-Amp and raspberry pi module. In this article, we report study of multiple detector based real time monitoringsystem for small flyers. II SYSTEM DESCRIPTION In this section various units of systems are elaborated for time measurement and velocity computation purpose. These units must be able to work in a synchronous process which is described in operating principle section. Multiple detector based velocity measurement system consists of the follow suits: A Optical screen Optical screen is designed having Laser diode as a light source and PIN diode as an optical detector. A laser diode is solid state line laser emitting visible radiation of 635-nm wavelength and having 3mw power. Although laser beam divergence is low, but the distance between the source and detector is approx 1m, so there is no need of beam expander and collimator lens. PIN-5DI is used as Photo detector having response time 12ns, dark current of about 0.25nA.

Figure 1: Schematic Diagram ofOptical screen

Furthermore, it has responsivity and active area of about 0.33A/W and 2.5mm respectively at 632 nm wavelength. To enhance the responsivity and linearity of detectors, Photo detectors are operated in photo conductive mode in the circuit [6].Schematic Diagram of Optical Screen shown in Fig.1. B Electronic unit Main components of electronic unit are Power Supply, Detection unit and Data Acquisition Unit for time measurement. We designed a ±18V power supply limited by noise level of ±7mv. We use Op-amp having slew rate and gain bandwidth as 50V/us and 20 MHz respectively, is used for detection unit and with the power supply ranged ±18V. Data Acquisition unit is consist by ADC and raspberry pi. We can observe velocity directly on computer screen. Block diagram of Electronic unit is given in Fig.2. III OPERATING PRINCIPLE The proposed system works on the principle of obstruction of light by flyer whose velocity is under measurement. It leads to a situation where light does not reach to photo detectors and thus provide triggering signal to electronic unit for real time monitoring. Schematic diagram of the proposed system is shown in Figure 3. Laser source light is directly incident on photo-detectors mounted on a plate located at 1 meter distance electrical signal which is processed further for measurement of voltage using detection unit. Similarly another screen is constructed and both screens are kept at predefined distance to measure time elapsed to travel from one screen to another [11]. When projectile interrupts the first optical screen there is a loss of laser light which is falling on detector that drop off

Fig. 2 Electronic Unit

in output signal ; this alteration will act as triggering signal. The output of photo detector is present in the form of current so output fed to current to voltage converter circuit and amplifier circuit for desired amplification and then signal is send to Raspberry Pi where software module (program) will store the data and calculate the velocity of flyers and it will upload the data to the server. Flow chart of system is shown in Fig. 4 Using these triggering signals of the screens, time elapsed is measured with help of Data Acquisition unit. By the interscreen distance and Time elapsed, speed of the flyer can be observed. An authenticated user can see the data using typing URL on web browser on computer or mobile phone remotely. We can also make a registration page module, so that we can simultaneously attach same type of module for many experiments. So that user can concurrently perform many experiments and can see the result remotely. Experimental verification of the proposed technique has been done with different distances between optical screens.

Fig 4 Flow Chart of Proposed System

Figure 3 Schematic Diagram of System

IV RESULTS AND DISCUSSIONS Various experiments with the helpof laser, optical screen and data acquisition module were executed using a number of substances of different dimensions. Alteration in voltage signal depends upon the velocity and dimension of substances. In this experiment, Time elapsed was calculated by time difference between voltages dips which was generated due to light interruption by substances [11]. To test and validate the results of Opto-electronic unit of proposed velocity measurement technique, an experiment was performed to measure the velocity of 0.22 inch pellet fired via air pistol and low velocity flyer such as 4mm rod move by humans with different muscular arm effect. Ideal velocity of human arm is observed by standard velocity measurement system and compare with proposed technique. Resultant arm effect with 4mm rod is shown in Fig. 5 Under similar experimental conditions, air pistol pellet takes 3.2, 3.5, 4.0 and 4.7ms time to travel the inter-screen distance of 220, 240, 280 and 320mm respectively. Test results are shown in Fig. 6.

Velocity of air gun is measured at different distances with the help of detection unit. Resultant velocities are shown in Table I.Measurement accuracy of system is depending on numerous parameters like distance between screens and measurement of time elapsed. Both parameters are related to accuracy of components and optical alignment. Some parameters can be passing up or minimized by additional processing units for the optical signals [1, 3]. As per manufacturer specification, the standard velocity of the air gun bullet is 68.3 meter/sec. speed. Average velocity measured through experiments was found to be 68.88 m/s. Thus experimental results are found in close estimation with the manufacturer specifications. The proposed system with Raspberry Pi and web integration could be a low cost and effective solution.

Fig. 6 Measured V/s Ideal Air Gun Velocity

Table I: Resultant velocities Distance in mm

Fig. 5 Results of Different arm effect

240 260 280 320 360 420

Time Interval in ms 3.5 3.8 4.0 4.7 5.2 6.0

Velocity in m/s 68.57 68.42 69.12 68.08 69.35 69.78

V CONCLUSION In this article design & implementation ofthe Multiple Detectors based real time velocity measurement system has been discussed. The technique discussed in this article will be useful to measure the velocity of bomb debris and other projectiles. The sensitivity of the data acquisition system has been checked with the help of flyers having size 125 micrometer. Cost, sensitivity, safety and real time results availability via network are the beneficial point of proposed technique which makes it superior in contrast of other techniques. The technique can be used in automation of testing environment, which can save time and expedite experiments’ result analysis. This setup can be operated remotely, which can save the manpower cost and enhance safety. Further the result analysis, data mining and pattern recognizing techniques can help in explosive identification and classification systems. ACKNOWLEDGMENT The authors are thankful to the Dr. R C Kalonia, for valuable suggestions and CSIR-CSIO, Chandigarh for providing required facilities. REFERENCES [1] L. Qunhua, S. Huanfang& Y. Bingxian, “The infrared light screen system and accuracy analysis,”Acta Photonics Sinica, Vol. 33, pp.140911,March2004. [2] N J Lawson, “The application of laser measurement techniques to aerospace flows,” Aerospace Engineering, , Vol. 218, pp. 33-57, Jan 2004. [3]V.D Shivling, AmarendraGoap, C. Ghanshyam, Sudhir Kumar Sharma,DheeshaArora, Sanjay Kumar and Rakesh Kumar, “A Real Time Computational and Statistical Model (with high availability) of early warning for Plant Protection and Pest control for Crops (exp. Kutki),”IEEE International Conference on Computer Graphics, Vision and information security, pp. 22-26, 2015. [4] R. C. Kalonia& R. K. Varma, “Laser-based projectile speed measurement system,” Optical Engineering, Vol. 46, pp. 1-5, April 2007. [5] J.M.Sanchez-Pena, C. Marcos and M.Y. Fernandez, “Cost-effective optoelectronic system to measure the projectile velocity in high impact testing of aircraft and spacecraft structural elements,” Optical Engineering, Vol. 46, pp. 1-5, May 2007. [6] J. Haertig, M. havermann&C.Rey, “Flyer image velocimetry in Mach 3.5 and Mach 4.5 shock- tunnel flows, " Am Inst. Aeronaut Astronaut,Vol. 40, pp. 1056-1060, June 2002. [7] R.H. Kingston ,Optical Sources, Detectors and Systems, Isted, 1995,pp. 73-95. [8] Ram Gayakwad, Op-Amps and Linear Integrated Circuits, 4th Ed, 1999pp. 39-200. [9] Ji Liu1, Donge Zhao, Yangjun Li and Hanchang Zhou, “Optoelectronic System for Measuring Warhead Fragments Velocity,” 3rd International Photonics &OptoElectronics Meetings, In Journal of Physics. Conference Series, IOP Publishing 2011. [10] Muhammad Ali Mazidi, Janice GillispieMazidi&Rolin D. McKinlay, The 8051 Microcontroller and Embedded Systems Using Assembly and C, IInd ed., Pearson Education India, 2007, pp.418-467, 537-548. [11] D.Srivastava, M.Nokhwal, B. Gangwar, R. Kumar and R C Kalonia,"opto-electronic based time measurement unit with enhanced sensitivity," International Journal of Industrial Electronics and Electrical Engineering , Vol. 1, pp. 15-17, Nov 2013.