Published on February 15, 2014
Project prepared by: PRANAV GHILDIYAL 8
‘XII’ ‘B’ SESSION: 2013-14 ROLL NO::- 12227 KENDRIYA VIDYALAYA B.E.G CERTIFICATE ThIs Is To CERTIFy ThAT MAsTER PRANAV GhILDIyAL sTuDyING IN CLAss XII B oF KENDRIyA VIDyALAyA B.E.G DuRING ThE ACADEMIC yEAR 2013-14 CoMPLETED ThE AssIGNED PRojECT AND hAs suBMITTED A sATIsFACToRy ACCouNT oF hIs PRojECT. DATE : sIGNATuRE oF INTERNAL sIGNATuRE oF EXTERNAL EXAMINER EXAMINER 8
__________________ __________________ ACKNoWLEDGEMENT This word acknowledgement is to express my deep sense of gratitude towards those unseen hands which are my teacher Mrs. H. JADHAV (CHEMISTRY) , our principal Ms. N. GEETHA RAO and my Parents who gave me the golden opportunity to do this wonderful project on the fore mentioned topic without their contribution the successful completion of this project would not have materialized. The project helped me in doing a lot of Research and I came to know about so many new things I am really thankful to all of them for assisting me and helping me finish this project in the limited time I had. 8
SINCERELY PRANAV GHILDIYAL AIM OF THE PROJECT:CIRCUIT DIAGRAM:- 8
BACKGROUND :A metal detector is a portable electronic instrument which detects the presence of metal nearby. Metal detectors are useful for finding metal inclusions hidden within objects, or metal objects buried underground. They often consist of a handheld unit with a sensor probe which can be swept over the ground or other objects. If the sensor comes near a piece of metal this is indicated by a changing tone in earphones, or a needle moving on an indicator. Usually the device gives some indication of distance; the closer the metal is, the higher the tone in the earphone or the higher the needle goes. Another common type are stationary "walk through" metal detectors used for security screening at access points 8
in prisons, courthouses, and airports to detect concealed metal weapons on a person's body. The simplest form of a metal detector consists of an oscillator producing an alternating current that passes through a coil producing an alternating magnetic field. If a piece of electrically conductive metal is close to the coil, eddy currents will be induced in the metal, and this produces a magnetic field of its own. History and development Toward the end of the 19th century, many scientists and engineers used their growing knowledge of electrical theory in an attempt to devise a machine which would pinpoint metal. The use of such a device to find ore-bearing rocks would give a huge advantage to any miner who employed it. Early machines were crude, used a lot of battery power, and worked only to a very limited degree. Alexander Graham Bell used such a device to attempt to locate a bullet lodged in the chest of American President James Garfield in 1881; the metal detector worked correctly but the attempt was unsuccessful because the metal coil spring bed Garfield was lying on, confused the detector. Modern developments The modern development of the metal detector began in the 1920s. Gerhard Fisher had developed a system of radio direction-finding, which was to be used for accurate navigation. The system worked extremely well, but Fisher noticed that there were anomalies in areas where the terrain contained ore-bearing rocks. He reasoned that if a radio beam could be distorted by metal, then it should be possible to design a machine which would detect metal using a search coil resonating at a radio frequency. In 1925 he applied for, and was granted, the first 8
patent for a metal detector. Although Gerhard Fisher was the first person granted a patent for a metal detector, the first to apply was Shirl Herr, a businessman from Crawfordsville, Indiana. His application for a hand-held Hidden-Metal Detector was filed in February 1924, but not patented until July 1928. Herr assisted Italian leader Benito Mussolini in recovering items remaining from the Emperor Caligula's galleys at the bottom of Lake Nemi, Italy, in August 1929. Herr's invention was used by Admiral Richard Byrd's Second Antarctic Expedition in 1933, when it was used to locate objects left behind by earlier explorers. It was effective up to a depth of eight feet. However, it was one Lieutenant Józef Stanisław Kosacki, a Polish officer attached to a unit stationed in St Andrews, Fife, Scotland, during the early years of World War II, who refined the design into a practical Polish mine detector. They were heavy, ran on vacuum tubes, and needed separate battery packs. New coil designs Coil designers also tried out innovative designs. The original induction balance coil system consisted of two identical coils placed on top of one another. Compass Electronics produced a new design: two coils in a D shape, mounted back-to-back to form a circle. This system was widely used in the 1970s, and both concentric and D type (or widescan as they became known) had their fans. Another development was the invention of detectors which could cancel out the effect of mineralization in the ground. This gave greater depth, but was a non-discriminate mode. It worked best at lower frequencies than those used before, and frequencies of 3 to 20 kHz were found to produce the best results. Many detectors in the 1970s had a switch which enabled the user to switch between the discriminate mode and the non-discriminate mode. Later developments switched 8
electronically between both modes. The development of the induction balance detector would ultimately result in the motion detector, which constantly checked and balanced the background mineralization. • Types of Metal detectors:- Very Low Frequency (VLF) ► Uses two coils: o Transmitter coil (search head, antenna) o Receiver coil ► There is a delay in the received signal compared to the transmitted signal called phase shift ► The signal is sent to the control box where it is analyzed by sensors Pulse Induction (PI) ► Simple when compared to VLF detectors ► Generates “Pulses” of Current Through Search Coil ► Pulse reaches its peak and reverses direction, collapsing very suddenly, thus creating a sharp electrical spike. ► Pulses continue to be generated from a mere dozen to about a few thousand pulses per second. ► Reflected portion of signal becomes delayed which is sampled, amplified, and sent to audio circuit to notify user. = Beat Frequency Oscillator (BFO) 8
► Uses two coils and sends a current through each ► Coils use slightly different frequencies, which produces audible “beats” ► When passed over metal object, induces a current in object ► Current causes a magnetic field, which interferes with field produced by detector ► Interference changes frequency of current in large coil, and thus an audible change in “beats” ► BFO Metal Detectors are cheap to make, but aren’t as accurate or dependable as more expensive types Uses Archaeology As a hobby • Coin shooting • Prospecting • General metal detecting • Beach combing Security screening DISCLAIMER :I HAVE ALSO MADE THIS PROJECT TAKING HELP FROM INTERNET 8
I EXPREE MY REGARDS WHO ARE ACTUALLY BEHIND THIS PROJECT. I HAVE UPLOADED THIS ONLY SO THAT MORE PEOPLE CAN TAKE HELP FROM THIS UPLOAD THROUGH MY PROFILE IN SLIDESHARE… TO REGISTER YOUR OBJECTION TO THIS UPLOAD PLZ COMMENT UNDER THE PRESENTATION IN THE WEBSITE 8
BIBLIOGRAPHY www.cbseportal.com www.cbseportal.com www.cbseportal.com • www.wikipedia.org • www.google.com 8
• www.ehow.com 8
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