metal detector is an electronic device that detects the presence of nearby metals. Metal detectors are useful for finding metal inclusions hidden inside objects, or metal objects buried underground. They often consist of a handheld unit with a sensor probe that can sweep away soil or other objects. If the sensor is approaching a piece of metal, this is indicated by the changed tone in the earphone, or the moving needle on the indicator. Usually the device gives some distance indication; The closer the metal, the higher the tone in the earphone or the higher the needle. Another common type is a stationary "stationary" metal detector used for security checks at access points in prisons, courthouses, and airports to detect hidden metal guns in a person's body.
The simplest form of a metal detector consists of an oscillator producing alternating current passing through the coil generates an alternating magnetic field. If a piece of electrically conductive metal is close to the coil, the eddy current will be induced in the metal, and this generates its own magnetic field. If another coil is used to measure a magnetic field (acting as a magnetometer), the magnetic field changes because the metal object can be detected.
The first industrial metal detector was developed in 1960 and is widely used for mineral searching and other industrial applications. Uses include detecting land mines, weapon detection such as knives and weapons (especially in airport security), geophysical prospecting, archeology and treasure hunting. Metal detectors are also used to detect foreign objects in food, and in the construction industry to detect steel reinforcement in concrete and pipes and cables grown on walls and floors.
Video Metal detector
History and development
Towards the end of the 19th century, many scientists and engineers used the knowledge of electrical theory that developed in an attempt to design a machine that would define the metal. The use of such a device to find rocks containing ores will provide a great advantage for miners who use them. The initial machines are raw, use a lot of battery power, and work only for very limited levels. In 1874, the inventor of Paris Gustave TrouvÃÆ'  © developed a handheld device to find and retrieve metal objects such as bullets from human patients. Inspired by Trouvà © Ã… ©, Alexander Graham Bell developed a similar device to try to find 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 spring bed of Garfield metal coils lay in confused detectors.
Modern developments
The development of modern metal detectors began in the 1920s. Gerhard Fischer has developed a radio directional search system, which will be used for accurate navigation. The system works very well, but Fischer sees no anomalies in areas where terrain contains rocks containing ores. He reasoned that if radio rays could be distorted by metal, then it should be possible to design a machine that would detect metal using a search coil resonating on a radio frequency. In 1925 he submitted a petition, and granted, the first patent for a metal detector. Although Gerhard Fischer was the first patent for metal detectors, the first to be applied was Shirl Herr, an entrepreneur from Crawfordsville, Indiana. His application for the Handheld Metal-Hidden Detector was filed in February 1924, but not patented until July 1928. Herr helped Italian leader Benito Mussolini in recovering the remaining items from the galleon Caligula at the base of Lake Nemi, Italy in August 1929 Herr invention was used by the Admiral Richard Byrd Antarctic Expedition in 1933, when it was used to find objects left by earlier explorers. It is effective to a depth of eight feet. However, it is one of Lieutenant JÃÆ'³zef Stanis? Aw Kosacki, a Polish officer attached to a unit stationed at St Andrews, Fife, Scotland, during the early years of World War II, which refined the design into a practical Polish mine detector. These units are still quite heavy, as they run in vacuum tubes, and require separate battery packs.
The design created by Kosacki was used extensively during the Second Battle of El Alamein when 500 units were sent to Field Marshal Montgomery to clear the retired German mines, and were then used during the Sicilian Allied invasion, the Allied invasions of Italy and the Normandy Invasion.
Since the manufacture and refinement of the device was a wartime military research operation, the knowledge Kosacki made as the first practical metal detector was kept secret for more than 50 years.
The Mine Kafon Drone is an autonomous, efficient and safe redemption drone that has a metal detector mounted above ground using sensors and a retractable arm.
Further narrowing
Many of these new device manufacturers bring their own ideas to the market. White's Electronics of Oregon began in the 1950s by building a machine called Oremaster Geiger Counter. Another leader in detector technology is Charles Garrett, who pioneered the BFO (Beat Frequency Oscillator) engine. With the invention and development of transistors in the 1950s and 1960s, manufacturers of metal detectors and designers made lighter engines with better circuits, running on small battery packs. Companies are popping up all over the United States and Britain to supply increasing demand.
The modern top model is fully computerized, using integrated circuit technology to allow users to set sensitivity, discrimination, track speed, threshold volume, notch filters, etc., and hold these parameters in memory for future use. Compared to a decade ago, lighter detectors, deeper searches, used less battery power, and differentiated better.
The larger portable metal detector is used by archaeologists and treasure hunters to find metal items, such as jewelry, coins, bullets, and other artefacts buried underground.
Discriminator
The biggest technical change in the detector is the development of induction balance system. This system involves two electrically balanced rolls. When metals are introduced around them, they become unbalanced. What allows detectors to distinguish between metals is the fact that each metal has a different phase response when it is exposed to alternating current. Scientists have long known this fact; time detectors are developed that can selectively detect the desired metal, while ignoring the unwanted.
Even with discriminators, it is still a challenge to avoid unwanted metals, as some of them have the same phase response for example. tin and gold paper, especially in alloy form. Thus, incorrectly adjusting certain metals increases the risk of skipping a valuable invention. Another disadvantage of discriminators is that they reduce the sensitivity of the machines.
New coil design
Designers Coil also tried innovative designs. The original induction balance coil system consists of two identical coils placed on top of each other. The Electronic Compass produces a new design: two rolls in the D shape, reassembled to form a circle. The system was widely used in the 1970s, and both concentric and D types (or broad when they were known) had their fans. Another development is the discovery of a detector that can undo the effects of mineralization in the soil. This gives greater depth, but is a non-discriminatory mode. It works best at lower frequencies than used previously, and a frequency of 3 to 20 kHz is found to produce the best results. Many detectors in the 1970s have switches that allow users to switch between discrimination modes and non-discriminatory modes. The next development switches electronically between the two modes. The development of an induction balance detector will ultimately produce a motion detector, which constantly checks and balances the background mineralization.
The size of the coil may limit or optimize the size of the detected target. A very small coil can generally take smaller targets better than larger coils. In contrast, larger coils can usually detect larger objects from further distances, and sometimes sacrifices can detect smaller (even close) objects. There is a trade-off for what the "detectorist" sought. Usually the user of the detector needs to decide the size of the coil to be used. In some high performance detectors, sometimes the size of the coil remains (coils can not be changed) to optimize the circuit to detect smaller objects while still providing a good depth to larger objects. Some high performance metal detectors allow the user to change the size of the coil, to optimize what the user is looking for; a good example is a very small piece of gold, usually requiring smaller coils. Recent coil advances have smaller coils inside larger coils, and these circuits create a special timing between two coils to optimize the detection of smaller and larger objects simultaneously. Generally when using a metal detector the user should select the size of the coil based on the desired "ground coverage", "sensitivity" for smaller objects, the distance that large objects can be detected, and the amount of "ground noise" that the coil will pickup or can " ". Smaller scrolls are sometimes used to focus the detectable search area to be smaller, thus avoiding any "junk" that may exist in a location.
Pulse induction
At the same time, developers are looking at using different techniques in metal detection called pulse induction. Unlike pulse frequency oscillators or induction balance machines which both use uniformly alternating current at low frequencies, the pulse induction machine only draws ground with a relatively strong current, while through the search coil. In the absence of metal, the field decomposes at a uniform rate, and the time required to fall to zero volts can be accurately measured. However, if the metal is present when the engine is fired, a minor eddy current will be induced in the metal, and the time to sense the current damage will increase. This time difference is minute, but the increase in electronics makes it possible to measure it accurately and identify the presence of metal at a reasonable distance. These new machines have one major advantage: they are largely resistant to the effects of mineralization, and other rings and jewelry can now be found even under highly mineralized black sands. The addition of computer control and digital signal processing has improved the pulse induction sensor.
The advantages of using "PI detectors" include the ability to "puncture" heavy mineral soils; in some cases heavy mineral content can even help better PI detector function. Where the "VLF" detector is usually very negatively affected, "PI" does not.
Maps Metal detector
Usage
Archeology
Metal detectors are widely used in archeology with the use of the first recording by military historian Don Rickey in 1958 who used one to detect the firing lines at the Little Big Horn. Archaeologists, however, oppose the use of metal detectors by "artifact finders" or "looters of sites" whose activities interfere with archaeological sites. The problem with the use of metal detectors at archeological sites or hobbyists who find objects of fascinating archeology is that the contents of the objects were found to be lost and no detailed survey of the environment was made. Outside sites that are known to be the importance of objects may not be obvious to fans of metal detectors.
- United States
In the United States, collaboration between archaeologists hunting for colonial-era Native American villages and hobbyists has been productive.
- England and Wales
In England and Wales, metal detectors are legal provided the landowner has given permission and that the area is not a Scheduled Ancient Monument, a special scientific interest spot (SSSI), or covered by elements of the Rural Stewardship Scheme.
The 1996 Treasury Act governs whether goods that have been discovered or not are defined as property. Seekers of objects defined by the Act as possessions should report their findings to local inspectors. If they find items that are not defined as treasures but which are of cultural or historical importance, seekers can voluntarily report them to the Portable Anti-Age Scheme and the English Detector Finding the Database.
- Scotland
The situation in Scotland is very different. Under Scottish law principle of bona vacantia, the Crown has a claim on any object of any material value in which the original owner can not be traced. There is also no 300-year limit to find Scotland. Any artifacts found, whether by metal detector surveys or from archaeological excavations, should be reported to the Crown through the Treasury Advisory Panel at the National Museum of Scotland. The panel then determines what will happen to the artifact. Reporting is not voluntary, and failure to report the discovery of historic artefacts is a criminal offense in Scotland.
- French
Sale of metal detectors allowed in France. The first use of metal detectors in France led to archaeological discoveries occurred in 1958: people living in the town of Graincourt-lÃÆ'¨s-Havrincourt who were looking for copper from World War I with a military mining detector discovered a Roman silver treasure. French law on detecting metal is unclear because it refers only to the purpose pursued by users of metal detectors. The first law governing the use of metal detectors is Law no. 89-900 dated December 18, 1989. The latter is continued without any change in Article L. 542-1 of the inheritance code, stating that "no one may use equipment to detect metal objects, for purposes of research monuments and goods which draws prehistory, history, art and archeology without previously obtaining administrative authorizations issued on the basis of applicant qualifications and the nature and methods of research. "Beyond the research of ancient objects, using metal detectors requires no special authorization, except property of the landowner. We often read, from some archaeologists, that the use of the metal detector itself is prohibited without official authorization. This is wrong. To make this happen, one must look to the legislative intent in enacting Law no. 89-900 dated December 18, 1989. Asked about Law no. 89-900 dated December 18, 1989 by Mr. Calloud's MP, Jack Lang, Minister of Culture at the time, was answered with the following letter: "The new law does not prohibit the use of metal detectors but only regulates use. archaeological relic, required prior authorization of my service.Regardless of this case, the law requests to be reported to authorities in accordance with the accidental discovery of archaeological remains. "The entire letter of Jack Lang was published in 1990 in a French metal detection magazine , and then, to be viewed on the internet, is scanned with permission from the magazine writer on the French metal detection website.
As a hobby
There are different types of hobby activities involving metal detectors:
- Coin shootings specifically target the coins. Some coin shooters do historical research to find sites that potentially deliver historical and collectible coins.
- Prospecting is looking for precious metals such as gold, silver, and copper in their natural form, such as nuggets or flakes.
- Metal detectors are also used to search for discarded or missing man-made objects, such as jewelry, mobile phones, cameras, and other devices. Some waterproof metal detectors, to allow users to search for submerged objects in shallow water areas.
- Common metal detection is very similar to coin shooting, except that the user after all kinds of historical artifacts. Detectors may be dedicated to preserving historical artifacts, and often have considerable expertise. Coins, bullets, buttons, ax heads, and buckles are just some of the items usually found by relic hunters; in general its potential is much greater in Europe and Asia than in many other parts of the world. More valuable findings in the UK alone include the Staffordshire Hoard of Anglo-Saxon gold, sold for £ 3,285,000, Celtic Newark Torc, Ring Ringere, West Bagborough Hoard, Milton Keynes Hoard, Roman Crosby Garrett Helmet, Stirling Hoard, Collette Hoard and thousands smaller findings.
- Combing beaches is hunting for coins or jewelry lost on the beach. The beach hunt can be as simple or as complicated as one would want to make it. Many dedicated beach hunters also familiarize themselves with tidal movements and coastal erosion.
- Metal surveillance clubs across the United States, Great Britain and Canada are there for fans to learn from others, show off their hunting finds, and learn more about hobbies.
Politics and conflicts in hobby of detecting metals in the US
The metal detection community and professional archaeologists have different ideas related to the recovery and preservation of historic findings and locations. Archaeologists claim that detector fans are taking an artefact-centric approach, removing this from their context which resulted in the permanent loss of historical information. Archeological looting places like Slack Farm in 1987 and Petersburg National Battlefield serve as evidence against allowing the detection of unattended metals in historic locations.
Hobbyists often argue that the limited resources of professional archaeologists result in the loss or damage of many artifacts by plow, progression, erosion and livestock. The language and extent of the law on artifact collections is also a problem, as the 1979 Archaeological Resources Protection Act does not include scattered coins, a prime target for natural enthusiasts. Many fans are concerned about the vast prohibition of metal detecting bans, marking many undocumented properties that have been well documented or will never get professional attention. Suggestions for authorizing or offering limited permission to detect on historic sites have been attempted in some areas of the United States.
More recently, productive efforts for cooperation between metal detecting professionals and hobbyists have begun, including the Montpelier Archaeological Project and the Combat Restoration and Organization of Archeological Volunteers (BRAVO) and more. In these programs, skilled hobby enthusiasts work with experienced professionals with general goals on finding and extracting accurate and efficient sites. Away from supervised sites, hobbyists using improved recording and use of global positioning systems, GIS, notebooks, photo scales, and online databases can help professionals in evaluating possible sites. When searching for sites, fans can help with electronic scanning, reducing the need to test holes. Some land managers, such as the Tennessee Valley Authority have cited the role of amateur archaeologists in protecting sensitive sites from illegal looting and metal detector penghobi has helped in the location and preservation of many sites.
Security filtering
A series of aircraft hijacking led the United States in 1972 to adopt metal detector technology to filter passenger planes, initially using a magnetometer originally designed for logging operations to detect spikes in trees. The Finnish company Outokumpu adapted the metal mining detector in the 1970s, which is still housed in a large cylinder pipe, to make the security detector run-through commercially. The development of this system continues in the company's spin-off and branded systems such as Metor Metal Detectors evolved in the form of a now standard rectangular gantry at the airport. Similar to developments in the use of other metal detectors, alternating current systems and pulses are used, and coil and electronic designs have moved forward to improve the discrimination of these systems. In 1995 systems like the Metor 200 emerged with the ability to show the approximate height of metal objects above the ground, allowing security personnel to more quickly locate the signal source. Smaller metal detectors are also used to find a metal object in a person more precisely.
Industrial metal detector
Industrial metal detectors are used in pharmaceutical, food, beverage, textile, garment, plastics, chemical, wood, mining and packaging industries.
Contamination of food by metal fragments from the processing machinery damaged during the manufacturing process is a major security problem in the food industry. Metal detectors for this purpose are widely used and integrated into the production line.
The current practice in garment factories or apparel industry is to apply metal detection after the garment is fully stitched and before clothing is packaged to check whether there is metal contamination (needles, needles broken, etc.) in clothing. This needs to be done for security reasons.
Industrial metal detectors were developed by Bruce Kerr and David Hiscock in 1947. The founding company of Goring Kerr pioneered the use and development of the first industrial metal detector. Mars Incorporated is one of Goring Kerr's first customers using their Metlokate metal detector to inspect the Mars bar.
The basic principle of operation for a general industrial metal detector is based on the design of 3 coils. This design uses an AM (amplitude modulated) transmission coil and two receiver coils on either side of the transmitter. The design and physical configuration of the receiver coil is instrumental in the ability to detect very small metal pollution of 1 mm or less. Today modern metal detectors continue to use this configuration to detect metal bums.
The coil configuration is such that it creates an opening where the product (food, plastic, pharmaceutical, etc.) passes through the coil. This opening or aperture allows the product to enter and exit through a three-winding system that produces the same signal but is reflected on two receiver coils. The resulting signal is summed up effectively negating each other. Fortress Technology innovates new features, allowing the coil structure of their BSH Model to ignore vibration effects, even when examining conductive products.
When metal contaminants are inserted into the product, an unequal disturbance arises. This then creates a very small electronic signal. After appropriate amplification, mechanical devices fitted to the conveyor system are signaled to remove contaminated products from the production line. The process is fully automated and allows the manufacturer to operate without interruption.
Civil engineering
In civil engineering, a special metal detector (cover meter) is used to find a reinforcing rod inside the wall.
See also
- WHEN
- Detector (BBC television series)
- Inductive sensor
- Inductive circle
- Fishing with magnets
- Portable Antiquities Scheme
Note
References
Source of the article : Wikipedia
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