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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Metal detector accessories and other useful things. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / metal detectors Headphones They are especially useful when working in places where strong noise (vehicles, surf, stormy river, etc.) drowns out the signal from the speaker of the device. By masking external sounds, the headphones bring the sound signal from the object directly into the ear. Often, deep objects cannot form a signal sufficient for the speaker to sound, but we can already hear it in headphones. Thus, the headphones, as it were, increase the depth of object detection. In addition, by consuming less power compared to a speaker, the earbuds increase battery life by 70-80%. Headphones come in a variety of shapes, sizes and configurations. It is desirable to have headphones that sit comfortably on the head, do not slip off and do not press hard. There must be a volume control for each ear or, at worst, one common. The fact is that metal detectors, as a rule, do not have a volume control, since this is not necessary. However, when using headphones, the volume must be adjusted, otherwise strong signals from shallow or large objects may damage your hearing.
Fig.25. Increasing the depth of object detection when using headphones Finally, when working with headphones, the metal detector does not emit loud signals that usually attract unwanted onlookers. In hot weather, you can use lighter headphones from the player, but also with a volume control. The headphone plug has a diameter of 6 mm. If headphones from the player are used, then an appropriate adapter must be used to connect them. Do not buy overpriced headphones that are designed to listen to music and play a wide range of frequencies. For a metal detector, sound quality does not matter. search coils The search coil is an integral part of any metal detector. It is quite obvious that no metal detector can work without a coil. Less obvious is that the quality of the coil, its type and design will determine how effectively the metal detector performs its task. As a rule, two antennas are enclosed in the coil body - transmitting and receiving. The electromagnetic field emitted by the transmitter antenna passes into the environment - soil, stone, sand, water, wood, air, etc. The secondary signal from the object is picked up by the receiving antenna, amplified and informs us about the object in one way or another. By design, the coils are divided into concentric coplanar, wide coverage type 2D, coaxial, coils with antenna diversity. Concentric coplanar coils. This configuration is the most common in modern devices. It has high sensitivity, detection depth and good discrimination.
As a rule, two transmitting antennas and one receiving antenna are enclosed in the housing of such coils, located concentrically in one plane. The electromagnetic object detection zone created by such a coil has a conical shape with the highest intensity in the center. These coils are quite flat and light. They may have a hole in the center, making it easier to pinpoint the exact location of an object. Coils wide-cut type 2D. In these coils, the transmitting and receiving antennas have the shape of the letter D, which, partially overlapping, form an elliptical zone sensitive to metals. This design is less sensitive to soil minerals and covers a larger area with each stroke. Usually they use a fairly thick wire, so they are heavier than concentric coils.
As a rule, such coils are equipped with devices for searching for native gold. The disadvantages of such coils include unsatisfactory detuning from iron and difficult determination of the exact location of an object in the ground. These shortcomings are eliminated in Tesoro's latest elliptical coils, which feature high sensitivity, discrimination and pinpointing with a wide grip and low weight. Coaxial coils. This design is used in coils with a diameter of 2,5-10 cm. High requirements for manufacturing accuracy make them quite expensive. The transmitting antenna is located between the two receiving antennas. This creates an electromagnetic field - more or less uniform in flux density. They are usually not affected by interference from high voltage lines. The advantage of such coils is when working in heavily trashed areas, where they can detect valuable objects in close proximity, for example, from a nail or cork. In addition, they allow you to work close to metal fences and poles.
Diversity coils. The transmitter and receiver antennas are mutually perpendicular and separated from each other by 1 meter. They are used in deep instruments, they detect large objects at a depth of 4-6 m, but do not react to small (coin-sized) objects.
Coils of impulse devices. They can have one antenna, which serves as both transmitting (at the moment of emission of a pulse) and receiving (at the moment of absence of a pulse). However, two antennas are more commonly used, since in this case it will be much easier to decouple the high-voltage output circuits of the current pulse generator and the sensitive input circuits. For impulse devices, coil sizes can be both standard and large (1x1 m, 2x2 m or a loop with a diameter of 5-10 m).
Rice. 30. Coil pulse deep metal detector All coils of modern devices have electrostatic protection that prevents false signals (for example, from wet grass). Previously, such protection was carried out by wrapping the turns of the coil with foil, now the inner surface of the coil body is coated with graphite electrically conductive varnish or electrostatic inhibitors are injected directly into the plastic of the coil body (the so-called monolithic coils). VLF/TR searchcoil sizes range from 2,5cm to 60cm. As a general rule, the smaller the searchcoil, the smaller the object it can detect. Large coils are designed to search for large objects at great depths, but they can also find relatively small objects (coins, rings, etc.). Most metal detectors are equipped with a coil from 16 to 23 cm - this is the optimal size for general search purposes. These coils are light, have a wide grip and are quite sensitive to a range of objects, detecting them at a considerable depth. When working in areas with a high content of metal debris, it is recommended to use coils with a diameter of 7-12 cm. They have high sensitivity and resolution, and also allow you to more accurately determine the location of the object. When searching for coins, the detection depth is slightly reduced compared to a standard coil (1-2 cm). Due to the small size, the processing speed of the site is noticeably reduced, but it is examined more carefully, which increases the likelihood of finds. Large sized coils (30-60 cm) also respond quite well to small objects, but finding their exact location is more difficult than with small or standard coils. They do not give a noticeable increase in the detection depth of small objects (coins). Their advantage is manifested when searching for large objects in conditions of low soil mineralization. So, for example, when using a standard coil, the Spectrum XLT detects a helmet at a depth of 1 m, and with a Blue Max 1500 coil with a diameter of 35 cm, it detects at a depth of 1,5 m. However, if the ground is highly mineralized or contains a lot of metal debris, the advantages of a large coil are lost. due to the need to reduce the sensitivity of the device. It should be noted that each company produces different coils that are suitable for devices only of this company. Батареи Most metal detectors operate on 9V or 12V power sources. Accordingly, separate 9V batteries, a 8V battery pack (12 pcs.), As well as rechargeable nickel-cadmium batteries (NiCd), nickel-metal hydride batteries (NiMH) are used. , lithium-ion batteries (Li-Ion) and lead batteries.
Rice. 31. Batteries for metal detectors The cheapest zinc-carbon batteries. But they also have the shortest lifespan. Best of all work at temperatures from O °C to +40 °C. Most prone to leaks. Slightly more expensive, but longer lasting zinc chloride batteries. Also prone to leaks. Alkaline manganese batteries have a significantly longer life than the first two. In addition, they store better and work better at low temperatures. Although they are more expensive, they are generally cheaper than zinc-carbon and zinc-chloride batteries. Nickel-cadmium rechargeable batteries are much more expensive. When used properly, they last a very long time as they can be recharged up to 1000 times. However, due to their inherent "memory effect", they can fail much sooner if they are not used correctly. The "memory effect" is that a nickel-cadmium battery that has not been completely discharged to the end, as it were, remembers the residual capacity and subsequently is not fully charged. To combat this phenomenon, one or more charge-discharge cycles are required, which introduces certain inconveniences in the operation of nickel-cadmium batteries. It is because of this that they have ceased to be used to power mobile phones. Much better in this regard are NiMH batteries, which, unlike NiCd batteries, can be recharged at any time without the need to fully discharge the battery. However, for efficient operation of the battery, it is necessary to carry out 3-5 charge-discharge cycles of a new NiMH battery. To do this, it must be fully charged before the first use. We recommend that the battery be energized for at least 12-16 hours before first use. Ideally, 20 hours. There is no need to worry that leaving the battery connected to a working charger for too long will cause any harm. The device has built-in protection and changes the voltage according to the degree of battery charge. If the battery is fully charged, charging stops. Now you can use the battery. However, make sure that the first time you use the metal detector with a new battery, it can be completely discharged. Most likely, you will need 2-3 days of intensive work with a metal detector. The second charge time should not be less than 12 hours. Ideally - 16. Such cycles (full discharge - charging 16 hours) will require at least three. Better if five. These tricks only apply when you start using a new battery. There is no need to fully discharge the battery in the future. You will be able to recharge it, regardless of whether it is completely discharged or not. But the implementation of these recommendations will significantly extend the life of your battery. If the battery has not been used for a long time (6 to 9 months), you should follow the steps above as if it were a new battery. Only 3-5 charge-discharge cycles - and you have a fully prepared battery. You won't lose any performance. The most efficient are lithium-ion batteries, which, although more expensive, have higher capacity and lighter weight. In addition, a Li-Ion cell has a voltage of 4,2 V, and NiMH - only 1,2 V. This means that a Li-Ion battery can consist of 2-3 cells (it is called a battery because, in addition to the cell, it has also an electronic circuit that protects it from deep discharge, overcharging and short circuit), and NiMH - at least out of eight. And for batteries there is a rule: the fewer elements they have, the more reliable and longer they work with proper operation. One of the main quality characteristics of the battery is its capacity. It is measured in ampere-hours (Ah) or milliamp-hours (mAh, 1 mA = 0,001 A) and indicates the amount of discharge current at which a fully charged battery is discharged to the end-of-discharge voltage in 1 hour. The higher the battery capacity, the better. Knowing the capacity of the battery (or rechargeable battery), it is easy to calculate the operating time of an electronic device. To do this, you need to divide the battery capacity by the discharge current (load current). As a result, we obtain the duration of continuous operation of the metal detector. Usually it is 15-20 hours. for NiMH batteries and 50-60 h. for Li-Ion batteries. There are standard and accelerated methods for charging batteries. Standard charge is the safest for any battery. If a fast charge is used, then it is very important that the battery is completely discharged before starting the charge. Chargers that provide a fast charge start the charge cycle by discharging the battery in order to then charge it to full capacity. These devices, which have a special electronic charge management circuit, are more expensive than standard chargers. However, in addition to reducing the charge time, their use allows you to increase battery life, because. slow charge contributes to the development of the "memory effect". There are no clauses here. Manufacturers, saying that this effect is not typical for NiMH batteries, are cunning. It still takes place, although it is not as pronounced as in NiCd batteries. Lithium-ion batteries do not have a "memory effect". Please note that lithium-ion batteries are not compatible with nickel-metal hydride battery chargers. Despite the high cost of rechargeable batteries, in general, their use is more profitable in terms of money with frequent work with a metal detector compared to conventional batteries. Lead batteries used in AKA devices also do not have a "memory effect" and can be recharged at any time. Their disadvantage is their heavy weight. The performance and service life of a rechargeable battery is highly dependent on following the handling guidelines below. Charge and Discharge: 1. Optimum performance of a new battery is only achieved after three to five full charge/discharge cycles! This only applies to NiMH batteries. 2. A rechargeable battery can be charged and discharged hundreds of times, but will eventually wear out. If the operating time is significantly reduced, replace the battery with a new one. 3. When not in use, the charger must be disconnected from the power source (AC or vehicle electrical system). 4. Do not leave the battery connected to the charger for more than a day, as overcharging will shorten its life. 5. If a fully charged battery is not used, it will discharge over time 6. To extend the life of the NiMH battery, fully discharge it from time to time while leaving the instrument switched on. Attempts to discharge the battery in any other way are unacceptable. 7. Temperature extremes reduce the battery's ability to accumulate charge energy, so before charging, it is necessary that the battery temperature be within room temperature - + 15-25 ° C. Tools for retrieving finds To extract the finds, various tools are used - knives, screwdrivers, shovels, sapper and garden shovels, probes, drills, etc. Some of these tools can be conveniently attached to a belt. The authors recommend using a US military belt for this purpose, which can now be purchased in Russia in stores selling camping equipment and weapons. This belt is wide enough, durable, stiff, easy to fasten and adjustable. Screwdriver. To extract coins from a depth of 5-10 cm, an ordinary flat screwdriver is used. In order not to damage the coin, it is recommended to grind off sharp edges and corners. Нож. It is used for cutting turf plugs, crushing hard or frozen soil, cutting thin roots that interfere with work, etc. Blade length should be 15-18 cm, thickness 4-5 mm. Rubber or leather handle. The choice of knives is now quite large, and you can choose the right model to your liking. It is recommended to cut off the end of the sheath so that the earth that gets into the sheath with a knife gradually spills out of it. Scoop. To extract coins that lie at a shallow depth (5-10 cm), a garden scoop is sometimes useful. The end of it can be sharpened so that it can cut through the turf. The scoop should be rigid enough and comfortable when working. Probe. The probe is made from a long thin (3-4 mm) screwdriver, the end of which is rounded. By piercing a pound with a probe, you can easily find the exact location of the coin. To protect the coin from damage, a layer of epoxy resin can be applied to the end of the probe. Probe. If the soil is malleable enough, then a probe made of a hardened steel bar with a diameter of 8-10 mm and a length of 130-150 cm can be successfully used to check a deep find. A transverse handle is welded to the upper end, and a conical tip is screwed into the lower part, the base diameter which is 2-3 mm larger than the diameter of the rod. By piercing a pound with a probe and touching it to the find, you will learn to recognize the material that the find consists of (metal, bone, ceramics, glass, paper, wood). The probe saves time digging up what might be a rusty bucket. Unfortunately, it is not always possible to pierce a pound by 1,5 mef with a probe. In this case, a drill can help. Boer. When detecting deep objects, the metal detector is not able to recognize what metal, black or non-ferrous, this object is made of. To determine the type of metal, it is not necessary to dig a hole 1,5 m deep. You can drill a hole with a diameter of 4-5 cm with a hand drill, lower a cylindrical coil with a diameter of 2,5 cm into it and, using discrimination, determine the type of metal, and then make a decision - to dig pit or not to dig. Shovel. In those places where accurate digging of finds is not required (forest, arable field after harvesting, etc.), a shovel is usually used. It is more convenient to dig with a large shovel, but often a small shovel, the so-called "small sapper", is more practical. In the field, it can be used both as an ax and as a cold weapon. Very high-quality shovels were produced in Russia even before the First World War. The fastening of the handle consisted of two riveted parts and a clamping ring running at the end. The sleeve for the handle was long enough. The bayonet of the shovel was made of hardened steel. Now ordinary sapper shovels for the army are noticeably worse both in terms of workmanship and metal quality. However, a number of Russian firms have mastered the production of good shovels, among which one can note the shovel manufactured by the Spetsmaterialy company in St. Petersburg. It is made of armored steel and is capable of cutting nails and 15mm angle. A convenient folding blade is made at the Moscow Research Institute of Steel. 3 variants of the shovel are produced - from ordinary steel, armored steel and titanium. Occasionally, the "Special Forces" shovel and its civilian version "Mole" appear in stores. The shovel is based on the idea of a drop-down knife. In the open position, the latch pulls the halves of the handle together and a rigid structure is obtained. On the basis of this shovel, the so-called "small archaeological shovel" was developed. The spatula is small, all-metal, with overlays on the handle made of impact-resistant plastic. Magnets. Recently, permanent magnets based on compounds of rare earth metals have appeared on the market. Their shape is diverse - cylinders, plates, rings, rods. Such magnets, for example, the size of a matchbox, can lift a two-pound weight. They can be successfully used when searching for iron objects not only at the bottom of reservoirs, wells, but also in the ground. So, meteorite seekers, having received a signal, do not bother to determine the exact location of the meteorite, but simply loosen the ground under the coil and extract the meteorite from it using a magnet attached to a bayonet or a shovel handle. Knee Wraps. Knee pads are used by miners, parquet floorers and roller skaters. However, when working with a metal detector, they are no less useful, although they look rather ridiculous. Fastened with Velcro. They are easy to make yourself from suitable materials - sponge rubber, felt, etc. Bags for finds and trash. Made from fabric or plastic. Branded pouches look like an apron with two pockets - one for finds, the other for trash. Of course, you can put the finds in your pocket and not collect garbage, but the pocket will quickly wipe out, and you will collect garbage again if you come to the same place again in a few years. Gloves. There are many items in the ground that you can injure your hands with when digging up finds. These are glass fragments, sharp stones, nails, cans, etc. So it's better to wear gloves. Instrument cases. When working in rainy weather, it is recommended to put on a special protective cover on the electronic unit. Otherwise, water may get inside and damage the device. Such a cover can also be sewn from a suitable fabric. Carrying bags. Metal detectors are usually shipped in cardboard boxes. In such boxes it is convenient to store it when the device is not used for a long time. However, when going out into the countryside, it is more convenient to carry it assembled or semi-assembled in special bags similar to those in which guns are transported. Cards A map is a tool for navigating the terrain. When searching, you have to use a variety of cartographic materials. There are hundreds of types of maps, but two types are mainly used for orientation. These are, firstly, planimetric maps, where the existing territory is displayed as absolutely flat. The diagram lacks the nature of the relief and depicts only such objects as highways and railways, trails, rivers, lakes, cities and villages. Much more useful for search engines are military topographic maps (from which the stamps "secret" and "Soviet secret" were removed), giving an idea of the landscape and terrain of the depicted territory, including the designation of hills, lowlands, gorges, rivers, lakes, cliffs, forests and swamps, as well as roads, trails, towns and villages. Each map contains an indication of the scale used in its compilation, which makes it possible to judge the relationship between the length of the line on the map and the length of the corresponding line on the ground. Typically, the scale is indicated both in numerical form as a fraction, and in linear form. A numerical scale, such as 1:50, indicates that the real world is reproduced on a map at one fifty-thousandth of its actual size. Thus, 000 cm on a 1:1 scale map represents 50 cm, i.e. 000 m on the ground. A linear scale is a simple line divided into units of length, such as kilometers. The distance between two points on the map can be measured using a measuring compass, which is then superimposed on a linear scale with the reading of the real distance on the ground in the usual units of distance measurement. Unfortunately, maps become outdated, and in areas with a high population density this happens very quickly. , forests have been cut down, rivers have become shallow and small lakes have disappeared, suburbs have grown, many villages have disappeared, etc. Therefore, along with modern ones, old maps are also very useful for finding suitable places to work. These are land surveying plans of the late XNUMXth century, maps by Schubert and Mende (XNUMXth century). You can get acquainted with them in archives, large state libraries, on the Internet. Old maps of some areas around Moscow can be purchased at the "Rodonit" company. A location on a map is described using latitude and longitude markers. On the globe of the Earth, lines of latitudes, called parallels, encircle the globe in the form of rings parallel to the equator, the diameter of which decreases as it approaches the poles. Lines of longitude, known as meridians, run vertically through the poles, cross the equator at right angles, and divide the earth's surface into a series of segments.
Rice. 32. Ancient and modern maps of the city of Serpukhov and its environs Latitude. Imagine two lines emanating from the center of the Earth, one of which is extended towards you, and the other to the point of the equator closest to you. The angle formed by the lines is the latitude of your location. Thus, latitude is a measure of the distance of an object, expressed in angular degrees, to the north or south of the equator. The latitude of the equator itself is 0°, and the latitude of the North and South geographic poles is 90° N, respectively. and 90° S The latitude of, for example, Moscow is 55°45'N. Longitude is a measure of the distance of an object from the Prime Meridian, which is an imaginary line connecting the North and South Poles of the Earth and passing through the Greenwich Observatory (Greenwich Meridian) in London. The longitude of an object is expressed in degrees of an angle formed by two lines, one of which connects the center of the Earth with the point of intersection with the equator of the zero meridian, and the other - the same center of the Earth with the nearest point on the equator from the object. The maximum longitude value of 180° is fixed on the opposite side of the earth from London. When specifying the position of a place in latitude and longitude, latitude is always named and indicated first. Latitude and longitude are measured in angular degrees. Latitude varies from 0° at the equator to 90° at the poles. Longitude can range from 0° on the prime meridian to a maximum of 180° east or west. There are 60 minutes (60``) in one degree, and each minute consists of 60 seconds (60``). One minute of latitude is equivalent to one nautical mile (1,853 km). The distance between adjacent marks of minutes of longitude varies from zero at the poles to one nautical mile at the equator. The exact location is given in degrees, minutes and seconds (1 second equals approximately 30 m on the ground). GPS receivers GPS (Global Position System) is a modern system of global positioning and exact time based on satellite fixing of coordinates. It is considered one of the most effective navigation systems and has recently been increasingly used in everyday life. A portable GPS receiver, comparable in size and price to a mobile phone, will indicate your location anywhere in the world with an accuracy of 15 m or even less.
Rice. 33. GPS receivers from Garmin GPS is the brainchild of the US military. This system began to be developed in the early 1970s. as an accurate and reliable all-weather instrument for the US Army, Navy and Air Force. It was only fully operational in the mid-1990s. and soon found application in many other, quite peaceful areas of human activity. The GPS navigation system consists of three separate elements: the control segment, the space segment, and the user segment. The control segment includes five ground stations located at US Air Force bases around the world. These stations constantly monitor the operation of the satellites, control their exact position, correct the orbit, synchronize the atomic clock, and transmit accurate position and time data to the satellites. The space segment includes 24 GPS satellites orbiting the earth at an altitude of about 20 km. There are 200 orbits in total and each has 6 satellites. Each satellite makes one revolution around the Earth in 4 hours and constantly transmits radio signals, in which data are encoded both about its own position and speed, and about the position and speed of all other satellites. In addition, each satellite transmits accurate time signals using its own atomic clock. The user segment is represented by all the GPS receivers available in the world, the role of which is to receive signals from the satellite and decrypt them, thanks to which you can determine your exact location (with an error of up to 15 m) even in conditions of zero visibility, indicate the direction to the destination of your trip and distance to her. In addition, the receiver remembers your current position, so you can later restore this position, that is, return to its original place. When GPS was first made available to civilians, the US Department of Defense gave the military an edge in its use by including intentional errors in civilian GPS signals. As a result, if the military could determine their location with an accuracy of up to 15 m, and in some cases up to 1 m or less, then the accuracy for civilians was about 100 m. By order of B. Clinton on May 1, 2000, the practice of introducing errors into positioning for civilians has been abolished and now the accuracy of civilian and military receivers is quite comparable. The GPS market today offers a wide variety of receivers. Simpler models provide navigational information in the form of a set of coordinates, which are then transferred to a paper map. More expensive models store one or more electronic maps in their memory, which are displayed on the display screen with an exact indication of your location. An increasing number of GPS receivers are equipped with the ability to connect to a personal or laptop computer, onto which electronic maps can be downloaded from laser discs or from the Internet, after which the high-resolution color display provides the user with the same benefits that distinguish expensive GPS models with an integrated electronic map . Among these advantages is the indication of your location directly on the map, and not only the coordinates, which then need to be transferred to a paper map. Pinpointer Sometimes, when you find something in the ground, you can't find it because it's too small. Of course, eventually you will get it, but it takes time. There are devices, the so-called pinpointers, that allow you to find such objects in a few seconds.
Rice. 34. Pinpointer A pinpointer is a small-sized metal detector, the search coil of which is mounted on the end of a plastic rod. The device beeps when the target is at the end of the rod. Thus, when you receive a signal while working with a conventional metal detector and, having loosened the ground, cannot find an object in it, pierce the ground with a pinpointer rod and, having received a signal, grab the soil at the end of the rod. The item you are looking for will be in your hand. The pinpointer is especially useful when searching for small objects in sand, needles and other loose materials. Author: Bulgak L.V.
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