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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Choosing your first metal detector. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / metal detectors For the vast majority, the search for treasures and amateur archeology is a hobby: expensive, but exciting, akin to fishing, hunting and other outdoor activities. In most cases, you have to enjoy not the result, but the process in the fresh air. But there is also a result if you prepare well for the search. Conventionally, all metal detectors can be divided into three large categories (primarily by consumer properties, and not only by the methods of formation, signal processing and information presentation):
In turn, metal detectors are divided into 2 categories according to the principle of processing and displaying information:
Semi- and professional instruments are mostly digital, with powerful signal processing algorithms. As a rule, mid-level devices are simplified versions of professional devices and are more adapted for a novice user. Analog devices are built without the use of powerful signal processing and display processors, they contain 1-3 (more "advanced" models up to 5-6) regulators responsible, for example: for setting the volume of audio signals, sensitivity, discrimination, etc. Digital devices, along with a powerful processor and changeable search programs depending on the conditions (as well as the ability to create your own programs with many settings), contain a display that can display:
In addition, digital devices have many adjustable parameters that affect (and not so much) the depth and comfort of the search. Which device (analogue or digital) to choose for a novice user depends on his personal preferences. If there is no desire to deeply understand the numerous settings, but immediately turn it on and search, it is better to purchase an entry-level digital device. If it suits you to make the appropriate settings manually with potentiometers, you can choose an analog metal detector. The difference between the properties of expensive and cheap metal detectors The difference between cheap and expensive models is only in the methods of emitting radio waves and methods of capturing, processing and interpreting secondary signals. A more expensive device may:
Capabilities and Features of Good Metal Detectors Good metal detectors can have many different abilities:
This is partly solved by using a "Faraday" shield around the coils, with the shield made of iron oxide considered to be the best. When constructing metal detectors on your own, the screen is usually made of thin tinned copper foil. For better suppression of the influence of the earth, special circuit solutions are used. This method in foreign literature is called CEB (Ground Exclusion Balance) - the exclusion of the influence of the earth. It should be noted that the presence of the GEB system in metal detectors does not always allow you to effectively rebuild from the influence of the ground. Fortunately, in most of the territory of our country, "heavy" soils are rare. "Heavy" soils include: wet sea sand, red alumina, rocky soils, etc. What you need to know when choosing a metal detector about the depth of detection A coin with a diameter of 25 mm (nickle of the USSR) is found from 10 cm for the simplest devices to 50 cm for very serious ones. The depth of detection strongly depends on the size of the sensor (usually the diameter of the disk with coils). Tentatively, for such a coin, the detection depth is approximately equal to the diameter of the search coil. Smaller coins will be detected at shorter distances. For example, the detection depth of a coin with a denomination of 1 kopeck will be approximately two times less than indicated above for a nickel. A helmet, an axe, a small cannonball, a pistol can be detected at a depth of up to 1 m. In this case, the detection depth weakly depends on the size and type of the sensor. It can be both with coplanar coils and with orthogonal coils on the rod. For a sensor with larger diameter coils and for a sensor with an orthogonal coil system on the shaft, the detection depth will be only 20% more when moving from a 20 cm diameter disk sensor to a 30 cm diameter sensor. Metal shield, bell, large cannonball. The depth of their detection also weakly depends on the size and type of the sensor and is 1,5-2,5 m for models of metal detectors of different levels. There is a theoretical limit beyond which an electronic metal detector is not able to register objects in principle, despite their arbitrarily large sizes. After all, the amplitude of the reflected signal is inversely proportional to the 6th-7th power of the distance, and depends on the size of the object only to the 3rd-5th power. The value of the maximum theoretically possible detection depth ranges from 1 m for the simplest devices with a disk sensor to 4 m for complex devices with a large sensor of orthogonal coils on a rod. Unfortunately, it is this value that usually appears in advertising purposes, but at this depth you will not find anything! The most modern electronic metal detector can detect an average coin at a maximum depth of 50 cm, and a large massive all-metal object at a maximum of 2,5 m. In the search, 90% is decided by luck and preliminary preparation, and only 10% determines the quality of the metal detector. The main groups of metal detectors (metal detectors) suitable for searching for coins, treasures, relics According to the characteristics of metal detectors (metal detectors), which are suitable for searching for coins, treasures, relics, can be divided into several groups. Let's consider them according to the principle "From simple to complex". Group 1. Simple ground metal detectors Price level from $80 to $300. Peculiarities. Designed for beginners, have a small set of functions when searching. Work principles. To detect a target, one or two frequencies are used, they include discrimination, less often - determining the depth of the target. Detection depth (depending on the type of soil!):
Group 2. Semi-professional metal detectors Price level from $400 to $700. Peculiarities. Designed for people with sufficient experience in search, have a fairly wide range of functions when searching. Work principles. To detect a target, the use of multi-frequency radiation is provided, they have the ability to operate not only with sound, but also with visual information, i.e. visual information is displayed on the display, where you can see the VDI of the detected object:
Copper and silver coins always give a VDI value close to the maximum values. On different metal detectors, the digital minimum and maximum VDI values \u10b\u700bare different, for example, -30 to + 50 or -XNUMX to +XNUMX. That is why such devices can be classified as semi-professional. Detection depth (depending on the type of soil!):
Group 3. Professional ground metal detectors Price level - from $700. Peculiarities. Designed for experienced search engines, they have multi-voice discrimination, multi-frequency search range, many manual and automatic settings, i.e. a very wide range of search functions:
Analysis of these indications and makes it possible to determine:
Work principles. This is a search computer that makes full use of digital signal processing by a microprocessor. It provides search and selection of all "colored" objects located in the investigated surface. Detection depth (depending on the type of soil!):
Group 4. Metal detectors for searching for gold nuggets Price level - from $800. Peculiarities. Designed for experienced searchers, they have multi-voice discrimination, multi-frequency search range, many manual and automatic settings. Almost the entire range of such metal detectors can be classified as professional. They have the frequency to detect even the slightest gold content in any environment. Gold has quite a characteristic VDI, but very similar to foil (both in sound and visual discrimination). It is very difficult to cut off the foil from gold or find a gold grain in the ground. Gold metal detectors are designed to pick up the frequency of gold more than the frequencies of all other non-ferrous targets. At the same time, the indicators for finding other “colored” targets remain at a high level. Group 5. Underwater metal detectors Price level - from $800. Peculiarities. Designed for experienced searchers, they have multi-voice discrimination, multi-frequency search range, many manual and automatic settings. They have a sealed case, headphones. Visually, they do not give out information, only sound. Work principles. The settings in such metal detectors are designed to take into account not only mineralization, but also the interference created by water, while the interference is different in fresh and salty sea water. Usage area. Search at the bottom of the reservoir, on the beaches, in the coastal zone. The depth of detection depends entirely on the search environment. Group 6. Deep metal detectors Price level - from $700. Peculiarities. They are designed only to detect volumetric objects located at a depth and cannot find a coin that lies at a depth of several centimeters from the surface. Features of work. They practically do not have discrimination, that is, when an object is found, it is necessary to dig it out in order to see what is found. This kind of metal detectors are usually used during excavations at the battlefields of the Second World War, where objects can be covered with earth more than 1,5-2 meters. Detection depth (depending on the type of soil!):
Deep coil. Garrett has created a deep special coil for the GTI 2500 universal metal detector. It is significantly inferior in size to the coils of deep metal detectors, but it makes it possible to use one metal detector for all kinds of searches. Group 7. Pinpointers (metal detectors for pinpointing an object) Price level - from $400. The name comes from the English words Pin Pointer (dotted pointer). Features of work. Metal detector for detecting the exact, to the millimeter, location of an object. Such metal detectors do not have discrimination and are used to detect inside walls. Some search engines are used to detect small coins during excavations. The main purpose of the pinpointer is to indicate the exact location of a metal object at a small search depth (up to 5 cm). The main questions when choosing a metal detector First of all, you need to decide on several main questions before choosing a metal detector:
How to choose a metal detector for a specific task When buying a treasure-hunting device for the first time, try to avoid both too cheap models and expensive professional devices. A cheap, weakly sensitive device may not live up to your expectations and unnecessarily disappoint in the search for treasures with a detector. It is likely that when you encounter an expensive computerized instrument for the first time, it will be difficult for you to master it quickly and efficiently. Case 1. You need to find a specific treasure The probability that this treasure will be discovered is 5-10%. Such statistics and interesting examples are given by the site klad.kiev.ua/. It's worth a visit.
If you still decide to buy a metal detector, then it should be chosen strictly based on the tasks discussed above. Without these preliminary measures, choosing a metal detector based on the story of sellers and dealers is a waste of money. If, according to preliminary estimates, the treasure is located at a depth of more than 1,5-2 m, little metal detector will help. The maximum depth at which it is realistic to find something is up to 2 m, and only if there is a huge object there. Believe me, not a single person in their right mind digs to great depths. In this case, you do not need to buy a serious and expensive metal detector. The probability that something will be found and the money spent will be returned is too small. Perhaps an inexpensive entry-level metal detector is suitable to get acquainted with the capabilities of modern metal detectors. In any case, the adrenaline and healthy energy boost from regular trips to nature will outweigh the slight disappointments of financial expenses and prevent health problems from a sedentary lifestyle. Case 2. You are interested in archeology, ancient coins In this case, pay special attention to the quality of object discrimination and the sensitivity of the metal detector. Get a metal detector with a large search coil. Best of all - if you have two coils - 21 and 28 cm. It is highly desirable to buy a computerized metal detector with good service. Case 3. The task is to look for lost gold jewelry on the beach in Crimea As in the previous option, pay attention to discrimination. On the beach, it is better to work with coils with a diameter of 21 cm. You can choose a cheaper metal detector, but be sure to use a computerized one, otherwise you risk cleaning the beach from aluminum vodka corks (the ratio of finds of a cap and a golden thing is on average 400 to 1!). Pay special attention to the moisture resistance of the search coil and the entire device as a whole. Indicators by which you can evaluate the purchased device There are important technical indicators and features that it is desirable to consider when buying a metal detector (metal detector):
For some searchers making short-term sorties, the weight, ergonomics of the detector and battery life will not be the main criterion when choosing a device. While for others, scouring the fields all day long, these are important indicators. If you are going to search on the beach, then you should pay attention to the moisture resistance of the coil of the device. Opportunity/Price Ratio Calculations When Choosing Your First Metal Detector Consider the prices for several budget metal detectors, for example, from Bounty Hunter:
Of these, we should highlight the model "Discovery 2200" - light and compact from the new series "Metal detector for finding treasures, lost jewelry and coins". This is a universal, easy-to-learn device that allows you to search at a depth of up to 0,5 m, both on land and in salt and fresh water. It is equipped with a depth gauge and touch sensitivity and discrimination level adjustment. Three modes of operation of the discriminator make it possible to automatically exclude an unwanted group of objects. The LCD monitor of the metal detector has a clear and illustrative visual identification by the type of target (9 segments) in addition to a 4-tone audio signal for different types of metals. There is an automatic setting of the ground balance. But in some areas there are areas with increased soil mineralization, heterogeneity and various inclusions. The metal detector often reacts to such inclusions as a target. To avoid such false alarms, you can choose the "Tracker II" and "Sharp Shooter II" metal detectors. They have, in addition to automatic and manual adjustment to the soil. "Sharp Shooter II" also has a static search mode, is equipped with a depth gauge and a three-mode discriminator. If you have a $500 budget to buy a metal detector, then the Sharp Shooter II is a good choice. In addition to the modes discussed above, it contains:
Differences in consumer properties of expensive and cheap metal detectors Both the depth and accuracy of determination are different in cheap and expensive models. But not in the same proportion as their prices vary. Example. Coin 5 kopecks of the USSR:
The difference in detection depth of 11 cm (60% more) corresponds to the difference in the cost of these metal detectors of almost $1400 (680% more). Thus, when purchasing the device, you should remember the following:
In terms of discrimination accuracy (separation of targets from non-ferrous and ferrous metals), expensive metal detector models are ahead. In Explorer II, the found target is identified by the specific conductivity of the metal, as well as simple devices, but not at one frequency, but at 28 frequencies simultaneously. The results are processed by a computer and displayed on the LCD in graphical and digital form, as well as sounds of various tonality and volume. Thus, it is possible to more accurately determine the type of metal, the size of the target and its depth. In Tracker IV, the target is irradiated at only one frequency and is identified simply by three sounds: low, high pitch, intermittent ("broken") signal, and also with the help of a dial indicator. And it will also take a lot of work and time to fully master an expensive and complex metal detector. It is desirable to have prior practical experience in search. Explorer II and devices similar in terms of capabilities are recommended for experienced searchers who have more than one year of real searching behind them. Metal detectors of a high price category, using the properties of their discriminators for the accuracy of target identification, save time on searches and do not dig again! The truth is that the complete identification of complex targets is possible only when the object is actually excavated. Author: Dubrovsky S.L.
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