Scheme Depth Metal Detector Transmission Reception. The principle of operation of the metal detector. One coil induction metal detector

I propose to repeat a personally assembled recently and successfully earned a simple metal detector. This metal detector works on the "transmission-reception" principle. A multivibrator is used as a transmitter, and the sound frequency amplifier is used as a receiver. The schematic diagram was published in the radio magazine.

Diagram of the MD receiver - the second option

Metal detector parameters

Operating frequency - about 2 kHz;
- depth of the detection of the coin with a diameter of 25 mm - 9 cm;
- iron sealing cover from the can - 25 cm;
- aluminum sheet with dimensions 200x300 mm - 45 cm;
- Sewer hatch - 60 cm.

Search coils connected to it must be absolutely identical in size and wincise. They must be positioned so that in the absence of extraneous metal objects, the connection between them is practically absent, examples of coils are shown in the figure.

If the transmitter coils and the receiver are exactly the case, then the transmitter signal in the receiver will not listen. When it appears near this balanced system of the metal object, there are so-called vortex currents in it under the action of an alternating magnetic field of the transmitting coil and as a result, the own magnetic field, which brings the variable EMF in the receiving coil.

The signal received by the receiver is converted by phones into sound. The scheme of the metal detector is really very simple, but despite this, it works quite well, and the sensitivity is not bad. The transmitting block multivibrator can be collected on other transistors of a similar structure.

Metal dealer coils have a size of 200x100 mm and contain about 80 turns with a wire of 0.6-0.8mm. To check the transmitter, instead of the L1 coil, the headphones are connected and are convinced that when the power is turned on, the sound is heard in them. Then, connecting the coil into place, control the current consumed by the transmitter - 5 ... 8 mA.

The receiver is adjusted with a closed input. The selection of the R1 resistor in the first cascade and R3 in the second are installed on the collectors of transistors according to the transistors equal to about half of the supply voltage. Then the selection of the resistor R5 seeks that the transistor current of the VT3 transistor has become equal to 5 ... 8 mA. After that, opening the input, the L1 receiver coil is connected to it and accepting the transmitter signal at a distance of approximately 1 m, are convinced of the device efficiency.

Metal detectors are often needed for example, when searching for lost metal objects or pipes, cables, tanks, buried under the ground. More Metal detectors are associated with trekers andminers 🙂

Types of metal detectors

The most complex and sensitive, but also the most expensive, built on the principle radio transmission / reception. The complexity and high cost is not only in the abundance of electronic components of the circuit, but also in the need for qualified circuit settings.

There are some more species according to different principles: induction, frequency meters, impulse, generation of generation, method of beagi, impulse induction, disrete resonance ...

The meaning of all metal detectors in one: changing the generator frequency when inserting a metal object coil. This frequency change is usually very insignificant, and the second essence of one or another scheme is to catch this slightest change and transform into something.

The scheme of a simple metal detector is presented below.

Making a similar metal detector compact and taking it with him on a trip to the sea, he will help you, when looking for a gold jewel to you or relatives on the beach. But what is closer to you, so this is a search for hidden wiring in the wall of whether some carnation. This is such a simple and proven diagram of a metal detector for such purposes. We will look here to gather it with your own hands.

Scheme of a simple metal detector on transistors

The scheme of this simple metal detector, which the lover can repeat without much experience.

Metal detector characteristics:

• The detection of the coin is 10-15 cm (with good adjustment, some are enough that up to 50 cm!);
• Steel scissors - 20-25 cm;
• Large items - 1-1.5 meters.

The scheme consists of two high-frequency generators, each on one transistor (VT1 and VT2). The frequency of the left generator (VT1) is changed when the metal in the L1 field is inserted, and the frequency of the right (VT2) remains unchanged. The denominations of the elements of both generators are chosen so that the frequencies of the generators differ only slightly. Generators work on radio frequency (more than 100 kHz), and such a sound you can not hear either our ear, is reproduced by the speaker. But a small difference, for example, 160 kHz and 161 kHz is 1 kHz - this is already hearing oscillations. And both coils of generators (L1, L2) are inductively connected (located near), so both signals from the generators with a difference in 1 kHz are combined and we hear the so-calledamplitude beats The frequency of 1 kHz.

Metal detector setup

Best Metal Detector

Why was Volksturm called the best metal detector? The main thing is the scheme really simple and really working. From a variety of metal detectors schemes that I personally did, it is here that everything is simple, deep and reliably! Moreover, with its simplicity, in the metal detector there is a good discrimination scheme - the definition of iron or non-ferrous metal is in the ground. The assembly of the metal detector consists in an error-free solder of the board and setting the coils into the resonance and at zero at the output of the input stage on the LF353. There is nothing superser, there would be a desire and brains. We look constructive metal detector execution and a new enhanced Volksturm scheme with a description.

Since, in the course of the assembly, questions arise to save your time and not to force the hundreds of pages of the forum, here are answers to the 10 most popular questions. The article in the process of writing, so some items will be supplemented later.

1. Principle of operation and detecting the goals of this metal detector?
2. How to check whether a metal detector work works?
3. What resonance to choose?
4. What condensers are better?
5. How to set up resonance?
6. How to cut coils in zero?
7. What wire for coils is better?
8. What are the details and what can be replaced?
9. What is the depth of the search for goals?
10. Nutrition of the Volksturm Metal Detector?

The principle of operation of the Volksturm Metal Detector

I will try in two words about the principle of operation: transmission, reception and balance of induction. In the search sensor of the metal detector, 2 coils are installed - transmitting and receiving. The presence of a metal changes the inductive link between them (including phase), which affects the received signal, which is then processed by the indication unit. Between the first and second chip, the switch controlled by the generator shifted by phase relative to the transmitting channel (i.e., when the transmitter works, the receiver is turned off and on the contrary if the receiver is turned on the transmitter rests, and the receiver calmly catches the reflected signal in this pause). So, you turned on the metal detector and it beeps. Excellent, if stamps - it means many nodes work. Let's figure out why it is stamping. The U6B generator constantly generates a tone. Next, it enters the amplifier on two transistors, but the UHH will not open (will not miss the tone) until the voltage at the y2B (7th output) will not allow it. This voltage is set by changing the mode using this very resistor TRACH. They need to set such tension so that the UHR almost opened and missed the signal from the generator. And the input pair of Milvololt from the metal detector coil, passing the amplifying cascades, will exceed this threshold and it will open completely and the speaker will be discovered. Now let's follow the passage of the signal, or rather the response signal. At the first cascade (1-U1A) there will be a pair of Milcivolt, you can up to 50. On the second cascade (7-U1B), this deviation will increase, on the third (1-U2) will already be a couple of volts. But without a response everywhere at the outputs at zeros.

How to check whether the board is working

In general, the amplifier and key (CD 4066) is checked with a finger at the RX input contact with the maximum Sens resistance and the maximum background on the dynamics. If the change in the background is when pressing a finger for a second, the key and the operating rooms work, then connect the RX coils with the circuit condenser in parallel, the condenser on the TX coil sequentially, we give one coil to another and begin to reduce in 0 by the minimum AC indication on the first leg of the amplifier U1A. Next, we take something big and iron and check there is a reaction to metal in the dynamics or not. We will check the voltage on the U2B (7th output) it should be a trash regulator, change + volt. If not, the problem is in this Cascade of OU. To start checking the board, turn off the coil and turn on the power.

1. Must go sound when the sensor regulator is positioned on the maximum resistance, totto the finger on the Px - if there is a reaction, all the operatingors work, if not, we check the finger starting with U2 and change (survey the strapping) of non-working OU.

2. The generator operation is verified by the frequency meter program. Plug from headphones soldered to 12 withdrawal CD4013 (561TM2) prudently dropping P23 (so that the sound card does not burn). In the sound card to use in-lane. We look at the generation frequency, its stability is 8192 Hz. If it is strongly shifted, then the C9 capacitor should be harvested, if after it is not clearly highlighted and / or a lot of frequency bursts nearby - replace quartz.

3. Checked amplifiers and generator. If everything is fine, but still does not work - change the key (CD 4066).

What resonance to choose

When connecting the coil into a serial resonance, the current in the coil and the overall consumption of the circuit increases. Increases the distance detection distance, but it is only on the table. On the real soil, the earth will feel the stronger than the larger the pumping current in the coil. It is better to turn on parallel resonance, and raise the input cascades. Yes, and the batteries are enough much longer. Despite the fact that consistent resonance is used in all branded expensive metal plates, in the storm you need it precisely parallel. In imported, expensive devices, good configuration schematics from the ground, therefore, in these devices can be allowed to be allowed.

What condensers are better to install in the scheme metal detector

The type of capacitor connected to the coil is not when, and if it was experimentally changed two and saw that with one of them the resonance is better, then it is simply one of the supposedly 0.1 μF really has 0.098 Igf, and the other 0.11. So the difference between them in resonance is obtained. I used Soviet K73-17 and green imported pillows.

How to set up resonance coils metal detector

The coil, as the best option, is obtained from plastering grads glued with epoxy resin from the ends to the size you need. Moreover, its central part with a piece of the handle of this very grater, which is processed to one wide ear. On the bar, on the contrary, the fork of two bunches of fastening. This solution allows you to solve the problem of deformation of the coil, when tightening a plastic bolt. The windings for the windings make the usual delicate, then setting the zero and fill. From the cold end TX, we will leave 50 cm. Wires, which originally not to fill, and press the small coil from it (with a diameter of 3 cm) and place it inside the RX, moving and deforming it in small limits, you can achieve an accurate zero, but to do it It is better on the street by placing the coil at the Earth (as when searching) with the geb disconnected if it is, then finally pour the resin. Then the detuning from the Earth, it works more, less tolerable (the exception is strongly mineralized soil). Such a coil is obtained easy, durable, little prone to thermodood, and treated and painted very pretty. And one more observation: if the metal detector is assembled with downtown (GEB) and under the central location of the resistor's engine to set zero a very small washer, the geba adjustment range is 80-100 mV. If you set the zero large subject of a coin 10-50 kopeck. The adjustment range increases to + - 500-600 mV. For voltage in the process of adjusting the resonance, do not chase - I have about 40V with a 12V power with a consistent resonance. To discriminate, condensers in the coils turn on in parallel (the sequential inclusion is only needed at the selection stage for resonance) - on ferrous metals there will be a long sound, color - short.

Or even easier. We connect the coils in turn to the transmitting TX output. We configure one in the resonance, and configuring it - another. Step by step: they connected, parallel the coil was twisted by a multimeter at the limit variables, the condenser 0.07-0.08 ICF soldered the coil parallel to the coil, see the testimony. Suppose 4 V is very weak, not in resonance with a frequency. Pressed parallel to the first condenser of the second small capacity - 0.01 μF (0.07 + 0.01 \u003d 0.08). We look - already showed a voltmeter 7 V. Excellent, we will increase the container, connect to 0.02 μF - we look at the voltmeter, and there are 20 V. Great, we are going on - another dock is a couple of thousand peaks of tanks. Yeah. Already the beginning fall, roll up back. And so to achieve maximum voltmeter readings on a metal detector coil. Then, similarly on the other (reception) coil. Configure maximum and connect back to the receiving socket.

How to reduce metal dealer coils in zero

To adjust zero, we connect the tester to the first leg LF353 and we begin to compress, stretch the coil. After the epoxy bay - Nolik will definitely run away. Therefore, it is necessary to pour not the whole coil, but leave space for adjustment, and after drying, bring to zero and pour finally. Take a piece of twine and half the coil to tie in one turn to the middle (to the central part, the place of connecting two coils) insert a piece of a piece of sticks after which it is twisted (pulling the twine) - the coil will shrink, catching the spike sponge to be powered by glue Again, to adjust the nolik by turning the wand more slightly and pour the twine finally. Or easier: the transmitted is fixed in plastic stationary, and the reception is superimposed on the first 1 cm, such as wedding rings. At the first pin, U1a will be a peak of 8 kHz - can be controlled by a voltmeter of alternating current, but better just high-level headphones. So the receiving coil of the metal detection must be shifted, then shifted with transmitting until the output of the OU does not appeal to a minimum (or the testimony of the voltmeter will not fall to several milcialt). Everything, the coil is reduced, fix.

Which wire for search coils is better

Wire for winding coils does not matter. From 0.3 to 0.8 there will be any, it will still have to pick up the capacitance to adjust the contours to the resonance and the frequency of 8.192 kHz. Of course, a thinner wire is quite suitable, just what it is thicker, the kindness and, as a result of a little - better. But if you wind 1 mm - it will be quite hard to carry. On a sheet of paper, we draw a rectangle 15 to 23 cm. From the left upper and lower angle, we deposit 2.5 cm, and connect their line. We also do the same with the right top and bottom corners, but we post 3 cm. In the middle of the bottom we put the point and on the point left and right at a distance of 1 cm. We take Phaneur, we put this sketch and drive the carnations to all points specified. We take the wire of the PEV 0.3 and wind 80 turns of the wire. But honestly, no difference how many turns. All the same, the frequency of 8 kHz will be exhibited in a condenser resonance. How many wounds - so much wound. I wind 80 turns and a condenser 0.1 of the ICF, if you wog up 50 - the container, respectively, somewhere 0.13 μF will have to have. Next, without removing from the template, wind the coil is thick thread - such as wiring harnesses. After covering the coil with varnish. When dried, remove the coil from the template. Then there is a winding of the coil with insulation - FUM tape or tape. Next is the winding of the foil coil of the coil, you can take a ribbon from electrolytic capacitors. TX The coil can not be shielded. Do not forget to leave the gap in the screen 10 mm, in the middle of the coil. The foil winding is on the tinned wire. This wire, along with the initial contact of the coil, we will have a mass. And finally winding the coil with a tape. The inductance of coils is about 3.5 mg. Capacity is about 0.1μF. As for the fill of the coil epoxy, I did not stick it at all. Just tightly climbed the tape. And nothing, two seasons went away with this metal detector without setting. Pay attention to the moisture insulation of the circuit and search coils, because you will have to mock the grass. Everything should be hermetically - otherwise the moisture will fall and the setting will float. Worsen sensitivity.

What details and what can be replaced

Transistors:
BC546 - 3pcs or kt315.
BC556 - 1pc or kt361
Operations:

LF353 - 1pcs or change to a more common TL072.
LM358N - 2pcs
Digital microcircuits:
CD4011 - 1pc
CD4066 - 1pc
CD4013 - 1pc
Resistors permanent, Power 0.125-0.25 W:
5.6K - 1pc
430K - 1pc
22K - 3pcs
10K - 1pc
390K - 1pc
1k - 2pcs
1.5K - 1pc
100K - 8pcs
220K - 1pc
130K - 2pcs
56k - 1pc
8.2K \u200b\u200b- 1pc
Resistors variables:
100K - 1pc
330K - 1pc
Capacitors are notolar:
1NF - 1pc
22nf - 3pcs (22000pf \u003d 22nf \u003d 0.02222222222
220NF - 1pc
1MKF - 2pcs
47NF - 1pc
10nf - 1pc
Electrolytic condensers:
220MKF on 16V - 2pcs

The dynamic miniature.
Quartz resonator on 32768 Hz.
Two supermarket LEDs of different color.

If you can not get imported chips, here are the domestic analogues: CD 4066 - K561T3, CD4013 - 561TM2, CD4011 - 561L7, LM358N - kr1040ud1. The LF353 chip is there is no direct analogue, but boldly put LM358N or better TL072, TL062. It is not necessary to put the operational amplifier precisely - LF353, I simply raised the reinforcement on the U1A replacing the resistor in the negative feedback circuit of 390 kΩ per 1 mΩ - sensitivity increased significantly by percentage of 50, though after this replacement gave zero, I had to glue the coil in a certain place Scotch tape slice of aluminum plate. Soviet three kopecks feels over the air at a distance of 25 centimeters and this is 6 volts when nutrition, the current consumed without indication is 10 mA. And do not forget about the panels - convenience and simplicity settings will increase significantly. CT814 transistors, KT815 - to the transmitting part of the metal detector, CT315 in UH. Transistors - 816 and 817 It is desirable to choose with the same gain coefficient. Replace on any appropriate structure and power. In the metal detector generator, a special hour quartz is installed at a frequency of 32768 Hz. This standard is absolutely for all quartz resonators, which are in any electronic and electromechanical clock. Including wrist and cheap Chinese wall / desktops. Archives with a printed circuit board for the option and for (option with manual detuning from the Earth).

What depends the depth of the search for goals

The greater the diameter of the metal dealer coil, the more deeply. In general, the depth of detection of the target with this coil depends primarily on the size of the target itself. But with an increase in the diameter of the coil, there is a decrease in the accuracy of the detection of the object and even sometimes loss of small goals. For objects with a coin, this effect is observed with an increase in the coil size over 40 cm. Total: a large search coil, has a greater depth of detection and greater capture, but less accurately detects the target than the small one. The big coil is ideal for finding deep and large goals, such as treasures and large objects.

The coil shape is divided into round and elliptic (rectangular). The elliptical coil of the metal detector has the best selectivity compared to the round, because it is less than the width of the magnetic field and there are less extraneous objects in its field. But the round has a greater depth of detection and better sensitivity to the goal. Especially on weakly mineralized soils. The round coil is most often used when searching with a metal detector.

The coils with a diameter of less than 15 cm are called small, the coil with a diameter of 15-30 cm is called medium and coils over 30 cm - large. The big coil generates a greater electromagnetic field, so it has a large detection depth than small. Big coils generate a large electromagnetic field and, accordingly, have a greater depth of detection and coating when searching. Such coils are used to view large areas, but when using them, there may be a problem on highly messenger sites because in the field of the action of large coils can be caught several goals and the metal detector will react to a larger goal.

The electromagnetic field of a small search coil is also small, so with such a coil is best to search in the territories highly lit for all sorts of small metal objects. The small coil is ideal for detecting small objects, but has a small area of \u200b\u200bcoating and a relatively small detection depth.

For universal search, medium coils will fit well. This search coil size combines a sufficient depth of search and sensitivity to goals with different sizes. I made every coil with a diameter of about 16 cm and both of these coils laid in a round stand from under the old monitor 15. "In this embodiment, the depth of this metal detector will be the following: aluminum plate 50x70 mm - 60 cm, nut M5-5 cm, coin - 30 cm, bucket - near the meter. These values \u200b\u200bare obtained in air, in the ground will be 30% less.

Metal detector power

Separately, the metal detector scheme pulls 15-20 mA, with a connected coil + 30-40 mA, and there is up to 60 mA. Of course, depending on the type of dynamics used and LEDs, this value may vary. The simplest case - the power took 3 (or even two) consistently connected lithium ion batteries from Mobile by 3.7V and during charge of discharged batteries, when you connect any power supply to 12-13V, the charge current starts from 0.8A and drops to 50m An hour and then do not need to add something at all, although the restrictive resistor of course does not prevent. As general, the most simplest option - Krona on 9V. But note that the metal detector will eat it in 2 hours. But to configure this power option. Crown under any circumstances will not give a large current that can burn something in the board.

Homemade metal detector

And now a description of the metal detector assembly process from one of the visitors. Since I have only a multimeter from the devices, I downloaded the virtual laboratory of records OL. Assemmed the adapter, a simple generator and drove into a single oscilloscope. It seems like some picture. Next, I started searching for radio components. Since the sizes are mostly laid out in the "Lay" format, Sprint-layout50 downloaded. I found out that such a laser and ironing technology of manufacturing printed circuit boards and how to train them. Put the board. By this time, all microcircuits were found. What I did not find in my shed, I had to buy. I began to solder jumpers, resistors, microcircuit sockets, and quartz from the Chinese alarm clock on the fee. Periodically checking the resistance on the power tires so that no snotes were. I decided to start collecting the digital part of the device as the easiest. That is a generator, divider and switch. Collected. Put the generator chip (K561L7) and the divider (K561TM2). B / ear microcircuits, out of some boards discovered in the shed. Submitted power 12V controlling current consumption by amermeter, 561TM2 became warm. Replaced 561TM2, filed food - zero emotions. We measure the voltage on the legs of the generator - on 1 and 2 legs of 12V. I change 561l7. I turn on - at the exit of the divider, there are generation on 13 legs (I observe on a virtual oscilloscope)! The truth is not so good, but for the absence of a normal oscilloscope - will go. But on 1, 2 and 12 legs there is nothing. So the generator works, you need to change TM2. Installed the third chip of the divider - beauty at all outputs is generation! For myself, I concluded that the chips need to be filled as careful! This is the first step of the building made.

Now configure the metal detector's fee. The "SENS" regulator did not work - sensitivity, I had to throw out the C3 capacitor after that the sensitivity adjustment earned as it should. I didn't like the sound that occurs in the extreme left position of the "Thresh" regulator - threshold, got rid of this replacing the resistor R9 with a chain of a successively connected resistor by 5.6 kΩ + condenser by 47.0 μF (negative condenser withdrawal from the transistor). While there is no LF353 chip instead of her LM358, the Soviet three kopecks feels with it at a distance of 15 centimeters.

I turned on the search coil on the transmission as a sequential oscillating circuit, and on the reception as a parallel oscillating circuit. Called the first transmitting coil, connected the collected design of the sensor to the metal detector, the oscilloscope parallel to the coil and at the maximum amplitude, the capacitors picked up. After that, the oscilloscope connected to the receiving coil to the receiving coil and at the maximum amplitude, the condensers were picked up on RX. The adjustment of the contours in the resonance takes, in the presence of an oscilloscope, a few minutes. TX and RX windings in me contain 100 turns of the wire with a diameter of 0.4. We start mixing on the table, without a case. Just so that there were two wrap with wires. And to make sure that work and the possibility of information is generally - the collapse of the coil from the DRA half the meter. Then zero will be accurate. Then impoverish the coil of the flask about 1cm (as wedding rings) shift - to move away. The zero point can be quite accurate and catch it immediately difficult. But it is.

When, I raised the reinforcement in the RX path of MD, he began to work unstable on the maximum sensitivity, this was manifested that after passing over the goal and its detection was given a signal, but it continued and after the goals before the search coil did not have any manifested in the form of intermittent and oscillating sound signals. With the help of an oscilloscope, the reason for this was found: during the operation of the dynamics and a minor feeding drawdown of the supply voltage, "zero" and the MD scheme goes into an auto-oscillating mode, to exit from which you can only download the triggering threshold. It did not suit me therefore I put it on the food of KR142EN5A + over the bright white LED to raise the voltage at the output of the integral stabilizer, the stabilizer to a higher voltage was not in me. Such an LED can be used even to illuminate the search coil. The speaker connected to the stabilizer, MD after that it became immediately very obedient all began to work as it should. I think the Volksturm is really the best homemade metal detector!

Recently, this scheme has been proposed, which will allow us to turn Volksturm S in Volksturm SS + GEB. Now the device will have a good discriminator as well as the selectivity of metals and tuning from the soil, the device rolls on a separate board and is connected instead of C5 and C4 capacitors. The scheme of refinement and in the archive. Separate thanks for information on the assembly and configuration of the metal detector to everyone who participated in the discussion and modernization of the scheme, especially helped in the preparation of the material of the electrocity, festka, XXX, SLAVAKE, EW2BW, REDKII and other radio amateurs colleagues.

Metal detector on the principle of transmission-reception - theory

The terms "Transmission-reception" and "reflected signal" in various search devices are usually associated with the methods of the type of pulse echo and radar, which is a source of delusions when it comes to metal detectors.

Unlike various types of locators, in the metal detectors of the considered type as a transmitted signal (emitted) and the received signal (reflected) are continuous, they exist simultaneously and coincide in frequency.

Operating principle

The principle of action of metal detector type "Transmission-reception" is to register a signal reflected (or, as they say re-energized) with a metal object (target), see, p.225-228. The reflected signal occurs due to the impact on the target of the alternating magnetic field of the transmitting (emitting) coil of the metal detector. Thus, the instrument of this type implies the presence of at least two coils, one of which is transmitting, and the other receiving.

The main fundamental problem that is solved in metal detectors of this type is such a choice of the mutual arrangement of coils, in which the magnetic field of the radiating coil in the absence of foreign metallic items brings the zero signal in the receiving coil (or in the system of receiving coils). Thus, it is necessary to prevent the direct impact of the radiating coil on the receiving. The appearance near the coils of the metal target will lead to the appearance of the signal in the form of a variable E.D. In the receiving coil.

Sensor schemes

At first, it may seem that in nature there are only two variants of the mutual arrangement of coils, at which there is no direct transmission of the signal from one coil to another (see Fig. 1 A and 16) - coils with perpendicular and cross-moving axes.

Fig. 1. Options for the mutual location of the coils of the database of the metal detector on the principle of "Transmission-reception".

A more careful study of the problem shows that such various systems of metal detector sensors may be many, however, they will contain more complex systems with the number of coils more than two, appropriately included electrically. For example, in Figure 1, the system is depicted from one emitting (center) and two receiving coils included in the signal in the signal to the emitting coil. Thus, the signal at the output of the system of receiving coils ideally is zero, since they are injured in the coils E.D.S. Mutually compensated.

Systems of sensors with companary coils (i.e., located in the same plane) are of particular interest. This is explained by the fact that with the help of metal detectors, it is usually a search for objects in the ground, and bring the sensor to the minimum distance to the surface of the Earth is possible only if its coils are compartment. In addition, such sensors are usually compact and fit well into the protective housings of the "pancake" or "flying plate".

The main options for the mutual arrangement of compartment coils are shown in Fig. 2a and 26. In the scheme in Fig. 2a, the mutual arrangement of coils is selected so that the total flow of the magnetic induction vector through the surface bounded by the receiving coil was zero. In the Scheme Fig.26, one of the coils (receiving) is twisted in the form of "eight", so that the total ED, which is visited on the half of the turns of the receiving coil, located in one octoral wing, compensates for the similar total ED. p., Invited in another wing "Eight."

Fig. 2. Computerarial options for the mutual location of the coils of the metal detector on the principle of "Transmission-reception".

Other diverse designs of sensors with compartment coils, for example, Figure 2B are possible. The receiving coil is located inside emitting. Invited in the receiving coil E.D.S. Compensated by a special transformer device that selects a portion of the radiating coil signal.

Practical considerations

Sensitivity Metal detector depends primarily from its sensor. For the considered options for sensors, the sensitivity is determined by formulas (1.20) and (1.33). If the orientation of the sensor orientation is optimal for each case, it is determined by the same K 4 coefficient and the functions of the normalized coordinates f (x, y) ig (x, y). For comparison, in the square x o [-4,4], y about [-4.4], the modules of these functions are given in the form of an axonometric dialing of cross sections in a logarithmic scale in Fig.12 and Fig.13.

The first thing that rushes into the eyes is vividly expressed maxima near the point of the location of the sensor coils (0, + 1) and (0, -1). The maxima functions f (x, y) ig (x, y) do not represent practical interest and for the convenience of comparing the functions of the functions around 0 (dB). From the patterns and from the analysis of functions f (x, y) ig (x, y), it is also seen that in the specified square, the function f function f is almost everywhere, the module of the function G, with the exception of the most remote points in the corners of the square and except the narrow region near X \u003d 0, where the function f holds the "ravine".

Asymptotic behavior of these functions, away from the origin, can be illustrated at y \u003d 0. It turns out that the module of the function F decreases with the distance proportional to X ^ (- 7), and the module of the function G is proportional to x ^ (- 6). Unfortunately, the advantage of the sensitivity function G is manifested only at large distances exceeding the practical radius of the metal detector. The same values \u200b\u200bof modules F and G are obtained at x \u003e\u003e 4.25.

Fig. 12. Function Function F (X, Y).

Fig.13. The graph of the function G (x, y).

A very important practical importance is the "ravine" function. First, it suggests that the sensor of the system of coils with perpendicular axes has a minimal (theoretically zero) sensitivity to metal objects located on its longitudinal axis. Naturally, these subjects also include many elements of the sensor itself. Consequently, the useless signal reflected from them will be much less than that of the system of coils system with cross-going axes. The latter is very important, given that the reflected signal from the metal elements of the sensor itself can several orders of magnitude exceeding the useful signal (due to the proximity of these elements to the sensor coils). The point is not that the useless signal from the metal elements of the sensor design is difficult to compensate. The main difficulty lies in the slightest changes in these signals, which are usually caused by thermal and especially mechanical deformations of the specified elements. These slightest changes may be comparable to a useful signal, which will lead to incorrect readings or false responses of the device. Secondly, if with the help of a metal detector of coils with perpendicular axes, some small object is already detected, the direction of its accurate location can be easily "sechalted" to zero value of the metal detector signal at the exact orientation of its longitudinal axis to the object (with any rhin orientation) . Given that the "capture" area of \u200b\u200bthe sensor when searching can be several square meters, the last quality of SIS

the topics of coils with perpendicular axes are very useful in practice (less useless excavations).

The following feature of the graphs of functionsF (x, y) and g (x, y) is the presence of an annular "crater" of the zero sensitivity passing through the centers (circle of a single radius with the center at the point (0.0)). In practice, this feature allows you to determine the distance to small objects. If it is found that at some finite distance, the reflected signal is closed (with optimal orientation on the roll) - it means that the distance to the object is half the database, that is, the L / 2 value.

It should also be noted that the radiation patterns of the Roll of Roll y for metal detector sensors with different mutual positions of coils are also vary. In Fig. 14b, a diagram of the direction of the device with perpendicular axes at the coils, and in fig.14a, with cross-go-handles. Obviously, the second diagram is more preferable, so has a smaller number of insensitivity areas on the roll and fewer petals.

In order to evaluate the dependence of the induced tension coil from the parameters of the metal detector and the object, it is necessary to analyze the expression (1.19) for the coefficient to 4. The voltage induced in the receiving coil is proportional (L / 2) ^ 6. The arguments of the functions f and g are normalized by L / 2, the decrease of which is derived from the 6th - 7th degree of distances. Therefore, in the first approximation, all other things being equal conditions, the sensitivity of the metal detector does not depend on its base.

Food diagrams for coil system sensors:
- with cross-going axes (a)
- with perpendicular axes (b).

In order to analyze Selectivity Metal detector, that is, its ability to distinguish objects made of various metals or alloys, it is necessary to refer to the expression (1.23). Metal detector can distinguish objects by the reflected signal phase. In order for the resolution of the device by type

tallov was maximum, it is necessary to properly select the frequency of the signal of the radiating coil, so that the phase of the signal reflected from the objects was about 45 °. This is the middle of the range of possible changes in the phase of the first term expression (1.23), and there is a stees-frequency characteristic of the maximum. We consider the second term of expressions (1.23) to be zero, since when searching first, we are interested in selectivity for non-ferrous metals - nonferromagnets. Naturally, the optimal selection of the signal frequency implies knowledge of the standard size of the alleged objects. In almost all foreign industrial metal detectors, the size of the coin is laid as this size. The optimal frequency is:

With a typical diameter of the coin 25 (mm), its volume is about 10 ^ (- 6) (M ^ 3), which according to formula (1.25) corresponds to an equivalent radius of about 0.6 (cm). From here we obtain the optimal frequency value of about 1 (kHz) during the conductivity of the material of the coin 20 (H0m h m). In industrial devices, the frequency is usually an order of magnitude higher (according to technological reasons).

conclusions

1. According to the author, the system of coils with perpendicular axes is preferable to search for treasures and relics than the system of coils with cross-going axes. All other things being equal, the first system has a slightly higher sensitivity. In addition, it is much easier to determine whether to determine the exact direction in which the discovered object should be sacred.

2. The considered coil systems have an important property that allows you to estimate the distance to small objects by reducing the reflected signal at a distance to the object equal to half the base.

3. All other things being equal (dimensions and number of turns of the coils, the sensitivity of the receiving path, the value of the current and its frequency in the radiating coil), the sensitivity of the metal detector on the principle of "transmission-reception" is practically independent of its base, that is, from the distance between the coils.

The device allows you to find metal objects located in a neutral medium, for example, soil, due to their conductivity are called a metal detector (metal detector). This device allows you to find metal items in various environments, including in the human body.

In many ways, thanks to the development of microelectronics, metal detectors that produce many enterprises throughout the world have high reliability and small overall-weight characteristics.

Not so long ago, such devices could most often see from sappers, now they enjoy rescuers, treasures, communal service workers when searching for pipes, cables, etc. Moreover, many "treasures" use metal detectors that they collect do it yourself .

Design and principle of device operation

Metal detectors offered on the market work on different principles. Many believe that they use the principle of impulse echo or radar. Their difference from locators is the transmitted and received signals, act constantly and at the same time, to all of the time they work on the coinciding frequencies.

Instruments operating on the principle "Reception" are recorded reflected (re-infused) from the metal object. This signal appears due to the impact on the metal object by an alternating magnetic field, which generates metal dealer coils. That is, in the design of the devices of this type, there are two coils, the first - transmitting, the second - reception.

The instruments of this class have the following advantages:

• simplicity of design;
• great features for detecting metal materials.

At the same time, the metal detectors of this class have certain disadvantages:

• metal detectors may be sensitive to the composition of the soil, in which the search for metal objects produce.
• technological difficulties in the production of the product.

In other words, the devices of this type must be customized with your own hands.

Other devices are sometimes called metal detector on beats. This name came from the distant past, more precisely since the times when super-metrogenous receivers were widely exploited. Bilation is a phenomenon that becomes noticeable when summarizing two signals with close frequencies and equal amplitudes. The beating consists in pulsing the amplitude of the amplitude signal.

The signal pulsation frequency is equal to the frequency difference difference. Skipping such a signal through the rectifier, it is also called the detector, allocate, the so-called difference frequency.

Such a scheme was used for a long time, but these days, it does not apply. They were changed synchronous detectors, but the term remained in use.

The metal detector on the beyon works using the following principle - it registers the frequency difference from two generator coils. One frequency is stable, the second contains an inductor inductor.

The device is set up with your own hands so that the generated frequencies coincide or at least were close. Once, a metal falls into the action zone, a change in the specified parameters and the frequency changes. The frequency difference can be recorded in different ways, ranging from headphones and ending with digital methods.

The devices of this class are characterized by a simple sensor design, weak sensitivity to the mineral composition of the soil.

But besides this, when they are operating, it is necessary to take into account the fact that they have high power consumption.

Typical design

The composition of the metal detector includes the following components:

1. The coil is a box-type design, it has a receiver and a signal transmitter. Most often, the coil has an elliptical form and polymers are used for its manufacture. It contains a wire connecting it with a control unit. This wire transmits a signal from the receiver to the control unit. The transmitter generates a signal when the metal is detected, which is broadcast to the receiver. The coil is installed on the bottom bar.
2. The metal part on which the coil is fixed and its tilt angle is configured, called the bottom rod. Thanks to this solution, a more careful study of the surface occurs. There are models in which the lower part can adjust the height of the metal detector and provides a telescopic connection with a barbell called average.
3. The middle rod is a node located between the bottom and the upper rods. It fixes fixtures that allow you to adjust the device dimensions. On the market you can meet models that consist of two rods.
4. The upper rod, as a rule, has a curved view. It resembles the letter S. This form is considered optimal to fasten it on hand. It is installed on it, a control unit and handle. The armrest and the handle are made of polymeric materials.
5. The metal detector control unit is necessary for the processing of the data resulting from the coil. After the signal is transformed, it is sent to headphones or other means of indication. In addition, the control unit is designed to adjust the device mode. The wire from the coil is joined by a quick-release device.

All devices included in the metal detector are performed in moisture-proof.

This is such a relative simplicity design and allows you to make metal detectors with your own hands.

Varieties of metal detectors

The market presents a broad nomenclature of metal detectors used in many spheres. Below is a list in which some varieties of these devices are indicated:

Most of the modern metal detectors can find metal objects at a depth of up to 2.5 m, special depth products can detect a product at a depth of 6 meters.

Frequency of work

The second parameter is the frequency of work. The fact is that low frequencies allow the metal detector to see at a rather large depth, but they are not able to see small details. High frequencies allow you to notice small objects, but does not allow soil browsing to a large depth.

The simplest (budget) models operate at one frequency, models that refer to the average price level are used in 2 or more frequencies. There are models that, when searching, use 28 frequencies.

Modern metal detectors are equipped with such a function as metal discrimination. It allows you to distinguish the type of material on depth. At the same time, when the ferrous metal is detected in the search headphones, one sound will sound, and when the color is discovered.

Such devices refer to Ipulso - balanced. They use frequency from 8 to 15 kHz in their work. As a source, batteries are used in 9 - 12 V.

The devices of this class are able to detect a golden subject at a depth of several tens of centimeters, and products from ferrous metals at a depth of about 1 or more meters.

But, of course, these parameters depend on the device model.

How to assemble a homemade metal detector do it yourself

In the market there are many models of instruments for finding a metal in the ground, walls, etc. despite its external complexity, make metal detector with their own hands not so and difficult and can almost anyone can make it. As already noted above, any metal detector consists of the following key components - coils, decoder and a signaling device signaling device.

To assemble with your own hands, such a metal detector requires the following set of elements:

• controller;
• resonator;
• condensers of different types, including film;
• resistors;
• sound emitter;
• voltage regulator.

Metal detector simplest

The diagram of the metal detector is not distinguished by complexity, and it is possible to find it or on the expanses of the global network, or in specialized literature. The above is a list of radio elements that will be useful for assembling the metal detector with their own hands at home. A simple metal detector can be assembled with their own hands using a soldering iron or another available to the way. The main thing at the same time, the details should not touch the device's housing. In order to ensure the work of the assembled metal detector, power supplies of 9 - 12 volts are used.

For winding the coil, a wire with a cross-section diameter is used within 0.3 mm, of course, it will depend on the selected scheme. By the way, the wound coil must be protected from the impact of extraneous radiation. To do this, it is shielded with your own hands with the help of an ordinary food foil.

For the firmware of the controller, special programs are used, which can also be found on the Internet.

Metal detector without microcircuits

If a novice "treasure detector" does not have a desire to bind to chips, there are schemes without them.

There are simpler schemes based on the use of traditional transistors. Such a device can find a metal at a depth of several tens of centimeters.

Depth metal detectors are used to search for metals at large depths. But it is worth noting that they are not suiced and therefore it is quite possible to gather it with their own hands. But before proceeding to its manufacture, it is necessary to understand how a typical scheme works.

The diagram of the deep metal detector is not the simplest and there are several options for its execution. Before assembling it is necessary to prepare the following set of details and elements:

• condensers of different types - film, ceramic, etc.;
• resistors of different nominal numbers;
• semiconductors - transistors and diodes.

Nominal parameters, quantities depend on the selected device concept. To assemble the above elements, you will need a soldering iron, a set of tool (screwdriver, pliers, nippers), material for the manufacture of the board.

The process of assembling the deep metal detector looks approximately as follows. First collect control unit, the basis of which is a circuit board. It is made of textolite. The assembly scheme is then transferred directly to the surface of the finished board. After the drawing is transferred, the board must be emitted. For this purpose, a solution is used, which includes hydrogen peroxide, salt, electrolyte.

After the board is met, it needs to perform holes for installing the circuit components. After the logging of the board is performed. The most important stage occurs. Installation and soldering with your own hands on the prepared fee.

For winding the coil with their own hands, the wire of the PEV brand with a diameter of 0.5 mm is used. The number of turns and the diameter of the coil depends on the selected depth metal detector scheme.

A little about smartphones

There is an opinion that it is quite possible to make a metal detector from a smartphone. This is not true! Yes, there are applications that are installed under the Android OS.

But in fact, after installing such an application, it will really be able to find metal objects, but only pre-magnetized. Search and even more so discriminating metals he will not be able.