Measuring technology ferromagnetic probes. Magnetometry in the simplest version The ferrozond consists of a ferromagnetic core and two coils on it

We construct a vector diagram of the ideal transformer at idle course (Fig.15.34).

Magnetizing force at idling

Now we are now a scheme for replacing the ideal transformer during its load (Fig.15.35).

If you connect the load with resistance to the secondary winding clips Z. n. then it will pass the current which, in turn, will strive to reduce the magnetic flux and this will lead to a decrease in EDs. , as a result of what the current age to such a magnitude at which the magnetic flow it will acquire the original value and equation (15.35) will be performed.

Thus, the appearance of the current in the secondary circuit leads to an increase in the current in the primary circuit. In a loaded transformer, the magnetic flux in the core is equal to the magnetic flow at idling, i.e. always F. \u003d const. When loading a magnetic stream created under the action of the magnetizing forces of primary and secondary windings:

We construct a vector diagram of the perfect transformer with a load (Fig. 15.36).

We convert the ideal transformer substitution scheme for which you get rid of inductive communication. If you connect the same clips of the transformer winding clips, then the transformer operation mode will not change.

Consider first inductively related elements that now have a common point. The coupling coefficient of two elements in this case is one equal, since the entire magnetic flux is completely unlocked with the tweeters of the primary and secondary windings, i.e.

therefore, considering that w. 1 = w. 2, we find:

Replace now part of the scheme with inductively connected elements with a common point (Fig.15.37 but) on an equivalent circuit without inductive communication (Fig.15.37 b.).

;

;

Taking into account the found scheme takes the view shown in Fig. 15.37 in, and the replacement scheme of the ideal transformer is a view depicted in Fig. 15.38.

If you now consider active and inductive scattering resistance to both windings, then for a transformer that w. 1 = w. 2, we obtain a substitution scheme shown in Fig. 15.39.

We write the equations of the primary and secondary circuit contours:

We construct a vector chain diagram (Fig.15.40).

This device measures the magnetic field of the Earth at a specific point. When moving the device near ferromagnetic materials (in our case, steel, cast iron), a change in the magnetic field is recorded compared to the background. The instruments of this group are suitable for finding large cast iron and steel objects (tanks, locomotives, cars). Of the principle of operation of the magnetometer, the following feature flows: the degree of distortion of the magnetic field depends mainly on the mass of the object. Thus, on the tank and on the stack of rail, the magnetometer will work the same weight equally. Consequently, the magnetometer is suitable for searching for weapons and ammunition warehouses. On non-ferrous metals, the magnetometer does not react.

Basic concepts

Magnetometer - device for measuring the characteristics of the magnetic field and magnetic properties of substances (magnetic materials). Depending on the determined value, the instruments for measurement are distinguished: field stresses (estate), field directions (inclinators and decals), field gradient (gradatenetometers), magnetic induction (teslametters), magnetic flux (Websometers, or fluxeters), coercive force (coercimetimeters) ), magnetic permeability (MJ meters), magnetic susceptibility (kappa meters), magnetic moment.

In search of goals used teslameterand Gradientometry. The main idea of \u200b\u200busing a magnetometer to search for iron-containing objects is as follows. As you know, the Earth has its own magnetic field. The magnitude and direction of this field is almost constant on sufficiently large areas. However, near the ferromagnetic object, the magnetic field changes, both in the direction and magnitude. By fixing using a magnetometer, changing the magnetic field, such an object can be detected. Moreover, applying the calculation methods used in geophysics, you can calculate the dimensions of the object and the depth on which it is located.

What tells us geophysics? On the poles, the vertical components of magnetic induction are approximately equal to 60 mkl, and horizontal - zero. At the equator, the horizontal component is approximately 30 mkl, and the vertical is zero. Some numbers: an iron object weighing 1 pound (453 grams), at a distance of 3 m changes the magnetic field to 1 NTL. Thus, a decent magnetometer should measure the magnetic field within 30,000 - 60,000 NTLs with an accuracy of 1 NTL.

Principle of operation

Main sensors used in magnetometers:

Operating principle optical-mechanical magnetometers are similar to the work of the compass. A sensitive element (sensor) of such devices is a permanent magnet that can freely rotate. Depending on the orientation of the axis of rotation of the permanent magnet, its magnetic moment and the magnetic field strength of the Earth, the constant magnet occupies a certain position relative to the horizontal or vertical plane. The change in the tension of the magnetic field of the Earth leads to the corresponding change in the angle of inclination of the permanent magnet (with other things being equal). To increase the accuracy of determining the angle of inclination of the system, special optical devices are used. For a decrease in error when orientation of magnetic meridian uses a compensation method of measurements. To do this, the device has a compensation magnet that is rigidly related to the counting scale. Smooth compensation is carried out by rotating this magnet until the permanent magnet does not establish horizontally. The moment of compensation is fixed with the help of a special optical system by combining the mirror reflected on the mirror and fixed horizontal indexes. To expand the measurement limits Δz, there is a second, so-called Range magnet of the step compensation. Measurement error with such an instrument is 2-5 NTLs.

The basis of the design of the ferrorsond (sensitive element) ferrorsondo Magnetometer The electric coil wound up on the elongated rod of a ferromagnet, which has a small coercive force and a large magnetic permeability in weak magnetic fields (for example, from an alloy of iron and nickel - Permalloe). In the absence of an external magnetic field when transmitted through a generator (primary) coil of an alternating electric current with a frequency f and an amplitude sufficient to create an excitation field, exceeding the level of the core saturation level, an emf of a double frequency 2F appears in the measuring (secondary) coil. In the presence of an external permanent magnetic field, which is different from zero along the rod axis, the frequency coinciding with the frequency of the excitation field F will prevail in the induction. The ferrozond magnetometer consists of two identical permalloe rods located in parallel to each other and oriented along the measured component of the magnetic field of the Earth. The windings of the excitation coils are connected in such a way that the variable field in two cores is directed opposite. To measure the outer magnetic field (its component directed along the rod axis), a compensation method is usually used, which consists in compensating for the permanent magnetic field of the Earth by the permanent adjustable current field. The magnitude of the compensation current is judged on the tension of the magnetic field of the Earth along the axis of the ferrorsond. Such devices include AMF-21 Aeromagnetometer. Due to the error in the orientation of the ferrorsond, the accuracy of shooting such a magnetometer reaches tens of nanotex. At wells, a well-type ferromagnetometer is used (for example, TSMK-30), which allows measuring the components of the magnetic field AZ, AH, AU with an error of up to ± 100 NTL.

Firm Precision Navigation Inc. (US) developed an improved version of the ferroresonance sensor, which received the name magnetic Industrial Sensor - Magneto-Inductive (MI) Sensors. The sensor is a microminiature inductor inductance with a ferromagnetic core. The coil contains only one winding and registers the magnetic field in the direction of only one of the axes.

Hall Sensor It works, approximately, as follows (see Figure): If you skip the current through the semiconductor plate in the A-B direction, then with the magnetic field, the intensity H, directed perpendicular to the plane plane, on the edges of the E-F plate there will be an EDC. The value, the EMF depends on the magnetic field strength. The sensitivity of the magnetometers with the Hall sensors is about 10 NTL.

magneticistor.

Magneticistor. (See Fig.) Contains a semiconductor plate 2 located on a substrate 1 from an anisotropic high-efficiency ferromagnet. The principle of operation of the magnetic resistor is as follows: a domain structure is formed in the ferromagnet, at least of two domains. The magnetization in the domains is normal plane of the substrate and are opposite to one another. The plate is located along the domains with the same direction of magnetization. The domain structures of the ferromagnetic substrate create an initial magnetic field in a semiconductor plate, increasing its resistivity and shifting the operating point. When placing a magnetic resistor into a measured magnetic field, it leads to an additional change in the resistivity. The threshold of the sensitivity of magnetoresistors is about 0.1 NTL.

Operating principle protonny or Nuclearmagnetometerbased on the phenomenon of the free precession of protons in the earth's magnetic field. After a certain electromagnetic effect on the proton-containing sensor, the protons is precessed around the direction of the earth's magnetic field with an angular velocity ω, proportional to the total tension of the magnetic field of the Earth T: Ω \u003d AT, where A is the coefficient of proportionality, which is equal to the gyromagnetic ratio of the kernel (the magnetic point of the kernel to mechanical) . The proton magnetometer consists of a magnetically sensitive unit or sensor (proton-containing vessel with water, alcohol, benzene, etc., around which exciting and measuring coils are wound); connecting wires; electronic block (preamp, switching scheme, frequency multiplier, frequency meter and light indicator); Registering device and power supply. The operating cycle, i.e., the time for determining the values \u200b\u200bof the magnetic field at each point, consists of time to polarization of the sensor (it is 3-8 c), the time of switching the sensor and the time for determining the signal frequency induced in the sensor coil (0.1- 0.4 s). Depending on the proton-containing substance and accuracy of determining the frequency of the precession, the operating cycle is 1-10 s. With a small speed of movement of the carrier of the magnetometer (ground or maritime options), the data on the magnetic field of the Earth T is obtained almost continuously. At high speed, for example, at the aircraft speed of 350 km / h, the distance between measurements is 300 m. With the help of a proton magnetometer, it is possible to carry out magnetic surveillance using metal carriers - ships or airplanes with their own magnetic field. At the same time, the magnetometer sensor is towed on the cable, the length of which must several times exceed the longitudinal size of the carrier. With the help of a proton magnetometer discretely (1 time in 1-10 ° C), the absolute value of the magnetic induction of the geomagnetic field with an error of ± 1-2 NTL is measured at low sensitivity (± 45 °) to the sensor orientation of the magnetic meridian, independence on temperature and time (missing zero offset). Proton magnetometers are used with ground (for example, the domestic MMP-203) and marine (MMP-3) shooting, less often with air films (MCC-214) and borehole observations.

IN quantummagnetometersintended for measuring the absolute values \u200b\u200bof the magnetic field induction module, use the so-called zeeman effect. In the electronic structure of atoms with a magnetic moment, when entering the magnetic field, the energy levels are cleavaged on the slope, with the difference in energy and, accordingly, the radiation frequency in the proportional module of the total magnetic induction vector at the observation point. The sensitive element of the magnetometer is a vessel in which there are cesium pairs, rubidium or helium. As a result of the outbreak of monochromatic light (optical pump method), the vapor electrons are translated from one energy sublayer to another. Returning them to the previous level after the end of the pump is accompanied by energy emission with a frequency proportional to the magnetic field. With the help of a quantum magnetometer, the measurement T is carried out with an error of ± (0.1-1) NTL with weak sensitivity to the orientation of the sensor, high speed and stability of the readings (slight zero offset). The main domestic quantum magnetometers are the devices of the following grades: ground (pedestrian) M-33 and MMP-303, sea km-8, Aeromagnetometer Kam-28. In the magnetometers for shooting in motion (marine, air or automotive), the registration of magnetic induction is carried out automatically, almost continuously. Profiles are tied in various ways (radio navigation, with aerial photography, etc.). The results of the observations are sometimes present in analog form in the form of a magnetogram, but more often - in digital form, which ensures the subsequent processing of information on onboard computers or in expeditionary computing centers.

The ferrorsond magnetic field converter, or ferrozond, is designed to measure and indicate constant and slowly changing magnetic fields and their gradients. The effect of ferrozone is based on the change in the magnetic state of the ferromagnet under the influence of two magnetic fields of different frequencies.

In fig. Schematically show some options for the designs of ferrorsonds.

In the simplest version, the ferrorsond consists of a ferromagnetic core and two coils on it:

cutting coils powered by alternating current

and measuring (signal) coil.

The core of ferrorsond is performed from high magnetic permeability materials.

A variable voltage is supplied to the excitation coil from a special generator with a frequency of 1 to 300 kHz (depending on the level of parameters and the appointment of the device).

In the absence of a measured magnetic field, the core under the action of an alternating magnetic field H, created by the current in the excitation coil, is released along a symmetric cycle.

The change in the magnetic field caused by the magnetization of the core along a symmetric curve, induces an EDC in a signal coil, varying for a harmonic law.

If simultaneously on the core, the measured constant or slowly changing magnetic field acts, but the magnetization curve changes its dimensions and shape and becomes asymmetrical. This changes the magnitude and harmonic composition of the EMF in the signal coil.

In particular, even harmonic components of the EMF appear, whose magnitude is proportional to the intensity of the measured field and are not available with a symmetric magnetization cycle.

Ferrorsonds are divided into:

side-element rods (Fig. A)

Differential with open core (Fig. B)

Differential with a closed (ring) core (fig. in).

Differential ferrozond (Fig. B, B), as a rule, consists of two cores with windings, which are connected in such a way that odd harmonic components are virtually compensated. Thus, the measuring equipment is simplified and the sensitivity of ferrorsond increases.

Ferrorsonds are characterized by very high sensitivity to the magnetic field.

They are able to register magnetic fields with tension up to 10 -4 -10 -5 a / m (~ 10 -10 -10 -11 TL).

Modern designs of ferrorsonds differ compactness.

The volume of ferrorsond, which completes the domestic magnetometers G73, is less than 1 cm 3, and the three-component ferrozond for the G74 magnetometer fits into the cube with a side of 15 mm.

As an example in Fig. The design and dimensions of the miniature rod ferrorsond are given.

The design of ferrorsond is quite simple and does not require special explanations.

His core is made of Permallo.

It has a variable length cross section, decreasing about 10 times in the central part of the core, which is wound to the measuring winding and excitation winding.

This design provides with a relatively small length (30 mm) high magnetic permeability (1, 5x10 5) and a small value of the intensity of the saturation field in the central part of the core, which leads to an increase in the phase and temporal sensitivity of ferrorsond. Due to this, the shape of the output pulses in the measuring winding of the ferrozond is also improved, which reduces the errors of the "time-impulse" signal formation scheme.

The measurement range of the ferrozond converters of a typical design is ± 50 ... ± 100 a / m (± 0, 06 ... ± 0, 126 mT).

The density of magnetic noise in the frequency band up to 0.1 Hz for ferrorsonds with rod cores is 30 - 40 μ / m (M x of Hz 1/2), depending on the excitation field, decreasing with increasing the latter. In the frequency band up to 0.5 Hz, noise density is 3-3.5 times higher.

Magnetometer Designed to measure the induction of the magnetic field. The magnetometer uses a support magnetic field that allows us through certain physical effects. convert the measured magnetic field into an electrical signal.
Applied application of magnetometers to detect massive objects from ferromagnetic (most often, steel) materials based on local distortion by these objects of the magnetic field of the Earth. The advantage of using magnetometers in comparison with traditional metal detectors is large detection range.

Furrorsonda (vector) magnetometers

One of the types of magnetometers are . Ferrorsond was invented by Friedrich Ferstern ( )

In 1937 and serves to determine magnetic field induction vector.

Ferrozond design

single-lighted ferrozhd.

The simplest ferrozond consists of a permalloe rod, which contains an excitation coil (( dRIVE COIL.), powered by alternating current, and measuring coil ( detector Coil.).

Permalloy - Alloy with magnetic and soft properties, consisting of iron and 45-82% nickel. Permalla has high magnetic permeability (maximum relative magnetic permeability ~ 100,000) and low coercive force. Popular brand Permalloe for the manufacture of ferrorsonds is 80% of nickel + chrome and silicon with saturation induction 0.65-0.75 TL, used for cores of small-sized transformers, chokes and relays working in weak margins of magnetic screens, for cores of pulse transformers, Magnetic amplifiers and contactless relays, for cores of magnetic heads.
The dependence of the relative magnetic permeability from the field strength for some varieties of Permalloe has the form -

If a constant magnetic field is superimposed on the core, voltage appears in the measuring coil even Harmonic, the magnitude of which serves as a measure of the constant magnetic field. This voltage is filtered and measured.

two-barrel ferroysond

As an example, you can bring the device described in the book. Karalysa V.N. "Electronic circuits in industry" -



The device is designed to measure constant magnetic fields in the range of 0.001 ... 0.5 earsted.
Sensor excitation windings L1. and L3. Included ones. Measuring winding L2. Winched over the windings of excitement. Excitation windings are powered by a 2 kHz frequency current from a two-stroke generator with inductive feedback. The generator mode is stabilized by DC divisory on resistors R8. and R9.

furrorsond with a toroidal core
One of the popular design options for the ferrozond magnetometer is a ferrozond with a toroidal core ( ring Core Fluxgate.) -

Compared with rod ferrozonds such a design has smaller noise and requires creation much less magneto-livestorm.

This sensor is harrow windingwound on a toroidal core, which flows alternating current with amplitude sufficient to enter the core in saturation, and measuring windingWith which an alternating voltage is removed, which is analyzed for measuring the external magnetic field.
The measuring winding is wound on top of the toroidal core, covering it entirely (for example, on a special frame) -


This design is similar to the initial design of ferrorsonds (the condenser was added to achieve resonance on the second harmonic) -

The use of proton magnetometers
Proton magnetometers are widely used in archaeological studies.
Proton magnetometer is mentioned in the science fiction novel Michael Childon "in a trap" (" Timeline.") -
HE Pointed Down Past His Feet. Three Heavy Yellow Housings Were Cameped to the Front Struts of the Helicopter. "Right Now We're Carrying Stereo Terrain Mappers, Infrared, UV, and Side-Scan Radar." Kramer Pointed Out The Rear Window, Toward a Six-Foot-Long Silver Tube That Dangled Beneath The Helicopter AT The Rear. "And What's That?" "Proton Magnetometer." "Uh-Huh. And It Does What?" "Looks for magnetic anomalies in the ground below us so Could Indicate Buried Walls, Or Ceramics, Or Metal."

Cesia magnetometers

A variation of quantum magnetometers are atomic magnetometers on alkali metal with optical pumping.

cesium magnetometer G-858

Magnetometers Overhauser

Solid-state magnetometers

The most accessible are magnetometers embedded in smartphones. For Android a good application using a magnetometer is . Page of this application - http://physics-toolbox-magnetometer.android.informer.com/.

Setup magnetometer

For testing ferrozone, you can use. Helmholtz coils are used to obtain a practically homogeneous magnetic field. In the ideal case, they are two identical ring turns connected in each other sequentially and located at a distance of the radius of the coil from each other. Usually, the coils of the Helmholtz consist of two coils, on which a number of turns are wound up, and the coil thickness should be much less than their radius. In real systems, the coil thickness can be comparable to their radius. Thus, we can consider the Helmholtz rings system two coaxially located the same coils, the distance between the centers of which is approximately equal to their average radius. Such a system of coils is also called the split solenoid ( split Solenoid).

In the center of the system there is a zone of a homogeneous magnetic field (the magnetic field in the center of the system in the amount of 1/3 of the radius of the rings uniformly within 1%), which can be used for measuring purposes, to calibrate the magnetic induction sensors, etc.

Magnetic induction in the center of the system is defined as $ B \u003d \\ Mu _0 \\, (\\ left)) ^ (3/2) \\, (IN \\ OVER R) $
where $ n $ is the number of turns in each coil, $ I $ - current through coils, $ R $ is the average radius of the coil.

Also, the coils of the Helmholtz can be used to shield the magnetic field of the Earth. To do this, it is best to use three mutually perpendicular pairs of the rings, then their orientation does not matter.

The proposed differential magnetometer can be very useful for searching for large iron items. Such a device is almost impossible to search for treasures, but it is indispensable when searching for a shallow sunken tanks, ships and other samples of military equipment.

The principle of operation of the differential magnetometer is very simple. Any item from the ferromagnet distorts the natural magnetic field of the Earth. Such subjects include everything made of iron, cast iron and steel. To a large extent, affect the distortion of the magnetic field may also have its own magnetization of objects, which often takes place. Fixing the deviation of the magnetic field strength from the background value, it can be concluded that it is near the measuring instrument of the object of the ferromagnetic material.

The distortion of the magnetic field of the Earth away from the target is not enough, and it is estimated by the difference in signals from two space-sided sensors. Therefore, the device is also named differential. Each sensor measures the signal, proportional magnetic field strength. Ferromagnetic sensors and sensors based on the magneton precession of protons were obtained the greatest distribution. In the instrument under consideration, the first-type sensors are used.

The basis of the ferromagnetic sensor (also called the ferrorsondo) is a coil with a core of ferromagnetic material. The typical magnetization curve of such a material is well known from the school course of physics and has the following form, taking into account the influence of the magnetic field of the Earth, shown in Fig. 29.

Fig. 29. Magnetization curve

The coil is excited by a variable sinusoidal bearing frequency signal. As can be seen from fig. 29, the displacement of the magnetization curve of the ferromagnetic core of the coil by an outer magnetic field of the Earth leads to the fact that the induction of the field and the associated voltage on the coil is beginning to be distorted as an asymmetrical manner. In other words, the sensor voltage in the sinusoidal current of the carrier frequency will differ from the sinusoids more "surrendered" the tops of half fell. And these distortions will be asymmetrical. In the spectral analysis language, this means the appearance in the spectrum of the output voltage of the coil of even harmonics, the amplitude of which is proportional to the tension of the magnetic field of the offset (field of the Earth). These are even harmonics and you need to "catch."

Fig. 30. Differential ferromagnetic sensor

Before mentioning a naturally configured synchronous detector, working with a doubted bearing frequency reference signal, consider the design of the complicated version of the ferromagnetic sensor. It consists of two cores and three coils (Fig. 30). In essence, this is a differential sensor. However, for simplicity, we will not be called differential in the text, since the magnetometer itself is already differential (©).

The design consists of two identical ferromagnetic cores with identical coils located in parallel next to each other. In relation to the exciting electrical signal of the reference frequency, they are included in the counter. The third coil is a winding wound over two folded together the first two coils with cores. In the absence of an external shifting magnetic field, the electrical signals of the first and second windings are symmetrical and, in the ideal case, they act so that the output signal in the third winding is missing, since the magnetic flows are completely compensated through it.

If there is an external shifting magnetic field, the picture changes. Then one, then another core at the peak of the corresponding half-wave "flutter" into saturation deeper than usual due to the addition of the magnetic field of the Earth. As a result, at the output of the third winding, a diversion frequency mismatch appears. The signals of the main harmonica ideally are completely compensated.

The convenience of the sensor considered is that its coils can be included to increase the sensitivity to the oscillatory circuit. The first and second-in the oscillating circuit (or contour) configured to the carrier frequency. The third is a vibrational contour configured to the second harmonic.

The described sensor has a pronounced pattern of the orientation. Its output is maximum at the location of the longitudinal axis of the sensor along the power lines of the external permanent magnetic field. When the longitudinal axis is perpendicular to the power lines - the output signal is zero.

The sensor of the considered type, especially in conjunction with the synchronous detector, can work successfully as an electronic compass. Its output after straightening is proportional to the projection of the magnetic field of the magnetic field of the earth on the sensor axis. Synchronous detection allows you to learn and sign this projection. But even without a sign - oriented the sensor at a minimum of the signal, we will receive the direction to the West or east. Oriented to the maximum - we get the direction of the magnetic power line of the Earth field. In medium latitudes (for example, in Moscow), it goes obliquely and "sticks out" to the ground towards the north. In the corner of magnetic decline, you can approximately evaluate the geographical latitude of the terrain.

Differential ferromagnetic magnetometers have their advantages and disadvantages. The advantages include simplicity of the device, it is not more complicated by a direct strengthening radio. The disadvantages include the complexity of the manufacture of sensors - in addition to accuracy, absolutely accurate coincidence of the number of turns of the corresponding windings is required. The error of one or two turns can strongly reduce possible sensitivity. Another disadvantage is the "Compass" of the device, i.e. the impossibility of full compensation of the Earth's field by subtracting signals from two spaced sensors. In practice, this leads to false signals when the sensor turns around the axis perpendicular to the longitudinal one.

Practical design

The practical design of the differential ferromagnetic magnetometer was implemented and tested in a dumping version without a special electronic part for sound indication, using only a microammeter with zero in the middle of the scale. The sound indication circuit can be taken from the description of the metal detector on the principle of "Transmission-reception". The device has the following parameters.

Main technical characteristics
Supply voltage 15 ... 18 V
Current consumption no more than 50 mA
Depth of detection:
pistol 2 M.
cannon Stem 4 m
tank 6 M.

Structural scheme

Fig. 31. Structural diagram of a differential ferromagnetic magnetometer

The structural scheme is shown in Fig. 31. Quartz-stabilized Splancing generator issues clock frequency synchrums for signal generator.

At one outlet, there is a meander of the first harmonic, which arrives at the power amplifier, exciting radiating sensor coils 1 and 2. Another output generates a meander of the doubted clock frequency with a 60 ° shift for a synchronous detector. The difference signal from the output (third) windings of the sensors is amplified in the receiving amplifier and is straightened with a synchronous detector. The straightened permanent signal can be recorded by a microammeter or described in previous chapters of sound indication devices.

Schematic scheme

The schematic diagram of the differential ferromagnetic magnetometer is depicted in fig. 32 - part 1; Specifying generator, signal generator, power amplifier and emitting coils, Fig. 33 - Part 2: Reception coils, receiving amplifier, synchronous detector, indicator and power supply.

Fig. 32. Concept electrical scheme - Part I

Specifying generator (Fig. 32)

The specifying generator is assembled on inverters D1.1-D1.3. The frequency of the generator is stabilized by a quartz or sub-zocheramic resonator q with a resonant frequency of 215 Hz \u003d 32 kHz ("hour quartz"). The R1C1 chain prevents the excitation of the generator on higher harmonics. Through the R2 resistor, the circuit of the OOS is closed, through the resonator Q -Cile pic. The generator is characterized by simplicity, small current, it works reliably at a power supply voltage of 3 ... 15 B, does not contain trimmed elements and too high-resistant resistors. The output frequency of the generator is about 32 kHz.

Signal former (Fig. 32)

Signal generator is assembled at a binary counter D2 and D3.1 D3.1 D-trigger. The type of binary meter is not sufficient, its main task is to divide the clock frequency by 2, by 4 and by 8, thus obtained, meandras with frequencies 16, 8 and 4 kHz, respectively. Carrier frequency for excitation of emitting coils-4 kHz. Signals with frequencies 16 and 8 kHz, affecting the D-trigger D3.1, form at its outlet of the meander doubled to the carrier frequency of 8 kHz, shifted 90 ° relative to the output signal of 8 kHz binary meter. Such a shift is necessary for normal operation of the synchronous detector, since the same shift has a beneficial disorder of the double frequency at the output of the sensor. The second half of the chip from two D-triggers - D3.2 in the diagram is not used, but its unused inputs should be connected either to logical 1, or to logical 0 for normal operation, as shown in the diagram.

Power amplifier (Fig. 32)

Power amplifier with sight does not seem likely and represents only powerful inverters D1.4 and D1.5, which in the antiphase split a oscillatory circuit consisting of sequentially parallelly turned on the radiating coils of the sensor and C2 condenser. An asterisk near the rating of the condenser means that its value is indicated approximately and that it must be chosen when adjusting. An unused inverter D1.6 so as not to leave its input uncontmit, inverts the signal D1.5, but practically the "fast". R3 and R4 resistors limit the output current of the inverters at a permissible level and together with the oscillatory contour form a high-risk strip filter, so that the voltage and current form in the emitting sensor coils almost coincides with the sinusoidal.

Fig. 33. The fundamental electrical scheme is part II. Receiver amplifier

Receiver amplifier (Figure 33)

The receiving amplifier enhances the difference signal coming from the receiving coils of the sensor forming together with the capacitor of the oscillating circuit, configured to the twice frequency of 8 kHz. Due to the rapid resistor R5, the subtraction of signals of the receiving coils is made with some weighing coefficients, which may vary by moving the R5 resistor engine. This comes compensation for non-identity of the parameters of the sensor's reception windings and minimizing its "compassibility". Reception amplifier double-stage. It is assembled for OU D4.2 and D6.1 with parallel OS voltage. Capacitor C4 reduces the amplification at higher frequencies, thereby preventing the reinforcement of the amplifying path with high-frequency tips from power networks and other sources. OU - standard correction circuits.

Synchronous detector (Fig. 33)

The synchronous detector is made on the OU D6.2 according to the typical scheme. As an analog key, a chip D5 CMOS Multiplexer-Demultiplexer 8 to 1 is used (Fig. 32). Its digital address signal is shifted only in the younger discharge, providing alternate switching of points K1 and K2 on a total tire. The straightened signal is filtered by the C8 capacitor and the D6.2 is enhanced with the simultaneous additional attenuation of non-filtered RF components R14C11 and R13C9. Correction circuit OU is standard for used type.

Indicator (Fig. 33)

The indicator is a micro ammeter with zero in the middle of the scale. In the indicator part, the circuitry of the previously described metal detectors of other types can be successfully used. Including, as an indicator, you can use the design of the metal detector on the principle of an electronic frequency meter. In this case, its LC generator is replaced with an RC generator, and the measured output voltage through the resistive divider is fed to the frequency chain of the timer. You can read more about this on the website of Yuri Kolokolov.

The chip D7 stabilizes a single-polar supply voltage. With the help of OU D4.1, an artificial average power point is created, which allows the use of a conventional bipolar circuit engineering for OU. Ceramic blocking capacitors C18-C21 are mounted in the immediate vicinity of digital chip housings D1, D2, D3, D5.

Types of details and design

The types of microcircuits used are indicated in Table. 6.

Table 6. Types of microcircuits used

Instead of the K561 series chip, it is possible to use the K1561 series microcircuits. You can try to apply some K176 series chips or foreign analogues of the 40xx and 40xx.

Dual operating amplifiers (OU) of the K157 series can be replaced by any similar to the parameters of general purpose (with appropriate changes in the basement and correction circuits).

The resistors are not presented to the resistors used in the differential magnetometer diagram. They only need to have a solid and miniature design and be convenient for installation. Ratary power of 0.125 ... 0.25 W.

Potentiometers R5, R16 are desired multi-turn for the convenience of accurate instrument setting. The R5 potentiometer handle should be made of plastic and should have sufficient length so that the operator's hand touch does not cause changes to the indicator readings by pressing. Condenser C16 - electrolytic any small-sized type.

Capacitors of oscillatory contours C2 * and SZ * consist of several (5-10 pcs.) Capacitors included in parallel. Setting the contour into the resonance is carried out by selecting the number of capacitors and their nominal. Recommended type of capacitors K10-43, K71-7 or foreign thermostable counterparts. You can try to use conventional ceramic or metal capacitors, however, when the temperature is oscillations, it will be necessary to adjust the device more often.

Micronmmeter - any type of current 100 μA with zero in the middle of the scale. Convenient small-sized microammeters, for example, type M4247. You can use almost any microammeter, and even a milliammeter - with any limit of the scale. To do this, it is necessary to correctly adjust the rates of resistors R15-R17. Quartz resonator Q - any small hour quartz (similar to those used in portable electronic games).

Switch S1 - any type, small.

Fig. 34. Construction of an antenna sensor

The sensor coils are made on round ferrite cores with a diameter of 8 mm (used in magnetic antennas of radio and dw-range radio receivers) and about 10 cm long. Each winding consists of smoothly and tightly wounded in two layers 200 turns of the copper winding wire with a diameter of 0.31 mm. In double varnish-silk isolation. On top of all the windings, the layer of the screen foil is attached. Screen edges are isolated from each other to prevent the formation of a short-circuited turn. Screen output is performed by copper tinned single-core wire. In the case of an aluminum foil screen, this output is applied to the screen for its entire length and is tightly primed by the tape. In the case of a screen from a copper or brass foil, the output is solder.

The ends of ferrite cores are fixed in fluoroplastic centering discs, thanks to which each of the two halves of the sensor is held inside a plastic tube from a textolite serving the case, as schematically depicted in Fig. 34. The length of the pipe is about 60 cm. Each of the halves of the sensor is located at the end of the pipe and is additionally recorded by silicone hermethos, which is filled by the space around the windings and their cores. Filling through special holes in the pipe housing. Together with fluoroplastic washers, such a sealant gives the fastening of fragile ferrite rods the necessary elasticity that prevents them in cracking during accidental blows.

Establishing the device

1. Make sure the installation is correct.

2. Control the current consumed, which should not exceed 100 mA.

3. Check the correct operation of the specifying generator and the remaining elements of the formation of pulse signals.

4. Customize the oscillatory sensor circuit. Emitting - on the frequency of 4 kHz, receiving - on 8 kHz.

5. Ensure the correctness of the enhanced path and the synchronous detector.

Work with the device

The method of setup and work with the device is as follows. We go to place of search, turn on the device and start rotating the sensor antenna. Best of all in the vertical plane passing through the north-south direction. If the device sensor is on the rod, then you can not rotate, but to rock as far as it allows you to make a bar. The indicator arrow will deviate (compass effect). Using a variable resistor R5, we are trying to minimize the amplitude of these deviations. It will "move" the average point of the microammeter readings and it will also need to be adjusted to another variable R16 resistor, which is designed to set zero. When the "compass" effect becomes minimal, the device is considered to be balanced.

For small objects, the search technique using a differential magnetometer does not differ from the technique of working with a conventional metal detector. Near the object, the arrow can deviate in any direction. For large objects, the indicator arrow will deviate in different directions on a large space.