Offered to your attention impulse
metal detector is a joint development of Yuri Kolokolov and
Andrey Shchedrin. The device is intended for amateur treasure hunting and
relics, search on the beach, etc. After the publication of the first version
metal detector in , this device has received high praise among
amateurs who repeated the design. However, useful
comments and suggestions that we took into account in new version device.
At present, the metal detector is standard
is produced by the Moscow firm "MASTER KIT" in the form of "make
himself” for radio amateurs.
The kit contains a printed circuit board, a plastic case and electronic
components, including the already programmed controller. Possibly for
many fans, the acquisition of such a set and its subsequent uncomplicated
assembly will be a convenient alternative to purchasing expensive
industrial appliance or completely self-manufactured
metal detector.
Operating principle impulse or
eddy current metal detector is based on excitation in a metal
object of pulsed eddy currents and measurement of the secondary
the electromagnetic field that these currents induce. In this case
the exciting signal is supplied to the transmitter coil of the sensor not constantly, but
periodically in the form of impulses. In conducting objects are induced
damped eddy currents that excite damped electromagnetic
field. This field, in turn, induces in the receiving coil
damped current sensor. Depending on conductive properties and size
object, the signal changes its shape and duration. On fig. one.
Schematically shows the signal on the receiving coil of a pulsed
metal detector. Oscillogram 1 - signal in the absence of metal
targets, oscillogram 2 - signal when the sensor is near
metal object.
Pulse metal detectors have their advantages and
limitations. Advantages include low sensitivity to
mineralized soil and salt water, to the disadvantages - poor
selectivity by metal type and relatively high consumption
energy.
Figure 1. Signal at the input of the pulse
metal detector
Most practical pulse designs
metal detectors are built either according to a two-coil scheme, or according to
single-coil circuit with an additional power supply. In the first
case, the device has separate receiving and emitting coils, which
complicates the design of the sensor. In the second case, there is only one coil in the sensor, and
an amplifier is used to amplify the useful signal, which is powered by
from an additional power supply. The meaning of this construction
is as follows - the self-induction signal has a higher
potential than the potential of the power supply that is used to
supply current to the transmission coil. Therefore, to amplify such a signal
the amplifier must have its own power supply, the potential of which
must be higher than the voltage of the amplified signal. It also makes it difficult
device diagram.
The proposed single-coil design is built
on original scheme, which is devoid of the above drawbacks.
Specifications
Supply voltage ……………….7.5 - 14 (V)
Current consumption, not more than ……..….90 (mA)
Depth of detection:
– a coin with a diameter of 25 mm ….…….…. 20 (cm)
– pistol ………………………..………40 (cm)
– helmet ……………………………..…….. 60 (cm)
The block diagram of the metal detector is shown on
fig.2 The basis of the device is a microcontroller. With his help
time intervals are formed to control all
nodes of the device, as well as indication and general management device. FROM
using a powerful key, pulsed accumulation of energy is carried out in
coil of the sensor, and then interruption of the current, after which there is
self-induction pulse that excites the electromagnetic field in the target.
Figure 2. Structural diagram of a pulse
metal detector
The “highlight” of the proposed scheme is the use
differential amplifier in the input stage. It serves to reinforce
signal whose voltage is higher than the supply voltage and linking it to
a certain potential - + 5 (B). For further reinforcement,
receiving amplifier with high gain. For measuring
useful signal is the first integrator. During direct
integration, the useful signal is accumulated in the form
voltage, and during back integration,
converting the result into pulse duration. Second integrator
has a large constant of integration and is used for balancing
amplifying path for direct current.
Schematic diagram of a simple pulse
metal detector is shown in Fig.3.
Figure 3. Circuit diagram
simple pulse metal detector
The proposed design of the device was developed
completely on imported element base. The most
common components from leading manufacturers. Some
you can try to replace the elements with domestic ones, this will be
said below. Most of the applied elements are not scarce and
can be purchased in large cities of Russia and the CIS through companies
selling electronic components.
Differential Amplifier assembled at OU
D1.1. Chip D1 is a quad operational
amplifier type TL074. Its distinguishing features are high
speed, low consumption, low noise, high input
resistance, as well as the ability to work at voltages at the inputs,
close to the supply voltage. These properties led to its use in
differential amplifier in particular and in the circuit as a whole. Coefficient
differential amplifier gain is about 7 and is determined by
resistor values R3, R6…R9, R11.
Receiving amplifier D1.2 is
non-inverting amplifier with a gain of 57. During operation
high-voltage part of the self-induction pulse, this coefficient decreases
to 1 with analog switch D2.1. It prevents overload
input amplifying path and provides a quick entry into the mode
to amplify a weak signal. Transistors VT3 and VT4 are designed for
matching the levels of control signals supplied from the microcontroller
for analog keys.
By using second integrator D1.3
automatic balancing of the input amplifying path is performed
by direct current. Integration time 240 (ms) selected
large enough that this feedback does not affect the gain
rapidly changing useful signal. With this integrator
the output of the amplifier D1.2 in the absence of a signal is maintained at a level of +5
(AT).
Measuring first integrator performed on
D1.4. At the time of integration of the useful signal, the key D2.2 is opened
and, accordingly, the key D2.4 is closed. Implemented on D2.3 key
logic inverter. After the signal integration is completed, the key D2.2
closes and opens the key D2.4. Storage capacitor C6
starts to discharge through the resistor R21. The discharge time will
proportional to the voltage that is established on the capacitor C6 to
end of useful signal integration. This time is measured using microcontroller,
which performs analog-to-digital conversion. For measuring
the discharge time of the capacitor C6, an analog comparator and
timers that are built into the D3 microcontroller.
Button S1 is for initial reset
microcontroller. Switch S3 sets the display mode
devices. With the help of a variable resistor R29 is regulated
metal detector sensitivity.
With the help of VD3 ... VD8 LEDs, light
indication.
Functioning algorithm
To clarify the principle of operation of the described
pulse metal detector in Fig. 4 shows oscillograms of signals in
the most important points of the device.
Figure 4. Oscillograms
For the duration of interval A, the key VT1 is opened. Through
a sawtooth current begins to flow through the sensor coil - waveform 2.
When the current reaches about 2 (A), the key closes. On stock
transistor VT1 there is a self-induction voltage surge -
oscillogram 1. The magnitude of this surge is more than 300 volts (!) and
limited by resistors R1, R3. To prevent overload
the amplifying path are limiting diodes VD1, VD2. Also for
this goal for the time interval A (accumulation of energy in the coil) and
interval B (ejection of self-induction) opens the key D2.1. It reduces
end-to-end path gain from 400 to 7. Waveform 3
shows the signal at the output of the amplifying path (pin 8 D1.2). Beginning with
interval C, the D2.1 key is closed and the path gain
becomes big. After the end of the guard interval C, during the time
which the amplifying path enters the mode, the key D2.2 opens and
key D2.4 closes - useful signal integration begins -
interval D. After this interval, the key D2.2 is closed, and the key
D2.4 opens - "reverse" integration begins. Over this time
(intervals E and F) capacitor C6 is completely discharged. By using
built-in analog comparator, the microcontroller measures the value
interval E, which turns out to be proportional to the level of the input
useful signal. For current firmware versions
the following interval values are set:
A - 60 ... 200 µs, B - 12 µs, C - 8 µs, D - 50
(μs), A + B + C + D + E + F - 5 (ms) - repetition period.
The microcontroller processes the received digital
data and indicates with the help of LEDs VD3 ... VD8 and sound emitter Y1
degree of impact of the target on the sensor. LED indication
is an analogue of a pointer indicator - in the absence of
target, the VD8 LED is lit, then, depending on the level of exposure
sequentially light up VD7, VD6, etc.
Click on the picture to enlarge
Figure 5. Schematic diagram of the second
improved version of the microprocessor pulse
metal detector
Differences (Fig.5) from the first version of the device (Fig.3)
are as follows.
1. Added resistor R30. It's made for
to reduce the influence of the internal resistance of various batteries on
device setting. Now you can painlessly change the acid
accumulator for 6-8 pieces of salt batteries. Setting up the device does not
"will move out".
2. Added "accelerating" capacitors
C15,C16,C17. This significantly improved thermal stability.
scheme. In the old scheme, the keys VT2 ... VT4 were the most vulnerable spot in that
plan. Plus, continuous auto-balancing has been added to the program.
zero.
3. Added chain R31 , R32, C14 . This chain
allows you to continuously monitor the battery status. FROM
using resistor R32, you can now set any safe threshold (for
battery) to discharge various types of batteries. For example, for 8pcs
NiCd or NiMH AA batteries will need to be installed
level 8 Volts, and for 12 V acid battery- 11 volts ... When
the threshold level will be reached, the light and sound will turn on
indication.
This mode is easy to set up. device
powered by the power supply. The required value is set on the power supply
threshold voltage, the slider of the resistor R32 is first set to the “upper”
according to the scheme position., and then, rotating the rotor of the resistor R32, you need to achieve
indication is triggered - the VD8 LED starts flashing, the sound source
will emit an intermittent signal. The device exits this mode only
by reset.
4. As alternative device indications
a two-line sixteen-character LCD can now be used. This
the mode is activated when switch S3 is closed. In this case
LCD signal outputs are connected according to the diagram instead of LEDs.
Also, it is necessary to apply +5 V voltage to the LCD module and connect
ground wire. Resistor R33 is mounted directly on the contacts
LCD module (fig.6).
Figure 6. Alternative LCD - indicator
In this case, the top line always displays
the name of the metal detector, and in the bottom line, depending on the mode:
"Autotuning", "Low battery". In search mode, this line is drawn
column for 16 gradations of signal level. At the same time, the sound signal
has 16 gradations of tone.
Part types and design
Instead of the operational amplifier D1 TL074N, you can
try to apply TL084N.
Chip D2 is a quad analog switch
type CD4066, which can be replaced with a domestic chip K561KT3.
Microcontroller D4 AT90S2313-10PI direct analogs
does not have. The circuit does not provide circuits for its in-circuit
programming, so it is advisable to install the controller on
socket so that it can be reprogrammed.
Transistor VT1 type IRF740 you can try
replace with IRF840.
Transistors VT2 ... VT4 type 2N5551 can be replaced with
KT503 with any letter index. However, attention should be paid to
the fact that they have a different pinout.
LEDs can be of any type, VD8 is desirable
take a different glow color. Diodes VD1, VD2 type 1N4148.
Resistors can be of any type, R1 and R3 must
have a power dissipation of 0.5 (W), the rest can be 0.125 or
0.25 (W). R9 and R11 are desirable to choose so that their resistance
differed by no more than 5%.
Capacitor C1 - electrolytic, for voltage
16V, the remaining capacitors are ceramic.
Button S1, switches S3,S4, variable
resistor R29 can be of any type that fits in size. AT
as a sound source, you can use a piezo buzzer or headphone
phones from the player.
The body structure of the instrument can be
arbitrary. The boom near the sensor (up to 1 meter) and the sensor itself must not
have metal parts and fasteners. As a starting point
material for the manufacture of rods it is convenient to use plastic
telescopic rod.
The sensor contains 27 turns of wire with a diameter of 0.6 -
0.8 mm, wound on a mandrel 190 (mm). The sensor does not have a screen and it
fastening to the rod should be carried out without the use of massive
screws, bolts, etc. (!) For connecting the sensor and the electronic unit
shielded cable cannot be used due to its high capacitance. For
these purposes, you must use two insulated wires, for example, type
MGShV, twisted together.
Setting up the device
ATTENTION! The device has a high
potentially life-threatening voltage - on the collector VT 1 and
on the sensor. Therefore, when setting up and operating, care must be taken
electrical safety.
1. Make sure the installation is correct.
2. Apply power and make sure that the consumed
the current does not exceed 100 (mA).
3. Using the tuning resistor R7 to achieve
such balancing of the amplifying path so that the waveform at pin 7
D1.4 corresponded to waveform 4 in Fig.4. At the same time, it is necessary
make sure that the signal at the end of the interval D is unchanged, i.e.
the waveform at this location should be horizontal.
In further configuration, a correctly assembled device
does not need. Bring the sensor close to a metal object and
make sure that the indicators are working. Description of the operation of the controls
below in the description of the software.
Software
At the time of this writing, it has been developed and
tested software versions V1.0-demo, V1.1 for
the first version of the device and V2.4-demo, V2.4 for the second version. Demo version
The program is fully operational and differs only in the absence
precise sensitivity adjustment. Full versions shipped in already
firmware microcontrollers included in the MASTER KIT NM8042
.
firmware HEX file V1.0-demo and V2.4-demo can be downloaded here.
Work on new software versions
security continues, it is planned to introduce additional regimes.
New versions, after extensive testing, will be available in
sets MASTER KIT. Get information about new versions, as well as download
demo versions of programs for self-production
metal detector can be found on the personal page of Yuri Kolokolov and
on our website.
Working with the device
Power must be turned on before starting work.
device, raise the sensor to a level of 60-80 cm from the ground and press the button
"Reset". Within 2 seconds, the device will auto-tune. By
At the end of autotuning, the device will emit a characteristic short sound. After
To do this, the sensor must be brought closer to the ground (in a place where there are no
metal objects) at a distance of 3-7 cm and adjust
sensitivity with resistor R29. The handle must be turned to
elimination of false positives. After that, you can start searching.
When an indication of a low battery appears, the search must be stopped,
turn off the device and replace the power supply.
Conclusion
To save time and relieve you of the routine
work on the search for the necessary components and the manufacture of printed circuit boards
MASTER KIT offers a set NM8042.
On fig. 7 shows the figure printed circuit board(for
diagrams fig. 3) and the location of the components on it.
Figure 7.1. PCB top view
Figure 7.2. PCB bottom view
The set consists of a factory printed circuit board,
firmware controller with program version V 1.1, all necessary
components, plastic case and instructions for assembly and operation.
Design simplifications were made deliberately, in order to reduce
set cost.
Search coil manufacturing
The coil is 27 turns
enameled wire with a cross section of 0.7-0.8 mm, wound in the form of a ring
180-190 mm. After winding the coil, the turns must be wrapped with insulating
tape. To connect the sensor, it is necessary to make a twisted pair of
mounting wire. To do this, take two pieces of wire of the desired length, and
twisted together at the rate of one twist per centimeter. One side
this cable is soldered to the coil, on the other to the board. sensor housing and
the metal detector rod must not contain metal parts!
Case completion
Before installing the metal detector board into the case,
it is necessary to make holes for the external elements.
On the fig.8 openings shown on the front
panels for LEDs, sensitivity regulator R29, switch
power supply S4 and reset button S1. On the fig.9- hole on the side
housing surface for the Earphone JACK telephone jack. On the fig.10
– openings on the rear panel for the power cable and for the search engine cable
coils.
Appearance assembled electronic stuffing is shown
on the rice. eleven.
Figure 8. Holes on the front panel of the case for LEDs
Figure 9. Hole on the side surface
phone jack housings
Figure 10. Holes on the rear panel for cable
power supply and under the search coil cable
Figure 11. Appearance of the electronic filling
microprocessor pulsed metal detector from MASTER KIT NM8042
Learn more about our range
products can be found using the “MASTER KIT” catalog and on our website, where
many useful information on electronic kits and modules
MASTER KIT, addresses of stores where you can buy them are given.
How they differ from conventional detectors and where it is best to use them, let's look at examples.
Principle of operation
Any metal detector generates a magnetic field around the coil transmitter. Due to this, a magnetic flux also appears at the target under the coil, which catches the coil receiver. This magnetic flux is then converted into visual information on the screen and into an audio signal.
Conventional ground metal detectors (VLF) generate a constant current in the transmitter coil, and changes in the phase and amplitude of the voltage at the receiver indicate the presence of metal objects. But devices with impulse induction (PI) differ in that they generate a transmitter current that turns on for a while, and then turns off abruptly. The coil field generates pulsed eddy currents in the object, which are detected by analyzing the attenuation of the pulse induced in the receiver coil. This cycle repeats continuously, perhaps hundreds of thousands of times per second.
Advantages of metal detectors with pulsed induction
1. The detection speed does not depend on the material between the metal detector and the target. This means that the search can be conducted through air, water, silt, corals, different types soil.
2. Sensors are highly sensitive to all metals and do not react to high level soil mineralization, hot rocks and salt water.
3. You can search for metal objects and find them at a greater depth, it works especially well on mineralized soils.
4. There will be no interference in mineralized soils, salty sand, salt water, and the performance will be higher than that of VLF detectors.
5. Pulse induction metal detectors have been specially designed to find gold objects, even very small ones (nuggets, chains).
The disadvantages of metal detectors with pulsed induction may be not very good discrimination and high price.
Where do pulse induction metal detectors perform best?
The pulse repetition rate (transmitter frequency) of a typical pulse induction metal detector is approximately 100 hertz. Different models of MD use frequencies from 22 hertz to several kilohertz. The lower the transmission frequency, the greater the radiated power. At lower frequencies, a greater depth and sensitivity of detection of objects made of silver is achieved, however, sensitivity to nickel and gold alloys decreases. Such devices have a slow response, so they require a very slow movement of the frame.
Higher frequencies increase the sensitivity to nickel and gold alloys, but are less sensitive to silver. The signal may not penetrate as deep into the ground as at lower frequencies, but you can move the coil more quickly. This allows you to check large area for a given period of time, as well as such devices are more sensitive to the main beach finds - gold items.
Thus, it is best to use PI-metal detectors for beach search on the coasts of the seas and oceans, underwater search, gold search, search in desert and mountainous areas. They are also good at cleaning up “knocked out” terrain and during geological exploration.
Top 5 Best Pulse Induction Metal Detectors:
Characteristics and principle of operation of pulsed metal detectors
Updated 07.10.2018Pulse Metal Detector ( Pulse metal detector or - English) the most sensitive among all detectors, reacts to any metals, does not distinguish ferromagnets from diamagnets. Search features allow the detector to detect gold and gold nuggets in alkaline conditions and extreme ground (or rock) temperatures that are too difficult for VLF/TR devices. It also allows you to detect metal ores found in rocks and clay.
Pulse metal detectors are indispensable when searching in the coastal zone, under water and on highly mineralized soil. The operation of the devices does not depend on the influence of earth and water. They work equally well underwater and on land. That's why PI technology used in underwater metal detectors. Devices have good results when searching on sandy and wet beaches. The depth of detection of objects in the ground and salt water is greater compared to VLF metal detectors.
Pulse metal detectors behave better than VLF metal detectors near power lines, as well as transmitting antennas of mobile communication systems. Servicing this type of metal detector is quite simple. As a rule, they are equipped with a single sensitivity control, although more advanced models may have other controls.
The devices have a high power consumption, they require powerful batteries. Conventional batteries last no more than 12 hours of continuous operation. If alkaline batteries are used, the operating time will increase.
Technology pulse induction is not universal, and the shortcomings of pulsed metal detectors limit their capabilities. Currently, the best metal detectors for all purposes are those using VLF (Very Low Frequency) technology. However, PI technology may have further development and new detectors with new capabilities may be developed in the future.
The device and principle of operation of pulsed metal detectors
Pulse metal detectors have a simple design. The device consists of a pulse generator, a search coil, a signal amplification unit, an analyzer and an indication unit. The design of the coil is also simple. It is transmitting and receiving at the same time. This significantly reduces the weight of the device.The search coil acts on the ground with a pulsating electromagnetic field. The pulses are emitted with a frequency of 50 ... 400 Hz and an energy of about 100 W. Due to magnetic induction, eddy currents arise on the surface of a metal object located in the field of action.
These currents are the source of the secondary signal (reflected pulse, response). In between pulses, the receiver receives a response, which is amplified and processed by the analyzer and then output to the display unit.
The decay time of the reflected pulse is longer than the decay time of the emitted pulse (due to the phenomenon of self-induction). The time difference is a parameter for analysis and logging. The attenuation of eddy currents from soil or water occurs much faster and is not captured by the device. That's why pulse metal detectors work effectively under water, on mineralized, salty and wet soils.
related tags: pulse metal detectors, pulse metal detectors, PI technology, Pulse Induction, the principle of operation of pulse metal detectors, the device of pulse metal detectors, how a pulse metal detector works
Radio amateurs for the national economy 1992.
Creating sufficiently sensitive metal detectors is a rather difficult and thankless task. Radio amateurs periodically take up its decision, present exhibits at the exhibition, but rare of them meet the required parameters. So, for a long time, metal detectors were designed on the basis of two high-frequency generators tuned to close frequencies, one of which was stable in frequency (usually stabilized by a quartz resonator), and the other - the working one - was connected to the receiving frame and changed its frequency when approaching metals . The signals of the two generators were summed, a low-frequency beat signal was isolated, and it was used to judge the presence of metal. After the emergence of a new element base instead of reference signal generators, they began to design a metal detector with a voltage-frequency converter, analog-to-digital converters, frequency synthesizers and other possible novelties.
Archaeologists and criminologists could be advised another measurement scheme - geophysical. On the area where metal inclusions are searched, it is necessary to lay out a loop of wire with a diameter of 5 ... 25 m or more, power it from an autonomous generator with a frequency of 500 Hz (the higher the frequency, the less depth). It is very convenient to use aircraft DC-to-AC converters with a frequency of 400 Hz (umformers). They have sufficient power. You can also use DC-to-AC converters made on power transistors. They can be made at several frequencies, and thereby carry out "frequency sounding", i.e., determine the depth of the alleged metal object. To conduct searches, in addition to the generator, it is necessary to have a receiver, which can be a selective amplifier tuned to the frequency (frequencies) of the generator and have a receiving magnetic antenna at the input, also tuned to the frequency (frequencies) of the generator. The idea of this search method is that in the area of action of the electromagnetic field of the wire loop, any metal bodies of continuous conductivity begin to radiate their field, which is ideally 90 ° shifted in phase relative to the primary one. receiving frame regarding primary field usually oriented so that in the absence of metal inclusions, the signal at the output of the receiver would be minimal or completely absent, and in the presence of metal inclusions it would reach a maximum. Having carried out measurements at several frequencies, it is possible to determine the approximate depth of occurrence, and using receiving frames differently oriented in space, and the location of objects. The main advantage of this method of measurement is that the desired metal object itself becomes a source of radiation.
Equipment of this kind can be used for tracing underground pipes, laying cables, tracing hidden wiring, and other purposes. To do this, the generator is connected at one end to a traceable metal system, and the other end is grounded (if the search is carried out on the street, in the field) or connected to the pipes of the heating network, water supply (if tracking is carried out in the building).
The loop induction method was widely presented at VRV as an application to contactless induction methods for turning on household electrical appliances (contactless headphones for listening to radio, television programs, etc., contactless telephones that are not connected by wires to the telephone network, which can be freely carried in hands while moving around room). It would seem that the task is different, but the principle of the solution is the same: an inductive connection between the loop in which the signal is generated and the receiver that picks up this signal.
Pulse Metal Detector(Fig. 27). The author of the design is radio amateur V. S. Gorchakov. At 33 ER, the exhibit was awarded the Third Prize of the exhibition.
The device is designed to find metal objects in the ground. Its tests have shown that it can detect a 100 x100 x 2 mm aluminum plate at a depth of 75 cm, the same 200 x 200 x 2 mm plate at a depth of 100 cm, a long length steel pipe with a diameter of 300 mm at a depth of 200 cm, a manhole sewer well at a depth of 200 cm, a long steel pipe with a diameter of 50 mm at a depth of 120 cm, a copper washer with a diameter of 25 mm at a depth of 35 cm.
The device (Fig. 27, a) consists of a master oscillator 1 at a frequency of 100 Hz, a pulse current amplifier 2, a radiating frame 3, a delay generator 4 for 100 μs, a strobe pulse generator 5, a matching amplifier 6, an electronic switch 7, a receiving frame 8 , bilateral limiter 9, signal amplifier 10, integrator 11, DC amplifier 12, indicator 13, voltage stabilizer 14.
The metal detector works as follows. The master oscillator emits a pulse of duration T and (Fig. 27, b), the decline of which triggers the delay generator. The master oscillator pulse is amplified in power by a current amplifier and fed to the radiating loop. The delay generator generates a pulse with a duration of 100 µs, the decay of which triggers the gating pulse generator. This generator generates a strobe pulse with a duration of 30 μs, which controls the operation of the electronic switch through a matching amplifier. The switch opens the signal amplifier for the duration of the strobe pulse and passes the signal from the amplifier 10 to the integrator. The signal from the output of the integrator through the DC amplifier is fed to the pointer indicator.
On fig. 27b shows the time distribution of signals on the transmitting (radiating) frame (curve 1), on the receiving frame in the absence (curve 2) and in the presence of metal (curve 5). As a result of the experiments, it was found that in the absence of metal, the received pulse decreases rather sharply in amplitude over a time of 100 μs. If there are metal inclusions in the control zone, the duration of the decrease in amplitude of the received pulse is significantly delayed, mainly due to the action of Foucault currents. The property of deformation of the shape of the received signal due to the impact of metallic inclusions is the basis for the design of this device.
The design of the sensor of the device is shown in fig. 27, c. The emitting and receiving frames are wound on a dielectric frame with an outer diameter of 300 mm. The receiving frame is wound inside the emitting frame. Its inner diameter is 260 mm. The transmitting frame contains 300 turns of PEV-2 0.44 wire, and the receiving frame contains 60 turns of PEV-2 0.14 wire. The fastening of the handle 1 is arbitrary and does not require special explanations.
On fig. 28 pictured circuit diagram device. The master oscillator is made on microcircuits DD1.1 and DD1.2. The signal from the output of the generator through the resistor R9 is fed to the input of the pulse current amplifier - transistors VT3-VT5, the load of which is the radiating frame L1.1. Through the capacitor C3, the pulse from the master oscillator is fed to the input of the delay generator, made on the elements DD1.3, DD1.4 according to the Schmidt trigger circuit. The decay of the delay pulse starts the strobe pulse generator, made on the elements DD2.1-DD2.3. The strobe pulse through a matching amplifier (transistors VT1, VT2) is fed to the electronic switch DA1, which controls the operation of the signal amplifier (DA1.1 and DA1.2) and the integrator (C12, R30), passing the DC signal to the DC amplifier (DA2) during the duration of the strobe pulse. The load of the DC amplifier is the pointer device RA1. To increase the measurement stability, the power supply of the amplifying stages is additionally stabilized. Electronic stabilizers are made on transistors VT6, VT7.
