METAL PIPE

The device allows you to look for underground cables and metal pipelines of all kinds located at a depth of 1.5- 2 m , To detect (at the same depths) individual metal objects (pieces of pipes, manhole covers, sheets with an area of ​​at least 250 X 250 mm ), And also to locate the detected objects in the plan with an error up to 20- 30 centimeters .

Structurally, the finder consists of two main units of the induction unit with mutually orthogonal (spaced along the axis) excitation and receiving frame antennas and an electronic unit into which the generator and receiver enter. The frame antennas are located in a rigid cylinder with a diameter 260 mm And length 700 mm , Made of fiberglass. They have an electrostatic shield in the form of a layer of copper deposited on the outer surface of the plastic frame. The electronic unit and the cylinder are mounted on a rigid bracket, equipped with shoulder straps for carrying. Controls (switches, potentiometers, as well as connectors, visual indicator and telephone jacks) are placed on the top panels of the generator and receiver.

In foreign pipe- cable detectors, the installation with vertical excitatory and horizontal receiving frame antennas prevailed. When moving such a device along a profile perpendicular to the cable or pipeline route, the curve of the change in the secondary induced signal is asymmetric and has two extreme values ​​(maximum and minimum, and with phase- sensitive indication - two maxima) of different magnitude away from the cable route (pipeline). In order to determine the route, it is necessary to cross the profile twice in mutually opposite directions and make measurements on the terrain (determine the middle of the distance between the two marks). This device is free from this disadvantage: due to the location of the frame antennas at an angle of 45 ⁰ and 135 ⁰ to the horizon, it allows to obtain maximum indications directly above the object's path, and also to separate objects located parallel to each other at short distances in the horizontal plane (on the order of 1- 2 m ).

Schematic diagram

The electronic unit consists of a generator loaded with an excitation loop antenna and an amplifier with a receive loop antenna. The latter also includes a compensation device serving for fine (lasing) compensation of the primary induced signal (i.e., the signal induced directly from the excitation antenna to the receiver). The input of the compensation device is connected directly to the generator. Both units are powered by the batteries located in the generator block. The generator block (Fig. 1) consists of a master oscillator (T1), a cascade (T2), two amplifier stages (T3, T4, T5) and a power amplifier (T6, T7). The master oscillator, tuned to a frequency of 12 kHz , was assembled in a three-point circuit with a capacitive coupling. The coil L 1 of the oscillatory circuit is wound on a core of the TCHK-55P type and has an inductance of about 25 mg . The number of turns of the winding and the tap are selected during the adjustment.

To reduce the influence of the parameters of the transistor T 1 on the generation frequency, a partial inclusion of the circuit in the collector circuit is applied. The supply voltage of the master generator is stabilized by a stabilitron D 1 . The emitter follower, assembled on transistor T 2 , eliminates the effect of load changes on the master oscillator. The thermistor R 5 retains the necessary stability of the output voltage in the operating temperature range. Transformer Тр 1 - matching. The pre-term and output stages of the amplifier are made on transistors T4-T7 using a two- cycle transformerless transformer . The exciting loop antenna is connected through the capacitor C 9 to the transistors T6, T7. Diodes D2-D5 serve to prevent thermal breakdown of transistors T 6 , T 7 with increasing their temperature; To protect these transistors in the event of a short circuit of the output of the amplifier is the fuse Pr1 at a rated current of 0.15 A. From the generator output, the voltage is applied to the input of the compensation device via the voltage divider and the transformer Tp 2 . To facilitate electrical compensation, a polarity switch Tp 2 can be inserted into the device. The exciting VHF antenna is matched to the output resistance of the generator by means of partial switching. To increase the radiated power and reduce the non-linear distortion of the exciting signal, the antenna VR tunes in resonance to the operating frequency. To protect the generator from improperly turning on the batteries, diode D6 is installed. In the supply battery, the "Mars" type elements (373) are used to ensure continuous operation of the searcher for about 50 hours. When working with interruptions, the service life of the elements increases. The acquisition of the finder (see the diagram in Fig. 2) consists of a compensating device for the amplifier and a block of indicators.

The main attenuation of the primary signal induced in the receiving frame antenna of the OL is due to its arrangement orthogonally and symmetrically with respect to the exciting loop antenna BP. The compensation device, connected together with the antenna PR to the input of the amplifier, serves to bring the residual primary signal to a level comparable to the secondary induced signal that appears when The seeker is approaching the desired metal objects. Adjustment of the amplitude and phase of the compensating voltage is carried out by the variable resistors R 1 and R 4, respectively. The amplifier contains six stages: the input on the transistor T 1 , the aperiodic (T2) resonant (T3), the limiter (T4), the two aperiodic (T5 and T6). The connection between transistors T 2 , T3 and T5, T6 is direct. In the indicator box, two types of indication are applied: visual (by microampere meter) and acoustic (by sound in telephones). The visual indication channel has a detector (diode D 1 ), to which a microammeter is connected per 100 μA , the acoustic indication channel consists of an amplifier (transistor T7), a detector (diode D2) and a multivibrator (transistors T8, T9). A voltage is applied to the base T8, detected by the diode D2. Its constant component is the bias voltage on the base of T8, which changes the frequency generated by the multivibrator, and consequently also the pitch of the phones.

The sensitivity of the amplifier can be adjusted roughly by the switch P 1 and the continuously variable resistor R 37, and the sensitivity of the acoustic indication channel by the variable resistor R 26. The cascade on the transistor T 4 is the limiting of the resulting signal (secondary and uncompensated primary) to a minimum. Such a limiter makes it possible to use an uncompensated primary signal whose amplitude is comparable to or greater than the amplitude of the secondary signal. As a result, irregular interference (eg, impulse) will be effectively suppressed. In addition, in the presence of a limiter, the requirements for the depth of compensation of the primary signal can be relaxed. Finally, the limiter allows to increase the sensitivity of the amplifier to small changes in the secondary signal and to facilitate the adjustment of the compensation device.

Design

The device consists of a housing in which the exciting and receiving frame antennas are located at an angle of 45 ⁰ to the horizon; Bracket on which the housing with antennas is placed, as well as amplifier and generator blocks; A generator block with a power supply, an amplifier unit with a compensation device. The enclosure, in which the exciting and receiving frame antennas are fixed, is made of glass fiber reinforced plastic 4 mm In the form of a cylinder with an internal diameter 260 mm And length 700 mm . To increase the stiffness inside the body, two rings are also made of fiberglass, located perpendicular to the generatrix of the cylinder. The body is made by gluing fiberglass with epoxy resin. Instead of fiberglass, other layers of mass can be used (for example, vinyl plastic).

Inside the cylinder along its axis, both the excitation and receiving frame antennas are inserted from both ends and fixed by means of brackets. Antennas to the brackets and bevels to the body are fixed with screws; After setting the device attachment points, pour epoxy resin. Antenna spacing along Axis of the cylinder (the distance between their centers) should be approximately 450 mm . The frames of the exciting and receiving antennas of cylindrical shape are machined from textolite and impregnated with bakelite varnish. Average winding diameter of antennas 225 mm . The annular groove for laying the turns of the antenna has dimensions (in cross section) of 18 X 18 mm. On its inner surface by the method of electrochemical deposition, a layer of copper, serving as a static screen, is applied. The receiving antenna contains 800 turns of PEL 0.1 wire, exciting - 400 turns (withdrawal from the 10th turn) of PEV-2 wire 0.6. On the outside of the coil, the frames are shielded with copper or brass tape. To reduce the losses introduced by the screens, narrow slots (slots) should be left in 1-2 places on the screen. The bracket on which the units are located is made of thick plywood. Its rear wall has two protrusions for securing belts covering the operator's back. On this wall there are staples, where the body with antennas, strapped, is laid. The front wall of the bracket has a hinge on the left and a latch on the right, which allows the operator to put on the bracket, and then close the front wall. Carrying straps are attached to the bracket so that the load on the operator's shoulders from the blocks located on the front wall of the bracket and the housing with the antennas located on the rear wall is distributed evenly. On the side walls of the bracket are fixed the cables coming from the exciting to the receiving antenna. The generator of the device is assembled in a metal casing. In the lower compartment of this body is placed a battery of 15 elements of type 373 ("Mars"). To access the battery compartment, its bottom cover is removable. It has a rubber seal. The top cover (also detachable and sealed) serves as the front panel of the generator. To it a getinax board is attached, on which the generator parts are mainly mounted. On the top cover of the generator there are: switch Vk 1 ; The socket part of the connector for connecting the generator to the excitation loop antenna and the amplifier unit; The fuse holder is Pr1. The amplifier is assembled in a separate metal casing and mounted on two getinaksovaya mounting boards, located in parallel. The boards are attached on the racks to the upper (front) panel. Between them there is an electrostatic screen made of foil sheath. On the board located closer to the front panel, the details of the first four stages of the amplifier are located, and on the second board - the remaining stages. The boards can be thrown back on hinges, which allows you to access all the details. On the front panel of the amplifier there are: a microammeter; Connector base; Controls for the amplifier; Sockets for connecting headphones. The winding data of the transformers and choke of the generator and amplifier are summarized in the table. To protect the installation from moisture between the front panel of the amplifier and its body are placed rubber gaskets.

Customization.

The device is adjusted in the following order: first the loop antennas, then the compensator and finally the generator and amplifier. The adjustment of the loop antennas is reduced to adjusting their mutual arrangement until a minimum primary signal is obtained, measured in tens of microvolts. The found optimal position of the antennas is rigidly fixed by pouring fasteners with epoxy resin. To obtain the necessary depth of suppression of the primary signal (of the order of 100,000 times), one can use small adjustment frames or metal plates located near the receiving frame antenna. After adjustment, they are also filled with epoxy resin. Adjustment of the compensator reduces to a further reduction of the primary signal at the input of the amplifier by means of successive adjustments of the variable resistors R 1 and R 4. The tuning of the generator and amplifier does not have any specific features and therefore is not described here. When properly configured, the instrument generator must have the following parameters: operating frequency 12 kHz ± 60 Hz; Instability in the temperature range -20 ⁰ - + 50 ⁰ С - ± 120 Hz; The exciter frame quality is about 30; The active power, allocated in the excitation frame, is not less than 0.8 W; The instability of the output voltage in the temperature range -20 ⁰ - +50 ⁰ C - not worse than ± 5%. The parameters of the amplifier should be as follows: tuning frequency 12 kHz ± 120 Hz; Relative instability of the tuning frequency in the temperature range -20 ⁰ - +50 ⁰ С - about ± 2%, and the gain factor - about 2 times.