CA2011141A1 - Detector of metalliferous objects - Google Patents

Abstract

DETECTOR OF METALLIFEROUS OBJECTS

Abstract The detector of metalliferous objects comprising an electrically coupled to an alternating voltage generat-or driving loop, rigidly fitted to two pairs of receiv-ing loops, positioned at opposite sides of the driving loop, coaxial and parallel to one another. The receiv-ing loops are connected to connected in series balanc-ers, differential amplifiers, electric signal compens-ators with the control inputs thereof connected to the generator, selective amplifiers, data processors, logic OR gate, and signalling unit.

Description

201~141 Field of the Invention The invention relate~ to the technology of detect-ing metalliferous objects with the aid of electro-magnetic fields and, more specifically, to metallifer-ous objects detectors.
This invention can find wide application in vari-ous branches of industry snd economy, such as civil engineering, geodesy, agriculture, engineering struct-ures maintenance, archeology, geoiogy, etc., to detect both mgpped and unmapped metalliferous ~ervice lines and objects: pipeline~, electric cable3, geodetic datum marks, reinforced concrete slabs, covers of underground wells and other metalliferous objects, including tho~e of non-ferrous metals.
~his invention can also be used in woodworking, food industry, other industrie~, and in agriculture to detect metal inclusions in raw materials and fodder.

Background of the Invention Currently, the problem of detectin~ unmapped me-talliferous objects, including those o~ non-ferrous me-tals, is an urgent one. One of the possible approache~
to solving this problem is the use of small-size induct-ive devices, combining the functions of radiating an : - 2 -~: . .. . . ., . .~ .

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original electromag~etic field and receiving the se-condary electromagnetic field induced by the metalli-ferous object irradiated by the original electromagnet-ic field of the device.
Known in the art are devices for detecting under- ~-ground metalliferous objectQ (high frequency M 480 de-tector from Seba Dynatronic, FRG, and the ~W-5 pipe and cable locator from Grigsby Co., USA) oi like de-.. . .
sign and each comprising: a generator loaded by a driv-ing loop, a receiver loop positioned orthogonally to this driving loop and loaded by connected in qeries ..
selective amplifier, data processor and acoustic sign-all~ng unit. The device use~ geometric cancelling of the signal induced in the receiving loop by the origin-al electromagnetic field of the driving loop.
Functioning of these devices i8 based on creating an original electromagnetic field with the aid of the driving loop, this field propagating in the area being searched, and reception o~ a secondary electromagnetic field generated by the metalliferous object.
Such devices are highly susceptible to e~ternal -.
.
interfering electromagnetic fields, including those from metalliferous ob~ects and service lines in the vi-cinity of the ~earch area, because they also generate secondary field~ in respon~e to irradiation by the ori-ginal electromagnetic iield of the driving loop.
Moreover, the reliability of detecting service .

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-`` 2011141 lineq located at an angle less than 20 to the direct-ion of device movement is low, due to the low _ignal induced in the ~ervice by the driving loop.
Alqo widely known in the art are metalliferous objects detector~ (V.F.Bakhmut~ky. "Indukt~ionnye kabe-lei~kateli" (Inductive cable locators), 1970, Svyaz Publi3hers, pp.75-78. - In Russian) compriqing a driv-ing loop and two rigidly fitted to it orthogonally and oppositely connected receiving loops mounted symmetric-tO ally to both ~ides of the driving loops. In one embodi-ment the driving loop i~ horizontal and the receLving loops are vertical, in another embodiment the loop ori-entation i9 opposite; the electric s~gnal recording circuitry ln both embodiments i9 identical and simil-15 ar to that described herein above. ~-It should be noted, that the direction of ths de-vicPs movement coincideq with that of the rod connect-ing the receiving loops.
Such devices are characterized by a low immunity to e~ternal interfering electromagnetic fields and me-talliferous objects in the pro~imity of the search area. Thi~ i~ due to the wide ~pacing of the receiving loops, necesi~ary to attain sufficient 3en~itivity and .
degree of geoinetric cancelling. Furthermore, the reli-ability of locating service lines positioned at angles less than 20 iQ low, due in the first ~mbodiment to low ~econdary fields from the service lines and in the ~: :

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.

`` 2~11141 second embodiment - to a low signdl induced in the service line by the driving loop.
It ~hould be noted, that the low interference im-.
munity of all the herein above described detecting de-vice~ make~ it impos~ible to u~e them in~talled ~nto a vehicle, which itself is a ~ource of interference for ~uch devices, ~o that thè productivity of search work is low.
A higher productivity and interference immunity is featured by the metalliferous objects detector tSU, A, 1190330), compri~ing a driving loop, two rigidly fitted to it receiving loops mounted coaxially and pa-rallel to one another and symmetrically and orthogonal to the driving loop located in the plane of the common a~is of the receiving loops, an alternating voltage generator electrically coupled to the driving loop, and connected in ~eries ~ignal balancer for the receiv-lng loop sign~ls with the inputs thereof connected to the receiving loops, and differential amplifier with the output thereof connected to the data input of an electric signal compensator to cancel the effects of the original electromagnetic field of the driving loop on the receiving loops with the control input thereof electrically coupled to the alternating voltage gene-rator and with the output thereof connected to the : input of a ~elective amplifier, the output whereof is connected to a recorder and electrically coupled to a ~ignalling unit.
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,- ., : - . , ,. , ~ : , .~ 2011141 The above mutual arrangement of the driving and receiving loopq, constituting the inductive system of the device, allows a significant improvement in its interference immunity due to 8 practically equal sign-5 al level induced in the receiving loop~q by external - -electromagnetic field sources (power distribution lines, electrified railways, communication~ line~, etc.) and cancelling out these interference signals by oppositely connecting the two receiving loops.
This known in the art device featureq a narrow coverage, i.e. the area in which the receiving loops are capable of picking up the secondary electromQgnet-ic field induced by a metalliferou~ object. A3 i9 known, the Nidth of the coverage area is a function ~f .. . . . .
the spacing between the receiving loops and is limited by a falling off of the interference immunity at great-er spaoing~, accompanied by a higher sen3itivity.
Moreover, if metalliferous objects (3ervice line~) .
are at an angle less than 20 relative to the direct-ion of searching, which is normal to the rod connect-ing the receiving and driving loops, the detection re-liability is low due to the weak signal induced in the service line by the original electromagnetic field of the driving loop.
To improve the detection probability, the search area has to be 9canned twice, at different orientation of the induction sy~tem relatlve to the direction of '` 2011i~

searching. However, even then the probability of de-tection is insufficient, because it is difficult to maintain the same ~earch direction when scanning in the oppo~ite direction, this being true both with manu-al 3canning and when the detector is mounted onto avehicle.

Summary of the Invention It is an objective of this invention to provide a metallife~ous objects detector, characterized by a 10 high search productivity.
Another ob~ective of the invention i~ to improve ..
the reliability o~ metalliferous ob~ect3 detection.
This i9 aohieved by that a detector o~ met~ rous objects comprising a driving loop ri~idly fitting two receiving loops, mounted coa~ially snd parallel to one another and symmetrically and orthogonally relat-ive to the driving loop located in the plane of the ¢ommon axis of.the receiving loops, an alternating voltage generator electrically coupled to the driving loop, and connected in series signal balancer for re-ceiving loop signals with the inputs thereof connected to the.receiving loops, and differential amplifier with the output thereof connected to the data input of ~: an electric signal compensator for cancelling the sign-... . . . . .
alQ induced in the receiving loops by the original ; ~ : electromagnetic field of the driving loop with the com-pen~ator control input eleotrically coupled to the .. .. .
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~ 2011141 alternatin~ voltage ~enerator and the compensator out-put connected to the input of a selective amplifier, the output whereof is connected to the input of a data processor with the output thereof connected to a re-corder and electrically coupled to a 9ignalling unit,according to thi~ invention, further compri~e~ two supplementary receiving loop~ identical to the main receiving loops and rigidly fitted to the driving loop symmetrically and orthogonally its oppo~ite side, co-axial and parallel to one another, connected in ~eriessignal balancer for receiving loop signals with the inputs thereof connected to the supplementary receiv-ing loops, and a supplementary differential amplifier, supplementary electric ~ignal compensator for cancel-ling the effect of the original electromagnetic fieldof the driving loop on the supp~ementary receiving loops with the data input thereof connected to the out-put oi the supplementary differential amplifier and with the control input thereof electrically c~upled to the alternating voltage generator, connected in series supplementary selective amplifier with the input thereof electrically coupled to the output of the supplementary electric ~ignal compensator for cancel-ling the effect of the original electrom~gnetic field of the driving loop on the supplementary receiving loop9, a supplementary data processor and recorder, and a logic OR gate with the inputs thereof connected .

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. : - ': , ': . ~ ' ` ' ` ` ' to the outputs of the main and supplementsry dsts pro-ces~ors and with the output thereof connected to the signslling unit.
It i~ sdvsntageous, thst the detector c~mpri~e two supplementary driving loops the first whereof is rigidly fitted to the main receiving loops snd locsted relative to them ~ymmetrically snd orthogonally in the plane of the common axis of the main receiving loops snd st an angle to the main driving loop, snd the se-cond whereof is rigidly fitted to the ~upplementaryreceiving loop~ and located ~ymmetrically and orthogon-ally to them in the plane of the common a~i~ of the ~upplementary receiving loops at an angle to the main driving loop, an electric ~ignal compensator for can-celling the effect of the first supplementary drivingloop'3 original electromagnetic field on the main re-c~iving loop3 with the data input thereof connected to the output of the main differential amplifier, an electric ~ignal compensator for cancelling the effect of the original electromagnetic field of the second ~upplementary driving loop on the supplementary receiv-ing loops with the data input thereof connected to the output of the supplementary differential amplifier, a second and third ~upplementary selective amplifiers, :: : 25 a switch with the inputs thereof connected to the alternating voltsge generator, to the output~ of the electric sig~al compens~tors for can¢elling the effect _ g _ . ~ . . .. . . . . . ..
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of tha main and first ~upplementary driving loops on the main receivin~ loops, and to the outputs of elec-tric signal compenQators for cancelling the effect of the original electromagnetic field of the main snd se-cond supplementary driving loops on the supplementaryreceiving loops, with the switch outputs connected to the main and first and second supplementary driving loops, to the control inputs of the electric signsl compensators for cancelling the effect of the original electromagnetic fields of the main and first supple-mentary driving loops on the main receiving loops, to the inputs of electric signal compensators for cancel-ling the effect of the original electromagnetic fields of the main and second driving loops on the supplement-15 ary receiving loop9, and to the inputs of the main and first, second and third supplementary 9electi~e ampli-fiers and providing consecutive connection to the alternatir.g voltage generator of, firstly, the main driving loop and the control inputs of the electric signal compensators for cancelling the effect of the original electromagnetic field of the main driving loop on the main and supplementary receiving loops, and the compensator outputs to the inputs of thR main and first supplementary 9elective amplifiers, then -. . . .
the first ~upplementary driving loop and the controlinput of the electric signal compensator for cancel-ling the effect of the first supplementary driving :
.- 10 -'- :. .. . .: . .,,, ~ ,..................... .

-` 20~1~41 loop on the m~in receiving loops, and the compensator output to the input of the second supplementary select-ive amplifier, and next the sècond supplementary driv-ing loop and the control input of the electric ~ignal compensator for cancelling the effect of the qecond supplementary driving loop's original electromagnetic field on the supplementary receiving loops and the com-pensator output to the input of the third supplementa-ry selective amplifier, a second and third supplement-ary data processors with the inputs thereof connectedto the outputs of the second and third supplementary selective amplifiers, respectively, and with the out-put3 thereof connected to supplementary inputs of the logic OR gate, and a second and third supplementary recorders connected to the outputs of the second and third supplementary data processorq, re~pectively.
It is highly reasonable, that the angle between the main and the first supplementary loops and between the main and the second supplemertary loops be within the range from 60 to 120.
It is ~uitable, that the switch comprise seven keys and a key controller with the outputs thereof con-nected to the key control inputs.
It i~ preferable, that the key controller com-prise connected in series rectangular pulse generator,ternary counter and decoder, three time delay circuits with the inputs thereof connected to the decoder out-~, . ,~, .

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puts serving a~ the outputs of the key controller,and three logic AND gates with ~ome inputs thereof connected to the decoder outputs, with the other inputs thereof connected to the outputs of the time delay circuits, and with the output3 thereof constitut-ing the other outputs of the key controller.
This invention allows an improved productivity of search work by expanding the width of the coverage area and by scanning the site during a single scan.
Another advantage iQ that the reliability of me-talliferous object~ detection is improved, irre~pect-ive of their orientation relative to the search direction.

BrLef De~cription of Aocompanying DrawingQ
The3e and other objective~ of the invention will become apparent from the following description of the invention and accompanying drawings, wherein:
Fig. 1 shows the functional diagram of the metal-liferous objects detector, according to the invention;
Fig. 2 ~hows the axonometric view of the layout of the receiving and driving loops, with conventional-ly denoted original and secondary electromagnetic fields and with a partial section along the driving and receiving loop~ of the embodiment presented in Fig. 1, according to the invention;
... .
Fig. 3 shows the embodiment presented in Fig. 1 with three driving loops, according to the invention;

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.

20~1141 Fig. 4 shows the embodiment presented in Fig. 2, without the partial seetion along the driving and re-cei~ing loop~, for the embodiment of Fig. 3, aecording to the invention;
~ig~ 5 shows the general view of an embodiment presented in Fig. 1 mounted onto a vehicle;
Fig. 6 (a,b,e,d,e,f,g,h,i,j~k,l,m,n,o,p) shousthe time diagrams illustrating the functioning of the switeh for the embodiment shown in Fig. 3.
~he detec~r o~met~ erous objects comprise~ driv-ing loop 1 (Fig. 1) and two pairs of receiving loops 2, 3 and 4, 5 constituting the integrated inductive sys-tem 6, and alternating voltage generator 7 conneeted . .
to driving loop 1.
Reeeiving loops 2,3 and 4,5 are eonneeted to, res-pectively, inputs 8,9 and 10,11 of receiving loop signal balaneers 12, 13. Conneeted in series to balane-ers 12, 13 are, respeetively, differenti~l amplifiers 14, 15, electrie signal eompensators 16, 17 for cancel-ling the effect of the original electromagnetie field of the driving loop on reeeiving lonps 2,3 or ~,~, res-peetively, selective amplifier~ 1~, 19, and data pro-eessors 20, 21, the outputs whereof are conne¢ted to reeorders 22, 23 and to ~nputs 24, 25 of lo~ie OR gate , . .
:; 25 26 with the output thereof connected to signallin~
unit 27.
Alternating voltage generator 7 drive9 eontrol : - 13 -:`
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inputs 28, 29 of electric signal compensators 16, 17, the dsta inputs 30, 3t whereof are the outputs of dif-ferential amplifiers 14, 15.
Signal balancers 12, 13 are of like design and are intended to balan¢e the signals arriving from re-ceiving loops 2,3 and 4,5, respectively, when induct-ive system 6 is under the action of external interfer-ing electromagnetic field~ due to the electromagnetic -parameters of receiving loops 2,3 and 4,5 being non-identical.
Signal balancers 12, 13 may be designed along any of the known circuit arrangements and in the embodi-ment being described compri~e each pha~s shifter 32 with the input thereof constituting input 9 of balanc-15 er 12 or input lt of balancer 13, potentiometer 33 con-nected across balancer 12 input 8 and one output or across balancer 13 input 10 and one output, and poten-tiometer 34 connected to the output of pha~e shifter 32 and to the other output of balancer 12 or 13.
Electric signal compensator3 16, 17 are of like design and eack ¢omprise~ phase qhifter 35 with the input thereof constituting control input 28 of compens_ ator 16 or control input 29 of compensatnr 17, potenti-ometer 36 connected to the output of phase shifter 35, and differential amplifier 37 with an input thereof connected to potentiometer 36 and with the other input thereof oon~tituting data input 30 of compens~tor 16 . : . ~ , . . .

20111Al or data input 31 of compensator 17.
Selective amplifiers 18, 19 provide amplification of electric ~ignals at the operating frequency of alternsting voltage generator 7~
Data proce~ors 20, 21 are designed with known in the art circuit arrangements and in this embodiment each compri~es connected in series logarithmic ampli-fier 38 providing an expanded range of detectable object sizes without sensitivity tuning during searches, detector 39 and negative limiter 40 provid-ing tuning out of constant factors (equipment noise, ~ibration effects, etc.).
Recorders 22, ~3 may be analogue or digital indi-cating meters (voltmeters).
... . . . .
Signal~ng unit 27 may be based on an acoustic signal source and an indicating lamp arranged into one .. . .
of the known circuits and providing a¢ou~tic and visu-al signaDing of tke detection of a metalliferous object.
In this embodiment receiving loops 2, 3 (Fig. 2) a~d 4, 5 of inductive system 6 are identical and posi-tioned relative to one another in coaxial and parallel pairs ~ymmetrically relative to driving loop 1 to both sides of it, Driving loop 1 is in the plsne o~ the com-- ~ .
mon axe~ 41, 42 of receiving loop~ 2,3 and 4,5, respect-ively, connected into pairs and fitted to driving loop 1 by tie rod~ 43, 44, thus uniting inductive system 6 - t5 -' ~, . . ..

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20~1141 into a ~ingle structure.
This mutual arrangement of the driving and receiv-ing loops 1, 2, 3, 4, 5 ensures minimal electromagnet-ic coupling between the driving loop and the receiving loops. Spacing L1 between driving loop 1 and receiving loops 2, 3, 4, 5 is selected proceeding from the re-quired stability o~ inductive ~ystem 6 a~ determined by the invariability of the arrangement ~f driving and receiving loops 1, 2, 3, 4, 5 and the specified geo-metric cancelling of the original electromagneticfield as set by the spacing between the driving and the receiving loop~. A~ i9 known, all other conditions be-ing equal, the greater i9 the ~pacing ~1~ the higher is the degree of geometric cancelling, but the lower .
i8 the 9tability, 80 that L1 is chosen for each Qpeci-fic application individually, proceeding from the e~-pected application area (portable, vehicle-mounted) and structural requirements (materials available, fab-rication methods) to en~ure the specified coverage area width, ~tability and geometric~l cancelling. ~he coverage area width will in any case exceed 2~1~
~ he driving and receiving loops 1, 2, 3, 4, 5 are of wires 45, the turns whereof are shown in Fig. 2, also showing lines of force 46 of the original electro-magnetic field generated by driving loop 1 in thecoverage area in solid lines and lines ~f force 47 of the secondary electromagnetic field generated by under-- 16 _ , ; . . i, - . : . , ; , . . , , ' ' . ' ' . ' , ~
`'~" ''' ;.','.''.;.'., ~' ', `',` '"' ~'' .',; ,. . ..

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ground metalli~erous object 48 in dashed line3.
The see.rch direction (movement of inductive sys-- tem 6) i~ denoted by arrow A.
In another embodiment cf the detector, to enable 5 detection of metalliferous object~ independent of their orientation relative to the search direction, the detector further comprises supplementary driving loops 49, 50 (Fig. 3), supplementary electric signal compensators 51, 52 cancelling the effect of the ori-10 ginal electror~agnetic field of supplementary drivingloops 49, 50, respectively, on receiving loops 2,3 and . . .

4,5 with their data input3 53, 54 connected to the out-puts of differential amplifier~ 14, 15, respectively.
To provide consecutive connection of alternating .
15 voltage generator 7 to driving loops 1, 49, 50 and to control inputs 28, 29, 55, 56 of electric sig~al com-.. . ..
pensators 16, 17, 51, 52, this embodiment further com-prises switch 57 with inputs 58, 59, 60 thereof con-nected to ~lternating voltage generator 7 and with out-20 puts 61, 62, 63, 64 thereof connected to the outputso~ electric signal compensators 16, 17, 51, 52. Switch 57 outputs 65, 66, 67 are connected to driving loops 1, 49, 50 and to control inputs 28, 29, 55, 56 of electric signal compensators 16, 17, 51, 52.
In this embodiment the metalliferou3 objects de-tector further comprises two selective amplifiers 68, . 69 connected to outputs 70, 71 of switch 57 and having : ~ , . . .
, . . . .
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~ 2011~41 their OUtplltS 72, 73 connected, re~pectively, to the inputs of selective ~mplifiers 18, 19.
Switch 57 provide3 conseoutive connection of the output~ of electric signal compensators 16, 17, 51, 52 5 to the inputs of 3elective amplifiers 18, 19, 68, 69 in accordance with driving loop~ 1, 49, 50 and control inputs 28, 29, 55, 56 of compensators 16, 17, 51, 52 connection to alternating roltage generator 7.
The metalliferous objects detector in this embodi-ment further comprises two data processors 74, 75 con-nected to the outputs of selective amplifiers 68, 69, respectively, and two recorders 76, 77 connected to the outputs of data processors 74, 75, connected also to supplementary inputs 78, 79 of logic OR gate 26.
15 Electric ~ignal compensators 51, 52 are of like design to compensators 16, 17 and data proce~ors 74, 75 are of like design to proces~or~ 20, 21.
In thi~ embodiment switch 57 comprigeg ~even keyQ
80, 81, 82, 83, 84, 85, 86 and key controller 87 con- .
nected to control inputs 88, 89, 90, 91, 92, 93, 94 of keys 80, 81, 82, 83, 84, 85, 86, with the inputs and outputs of keys 80, 81, 82 constituting, re~pectively, input3 58, 59, 60 and output~ 65, 66, 67 of switch 57, the 61, 62, 63, 64 inputs ~hereof and the 72, 73, 70, ~: 25 71 output~ whereof are the inputs and outputs of keys : 86, 83, 85, 84, re~pectively.
Key controller 87 in thi~ embodiment comprise~

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. .:: . . . , ~ , 20~1~41 connected in ~eri~s rectsngular pu19~ generator 95, ternary counter 96 and decoder 97, outputs 98, 99, 100 whereof are connected to time delay circuits 101, 102, 103 with the outputs thereof connected to inputs of logic AND gates 104, 105, the other inputi3 where~f are connected to outputs 98, 99, 100 of decoder 97. Out-puts 98, 99, 100 of decoder 97 co~sti.ute control inputs 88, 89, 90 of keys 80, 81, 82 in switch 57 and the outputs of logic AND gates 104, 105, 106 serve as control inputs 91, 94, 93, 92 of switch 57 keys 83, 86, 85, 84, respectively.
In this embodiment controller 87 compri~e~ rectan- -gular pulse generator 95 generating a quare wave, i~e.
with a duty factor of 0.5, this ensuring driving loops 1, 49, 50 being oonnected to alternating voltage gene-rator 7 for equal time intervals. ~he switching rate of generator 95 is set to 1/10 of the operating fre-quency of alternating voltage generator 7, this ensur-ing ~ duration of the time interval of driving loop connection to alternating voltage generator 7, suffici-ent for reliable detection of signals induced by the secondary electromagnetic field of the metalliferous object.
In this embodiment driving loops 49, 50 (Fig. 4) of inductive system 6 are positioned symmetrically and orthogonPl to recei~ing loops 2,3 and 4,5 in the plane of their common a~es 41, 42 and at an angle ~ to driv-_ 19 _ . . .~ ., . .; . .
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ing loop 1. Angle ~ i9 within the range from 60 to 120, depending on the specific application.
With inductive system 6 fitted to a bracket on the vehicle, at its front, angle ~ is preferably 60 or t20 (Fig. 5) to ensure vehicle trafficability. In case of stringent requirements to inductive system 6 size, angle ~ between driving loop 1 and driving loops 49, 50 is set to 60. Driving loops 49, 50 are at a distance of L2 from axes 41, 42 of receiving loops 2,3 and 4,5 and are rigidly fitted to them by tie rods 107.
For illustrativeness, Fig. 4 shows lines of force 46 of the original electromagnetic field generated by all driving loops 1, 49, 50 simultaneously.
It should be noted, that driving loop3 49, 50 are arranged to induce a minimally possible electromagnet-ic field in receiving loops 2,3 and 4,5.
A high reliability of metalliferous object 48 de-tect~n is ensured at any angle ~ within the specified range (60 to 120), becau~e the angle ~ between the object (for lnstance, service line) and tie rod 44 to one of the driving loops 1, 49, 50 is always less than 60, this en3uring a sufficiently high signal induced in the service line.
Spacing L2 between the driving and receiving loops 49, 50 and 2,3; 4,5, respectively, i3 selected, as in the case of spacing L1, proceeding from the - 20 - ;

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20111~1 required ~tability and geometrical cancelling of the original electromagnetic ~ield.
Fig. 5 shows the general view of the metallifer-ous object~ detector designed as shown in Fig. 1 and in~talled on a vehicle Inductive system 6 is mounted on the front bumper with the aid of bracket 107. The detector's electronic circuitry, including alternating ~oltage generator 7 (Fig. 1), is housed in case 108 (~ig. 5) and is located in the driver's cab, directly before th~ operator for convenience of observing the recorders 22, 23 (Fig. 1) readings. Receiving loops 2, 3 and 4, 5 are housed in case 9 109 .
The metalliferouq objects detector of this invent-ion will be better understood by studying the time dia-grams of Fig. 6 (a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p)illustrating functioning of switch 57 (Fi~. 3). ~hus, Fig. 6(a~ 3hows the time diagrsm of rectangular pulse , . . . . . .
generator 95 output signal~ U1; Fig. 6(b,c,d) sh~ws the output 8ig~ U2, U3? U4 of decoder 97; Fig. 6 (e, f,g) illuQtrate3 the output signals U5, U6, U7 ar-riving from time delay circuits 101, 102, 103; Fig. 6(~
i,;) presents the output signals U8, Ug, U10 of logic AND gates 104, 105, 106; ~ig. 6 (k,m,n,o,p) illustrates keys 80, 81, 82, 83, 84, 85, 86 states, ~ 25 w~th logic "1" corresponding to an open key and logic ; "0" corresponding to a cloqed key.
The metalliferous objects detector, according to - , . .. ., . ., . . , - .... . . . .

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the invention, functions as follows.
Prior to starting a search operation, the output signals from receiving loops 2,3 and 4,5 (Fig~ 1) have to be balanced to en~ure high interference immunity 5 and detection of metalliferous obJectq. To this end, -:
driving loop 1 is di~connected from alternating volt- -age generator 7, potentiometers 36 in electric signal -.
compensator~q 16, 17 are set to zero, and inductive sys- -. tem 6 is submitted to the external electromagnetic field. As a source of such a field a loop, similar to driving loop 1, may be used by ¢onnecting it to gene-rator 7 and placing it as symmetrically as pos~ible re-lative to receiving loops 2, 3, 4, 5 at a distance of at lea~t thrice the depth of metalliferous object de-t~¢tion, as determined by the available alternating voltage generator 7 power and the electromagnetic para-meters of inductive system 6. After this the readings o~ recorders 22, 23 are zeroed as far as poqsible with the aid of potentiometers 33, 34.
Balancing is performed only lf operating condi- :
tions are changed, for instance if the detector 19 installed on another vehicle, or if it was fir~t used as a portable device and then installed on a vehicle, or vice..versa.
Prior to each search 3es~ion? electric signal com-pen~ator~ t6, 17 have to be adjusted to provide aq com-pl~te a cancelling of signals induced in receiving .

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loops 2,3 and 4,5 by the original electromagnetlc field of driving loop 1 as possible, the~e si~nals re-maining after geometric cancelling and differential co~nection of receiving loops 2,3 and 4,5. Compensat-ors 16, 17 sre adjusted at a site free of metallifer-OU8 objects as follows.
Gradually in¢reasing the output signal of alter-nating voltage generator 7, the signal pha~e and ampli-tude in ~ompansators 16, 17 i8 ad~usted with the aid of phase shifter 35 and potentiometer 36 to obtain a~
near a zero reading of recorders 22, 23 as possible.
~his adjustment is continued till the output signal of .. .
generator 7 is set to its rated value.
In the absence of metalliferous ob~ects, the out-put signal of compensators 16, 17 is approximately ze-ro due to geometric and eleotric cancelling of the ori- -ginal ole¢tromagnetic field.
In the presence of metalliferous object 48 (Fig.2) .
in the ¢overago area, the lines of force 46 of th~
- 20 original electromagneti¢ field of driving loop 1 en¢lose ob~e¢t 48 and induco a current in it, which in turn generates a secondary magneti¢ field, the linés of force 4? whereof pier¢e receiving loops 2? 3~ 4~ 5 of induct$ve system 6 and induce an electromotive force therein, thls ele¢tromotive force being proportional to the distance of each receiving loop 2, 3, 4, 5 from me-talliferous object 48. Since the9e di9tance9 are differ-., . ~ .
: ~ .. . .
;..... : , . : -. . . .. . ~ ... . . .

2 o ~

ent, a difference signal i~ generated at the output of -.
electric signal compenqator 16 or 17 (Fig. 1), this signal varying with a ehange in distance (top view) between receiving loops 2, 3, 4, 5 and-metalliferous objeet 48 (~ig. 2). The output signal of one of the eompensators 16 or 17 i3 passed to its respective se-lective amplifier 18, 19 and from the output thereof - .
to the input of its respective data proee~sor 20, 21.
.. .. . . .. .
Here, logarithmic amplifier amplifies the signal, and after dstection it arrives at neg~tive limiter 40. ~he output signal of data processors 20,~21 is passed to its respective recorder 22, 23 and to an input 24, ?5 of logia OR gate 26, and from the output thereof - to sienalling unit 27.
The readings of indieating meters in recorder~ 22, . .
23 vary aeeording to ehanges in the dist~nee (top view) between reeeiving loops 2, 3, 4~ 5 and metalliferous objeet 48 (Fig. 2), SignaI~ng unit 27 (Fig. 1) gene-rates light and audio signals, indieating deteetion of a metalliferous ob~eet.
Prior to operation, the detector of Fig. 3 should be tuned as deseribed herein above, i.e. the signal~
from receiving loo.ps 2, 3, 4~ 5 balanced and electrie signal eompensators 16, 17, 5t, 52 ad~usted to maximum ¢aneelling of signals indueed in receiving loops 2, 3, 4, 5 by the original electromagnetie fields of driving loops 1, 49, 5~. After this preoperational tuning the , ~ "1 . . . , :
.. , ~ ;
. , :
..

`` 2011~1 detector ii~ ready for u~eO
Rectangular pulse generator 95 provides ~ignal~
U1 (Fig. 6a) of ~1 duration, passed to ternary count-. .
er 96 functioning as a frequency divider by three. The 5 output signals of ternary counter 96 arrive at the lnputs of decoder 97, wherein the binary coded ~igna~
from counter 96 is converted into a positional coded SigIlal (U2, U3, U4 in Figs 6 b,c,d) of 2 ?'1 duration passed to ~ontrol inputs 88, 89, 90 of keys 80, 1~1, 82, 10 to the inputs of time delay circuits 101, 102, 103, and to some inputs of logic AND gates 104, 105, 106.
~ ime delay circuits 101, 102, 103 delay these signals by a time ~nterval of ~ 2 and produce consecut-ive signals U5, U6, U7 (~ig9 6 e,f,g) of 2 ~ duration-Keys 80, 81, 82 are triggered by control i ignal~
U2, U3, U4 (Fig. 6 b,c,d) from the outputs of decoder 97 and provide consecutlve connectio~ of driving loops 1, 49, 50 (Fig. 3) to alternating voltage generator 7 for a time interval of 2 ~1 (Figs 6 k,l,m) via outputs 20 65, 66, 67 and inputs 58, 59, 60 of switch 57.
At the moment of time t1 (Fig. 6a) switch 57(Fig. 3) provides connection, for instance, of driv`ing loop 1 and control input~ 28, 29 of electric signal compensators 16, 17 to alternating voltage generator 7;
25 at the moment of time t2 (Figs 6 e,h) time delay ¢ir-cuit 101 and logic AND gate 104 are enabled and a 9ignal of 2 ~ 2 duration i9 pas9ed to contro]

; . . . ( .. ~ , : , .. . . . -.:: , . ,. ,,.. . . : .
. . '. . . ` ` .. :: :

201 1~41 inputs 94, 91 of key~ 86, 83 in switch 57, these ~eys are triggered (Fig. 6h) and csuse inputs 61,62 (Fig.3) and output~ 72, 73 of ~witeh 57 to eonnect electric ~ignal ~ompensator~ 16, 17 to ~elective amplifier~ t8, 19. At this time, electric ~ignal compensator~ 51, 52 are disconnected from ~elective amplifiers 68, 69, 80 that, in other word3, the fir~t and ~econd receiving ehannels eomprising electric ~ignal compensators 16, ~7, selective amplifiers 18, 19, data processors 20, 21, and recorders 22, 23 are simultaneously in operat-ion.
At the moment of time t3 (~ig. 6a), the control signal from decoder 97 (Fig. 3) disables keys 80, 83, 86 (Figs 6 k,n), this disconnecting driving loop 1 (Fig. 3) from generator 7 a~d selective amplifiers t8, 19 from electrie signal c~mpensators 16, 17. At the ~ame time, key 81 is enabled (Fig. 6 1) and connects drivi~g ioop 49 (Fig. 3) and control input 55 of elec-tric ~ignal ~ompen~ator 51 to generator 7 via output 66 and input 59 of switch 57.
At the moment of time t4 (Figs 6 f,i), time delay eircuit 102 and logi¢ AND gate 105 are enabled and a logie "1" signal from the output of lo~ic AND gate 105 i9 passed to ~ontrol input 93 of key 85, triggering ~5 this latter and thus eausing electric signal eompens-ator 51 eonnection to ~elective amplifier 68 via input 63 and output 70 of switeh 57. Thu~, the third recept_ ~ . .
-- . . .:
.. . . . .

., ion channel? ¢omposed of electric signal ~ompensator 51, ~ele¢tive amplifier 68, data processor 74 snd re-¢order 76, is established~
At the moment of time t5 (Fig. 6a), switc~ 57 disconnects driving loop 49 from generator 7 and se-lective ~mplifier 68 from electric signal compen3ator -51, at the 9ame time ¢onnecting (Fig. 6m) driving loop 50 and ¢ontrol input 56 of electric signal compensator 52 to generator 7~
At the moment of time t6 (~igs 6 j,p), a logic "1" signal from the output of logi¢ AND gate 106 ar-... ..
rives at control input g2 (Fig. 3) of key 84 and .
enable~ it, cau~ing electric 8ignal compensator 52 to be connected to selective amplifier 69 vla input 64 .. .. . ..
and output 71 of swit¢h 57, thi~ establishing the fourth re¢eption channel of ele¢tri¢ signal ¢ompensat-or 52, selective amplifier 69, data processor 75, and recorder 77.
~hereafter, this sequence ofswitching operations is repeated in the order de~cribed herein above.
- ~he time interval ~2 (Figs ~ e,f,g) by which the pulse sequence from generator 95 is delayed in time delay ~ir¢uits 101, tO2, 103 is a fun¢tion of the dur-ation of trsnsient~ and should exceed the time of ori-ginal electromagnetic field from drivin~ loop 1, 49, 50 decay after its dis¢onnection from generator 7.
The flrst, se¢ond, third and fourth reception . , . . . . , .: .

. . .
,, . , , , , ' , - , , : ,: . , 201~

channels are adjusted to generate a nearly zero output signal (on recorders 22, 23, 76, 77) in the absence of metalliferou~ objects in the coverage area.
In case of a metalliferou3 object 48 (Fig. 4) in 5 the coverage area, the original electromagnetic field .
of one of the driving loops 1, 49, 50, the lines of force 46 whereof enclose metalliferou~ ob~ect 48, lnduces ¢urrents in it, in turn generating a second . .
electromagnetic field, the lines of force whereof ~0 pierce receiving loops 2, 3, 4, 5 and induce electro-motive forces in them proportional to the distance bet-ween each receiving loop 2, 3, 4, 5 and metalliferous ob~ect 48.
The output 9~ B l3 of electric signal compensat- :
ors 16 (Fig. 3) or 17, or 51, or 52 are passed by switch 57 as described herein above to the inputs of respectire selective ampllfler9 18, 19 or 68 or 69.
Functioning of the detector thereafter is as described herein above.
The productivity of search operations with the detector of this invention i8 by far superior to that with known like devices due to an e2panded coverage area and ~canning the search area during a single pass.
~urthermore~ the detector of this in~ention provides a higher reliability of metalliferous ob~ects detection, irrespective of their orientation relative to the 3ear¢h direction.

" ~' ' '' ' , ' ' .
:

.

Claims (5)

1. A detector of metalliferous objects comprising:
- a first driving loop generating an original electromagnetic field;
- a first, second, third and fourth receiving loops receiving the secondary electromagnetic field of a metalliferous object and rigidly fitted to said driv-ing loop, with the first and second, third and fourth receiving loops mounted in pairs coaxially and parall-el to one another, symmetrically and orthogonal at op-posite sides of said driving loop located in the plane of the common axes of the first and second, third and fourth receiving loops;
- an alternating voltage generator having an out-put electrically coupled to the first driving loop;
- a first signal balancer to balance the signals from the first and second receiving loops, having inputs connected to the first and second receiving loops, and an output;
- a second signal balancer to balance signals from the third and fourth receiving loops, having inputs connected to the third and fourth receiving loops, and an output;
- a first differential amplifier, having an input connected to said output of the first signal balancer, and an output;
- a second differential amplifier, having an input connected to said output of the second signal balancer and an output;
- a first electric signal compensator cancelling the effect of the original electromagnetic field of the first driving loop on the first and second receiv-ing loops, having a data input connected to said out-put of the first differential amplifier, a control input electrically coupled to said alternating voltage generator, and an output;
- a second electric signal compensator cancelling the effect of the original electromagnetic field of the first driving loop on the third and fourth receiv-ing loops, having a data input connected to said output of the second differential amplifier, a control input electrically coupled to said alternating voltage gene-rator, and an output;
- a first selective amplifier, having an input electrically coupled to said output of the first elec-tric signal compensator, and an output;
- a second selective amplifier, having an input electrically coupled to said output of the second elec-tric signal compensator, and an output;
- a first and second data processors, having inputs connected to said outputs of the first and se-cond selective amplifiers, and outputs;
- a first and second recorders connected to said outputs of the first and second data processors;

- a logic OR gate, having a first and second inputs connected to said outputs of the first and se-cond data processors, and an output;
- a signalling unit connected to said output of said logic OR gate.

2. A detector as claimed in Claim 1, comprising:
- a second and third driving loops mounted at an angle to the first driving loop and generating origin-al electromagnetic fields, with the second driving loop rigidly fitted to the first and second receiving loops and located symmetrically and orthogonal to them in the plane of their common axis, and with the third driving loop rigidly fitted to the third and fourth receiving loops and located symmetrically and orthogonal to them in the plane of their common axis;
- a third electric signal compensator to cancel the effect of the original electromagnetic field of the second driving loop on the first and second receiv-ing loops, having a data input connected to said out-put of the first differential amplifier, a control input, and an output;
- a fourth electric signal compensator to cancel the effect of the original electromagnetic field of the third driving loop on the third and fourth receiv-ing loops, having a data input connected to said out-put of the second differential amplifier, a control input, and an output ;

- a third selective amplifier, having an input connected to said output of the third electric signal compensator, and an output;
- a fourth selective amplifier, having an input electrically coupled to said output of the fourth elec-tric signal compensator, and an output;
- a switch, having a first, second, third, fourth, fifth, sixth and seventh inputs, and a first, second, third, fourth, fifth, sixth and seventh outputs, with the first, second and third inputs connected to said output of the alternating voltage generator, with the fourth and sixth inputs connected to said outputs of the first and third electric signal compensators, with the fifth and seventh inputs connected to said outputs of the second and fourth electric signal compensators, with the first output connected to the first driving loop and to said control inputs of the first and se-cond electric signal compensators, with the second and third outputs connected to the third driving loop and to said control inputs of the third and fourth elec-tric signal compensators, and with the fourth, fifth, sixth and seventh outputs connected to said inputs of the first, second, third and fourth selective ampli-fiers, this switch providing consecutive connection to said output of the alternating voltage generator of, first, the first driving loop and said control inputs of the first and second electric signal compensators and said outputs of these compensators to said inputs of the first and second selective amplifiers, next, the second driving loop and said control input of the third electric signal compensator and said output of this compensator to said input of the third selective amplifier, and then, the third driving loop and said control input of the fourth electric signal compensat-or to said input of the fourth selective amplifier;
- a third and fourth data processors, having inputs connected to said outputs of the third and fourth selective amplifiers, and outputs;
- a third and fourth recorders connected to said outputs of the third and fourth data processors, with said logic OR gate having a third and fourth inputs connected to said outputs of the third and fourth data processor.

3. A detector as claimed in Claim 2, wherein the angle between the first and second, first and third driving loops is within the range from 60° to 120°.

4. A detector as claimed in Claim 2, wherein said switch comprises:
- a first, second, third, fourth, fifth, sixth and seventh keys having an input, a control input, and an output, with said inputs and outputs of the first second, third, fourth, fifth, sixth and seventh keys constituting the first, second, third, fourth, fifth, sixth and seventh inputs and outputs of said switch;

- a key controller to control switching of the first, second, third, fourth, fifth, sixth and seventh keys and having a group of outputs connected to res-pective said control inputs of the first, second, third, fourth, fifth, sixth and seventh keys, and pro-viding, first, enabling of the first, fourth and fifth keys, next, enabling of the second and sixth keys and disabling of said first, fourth and seventh keys, and then, enabling of the third and seventh keys and dis-abling of the second and sixth keys.

5. A detector as claimed in Claim 4, wherein said key controller to control the switching of the first, second, third, fourth, fifth, sixth and seventh keys comprises:
- a rectangular pulse generator having an output;
- a ternary counter having an input connected to said output of said rectangular pulse generator, and an output;
- a decoder having an input connected to said out-put of said ternary counter and a first, second and third outputs constituting the said control inputs of the first, second and third keys;
- a first, second and third time delay circuits, having inputs connected to the first, second and third outputs of said decoder, and outputs;
- a first, second and third logic AND gates hav-ing each a first and second inputs connected to the first, second and third outputs of said decoder and to said outputs of the first, second and third time delay circuits, and an output, with said output of the first logic AND gate constituting the control inputs of the fourth and fifth keys and with said outputs of the second and third logic AND gates con-stituting the control inputs of the sixth and seventh keys.