CA2011140A1 - Metalliferous objects detector - Google Patents

Abstract

METALLIFEROUS OBJECTS DETECTOR
ABSTRACT
The detector of the invention comprises two driving loops mounted at an angle to one another and rigidly tied to receiving loops connected to a balancer, differential amplifier and to the data inputs of electric signal compensators. The detector is equipped with a switch, providing alternate con-nection of a generator to one driving loop and to the control input of one compensator and the output thereof to the input of an amplifier, and then to the other driving loop and to the control input of the other compensator and its output to the input of the other amplifier. The amplifiers are connected to data processors, recorders, an OR gate, and a signalling unit.

Description

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Field of the Invention he invention r~lates to the area of de-tecti~æ
metalliferous o`ojects witn the aid of elactromagne-~ic fields, and more specifically to detectors of metalliferous objects.
'~ ~he invention can be widely used in di~erse branches of industry and national economy, such, -:
for instance, as civil engineering, geedesy, agriculture, maintena~ce of engineering structures, 10 archeolo~y, ~eolo~y, etc. to detect a locality or an installation both mapped and unmapped metalli-. ferous utility systems and objects, such as pipeli-: nes, electric cables, geodetic bench marks, rein-forced aoncrete plates, buried well covers, and 15 other metalliferous obJects, including those with ~: non-ferrous metal 9.
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~he invention can also be used in wood working, food and othèr industries a~d in agricul~ure to track ; buried electric distribution networks in buildings .:, 20 and structures, and also metal inclusions in raw ma-; terials and fodder.
- Baskground of the Invention Currently, the problem of sear¢hing for unmapped -2~

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metalli~erous objects, includin3 oojects vJith non-ferrous metals, has become most urgent. One approach to solvin3 this problem is the use of compact i~-ductive devices combini~ the functions of radiati~g an original electromagnetic ~ield and reception of ~ secondary electromagneti¢ field induced by the metalliferous object positioned within the ran~e of the original electroma~netic field.
~nown in the art are detectors of buri~d metalli-10 ferous objects (high-frequency F~ 48~ finder from Seba Dyn~tronic, ~RG, and pipeline and wire finder ~W=5 from Grigsby Co., USA), of similar design and -~
each comprisinæ: a ~enerator loaded onto a drivin~
loop, a receiving loop orthogonal to the ~riving loop 15 and loaded by conn~cted in series selective ampli data prooessor and acoustic si~nal~ng device. ~he dete¢tor i9 also equipped with a geometric ~eana to cancel the signal inducad by the original electro-magnetic field of the driving loop in the receiving ` 20 loop.
These detectors ~unction by radiatin~ an original electromagnetic field from the driving loop into ~, the area under study and picking up a secondary elect-romagnetic field induced by the metalli~erous object.

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~ hese detectors are highly sensitive to external electromagnetic fields and to interference from utility systems located in the vicinity of the search site~ because they also radiate a seoondary electromagnetic field under the e~fect of the original electromagnetic field of the drivin~ loop.
~- ~urthermore, the reliability o~ detecti~ utility systems positioned at an~les less than 2~ relative to the direction of receiving loop movement is rather : 10 low, due to the low level oY signal induced by the driving loop in the utility system.
Also widely known in the art are metalliferous obj 8 cts dotectors (V.F.Bakhmutsky , G.I.Zuenko ~i "Induktsyonnye kabeleiskateli" (Induction Wire-Finders), 197~, ~09COW, Svyaz Publishers, pp. 75-78, Fig~. 31-32. In ~ussian), each comprisin~ a driving loop and two rigidly tied to it receivin~ loops, ortho~o-nally positioned and dif~erentially connected, located symmetric~lly to both sides of the driving loop. In ;~ 20 one case the driving loop is positioned vertically and the reoeivin~ loops are horizontal, in another ~-~
ca~e loop orientations arereversed~ ~he electric signal recording circuitry in bothcases are identioal ~ .
and similar to that described herei~ above.
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, It should be ~oted, that the direction o~ de-tector movement coi~cides with that of the rod carrying the receivi~g loops.
; Such detectors are prone to inter~ere~ce from external electro~agnetic fields and metalli~erous objects in the vicinity of the search site. Thi9 is due to the considerable spacing between the receiving loops, nec~issary to ensure a~ adequate sensitivity - and adequate de3ree of geometric canoellii~g. However, ~ at a large spaci~g between receiving loops a~d ~t ;~ utility sy~tems positio~ed at an angle less than 20 relative to the directio~ o~ detector movement, tha -l detection reliability i5 poor because of the low intensity o~ the seco~dary electromagnetic field from the utility system at vertical receivin~ loop~ or low signal i~duced i~ the utility systom at horizo~tal receiving loops.
It should be noted, thst due to the poor inter-ferenco immunity o~ the herein above cited detectors, ~;`.`! 20 they cannot b~ used when mounted on tran~portation !., mean~, which would itself be a souroe o~ interference, so that searches have to be per~ormed ma~ually, this impairiLg productivity. ~
The metalli~erous 03 jects detector (SU, A, ;
1190~0) ~eaturss a higher productivity and higher -5_ : " ~ ~ ~

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immunity ~ external electromagnetic fields and compri-; ses a driving loop rigidly tied to two receivinæ loops positioned coaxially and in parallel to one another and symmetric~lly and orthogonally relative to the driving loop positioned in the plane o~ the common axis !
of the reaeiving loops, an AC voltage ge~erator elect-rioally connected to the driving loop, a~d conne¢ted in series balancer to provide b~lancinæ of the si~nals ~rom the receiving loops and with inputs con-1~) nected to the receiving loops, and dif~erential ampli-fier with the output thereof connected to the dats input o~ an electric signal coi~pensator intended to cancel the effect o~ the original eleotrom~gnetic field of the driviDg loop on the receiving loops and having a control input connected to the AC volta~e genera~
tor and with the output thereof driving the input -~
.~ of a selectivo amplifier, the output whereof is con- :
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nected to the input of a data processor with the output thereof connected to a recorder and electri-cally coupled to a signa~ unit.
The mutual arrangement oY the driving ~nd recei-ving loops herein above described provided a substan-tial improvement in the detector's inter~erence be-cause external electromagnetic fields (from power 25 distribution lines, electrified railways, communica- ;

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''' tions lines, etc induce practically identioal signal levels in both receiving loops, and these signals are mutually cancel~d out due to their opposite con-nection.
However, at metalli~erous object (utility system) positioned at an angle less than 20 relative to the search direction, which is normal to the rod car-rying the receiving loops, the detectio~ reliability `. i9 poor due to the low intensity of the electromag-.~
~ 10 netic field induced by the driving loop in the metalli-!'-, ferous object.
' To improve the detection probability when sear-`!1 ching for utility systems one and the same ground has to be covered twice, at different orientation of 1~ the induction system relative to the direction of movement. However, even this does not ensure adequate detection probability because it is difficult to i~l maintain the same search direction when movlng in ~-i the opposite direction and this is true o~ both ma- ~-23 nual a~d mechanized searching.
Summary of the Invention It i9 an objective of this invention to provide a metalli~erous objects detector with a high reliabi~
lity o~ metalliferous objects detection.

~i 25 Another objective of the invention is to provide a hi~her search productivity.

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2 0 ~ a This is achieved by that the metalli~erous obaects deteotor, comprisin~ a driving loop rigidly tied to two recsiving loops, mounted coaxially and in parallel to one a~other and symmetrically and orthogonal relative to the driving loop positioned in the plane o~ the common axis of the receiving loops, and AC voltage generator electrically connec-ted to the drivi~g loop, and connected in serie~
signal balancer with the inputs thereof connected to ~: .
1~ the receiving loops and dif~erential amplifi~r with the output thereof connected to the data input of an electric signal compensator to cancel the effect ` o~ the original electromagnetic field on the receiving ' loops with the control input thereo~ electrically .~' 15 connected to the AC voltage ~enerator and with the ~ :
output thereof connected to the input of a selective ~:
~ amplifier, the output ~hereof i9 connected to the i! input o~ a data processor driving a si~naL~ unit .1 and a recorder, accordi4g to the invention,further 2~comprises a supplementary driving loop identical to the main driving loop, rigidly tied to the receivi~g ~
loops and positioned relative to them symmetrically ~:.
and ortho~onally in a plane passing through the~r common axis at an angle to the main dr ving loop, an electric 5ignal compensator to cancel the ~ignal~
induc~d i~ the receiving loops by original el~ctro-.. " .
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magnetic field o~ the supplementary driving loop with the data input thereof connected to the output of the di~ferential amplifier, a supplementary selec- :
tive amplifier, a switch with the inputs thereo~
. 5 connected to the AC voltage generator and the out-: puts of the electric signal~ compensators and with the outputs thereo~ connected to the main and supple-mentary driving loops, to the control iuputs of the electric sigrlal compensators, and to the inputs 10 of the main ani~ supplementary selective ampli~iers and providing alternate connection of the AC voltage i generator, on the one hand to the main drivi~g loop and to the control input of the electric signal compensator providin~ cancel~ng of signals induced ' 15 in the receiving loops by the oriOinal electromagnetic ~;
l fields of the main and supplementary driving loops and connecting the electric signRl compensator output to the input o~ the main selective amplifier, and, on the other hand, to the supplementary driving loop 2~ and to the input of the electric signal ampli~ier and connecting the o~tput o~ this latter to the input of the supplementarJ- selective ampli~ier, a supplemen-tary data processor with the input thereof connected to the output of the supplementary selective ampli~ier, 25 a supple.mentary recorder connected to the output of t~e ~upplementary data processor, a~d a logic 3R gate .~

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with the inpllts thereof connected to the outputs o~ the main and &~pplementary data processors and with the output thereof connected to the signalling unit.
It i9 expedient that the an~le betwsen the main and supplementary driving loops be i~ the range :~
from 6~ to 12~.
It is highly suitable that the switch comprise : three normally closed and one normally open keys : 10 and a switch controller with the outputs thereof connected to the keg co~trol inputs, wherein the inputs of the normally open key and the first normally . closed key constitute the switch inputs connected .i to the AC voltage generator, the output of the first normally closed key constitutes the switch output 1i connected to the main driving loop, the output o~ the ~:-~, norm~lly open key constitutes the switch output con~
nected to the supplementary drivinæ loop, the inputs - o~ the second and third normally closed keys conati-., .
` 2~ tute the switch inputs connected to the inputs of ;; the electric signal compensators providin~ cancelling -~
'f'~`, 0~ the si~nal~ induced in the receiving loops by the original electroma~netic fields of the mai~ a~d o~ the supplementary driving loops, respectively, .~1 `.~ 25 and the outputs of the second and third normally ., r;

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2011~3 closed keys constitute the switch outputs connec-ted to the inp~ts o~ the main and supplementary seleotive amplifiers, respectively.
It is use~ul that the switch controller comprise a rectangular pulse ~enerator, the output si~nals whereo~ are applied to the control inputs of the first normally closed key and normally open key, a tiLIe delay circuit with the input thereo~
connected to the output o~ the rectangular -` 10 pulse ~enerator, two inverters with the input o~ the :~
i ~irst thereof connected to the output of the rec-i tan~ul~r pulse ~enerator and with the input of the :~:
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second thereof connected to the output o~ the time delay circuit, and two logio AND gates with the ~;
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J, 15 inputs of the first thereof connected to the rectan-`1 gular pulse generator and to the output of the time delay circuit and with the inputs of the second thereof connected to the inverter outputs, wherein the outputs of the lo~ic AND gates constitute the outputs of the switch controller connected to the .` control inputs of the second and third normally closed keys.
~l This desi~n configuration o~ the metalliferous objects detector provides a higher reliability o~
- 25 metalliferous object detection, irrespective o~ the -:

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, object orientation relative to the direction of search.
Furthermore, search productivity i9 improved ~
at least two~old due to the search site (buildin~) -being scanned durin~ a single pass.
Brief Description of Accompanying Drawin~s These and other objectives o~ the invention will become apparent fro~ the ~ollowin~ desoription o~ the invention with rePerence to specific e~bodi-ments thereof and to the accompanying drawings, wherein:
Fig. 1 shows the functional dia~ram of the i metalli~erous objects detector, according to the invention;
Fig. 2 shows the relative layout of the driving ; and re¢eiving loops (perspective view), with the original and secondary electromagnetic fields shown schematically and with a partial section along the drivin~ ~nd reoeiving loops, aocording to the in-vention;
~ ~ig. 3 shows the general view of a portable ; embodiment of the detector shown in ~ig. 1;
Fig. 4 (a,b,c,d,e,f,g,h) show~the timi~g diagrams illustrati~g ~unotioning o~ the switch.
~he metalliferous objects detector comprises two , '.

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., drivi~g loops 1,2 (Fig. 1) and two reoeiving loopis 314 con~tituting an integrated induction system 5, AC
voltage generator 6 and signal balancer 7 providing baL~ncing o~ sign~ls from receiving loops 3,4 with inputs 8,9 thereof connected to recoiving loops ~,4.
Signal balancer 7 equalizes the aignals from recei~
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ving l~ops 3,4 induced in induction system 5 by ` external interfe~ng electromagnetic fields and due to non-identity of receiving loops 3,4 electro-10 magnetic parameters.
0utputs 1~, 11 of balancer 7 drive di~ferential amplifier 12, the output ~hereo~ is connected to the dat~ inputs 13, 14 of electric signal compensators 15, 16 providing canceUingo~ electric signals induced 15 in receiving loops 3,4 by the original fields of drivi~g loops 1,2,respectively.
~o provide connection in turn to ~C voltage generator o~ driving loops 1,2 and control i~puts 17, 18 of èleatric signal compensator~ 15, 16 the detector i~ 20 of the invention is equipped with swi-tch 19 with in~
puts 2V, 21 thereof connected to AC voltage generator 6 ~ i ~ and with inputs 23, 24 thereof connected to the out-m puts o~ compensators 15, 16. 0utputs 24, 25 of switch 19 accommDdats driving loops 1,2 and control inputs 17, 18 o~ compensators 15,16, r~spectively.
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., , ~he metalliferous objects detector of this - ~--, invention further comprises two selective ampli-fiera 26, 27 driven from outputs 28, 29 of switch 19 - providing connection of compensators 15,16 outputs c 5 to the inputs of selective amplifiers 26, 27 accor-~ ding to the connection of AC voltage generator 6 !~ to driving loops 1 or 2 and to control inputs 17 ~-'~ or 18 of compensators 15,16.
In this embodiment switch 19 comprises three 10 normally closed keys 3~, 31,32, one normally open key 33, and switch controller 34 connected to control ~ inputs 35, 36, 37 of keys 30~ 31, 32, respectively.
'`! Inputs and outputs of keys 30, 33 constitute inputs 20, :~
21 and outputs 24, 25 of su~itch 19, respectively, ~:
15 and the inputs and outputs of keys 31, 32 serve as ~', inputs 22, 23 and outputs 28, 29, respectively, of switch 19.
The metalliferous objects detector o~ the inven-`', tion yet further comprises two data processors 39,40 20 oonnect9d to the outputs of selective amplifiers 26,27, and two reccrders 41, 42 connected to the outputs of ~, data processors 39,40 also connected to the inputs - 43,44 of logic OR gate 45, th~ output whereof is ~.
conneoted to signal~g unit 46.
`~ 25 Balancer 7 may be designed with any known in the art circuit arran~ement and in this embodiment "`

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comprises phase shifter 47 with the input thereof ~ constituting input 9 of balancer 7, potentiometer 48 :~ connected to input 8 and output 11 of balancer 7, :
and potentiometer 49 connected to the output o~ phase shi~ter 47 and to output 1~ of balancer 7.
: Compensators 15,16 are identical in design and each comprises phase shi~ter 50 with the input thereof constitu-ting control inputs 17 or 18 o~
:~ oompensators 15 or 16, respectively, potentiomebcr 51 10 conne¢ted to the output o~ phase shifter 5~, ~nd ;dif~erential ampli~ier 52 with one input thereof connected to potentiometer 51 and with the other input thereo~ constituting data input 13 or 14 of compensator 15 or 16, respectively,and output o~ the 15 dif~erential amplifier 52 constitutes output o~ the compensator 15 or 16.
Seleotive ~mpli~iers 26, 27 provide amplifioation `` at the operatiLg frequency o~ AC voltage generator 6.
Data processors 39, 40 are designed with any known ~ 20 in the art circuit configuration and in this embodi-- ment comprise each connected in series lo~arithmic ~.
amplifier 53 providing an expanded range o~ detectable object sizes without sensitivity adjustments durinæ
searches, deteotor 54 and negative limiter 55 provi-. 25 di~ detuning ~rom constant effects (e~uipment noise, vibrations, eto.).
Analogue Dr di~ital meters (vDltmeters) may serve as r~cDdars 41, 42.

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The si~nalling unit 4~ may b~ ~ade Dtl ~h~ bas~
Df sound sDurc~ and indic-tDr lamp accDrdin~ tD any known in th~ art circuit c~nfiguratiDn and p~r~rms sound and light signalizatiDn indicatin~ d~tectio~ Df metalli~erous objects.
In this embodiment switch controller 34 compri-ses reotangular pulse generatox 56 connected to control inputs 35, 33 of keys 30, ~3, time delay circuit 57 with the input thereo~ connected to rectan-;~ 10 gular pulse generator 56, and twQ inverters 58, 59 with the input of the ~irst thereof connected to rectangular pulse ~enerator 56 and with the input o~
the second thereof connected to the output o~ time delay circuit 57. Controller 34 further comprise~ two logic AND ~ates 60, 61 with the inputs of the firstthereo~ connected to reotangular pul~e generator 56 and to the output of time delay circuit 57 and with the inputs o~ the second thereo~ connected to the i outputs o~ inverters 58, 59. The outputs o~ logic 1 20 AND gates 6~, 61 are connected to the control inputs ; oi keys 31, 32.
In this embodiment rectangular pulse generator 56 ~! operates at a duty factor of 0.5 (i.e. is a s~uare-~i wave generator) providinO driving loops 1,2 being ., , connected to AC voltage generator 6 for equal time interval~. The repetition rate o~ rectangular pulse generator 56 operation is sct to 0.1~, where f is the operating frequency of AC voltage generator 6. Under ~ these conditions the metalli~erous objects detector i3 `j -16-,, .
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capable of detecting signals induced by the secondary electromagnetic field gener~ted by a metalliferous object.
Receiving loops 3,4 of integrated induction system 5 are identical in design and are positioned in coaxial and parallel arran~ement relative to one another, with drivin~ loops 1,2 positioned ortho onal-ly and symmetrically relative to receiving loops 3,4 in planes passinO through common axis 62 (~ig. 2) of receiving loops 3,4 and at an angle ~ relative to i one another within the range from 6~ to 12~.
Driving loops 1,2 and receiving loops 3,4 are mechanically interlinked by rods 63,~4 to constituto ;~
a riOid structure.
A high reliability of metalliferous object detec-~'~ tion is ensured at any anæle.~ within the range .^~ . .-cited (6~ to 12~) because a~gle ~ between the metalliferous object (utility system) and tie rod Z3 connectinO one o~ the drivin~ loops 1,2 (in this embodiment - loop 2) to tie rod 64 is always less than 6~, thus ens~urinO a suf~iciently high level ~''`! of the signal induced in the metalli~erous object.
~ he design arran~ement de~cri~ed herein above provides mutual positioning o~ driving loops 1,2 and receivin~ loops 3,4, wherein electromagnetic ~-; coupling between them is minimized. ~he spacing i~
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L between drivi~a and receiving loops is selected :~ from the viewpoint of ind~ction system 5 stability . as determined by a constant degree of geometric ~:' cancel~g of the oriOinal electromaænetic field (which depends on the spacing between driving and receiving loops) and b~ a constant mutual posi-` tioning of driving and receivin~ loops. As i9 well : known, all other conditions beinæ equal, the degree of geometric cancell~ is increased at higher -L
. 10 values whereas the stability increases at smaller ;~ spacings ~. Therefore, depending on the specific application area (portable or mounted on a vehicle) . ~
and on structural considerations (materials used, . production en~ineerin~) spacing L is selected in each ;~ 15 case individually so as to provide the specified stability and degree of æeometric cancel~g.
i~ Driving and receiving loops 1,2,3,4 are of conductors 65, the turns whereof are schematically `~. shown in Fi~g. 2, wherein solid lines schematically ~, 20 depi¢t lines of force 66 of the original electro-magnetic field induced by driving loops 1,2 in the search site and dashed lines depict lines of force 67 :
of the secondary electromaænetic field induced by ;~ buried metalliferous object 68. ~-The search direction (direction of movement of induction system 5) is shown by arrow A~
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Angl~ ~ ~ selected accordin~ to the speci~ic appli-~ication of the detector. Thus, in case o~ mounting on a vehicle, to provide vehicle manoeuvrability, driving 1DOPS 1,2 are to be positioned at angles approachin~ or equal to 12~. In case of portable design arran~ements (Fig. 3) driving lo~ps 1,2 are to be positioned at an~les approaching or equal to 6~ and the detector in use i9 held so as to position driving loops 1,2 to both sides of the ope-10 rator, with all the electronics, incl~din~ AC voltagegenerator 6 (Fig. 1) housed in case 6~ direatly in front of the operator to provide convenience of rea-ding the readin~s of recorders 41, 42. Receiving ~, ~ loops 3,4 are housed in body 7~ (Fig. 3).
'! 15 Better understandinO of the spirit o~ the detector of this invention may be obtained b~ studyi~g the ti-ming dia~rams show~ i~ Fig. 4 and illustrating the functioni~ of switoh 19. Fig. 4a shows the time dia~ram of signals U1 from rectan~ular pulse ~ene-rator 56, Fig. 4b shows output signals U~ from time delay circuit 57, Fig. 4c shows control signals U3 arriving at key 31, Fi~. 4d shows control signals U4 , arriving at key 32, Figs 4e,4f,4g,4h show the states ~i of keys 3~, 33, 31, 32, wh~rein position 1 corres-ponds to an open state and position 0 corresponds to a closed state.
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The metalliferous objects de-tector Gf the in-vention functions as ~ollows.
Prior to actual use, to provide hi~h interference immunity and high r~liability of metalliferous objects detection, the output siOnals from receivin~ loops ~,4 (Fig. 1) are balanced. ~o this end AC voltaOe gene-rator 6 is disconnected from driving loops 1,2 and potentiometers 51 in compensators 15, 16 are zeroed, this submittin~ induction system 5 to the , !:; 10 effects of external electromaOnetic fields. The source of such extraneous fields may be imitated by a loop similar to the driving loops, connected to AC voltage ~enerator ~, and position~d as sym-metrically as possible at a distance equal to thrice the maximum detection depth, as determined by the power of generator 6 and the electroma~netio para-~`~ meters o~ induction system 5. Using potentiometers 4~,49 . .,~
~ and the phase shifter 47 the readin~s of recorders ~ .
41,42 are then set as near to zero as possible.
2~ Balanci~g is to be performed only if the detec-tor operating conditions are changed. Thus, for ~. . .
instance, if the detector is trans~ered to another vehicle or if used first as a portable device and subsequently mounted onto a vehicle, or vice versa.
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., Eaah time, prior to use, electric signal compen-isators 15,16 are adjusted to maxi~al cancel~g of signals induced in receivi~ loops ~,4 by the original electromagnetic field of driving loops 1,2 and in-col;lpletely cance~d out by geometric compensation and by the opposite connection of receiving loops 3,4.
Adjustments o~ compensators 15,10 are carried out at a site free of metalliferous objects as follows.
Gradually increasi~g the output si~nal of AC
10 voltage Oenerator o, and adjusting the phase and a~plitude with the aid of phase snifter 5~ and po-tentiometer 51, respectively, in compensators 15,1~, the readin~s of recorders 41,42 are set as near to -~i zero as possible. This adiustment is carried out .,, 15 till AC volta~e ~enerator is set to its operating ~i power.
~he thus adjusted metalliferous objectsdetector ,., is ready for use. Rectangular pulse ~enerator 56 pro-~ vides pulses U1 (Fio. 4a) of a ~1 duration passed - 20 to control inputs 35,38 (Fig. 1) of keys 3~,33 respectively, and to ti~e delay circuit 57 providingr `; control si~nals U2 (Fig. 4b) delayed by ~2 ~eys 3~, `! 33 (Fig. 1~ periodically, with an interval of (Figs 4e,4f), connect drivin~r loops 1,2 (Fig. 1) via outputs 24, 25 and inputs 2~, 21 of switch 19 to AC voltaæe generator 6. Drivi~ loops 1,2 i~duce .
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an original electromagnetic ~ield in the site under . study, this field being of a frequency f' and di-rectivity depending on which of the driving loops 1,2 is currently connected to AC voltage generator 6, the connection duration bein~ equal for both loops and set by duration ~1 (Figs 4a,4b).
At a moment of time t1~ switch 19 (Fig. 1 ) connects, ~or instance, drivinO loop 1 to AC voltage generator 6, and at -the moment o~ time t2 (Fi~. 4c) 10 the logic AND gate Z0 (Fig. 1) is enabled; this ate receives the output signals of reotan~ular pulse æenerator 56 and time delay circuit 57 and ., outputs a logic "1" passed to control input 36 o~
~' key 31, openi~g this latter (Fig. 4g) and thus connec-i 15 ting electric si~nal compensator 15 to selective ampli~ier 26 via input 22 and output 28 o~ switch 19. .
, At the same time electric si~nal co~pensator 16 is ~ ~:
~, disoonnected ~rom selective ampli~ier 27, in other , words - the first reception channel is set up, "'! 2v comprising electric signal compensator 15, selective ~:~
- ampli~ier 26, data processor 39, and recorder 41.
~ At the moment o~ time t3 (Fig. 4a) ke~ 30, 31 - . (Fig. 1) are closed (Figs 4e,4g) under command o~ the control signal from switch controller 34 25 (Fig. 1), thus disconnectin~ driving loop 1 from AC
voltage generator 6 and disconnecting selective ampli-~ ...

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fier 26 ~rom electric signal compensator 15. At the sam~ time key 33 i9 opened (~ig. 4~) and connects driving loop 2 to AC voltage ~enerator 6 i viâ output 25 and inp:lt 21 o~ switch 19.
At ths moment o~ time t4 (Fi~. 4d) logic AND
gate 61 is enabled; this gate receives the inverted 1 output signals of rect,angular pulse generator 56 , and tim~ delay circuit 57 and outputs a logic "1"
to control input 37 of key 32 to open this key 1 10 and connect electric si~nal compensator 16 to selec-tive amplifier 27 via input 23 and output 29 o~
switch 19. This establishes the second reception channel, comprising electric signal compensator 16, selective ampli~ier 27, data processor 4~, and re-corder 42.
At the moment of time t5 (~ig. 4a) switch 19 disconnects driving loop 2 ~rom AC voltage generator 6 , and selective ampli~ier 27 ~rom compensator 16, at the same time connecting driving loop 1 to AC
20 volta~ge generator 6. Therea~ter the process of sig- .
nal switching is repeated in the sequence described herein above.
,~ime interval ~2 (Fig. 4b) by which time delay ,`circuit 57 delays the pulse train from rectanOular pulse generator 56 (~ig. 1) is determined by the dura-.
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;' tion of transients and should exceed the duration I of extinction of the original electromagnetic field i generated by drivin6 loop 1 cr 2 after its discon-nection ~rom AC voltage generator 6.
~he first and second reception channels are tuned so, that in the absence of metalli~erous ; objects in their search area the readin~s of recor-ders 41, 42 are approximately zero.
~ The presence o~ a metalli~erous object 68 in -;`l 15 the search area (Fio. 2) causes the ori~inal electro-ma~netic field from drivin~ loop 1 or 2, ma~netic lines of force 66 whereof intersect metalliferous ; ~ .
object 68, to induce currents in this latter and thus generate a secondary electromagne-tic field, the maOnetic lines of force 67 whereo~ pierce recei-ving loops 3,4 o~ in~uction system 5. ~his secondary electromagnetic field induces signals in receiving loops 3,4, the electromo-tive force whereof is propor-tional to the distance between each of the receiving 25 loops and metalliferous object 68 and, since this ;~
distance is dil`ferent, a dif~erence si~nal, propor- ~;
tional to chanOes in the distance (plan view) from receivin~ loops 3,4 to metalliferous object 68 (Fi~. 2), is generated a-t the output of electric -siOnal compensator 15 or 16 (Fio. 1) to be passed ., ~ .

2 0 ~

~ by switoh 19, as described herein above, to the i correspondin~ selective amplifier 26 or 27 and therefrom to the input of corresponding data pro-cessor 39 or 4~. In data processor ~9, 4~ the signal ~, , l 5 i9 amplified by loOarithmic amplifier 53, then : detected ~nd passed to negative li~iter 55 and from , the output of data processor 39 or 40 applied to an input 43 or 44 of logic OR gate 45 and from the output thereof - to siglla l~ng unit ~.
Meters of recorders 41, 42 vary their readings - in accordance to variations in the distance (plan view) from receiving loops 3, 4 to ~aetalliferous object 68 (~iô~ 2) and the signal applied to si~nal~g unit 46 causes it to generate a light and sound signal 15 indicatin~ detection of the metalliferous objeot.
On the whole, the metalliferous objects detector of this invention provides a hi~h reliability of detection and can be used both for ~anual operation, as shown in Fig. 3, and mounted on a vehicle. The 20 productivity of search works with this detector is substantia~superior to that with other known in the art si~ilar devices, due to scannin~ the search area duri~g a sin~le pass.
', , '' , ~ .

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Claims (4)

1. A metalliferous objects detector, comprising:
- a first and a second driving loops, positi-oned at an angle to one another and generating original electromagnetic fields;
- a first and a second receiving loops picking up the secondary electromagnetic field generated by a metalliferous object, with the first and second receiving loops rigidly connected with the first and the second driving loops mounted coaxially and parallel to one another, and symmetrically and ortho-gonally relative to the first and second driving loops positioned in planes passing through the common axis of the first and second receiving loops;
- an AC voltage generator having an output con-nected to the first and second driving loops;
- a balancer providing balancing of the signals from the first and second receiving loops and having inputs connected to the first and second receiving loops, and an output;
- a differential amplifier having an input con-nected to said output of said balancer providing balancing of signals from the first and second receiving loops, and an output;
- a first electric signal compensator providing cancelling of signals induced in the first and second receiving loops by the original electromagne-tic field of the first driving loop, and having a data input connected to said output of said dif-ferential amplifier, a control input, and an output;
- a second electric signal compensator providing cancelling of signals induced in the first and second receiving loops by the original electromagnetic field of the second driving loop, and having a data input connected to said output of said differential amplifier, a control input,and an output;
- a first selective amplifier having an input electrically connected to said output of the first electric signal compensator, and an output;
- a second selective amplifier having an input electrically connected to said output of the second electric signal compensator, and an output;
- a switch having a first, second, third and fourth inputs and a first, second, third, and fourth outputs, with first and second inputs connected to said output of said AC voltage generator, with second and third inputs connected to said outputs of the first and second electric signal compensators, with first and second outputs connected to the first and second driving loops, and with third and fourth outputs connected to said inputs of the first and second selective amplifiers, and providing alternate connection to said output of said AC voltage gene-rator of at first the first driving loop and said control input of the first electric signal compensa-tor and its said output to said input of first selective amplifier, and then of the second driving loop and said control input of second electric signal compensator and its said output to said input of the second selective amplifier;
- a first data processor having an input con-nected to said output of the first selective ampli-fier, and an output;
- a second data processor having an input con-nected to said output of the second selective amplifier, and an output;
- a first recorder connected to said output of the first data processor;
- a second reorder connected to said output of the second data processor;
- a logic OR gate having two inputs connected to said outputs of the first and second data pro-cessors, and an output;
- a signalling unit connected to said output of said logic OR gate.

2. A metalliferous objects detector as claimed in Claim 1, wherein the angle between the first and second driving loops is within the range from 60° to 120°.

3. A metalliferous objects detector as claimed in Claim 1, wherein the said switch comprises:
- a first, second, and third normally closed key, and a fourth normally open key, each having an input, an output and a control input;

- a switch controller, controlling changing of states of the keys, having a group of outputs connec-ted to appropriate said control inputs of first, second and third normally closed keys and of the fourth normally open key and performing alternate opening of first normally closed key, said input and said output whereof constitute the first input and output of said switch, and of the second normally closed key, said input and said output whereof constitute the third input and output of said switch, and closing of the normally open key, said input and said output whereof constitute the second input and output of said switch, and closing of the third normally closed key, said input and said output whe-reof constitute the fourth input and output of said switch during one halfcycle, and than closing of the first and third normally closed keys and opening of the third normally closed and the fourth normally open keys during the other halfcycle.

4. A metalliferous objects degector as claimed in Claim 3, wherein said switch controller to control the states of the first, second and third normally closed keys and of the fourth normally open key comprises:
- a rectangular pulse generator having an out-put, the signals wherefrom are applied to the said control inputs of said first normally closed and fourth normally open keys;
a time delay circuit having an input cDnnacted to said output of said rectangular pulse generator, and an output;
- a first inverter having an input connected to said output of said rectangular pulse generator, and an output;
- a second inverter having an input connected to the said output of said time delay circuit, and an output;
- a first logic AND gate having a first input connected to said output of said rectangular pulse generator, a second input connected to said output of said time delay circuit, and an output constitu-ting the third output of said switch controller;
- a second logic AND gate having a first and second inputs connected to said outputs of said in-verters, and an output constituting the fourth output of the said switch controller.