Note: Descriptions are shown in the official language in which they were submitted.
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 -
~: . .. . . ., . .~ .
.. ... .
``` 201~
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
.
-- 3 --
.. . . .
. - , . .. . ~ ; . .
.. . . . . .
.
-`` 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
- 4 -
~: :
:; .: , ~ . ~ ................... -
. .
.
`` 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.
: - 5 -
- . .. ~ . . . . .. . . .
, , , ,.:;
. . ,, ~
- , . . . :
:, . , , ;, , .: . , , :
,- ., : - . ,
,. , ~ : ,
.~ 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
- 6 -
'` 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
.. .. .
. .. ~ ~ , , ~ .
", . ~ .
~ 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
.
~ - 8 -
.: ~ . . . . . ; ........ .:
. : - ': , ': . ~ ' ` ' ` ` '
2011141
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 _
. ~ . . .. . . . . . ..
:. :.. . . .
.. . . ~ , . ;
.~ ' '~ . ' .. .
2 0 ~
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-
-- 11 --
~, . ,~, .
. . ,.: . .
`~ 201114~
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;
- 12 -
- ~ ., : . . .
.
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 -
:`
~ .
- r. ~, . , . . ' '` '', ` ` ', `, ' ,. ' - '
. . . ` .
201~
. ~
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
- 14 -
. : . ~ , . . .
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 -
'
~, . . ..
: " ~ ; ,.
.
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, - . : . ,
; , . . , , ' ' . ' ' . ' , ~
`'~" ''' ;.','.''.;.'., ~' ', `',` '"' ~'' .',; ,. . ..
2 0 ~
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
-- 17 --
: ~ , . . .
, . . . .
.. .
~ 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~
- - 18 -
~ - , . .
::: . ., . . . . , ,: ..... : , . . .
~ , . . . . .
. .:: . . . , ~ ,
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 _
. . .~ ., . .; . .
- . . i"~
.; . . . . . .
. , .. ,, , - ,, :
.. .. .. ...... . . .
. . . .
~01~
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 - ;
.. :: . . .. , . ~ ! , . ... , . . . .
; , ' ., . ,' ' , . ' ! , , ,. ` .:: ' . ', . . '. : ,
~' ' ' ' ' ' ~ ,' . ' . ' . '.; ' ''.-.. '.:' " ' , ' ' .
' .'' : ' .. '' .,. :': , ,, ', , :,'. . . .
. ' ,' ,` , ' ',' . ; .: . , .
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
- 21 -
- , . .. ., . ., . . , - .... . . . .
.
, ~. . . .
i . . .. . .
2011141
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
.
- 22 -
., ~ . ..
.
; .
201~
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-
- 23 -
., . ~ .
: ~ .. . .
;..... : , . : -
. . . .. . ~ ... . . .
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
- 24 - -
, ~ "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]
- 25 -
; . . . ( .. ~ , : , .. . . . -
.:: , . ,. ,,.. . . : .
. . '. . . ` ` .. :: :
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_
- 26 -
~ . .
-- . . .:
.. . . . .
.,
2011141
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.
- 28 -
" ~' ' '' ' , ' ' .
:
.
