EP0153339A1

EP0153339A1 - A search device for localizing subterranean resonant fixpoint markers

Info

Publication number: EP0153339A1
Application number: EP19840902916
Authority: EP
Inventors: Willy Palle Pedersen
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-07-27
Filing date: 1984-07-27
Publication date: 1985-09-04
Also published as: GB2156632A; WO1985000666A1; DK137385D0; GB2156632B; AU3217184A; NO851237L; DK137385A; GB8507912D0

Abstract

Un dispositif de recherche pour la localisation de marqueurs de point fixe souterrains du type résonnant est pourvu d'un système émetteur (20, 38) ayant une orientation généralement verticale et d'un système récepteur (22, 44, 46, 48), monté dans le champ proche du système émetteur et à angle droit par rapport à ce dernier. Lors de l'utilisation, le système récepteur est orienté horizontalement, produisant ainsi un signal de lecture nul ou minimum lorsque sa ligne médiane-normale forme une intersection avec l'axe électromagnétique du marqueur, dans le champ proche de celui-ci, ce qui permet d'obtenir une très grande précision de localisation.A search device for locating underground fixed point markers of the resonant type is provided with a transmitter system (20, 38) having a generally vertical orientation and with a receiver system (22, 44, 46, 48), mounted in the near field of the transmitting system and at right angles to the latter. During use, the receiving system is oriented horizontally, thus producing a zero or minimum reading signal when its mid-normal line intersects the electromagnetic axis of the marker, in the field close to it, which provides very high localization accuracy.

Description

A search device for localizing subterranean resonant fixpoint markers.

The present invention relates to a search device for localization of subterranean markers of the resonant type, i.e. markers comprising a resonance circuit tuned to a specific search frequency, e.g. 100 kHz. Such markers, e.g. a disclosed in WO 83/01036, have been developed to such an extent as to be usable as official fixpoint markers, because by virtue of their electro- magnetical axis they can define a narrow spot on the surface of the ground even when they are buried at a depth of e.g. 50-200 cm. The narrowness of the said spot, however, will of course depend of the quality of the search device.

The search device shall comprise a transmitter unit operable to "pump" an electromagnetic wave of the relevant search frequency down into the ground from a tuned signal emitter system and a receiver unit including a correspond¬ ing tuned signal receiver system with a coil for receiving the electromagnetic or almost purely magnetic resonance signal from the buried marker. The resonance circuit of the marker will oscillate when receiving energy from the signal emitter system and it will continue oscillating for some time upon the transmitter signal being abruptly stopped. During that time of self-oscillation the marker will constitute another emitter system radiating the re- sonance frequency, and the receiver unit of the search device will receive this marker signal, which will generally, of course, be of an increasing intensity for a decreasing distance between the marker and the search device. Thus, the search can go on by moving the search device during intermittent operation of the transmitter/receiver unit until the intensity of the received signal is at a maximum as indicated by a suitable indicator.

For a more detailed discussion of the relevant measuring conditions reference can be made to DE-B-1 ,249,416. However, due to the configuration of the electromagnetic or magnetic near field as produced by the marker it has not been practically possible to base a high precision localiza¬ tion of the fixpoint, i.e. the point of intersection between the ground surface and the axis of the marker on a direct or absolute maximum signal reading, because the field in¬ tensity is found to be almost the same in and just outside the axis. Other methods have been proposed, e.g. determina¬ tion of diametrically opposed spots of identical non-maximum signal intensity and a following geometrical determination of the fixpoint, but such a method is both laborious and inaccurate when the desired accuracy should be in the centi¬ meter or even millimeter range.

It is the purpose of the invention to provide a search device, which is operable to more accurately localize the electromagnetical axis of a marker of the said resonant type.

According to the invention the signal receiver system of the search device is mounted in the near field of the emitter system thereof with an orientation generally per¬ pendicular to the axis of the emitter system such that the electromagnetic fields as emitted and received by the re¬ spective two systems are mutually orthogonally polarized, the signal receiver system being of the type comprising a narrow coil mounted on a flux concentrating core member such as a ferrite rod, and said indicator being operable to indicate a relative and absolute minimum of intensity of the received signal.

The search device according to the invention is usable in the near field of a marker, e.g. upon the marker having been roughly localized by means of a conventional search device. The combined emitter/receiver system is movably held or supported with the emitter system oriented in or close to the vertical and with the receiver system oriented horizontally. Principally, due to the orthogonal arrangement of the emitter/receiver system, the receiver system will not be able to receive the emitted signal, but the said inter- - mittent mode of emission is nevertheless preferable. When, during the searching movement of the emitter/receiver system, a minimum intensity signal is observed this will be indica- tive of the receiver system assuming a position in which it is directed orthogonally to a radius from the fixpoint to be localized, as explained in more detail below, and when thereafter the emitter/receiver system is moved along this radius with the receiver system oriented in the di- rection of the radius, then the combined system will be moved through or into a position, in which the receiver system produces a minimum or zero signal, and this position as defined by the middle point of the receiver system will indicate the location of the fixpoint. When thus located in the axis of the marker the receiver system, due to its orientation in a plane perpendicular to this axis, will produce a zero signal irrespective of its direction in the said plane, and the finding of the correct point is easy to control, simply by rotating the horizontal re- ceiver system through 90 about its vertical middel axis, whereby the indicator reading should still be zero.

It has been demonstrated that a remarkably high loca¬ lization accuracy is achievable with the use of the search device of the invention. Particularly in the final phase of the search the zero indication is produced as a distinct dip for a movement of the emitter/receiver system over few millimeters only. It is important that the receiver and the emitter system, both being in the near field, are oriented fieldwise mutually orthogonally, because the re- sonance circuit of the emitter system will then be unable to disturb the free configuration of the marker field components asreceived by the receiver system, what could otherwise give rise to considerable inaccuracies.

It should be mentioned that fixpoint markers are nor- mally mounted in the ground with their axis exactly vertical¬ ly oriented and that the receiver system, therefore, will be perpendicular to the marker axis when held horizontally,- preferably with the aid of a spirit level. On the other hand, the search device will be usable even for checking whether the marker axis is in fact vertical, as explained below.

The search device, of course, may be hand held, but in view of the achievable high accuracy it is preferred, according to the invention, to associate the emitter/re¬ ceiver system with a ground supportable guiding apparatus, which can be placed on the area as roughly localized and then be used for the final, accurate localization of the fixpoint.

A modified search device according to the invention comprises an additional receiver system arranged, like the first receiver system, orthogonally to the axis of the emitter system, but both angularly and midpointwise offset from the first receiver system. When a marker axis coincides with the intersection point between the normals of the two receiver systems the indicators of both systems will produce a zero signal, and the said intersection point, therefore, will be the "fixpoint marker point" of the search device.

In the following the invention is described in more detail with reference to the drawings, in which:- Fig. 1 is a perspective view of a search device accord¬ ing to the invention.

Fig. 2 a side view thereof.

Fig. 3 a vertical section of a ground area and the field of a marker mounted therein, Fig. 4 a top view of the area.

Fig. 5 a perspective view of a modified search device,

Fig. 6 a plan view of a further modified search device.

Fig. 7 a perspective view of a search device as com¬ prising a ground supported guiding apparatus, and Fig. 8 a modified ground supported search device.

The search device shown in Fig. 1 comprises a portable search unit 2 and a portable electrical apparatus unit 4, _- these units being interconnected through a cable 6. The unit 2 comprises a handle rod 8 having at its top end a switch 10 and at its lower end a cylindrical cross element 12 provided with a spirit level 14. Midways on the element 12 is provided a holding bushing 16 for a pointed pin member 18.

The lower end portion of the handle rod 8 houses an emitter system 20 as constituted by a ferrite rod, which is shown in dotted lines and carries the coil of a resonance circuit as tuned to a specific search frequency, e.g. 80 kHz. In a corresponding manner the cross element 12 houses a receiver system 22 likewise constituted by a ferrite rod and an associated resonance circuit. The apparatus unit 4 comprises a generator section for intermittently producing a search signal of said search frequency to the emitter system 20 and a receiver section for receiving signals from the receiver system 22. The in¬ tensity of the received signal is monitored by a meter 24 and/or by a loudspeaker 26, and the sensivity of the receiver is adjustable by a volume control button 28. A switch 30 is provided for enabling an inversion of the connections between the apparatus unit 4 and the respective emitter and receiver systems 20 and 22. ; A further receiver system 32 is arranged in the lower end of the handle 8 just above and in alignment with the emitter system 20. The handle switch 10 is a change over switch, by means of which the two receiver systems 22 and 32 are selectively actuated. Eor localizing the approximate position of a subterra¬ nean marker the switch 10 is set so as to actuate the re¬ ceiver system 32, and the search unit is moved over the ground until a maximum reading is observed on the meter 24. So far the search is carried out based on generally known principles, with uniform orientation of the emitter system 20 and the receiver system 32. The said maximum reading will be indicative of the search device now being located - in the near field of the marker to be localized, and the operator then actuates the switch 10 so as to make the receiver system 22 operative. The emitter system 20 will still "pump" electromagnetic energy down into the ground and thus cause the marker, de¬ signated 34 in Fig. 3, to respond by emitting an electro¬ magnetic or almost purely magnetic field as shown by field lines in Fig. 3. When the operator happens to move the receiver system 22 centrally and horizontally across the vertical axis a of the marker 34 the ferrite rod of the receiver system will experience a fully symmetrical distri¬ bution of the marker field to both sides of the center of the system, the resulting receiver signal hereby being zero. Such a "zero passage" is easily detectable on the meter 24 and/or by a characteristic change of an acoustic signal of the loudspeaker 26, and it has been found that the zero passage may refer to a movement of the receiver system 22 within a few millimeters. Such a zero reading, however, will occur not only when the receiver system 22 is localted right above the marker 34, but also whenever it is located normal to a horizontal radius of the marker axis a., principally independent of its distance from this axis, because in every such case the receiver system will receive equal and oppositely directed field signals from the marker 34, this being illustrated in Fig. 4. Therefore, when a minimum or zero reading is observed by a movement of the search device 2 generally laterally, i.e. in the longidudinal direction of the re- ceiver system 22, it is hereby indicated that the marker axis a will be located normally to the receiver system in the zero reading position thereof. Thereafter the location of the axis a_ is easily findable by turning the receiver system 22 through 90° in the horizontal plane and again displacing it in the longitudinal direction of the system 22 until a new minimum or zero reading is experienced. The midpoint of the receiver 22 will then be located in the marker axis and will thus be indicative of the crossing point P (Fig. 3) between the axis a and the ground surface, this point P being the fixpoint to be localized with high accuracy.

The point P may be localized not only by way of the receiver system 22 being located right above this point P, but also by way of the receiver system giving zero reading in two angularly different positions thereof, which are spaced the same distance from the point P. Thus, if the pin 18 according to Fig. 2 is placed vertically in the point P, Fig. 4, the receiver system 22 will produce a zero reading also when the unit 2 is rotated about the pin 18, e.g. 90° as indicated in Fig. 4. For an easy and exact localization of a point P, therefore, the pin 18 should not necessarily be located just underneath the receiver system 22, when it is only placed in the plane normal to the effective middle point of the receiver system.

The pin 18 could well be a lower pointed end portion of the handle rod 8, whereby the said rotation about the vertical pin axis would be facilitated.

It may happen that it is impossible to obtain a steady zero reading while rotating the receiver system 22 about the vertical pin 18. This will be indicative of the axis of the marker not being vertical, as the field diagram on a horizontal ground surface will in that case be ellipses rather than circles. It would of course be possible to detect the degree of inclination of the axis of the marker by determining the similar degree of inclination of the unit 2 in such an inclined position thereof, in which the receiver system 22 when rotated about the axis of the pin 18 will produce a steady zero reading all the way round. However, already the detection of the marker axis being non- vertical would normally be a sufficient result, viz. for a decision of the marker to be remounted with a correct vertical orientation. During the search the operator may actuate the switch 30 on the apparatus 4, whereby the transmitter unit will use the receiver system 22 for signal emission and the re¬ ceiver unit will use the former transmitter system 20 for receiving the marker signals. The operational conditions are hereby entirely changed, because the system 22 will supply very little energy to the marker 34, while on the other hand the system 20 will receive the marker signal with a high sensitivity so as to be operable to produce a maxi- mum signal when located in the marker axis a. This inverted use of the systems 20 and 22 is of secondary importance and will not be further described; it may be useful, how¬ ever, e.g. if field disturbing objects are located near the marker. An important feature of the invention is the receiver system 22 as constituted preferably by a narrow resonance coil or circuit mounted on a longish ferrite rod of a dia¬ meter of some 5-20 mm. The design of the transmitter system 20 is less important, because it should just "pump" energy down to the marker 34 sufficiently to cause the marker to create its own field of response as then detected by the receiver system. It is a practical possibility, therefore, to design the coil of the transmitter system as a short end wide air coil, whereby the height of the transmitter system may be reduced considerably. Hereby the lower "search head" of the unit 2 may be designed as shown in Fig. 5, in which the search head as designated 36 is a flat, round box containing a wide transmitter coil 38 and a ferrite rod based receiver system 40 mounted generally in the plane of the coil 38. The search head box 36 is provided with an upper spirit level 42 mounted parallelly with the receiver system 40, and it is connected with a handle rod 44. Operationally this unit will widely correspond to the embodiment shown in Figs. 1 and 2. Fig. 6 shows from above an embodiment which comprises two receiver systems 46 and 48 as mounted on a flat search head 50 angularly and midpointwise spaced from each other. The transmitter system comprises a flat air coil 38 as in Fig. 5, and the search head 50 is provided with a spirit level 52 of the cup shaped type. The search head 50 carries a mark 54 at its front edge, this mark being the point of intersection of the mid normals^ n₁ and n~, of the respective two receiver systems 46 and 48.

When the search head 50 is held in a horizontal position as marked by the spirit level 52 each of the receiver systems 46 and 48 will produce, on associated respective signal in¬ tensity meters on the unit 4, a zero reading whenever the respective normals n_. and/or τ intersect the axis a of the marker 34. When the search head 50 has been moved into a position, in which both receiver systems 46 and 48 give rise to zero readings, then the fixpoint P will be localized as situated immediately underneath the mark 54.

Once the fixpoint area has been roughly localized, with the use e.g. of the receiver system 32 of the device 2 of Figs. 1 and 2, it may be preferable to establish a firm guiding connection between the ground and the search head of the searching device, particularly in view of the fact that the search device of the invention will be operable to localize the marker axis within millimeters of its crossing point with the ground surface. A suitable apparatus to this end is shown in Fig. 7. It consists of a rectangular frame 60 having three height adjustable legs 62 and is pro¬ vided with one or two spirit levels (not shown) to facilitate adjustment of the legs for horizontal positioning of the frame on the ground above the roughly localized fixpoint. A traverse 64 is slidingly arranged for parallel displace¬ ment along two opposed frame side members 66, and on the traverse 64 is provided a block 68, which is slidable along the traverse and has an upper socket portion 70 for receiving the lower end of a search head, which could be identical with the search head of the device 2 of Fig. 1, but here it is shown as comprising an emitter member 72 and two parallel

VS OM Π receiver members 74, one at each side of the emitter membec- 72. The search head is connected with the apparatus unit 4 of Fig. 1 through a cable (not shown) .

With the use of the apparatus of Fig. 7 the search head is displaceable all over the frame area in a well controlled and convenient manner for precise localization of the marker axis. The emitter member 72 is rotatably held by the socket portion 70, whereby the final search can be effected by movements as described above. The emitter member 72 and the inner ferrite rod thereof is provided with a vertical, central passage 76, which is usable as a sighting channel for enabling a marking of the real ground fixpoint in an easy manner once it has been found. The addition of the second receiver member 74 will in¬ volve an increased receiving sensitivity. It also involves that a zero reading is obtained when the marker axis is located midways between the two receiver members, i.e. in the axis of the emitter member. This, however, does not change the fact that the operator shall have to rotate the search head through ca. 90 and again obtain a zero reading for ascertaining that the fixpoint is really located in the axis of the vertical element 76.

As shown in dotted lines in Fig. 7 the search head could be provided with one or more additional receiver members 78 mounted orthogonally to the emitter member 72 and also, at least approximately, orthogonal to the receiver members 74. This would correspond to the system as shown in Fig. 6, and in that case the fixpoint can be localized without any need of rotating the search head.

The socket portion 70 may be tiltable relative the block 68 so as to enable the search head to be tilted for the detection of a possible inclination of the marker axis. The guiding apparatus of Fig. 7 should preferably be made of non-magnetic materials, and the frame 60, moreover,

O PI shall have to be made such that it does not constitute an ^ electrically conducting coil turn.

Once the fixpoint has been finally localized, e.g. by the position of the emitter member 72 as shown in Fig. 7, it may be desirable to record this position relative the frame, and to this end one of the frame sides 66 may be provided with a scale indicating the position of the tra¬ verse 64, while the traverse 64 carries a scale indicating the position of the block 68. Alternatively or additionally, the frame 60 may be provided with means such as opposed brackets 78 for holding a horizontal marker plate under¬ neath the movable system, whereby the said final position can be marked on the marker plate.

If for some reason the entire apparatus is wanted to be temporarily removed from its place, e.g. for enabling the marker to be changed out or be remounted in a deeper position, the correct fixpoint location will be reproduceabl based on the said recording of the position of the element 72 relative the frame 60, provided the latter, upon its removal, can be replaced exactly in its original position. Such an exact replacement, however, is possible by various methods of premarking the position of the frame relative the ground surface, before removing the frame therefrom. Such a premarking may be effected well spaced from the frame itself, such that the marking will not interfere with the following digging and mounting work in the area of the marker axis, and such that the frame is exactly reposi- tionable for control of and guidance for the correct location of the axis of the remounted marker. With the apparatus of Fig. 7 the position of the fix¬ point, as mentioned, may be read in terms of rectangular coordinates along the frame sides 66 and the traverse 64, respectively. However, the same position may be read in polar coordinates when the guiding apparatus is designed as shown in Fig. 8.

The apparatus of Fig. 8 comprises a base plate member 80 to be placed horizontally on the ground just as the frame 60 of Fig. 7. On the plate member 80 is arranged a radial holder arm 82 which is rotatable about a central, vertical pin 84 of the plate member 80 and has a radial slot 86, in which a block member 88 is slidably arranged. The block member 8 is connected or connectable with the lower end of the said search head, which will thus be movable both around with the radial arm 82 and inwardly and outwardly along the slot 86. With suitably arranged scales for the respective movements the final position of the search head will hereby be indicated in terms of polar coordinates.

As mentioned, it may be desirable to switch between the vertical and horizontal systems for emission and reception, respectively, but in stead of effecting this change by a switch over of the electric connections with the apparatus unit 4 a corresponding switch over will be achievable by materially turning the search head through 90° such that thereafter it will be the receiver system which is vertically oriented while the emitter system is horizontally oriented.

Claims

CLAIMS j

1. A search apparatus for localization of subterranean markers of the resonant type, comprising a directional emitter system operable to transmit electromagnetic energy to the marker area and a directional receiver system for receiving a field component of the field as hereby reradiated by the marker, the receiver system being connected with indicator means operable to indicate variations of the intensity of the received signal, characterized in that the receiver system is mounted in the near field of the emitter system with an orientation generally perpendicular to the axis of the emitter system such that the electromagnetic fields as emitted and received by the respective two systems are mutually orthogonally polarized, the receiver system being of the type comprising a coil mounted on a flux concentrating core member such as a ferrite rod, and said indicator means being operable to indicate an absolute or relative minimum of the intensity of the received signal.

2. A search device according to claim 1 , in which the emitter system comprising a flat coil of a diameter substantially larger than the coil diameter of the receiver system, and that the receiver system is located substantially in the plane of the emitter coil.

3. A search device according to claim 1 and comprising two directional receiver systems both arranged orthogonally to the emitter system, but forming an angle with each other, preferably of 90°. 4. A search device according to claim 3, in which the line or point of intersection between the mid-normals of the respective two receiver systems is marked on or 66

1 4

by a marker member as rigidly connected with the two systems.

5. A search device according to claim 1, in which the two systems, as a unitary search head, are arranged on a carrier platform as mountable in a horizontal position on the ground overhead a subterranean fixpoint marker, the search head being rigidly or tiltably fixed to a holding member, which is horizontally displaceably arranged on said platform.

6. A search device according to claim 5, in which the holding member is displaceable in one direction along a carrier member, which is displaceable on the platform in an orthogonal direction, by a straightlined or rotary movement, whereby the position of the holding member is readable in terms of rectangular or polar coordinates, respectively.

7. A search device according to claim 5, in which the holding member permits for the search head to be rotated.

8. A search device according to claim 5, in which the receiver system is connected or provided with a sighting arrangement such as a central hole through the core member thereof, whereby the axis of the receiver system is visually observable.

9. A search device according to claim 1 , in which the emitter/receiver system is mounted adjacent one end of a handle rod, which also carries an additional receiver system, the axis of which is parallel with the axis of the emitter system, switch means being provided for selective actuation of the receiver system or the additional receiver system, respectively, the receiver system preferably being provided with spirit level means or the like.

10. A search device according to claim 1 , in which the emitter and receiver systems are bodily or electrically mutually interchangeable.