WO1999026086A1

WO1999026086A1 - A method of determining the type and the position of a closed electrical conductor, a measuring set-up for determining the type and the position of a closed electrical conductor, and use of the measuring set-up

Info

Publication number: WO1999026086A1
Application number: PCT/DK1998/000498
Authority: WO
Inventors: Niels Anderskouv; Erling Nielsen
Original assignee: Lk A/S
Priority date: 1997-11-19
Filing date: 1998-11-18
Publication date: 1999-05-27
Also published as: AU1332999A

Abstract

For determining the type and the position of a closed electrical conductor (4, 10), such as a ring (4) of electrically conductive material arranged in an electrical wiring box (1) which is concealed behind a wall/ceiling panel or below a floor, a method and a measuring set-up are disclosed wherein a current is induced in the ring (4, 10) from at least one movable magnetic field generating device, which thereby generates a magnetic field which is detected by one or more magnetic field detectors (A, B, C, D) which are fixed with respect to the magnetic field generating device (20). When the position of the magnetic field generating device provides a measuring signal with a given shape or value predetermined from the magnetic field detectors, the exact position of the closed electrical conductor (4, 10) may be determined. The measuring set-up for performing the invention consists of at least 3 coils, preferably 5 coils, where 1 coil serves as a transmitter coil (20), while 4 coils (A, B, C, D) in pairs serve as receiver coils for determining the co-ordinates (0, 0) of a system of co-ordinates in which a wiring box has its centre.

Description

A method of determining the type and the position of a closed electrical conductor, a measuring set-up for de^¬ termining the type and the position of a closed electrical conductor, and use of the measuring set-up

The invention relates to a method of determining the type and locating the centre of a closed electrical conductor.

Closed electrical conductors are found e.g. in boxes for electrical installations which are frequently mounted on a lath. Externally on the lath, a wall or a ceiling panel is applied over the boxes which are hereby concealed. When the boxes are to be provided with e.g. switches, the electrician mounting the switches must be able to find the concealed box. To find the position of the box, the carpenter, who has erected the wall panel, has marked the position of the centre of the box in pencil or by a nail. Frequently, this marking is not sufficiently accurate for the centre of the wiring box to be located within the necessary tolerances. When the electrician is to mount the switch, he must drill a hole in the wall/the ceiling panel with a diameter which is somewhat smaller than the diameter of the box, to avoid the risk that he drills di- rectly into the side walls of the box and thereby de^¬ stroys it. When drilling a hole having a smaller diameter than the diameter of the box, the electrician must subsequently adjust, i.e. remove, wall/ceiling panel material in the drilled hole, so as to provide full access to the wiring box, which may be a rather time-consuming process.

If the marking of the centre is totally wrong, a hole will be drilled which is so far away from the box that subsequent stopping of the hole is necessary. Finally, it is noted that misdrilled holes may cause thermal bridges to be formed, since drilling in a moisture barrier, which is frequently provided on the inner side of a wall/ceiling panel, allows cold air to penetrate into the box and to condense.

If it were possible to determine the exact position of the centre of a wiring box, it would be possible to use a drill having a diameter which corresponds to that of the box, thereby obviating further subsequent working. Of course, this will save time and thereby costs in the in- stallation of boxes, which are found in great numbers in constructions and buildings.

Generally, wiring boxes have a so-called mounting ring which is used in the mounting of switches and the like. This ring is of metal and typically provided with two threaded holes for the attachment of switches and the like .

EP-0 466 108 Bl discloses a measuring set-up for locating e.g. concealed wiring boxes. In this prior art a magnet which may be detected by means of two compass needles, is placed on a portion of the box. These compass needles are placed on a support having two depressions, which contain a compass needle each. Furthermore, two arrows pointing toward a marking part are marked in the depressions. If the marking part is opposite a permanent magnet, the two compass needles will be positioned in parallel with their respective marked arrows, so that the magnet may be located accurately.

This known method thus requires the use of a magnet which is mounted in a wiring box in order to the located. This is inexpedient in particular if already installed wiring boxes are to be located, and moreover, as mentioned, an additional fitting must be arranged in the wiring box, which thereby adds to the costs of the box. Further, French Patent Application No. 2 464 584 discloses a method of detecting a concealed wiring box, which also comprises placing a magnet in the box that can be detected by moving a detector which is sensitive to magnetic flux.

Accordingly, an object of the invention is to provide a method and a measuring set-up of the type mentioned in the opening paragraph, which allow the exact position of a wiring box to be determined, without it being necessary to modify the box with special signal generators, such as magnets, which add considerably to the costs of the product.

The object of the invention is achieved by a method of the type defined in the introductory portion of claim 1 which is characterized by comprising the steps of:

a) inducing a current in the conductor from at least one magnetic field generating device

b) detecting the magnetic field generated in the conductor by means of one or more magnetic field de- tectors

c) changing the position of one or more of the magnetic field detectors

d) determining the position where said one or more of the magnetic field detectors emit a measuring signal having a predetermined shape or value.

It is hereby possible to determine the centre of a closed electrical conductor with great accuracy, e.g. such a conductor as is found in a typical wiring box. In other words, it is possible to locate the centre of a wiring box which is concealed behind a wall with such a great accuracy that it is possible to expose the box in a quite few working operations, i.e. it is possible to drill the wall with a drill having a diameter which corresponds to the diameter of the box.

An alternative way of achieving the object of the inven- tion, as stated in claim 3, may comprise the steps of:

b) detecting the current induced in the conductor by means of a magnetic field generator

c) changing the position of one or more of the magnetic field generating devices

d) determining the position where the induced current in the conductor assumes a specific signal shape or value .

This method presents the same advantages as the method of claim 1. The difference is merely that instead of detecting the magnetic fields induced in the closed conductors, the induced current is detected as a target for the centre.

A measuring set-up of the type defined in the introductory portion of claim 10 may be used for performing the method, said measuring method being characterized by comprising a housing having at least three coils which are securely fixed with respect to each other, and a control circuit for controlling the coils. There is thus provided a measuring set-up which can perform the methods according to claims 1 and 3.

Expediently, as stated in claim 11, the measuring set-up is characterized in that the housing has 5 coils, of which the 4 coils are geometrically positioned in a ring- shaped arrangement, while the 5th coil is positioned in the centre of the ring-shaped arrangement of the 4 coils.

This set-up provides an extremely user friendly measuring set-up which is easy to operate, as will appear later.

To make the measuring set-up of claim 11 additionally easy to use, the measuring set-up is characterized, as stated in claim 12, in that the housing has an indicator with symbols to show the way in which the measuring setup is to be moved when determining the centre of the conducting ring.

This provides the advantage that a user always knows which way to move the housing to approach the centre of a wiring box.

As mentioned, the invention also relates to uses of the measuring set-up.

These measuring set-ups are defined in claims 14 and 15.

The invention will now be explained more fully with reference to an example shown in the drawing, in which

fig. 1 shows a typical wiring box,

fig. 2 shows a block diagram of a preferred embodiment of the invention, fig. 3 schematically shows a measuring set-up according to the invention,

fig. 4 shows a basic sketch of how the measuring set-up in fig. 3 is used,

fig. 5 schematically shows an example of an amplitude characteristic when the measuring set-up according to fig. 3 is moved along the X axis, and

fig. 6 shows the phase conditions when the measuring setup according to fig. 3 is moved in the vicinity of a closed electrical conductor.

In fig. 1, the numeral 1 generally designates a typical wiring box having pipe stubs 2, which total 6 in number in the example shown, and which are used for the insertion of cables into the interior of the box. Further, the box has mounting holes 3 for threaded connection with a lath. The centre of the box is designated 7, and, as will be seen, the box accommodates a metal ring 4 which has expanded areas 5 with threaded holes 6 for the installa^¬ tion of e.g. switches and the like. As mentioned previ- ously, such a box, which is arranged behind a lath, is covered by a wall which is arranged externally on the lath. In order to get into the interior of the box subsequently to mount switches and the like, it is necessary to remove material from the outer wall. Till now, this has been done in that a carpenter has marked a cross where the centre of the box should be. This cross is rarely positioned very accurately, which means that an electrician who is to expose the box drills or mills a hole which is somewhat smaller than the diameter of the box. This, of course, results in some time-consuming subsequent working to remove additional material in order to gain access to the entire box, and since there are fre^¬ quently many boxes in buildings and the like, this per se is a time-consuming operation. It should be noted that the above-mentioned types of boxes are also used behind ceiling and floor panels.

Thus, it is desirable that the centre of the box can be determined with such a great accuracy as to permit the use of a drill having a diameter which substantially cor- responds to the diameter of the box.

This diameter and its centre can now be determined according to the invention in an embodiment whose basic mode of operation is shown in the block diagram in fig. 2.

According to this block diagram a measuring set-up is controlled by a microprocessor 8, which receives a signal shown here to be generated by an analog sine generator. This, however, should not be regarded to be a restriction, as other generators having other curve shapes may be used. The sine generator 10 induces an electrical field in a magnetic field generating device, such as a coil, which generates an electrical magnetic field indi- cated at 11, causing, as shown at 12, a current (which may be 0 in some cases, cf. the following) to be induced in the ring 4 of the wiring box 1, cf. fig. 1. This current causes the ring 4 to emit a magnetic field, which, as shown here, is detected by two differential magnetic detectors (4 coils) 14 and 15, whose output signals are measured in a differential coupling consisting of two differential amplifiers 16 and 17, and these signals are fed to the microprocessor 8 which processes the signals, as will be explained more fully below. Finally, the block diagram includes a user interface 18 which is used inter alia for calibrating the measuring set-up. Fig. 3 shows a preferred embodiment of the measuring setup according to the invention. This measuring set-up as a whole is designated 19, and, as will be seen, it consists of a transmitter coil 20 which is positioned centrally in the measuring set-up 19. Four receiver coils, which are designated A, B, C, D, respectively, are positioned concentrically around the measuring set-up. As will appear later, the pair of coils A, C forms one direction in the measurement, while the pair of coils B, D forms another direction in the measurement. It is also noted that the coils A, B and C, D, respectively, are wound clockwise and counterclockwise, respectively, which means that, in a series coupling, the coils A, C and B, D in pairs con- stitute a differential coupling for measuring magnetic fields .

Fig. 3 additionally shows indicators 25 whose function will be explained when the principles according to the invention are explained in connection with figs. 4-6.

Fig. 4 schematically shows a closed electrical conductor, which is designated 10 here. This closed electrical conductor might e.g. be the same as is shown in fig. 1 with the designation 4. Fig. 4 also shows the transmitter coil 20 and the receiver coils A, B, C, D. For the purpose of explaining the invention, reference is now made to fig. 5 which is related to fig. 4.

As the coils A, C and B, D are coupled in pairs in a differential coupling, the measuring signal will assume the value 0 when the coils A, C and B, D are affected by a uniform field. This is utilized for detecting relative positions between the measuring set-up and an electri- cally conducting ring, e.g. for determining the values where the field which is affected by the coils assumes specific values, e.g. zero. If the measuring set-up in fig. 4 is moved from a position from the right-hand side of the electrically conducting ring to the left across the electrically conducting ring, the amplitude and phase characteristic of the signal measured by the pair of coils A, C will have a unique course, e.g. as outlined in fig. 5.

As will be seen in fig. 5, the differential magnetic field designated in general by 21 and generated by the measuring set-up to the left and to the right of the minimum positions on the X axis, which are designated 22 and 24, will have a relatively low amplitude at a distance from these positions which reaches a maximum shown at 30, 31, 44 and 45. These maxima occur as a combination of the coupling between the transmitter coil and the ring as well as the coupling between the receiver coils and the ring. The minimum points 22 and 24 indicate that the mutual position of the coil and the ring causes the cur- rent induced in the ring to be 0. Further, minima occur at the points 23, 40 and 41, the reason being that the same field is applied from the ring to the receiver coils .

As mentioned above, the amplitudes of the detected differential signal is lower to the left and to the right of the points 22 and 24, the reason being that the field induced from the transmitter coil in the ring is relatively weak. The detected differential signal decreases from the maximum points 44 and 45 toward 0, as shown at 42 and 43.

When the measuring set-up with the coil C in fig. 5 passes the point 22 on the X axis to the right, the detected differential field will increase to the maximum value 32, and then it will decrease until the minimum value 23 is reached, which is the point where, in the pair of coils, fields of the same size and opposite direction are detected in the ring 10. If the measuring set-up is then moved additionally to the right, a new maximum 33 will occur for reasons of symmetry from which the detected differential field will decrease. The maxima 32, 33 occur because of the position of the receiver coils with respect to the ring and the current induced in the ring by the transmitter coil (which is moved together with the receiver coils) .

Thus, by detecting the resulting field which is received in the coils A, C, it is possible to determine the point 23 which accurately determines the location where the zero point of the X axis coincides with the zero point of the ring. In a quite analogous manner, the pair of coils B, D may be moved in the direction of the Y axis, and when the zero point on this axis has been determined, the centre of the ring 10 will be determined.

Fig. 6 schematically shows the phase conditions of the pair of coils A, C. As will be seen,, a phase shift takes place at the points on the curve which are marked 22A, 23A, 24A, 40A, 41A.

As the measuring set-up contains a differential coupling, it is important that it shows zero when there is no ring or other object, in which a current can be induced, in the vicinity of the measuring set-up. This may be ensured by placing the measuring set-up on the wall at a place where there is no ring in the vicinity, and then causing it to measure. If a signal is present on the output of the differential coupling, then the measuring set-up is offset adjusted so that the measured signal being shown has the value zero. By performing this a couple of times, the measuring set-up may be adjusted optimally, it being possible by repeated calibration procedures to avoid calibrating at a point where metal parts capable of af^¬ fecting the measuring set-up are actually present. The calibration procedure may thus be performed as follows:

First, the measuring set-up is caused to measure at an arbitrary point, and the measuring set-up of the appara^¬ tus is calibrated to zero. Then, measurement is performed at another point, and if this measurement shows zero, the measuring set-up is ready for measurement.

Finally, it is noted that the output power of the trans^¬ mitter coil may be varied, which is an advantage if the accuracy of the measuring set-up is to be maintained, also when measuring under difficult conditions, e.g. if there are several layers of plasterboards between the box and the measuring set-up.

In the measurement proper, the indicators may be arranged such that they emit a signal only when the measured value from one of the coils exhibits a predetermined high value, which may e.g. be the value which is exhibited when a magnetic field detector is within the ring 10 where the magnetic flux is greatest. This takes place in practice in the manner that the measuring set-up is moved toward the ring, and when a threshold value is detected, then that one of the indicators which passes the ring will give out light and indicate a direction for the movement of the measuring set-up. Imagine that the indicator 25 in fig. 3 is moved to the right, then the oppo- site indicator may e.g. give out light, thereby showing that further movement to the right is necessary to reach the symmetry about Y. At the moment when e.g. the upper one of the indicators 25 shown in fig. 3 passes the ring 10, this will cause the opposite indicator to begin to give out light, showing that the set-up is to be moved upwards. That is, two of the indicators will show that the set-up is to be moved in the X direction and the Y direction, respectively. As soon as one of the pairs of measuring coils A, C or B, D is in a symmetrical position about the X axis and the Y axis, respectively, the indi- cators will be turned on simultaneously. For example, if the ring is moved to the right as shown in fig. 4, the pair of indicators positioned in the X axis direction will be turned on simultaneously, and then the measuring set-up may be moved in the direction of Y the axis, and when these indicators are also turned on simultaneously, the centre is located.

Although the invention has been explained in connection with four receiver coils and one transmitter coil, noth- ing prevents other coil set-ups from being used. For example, the measuring set-up may be constructed by means of three receiver coils and one switching device, acting in the manner that in one direction two of the coils are used as receiver coils and the last one as a transmitter coil, while in another direction two other coils are used as receiver coils and the last one as a transmitter coil, and then the centre may likewise be determined. If the coils are multiplexed, the centre may be found just as easily as when using five coils.

Since the induced current in the ring also indicates where the measuring set-up is present relatively to the metal ring in the wiring box, information on the induced current may be measured. In such a measuring set-up, the transmitter coil 20 may be omitted, and the other coils may alternately be transmitter and receiver coils. As an example, two of the coils may be transmitter coils, and when they are moved into the ring, they will induce a current in the ring, but each coil will induce currents which are oppositely directed, and when the resulting current is zero or assumes a predetermined value which may be detected by a receiver coil, the centre will be located.

The last way of detecting the centre may suitably be per- formed with three coils, of which two are transmitter coils wound oppositely, while the third one is a receiver coil. In this case, too, switching between the transmitter and receiver coils is necessary in order to determine two directions, so that one transmitter coil is switched to be a receiver coil, while the receiver coil previously used becomes a transmitter coil which must be wound oppositely to the other transmitter coil.

The foregoing description mentions the case where a given current value which is zero is detected, but of course nothing prevents the use of a current curve shape for determining the centre of the ring.

Claims

P a t e n t C l a i m s :

1. A method of determining the type and locating the centre of a closed electrical conductor (4, 10) , c h a r a c t e r i z e d by comprising the steps of:

a) inducing a current in the conductor (4, 10) from at least one magnetic field generating device

b) detecting the magnetic field generated in the conductor by means of one or more magnetic field detec^┬¼ tors (A, B, C, D)

c) changing the position of one or more of the magnetic field detectors (A, B, C, D)

2. A method according to claim 1, c h a r a c t e r i z e d by comprising the steps of:

a) first changing the position of said one or more of the magnetic field detectors and the magnetic field generating device in one direction to a position where said one or more of the magnetic field detectors emit a first measuring signal having a prede- termined shape or value, and then

b) changing the position of said one or more of the magnetic field detectors and the magnetic field generating device in another direction to the position where said one or more of the magnetic field detec- tors emit another measuring signal having a predetermined shape or value.

3. A method of determining the ype and locating the > centre of a closed electrical conductor (4, 10) , c h a r a c t e r i z e d by comprising the steps of:

a) inducing a current in the conductor (4, 10) from at least one magnetic field generating (20) device

b) detecting the current induced in the conductor (4, 10) by means of a magnetic field detector

4. A method according to claim 3, c h a r a c t e r i z e d by comprising the steps of:

a) first changing the position of the magnetic field detectors in one direction to a position where the induced current in the conductor assumes a predeter^┬¼ mined curve shape or value, and then

b) changing the position of the magnetic field detec- tors in another direction to a position where the induced current assumes another predetermined value.

5. A method according to claim 4, c h a r a c t e r i z e d in that the phase conditions of the current in- duced in the conductor are used for the type determination of the ring.

6. A method according to any one of the preceding claims, c h a r a c t e r i z e d in that at least 3 coils are used for the generation of the magnetic fields and the detection of the current induced in the conductor.

7. A method according to any one of the preceding claims, c h a r a c t e r i z e d in that at least two of the coils are coupled in a differential coupling.

8. A method according to any one of the preceding claims, c h a r a c t e r i z e d in that the coils are arranged alternately to generate magnetic fields and to detect induced current.

9. A method according to any one of the preceding claims, c h a r a c t e r i z e d in that, prior to the induction of current in the closed electrical conductor, the magnetic field generating device and the magnetic field detectors are activated in at least one position in which there is no closed electrical conductor in which a current may be induced.

10. A measuring set-up for determining the type of and locating a closed electrical conductor (10), e.g. a ring (4), which is concealed in a wall structure, c h a r a c t e r i z e d by comprising a housing having at least 3 coils (A, B, C, D) which are securely fixed with respect to each other, and a control circuit (8) for controlling the coils.

11. A measuring set-up according to claim 9 or 10, c h a r a c t e r i z e d in that the housing has 5 coils, of which the 4 coils (A, B, C, D) are geometrically placed in a ring-shaped arrangement, while the 5th coil (20) is positioned in the centre of the ring-shaped arrangement of the 4 coils.

12. A measuring set-up according to claims 9-11, c h a r a c t e r i z e d in that the housing has an indicator with symbols (25) to show the way in which the centre finder is to be moved when determining the centre (7) of the conducting ring.

13. A measuring set-up according to claim 12, c h a r a c t e r i z e d in that the indicators are arranged in pairs to indicate the direction of movement in the X or Y direction, and that they are activated only when at least one receiver coil of a pair defining the X or Y direction is moved within the ring whose centre is to be found.

14. Use of the measuring set-up according to claims Ills for determining the type and detecting the centre of an electrically conducting mounting ring (4) in a wiring box (1) .

15. Use of the measuring set-up according to claims 10- 12 for detecting the centre of a wiring box (1) which has applied thereto or painted thereon an electrically con- ducting ring.