METHOD AND APPARATUS FOR THE LOCALIZATION OF A POWER CONDUCTOR, PREFERABLY A SHORT-CIRCUIT

Abstract: An apparatus for the localization of an electrical conductor, e.g. a short-circuit between electrical circuits or conductors, where it is known beforehand which circuits or conductors are mutually connected, comprises means (W, E, F) for applying an electric current to the circuit or the conductors (U), an inductive scanning element (Sp1, Sp2) for the scanning of the electromagnetic field from the conductors or the circuits, data-processing means (X, W) for the processing of the scanned signals, and a display (G) for showing the result of the data processing. The display (G) is transparent, so that one sees (Z) directly through the display down on the circuit (U), which is scanned, and the course of the current is shown in the display (G). The apparatus can be moved continuously from one area to another in the circuit, in that the data-processing of the measurement signals and the presentation on the display (G) are effected continuoulsy.

Description: METHOD AND APPARATUS FOR THE LOCALIZATION OF A POWER CONDUCTOR, PREFERABLY A SHORT-CIRCUIT. The invention relates to a method and apparatus for the localization of a power conductor, said conductor con¬ sisting of, for example, a short-circuit between two electrical circuits or two electrical conductors, where it has already been ascertained which of the circuits or conductors are mutually connected or short-circuited. The method and apparatus is based on the measurement of the electromagnetic field around and electric current applied to the circuits or conductors which are to be examined. From DE publication no. 2,050,705 is known a magnetic field sensor in the form of a Hall-sensor or a ring core coil where the flux through the sensor is determined by measuring the level of intensity, and shown by means of a light source, a sound source, a digit display, an in¬ dicating instrument or the like. By moving the sensor from place to place across the circuit it is possible to get an impression of where the current runs. From USA patent no. 4,829,238 there is known a method and apparatus for the measuring of the electromagnetic emission from equipment and conductors, in that a sensor with a large number of sensor elements is used to detect the electromagnetic emission. This can be, for example, the emission from electrical or electronic equipment, or the emission from the current in the conductors on a printed circuit board. Each sensor element comprises a pair of coil windings which stand at right-angles to each other. After a data processing, the result of the scanning is shown on a display, e.g. in the form of the emission intensity together with a layout of the circuit or equipment on which the measurement is being made. These known methods are unreliable and difficult to use in practice, the reason being that it is left to the operator to interpret the intensity levels and the variations herein, so that the operator can form an im- presion of where the current is flowing, thus enabling a desired circuit identification to be carried out. If, for example, it is required to locate a short-circuit on a multi-layer print equipped with SMD (Surface Mounted Devices), it will be necessary alternately to identify the circuit physically, e.g. on a drawing or on a dis¬ play, which places great demands on the operator's rou¬ tine and concentration abilities. The process becomes even more difficult when capacitances or several short- circuits arise between the two circuits which are ac¬ tually being examined. The object of the invention is to provide a method and apparatus whereby it is possible to directly localize a conductor, e.g. a short-circuit,- during simultaneous measurement of the electromagnetic field from the con¬ ductor, in that one looks directly at the actual conduc¬ tor during the measurement and obtains the result of the measurement in view, so that the actual conductor and the result of the measurement are seen at one and the same time. This is achieved by proceeding as characterized in claim 1, e.g. during the use of an apparatus as characterized in claim 3. The data collected with the apparatus according to the invention consist of position signals and amplitude sig- nals, these signals being processed on a real-time basis by the data processing circuit of the apparatus, so that the result of the measurement is shown immediately and continuously on the display and immediately over the actual conductor on which the measurement is being made. Consequently, one looks directly at the physical conduc¬ tor being measured and obtains the results, e.g. in the form of a conductor signature, for instance a line, im¬ mediately above the pysical conductor, in that said con¬ ductor signature shows where the current is flowing. If the display is not placed directly in the field of vision, but at another place in the apparatus, or if it is desired to use a non-transparent display, the result of the data processing can be reflected from the display into the field of vision, e.g. by using a completely or semi-transparent mirror or the like, hereby achieving the same effect. By proceeding as characterized in claim 2, e.g. while using an apparatus as characterized in claim 4, it is possible, in addition to the position signals and signal amplitude, also to measure the phase of the signal amplitude in relation to the phase of the applied cur¬ rent. The phase difference indicates the current's con¬ tent of real current and capacitive or inductive cur- rent, so that the data processing circuit of the appara¬ tus can evaluate whether the current flows in an ohmic conductor, e.g. a short-circuit, or is the result of a capacitance, e.g. a condenser, betv;een the conductors. A phase difference of approx. 180 degrees between two positions indicates that a current passes in between these two positions, and the amplitude level reflects the distance from the current sensor to the actual cur¬ rent. On the basis of measurements from several posi¬ tions, it is therefore possible to analyse and calculate where a current is placed physically, and whether it is the result of a real short-circuit corresponding to a resistance. The calculations are made instantaneously, and the result is shown instantaneously by means of the built-in microcomputer and the display. Consequently, what is achieved is a practically-applicable apparatus with which it is possible to directly see the current's through-flow close to the physical conductor. Additional signal elements, e.g. light diodes or sound-producing elements, can signal various information concerning the measuring results scanned, e.g. that the detected con¬ ductor is not ohmic but, e.g. capacitive. The signal elements can naturally also be used to provide signals concerning the functions of the apparatus in general, and concerning whether the data processing circuit is functioning as desired. The additional optical signal elements can be positioned so that they can be observed at the same time that one is looking at the display. The apparatus according to the invention can be con- figured as characterized in claims 5-7. The current scanners are made up. of flat coils with transparent cores, where the coils are built up in one or more planes. The coil-set can thus be mounted at the display and, for example, in such a manner that it is situated between the display and those circuits which are being investigated. This provides the possibility in practice of reducing the size of the apparatus, in that the coils and the display are reduced to merely show a section of the implicated circuits. This section can then be moved continuously from one area in the circuit to another, merely providing that the subsequent data processing is effected in a real-time manner. A practically applicable apparatus is achieved when it contains a current genera¬ tor, a microcomputer and remaining associated circuits, so that purely physically the apparatus can be realized as a single unit which can be operated with one hand. In order to ensure that the display is read at right-angles hereto, the apparatus comprises a tube which the user shall look through in order to observe the display and the circuit on which the measurement is being made. This tube stands at right-angles to the display, and has a length which is considerably greater than the distance between the display and the circuits being measured. By configuring the apparatus according to the invention as characterized in claim 8, it can be made very user- friendly as a "telescope" through which one can directly oberve both the display and the underlying circuit being measured at one and the same time. By configuring the apparatus according to the invention as characterized in claim 9, it is particularly suitable for fault-finding on printed circuits which have not yet been mounted with components. The lens and display are thus brought immediately down over the printed circuit, hereby enabling the investigation of circuits with closely-lying conductors. The appartus can be placed in a holder as a fixed unit into which is inserted the printed circuit to be examined. If the apparatus according to the invention is configur¬ ed as characterized in claim 10, the measuring accuracy of the appartus can be improved. Since it is not neces¬ sary to see directly through the coils, considerably smaller coils cab be used, hereby achieving greater sen¬ sitivity and greater precision. The apparatus can thus be used for the examination of prints with extremely thin and closely-lying conductors. The invention will now be described in more detail with reference to the drawing, where: fig. 1 shows the principle of measuring electrical current with a current sensor, fig. 2 shows a pair of coils for a current sensor, fig. 3 shows a complete set of coils for a current sensor, fig. 4 shows a block diagram of the total electronic circuit for the measuring apparatus shown in fig. 5 or in fig. 6, fig. 5 shows a first embodiment of a measuring apparatus according to the invention, and fig. 6 shows a second embodiment of a measuring apparatus according to the invention. In fig. 1 is sketched a straight electrical conductor P and a coil S, both of which are shown as seen from the side and from above. To the conductor P there is applied a varying current which gives rise to an electromagnetic field around the conductor. This field can be measured by induction in the coil S. The coil has a radius R and the conductor P is placed at a distance from the coil's centre C, expressed by the height H and the distance L. The relationship between the signal level V and the distance from the coil's centre to the conductor P is shown by the following approximated expression: where K is a constant. In fig. 2 is sketched a coil core B made of transparent plastic on which there are wound two coils Sa and Sb of 0.04mm copper wire, each with 70 windings. The coils Sa and Sb each have a diameter D of 4.0 mm, a height I of 1.5 mm and a thickness T of 0.1 mm, which ensures that the coil core B can be seen through without the coils Sa and Sb appearing visible. In the drawing the viewing direction is shown with the arrow Z. The coils Sa and Sb have a distance A of 2.5 mm, so that the signal level Va and Vb respectively in each coil arises from the above formula for V, in that in the expression for Va one must replace H with H + A. The ratio between Va and Vb can be used in the evaluation of the height H. When several such pairs of coils are placed at the side of each other, so that together they comprise two coil planes in which all the coils are identically oriented, a sign change in the signal level between two adjacent sets of coils will indicate that there is a conductor corres¬ ponding to the conductor P in fig. 1 between these two adjacent coil sets. In fig. 3 is shown a current sensor system consisting of seven sets of coils Sa., Sb 1 ; Sa 2 , Sb 2 ; ... Sa„, Sb ? which are moulded into a transparent moulding material N, e.g. in the form of a tube. The tube N can be mounted on a printed circuit X with a central opening, corres¬ ponding to the area for the coils in the tube N as shown in fig. 5, or possibly on a plate Z without opening as shown in fig. 6. The ends of the coil windings Q are led through the wall of the tube and soldered to the printed circuit X or coupled hereto by means of a cable Y. In fig. 3 there are also shown three lamps 0 which serve to illuminate the area immediately under the coils. In fig. 5 is shown a printed circuit U which has been provided with components, and which via test leads E,F is coupled to the two short-circuited sub-circuits to be investigated in the circuit U. A current, e.g. 5 mA, 3 kHz, is applied via the test leads. The coils in the coil planes Sp 1 and Sp 2 collect information concerning the electromagnetic field from the printed circuit U, which is hereafter amplified by the circuits on the printed circuit X and sent further via a plug J to a printed circuit W on which the actual calculation cir¬ cuit is placed. Here, the signals are analysed and this results in a drawing on the display G, e.g. by means of 91 hexagonal segments, each with an edge length of 0.6 mm, and which together form yet another hexagon which lies in the clearance of the tube M. The tube M reduces parallax errors when the printed circuit U is viewed through the tube M via the display G, the hole in the printed circuit X, the tube N and the coil sets Sp. and Sp 2 . In fig. 6 the current sensor with the coil planes Sp 1 and Sp 2 has been moved down under the printed circuit U- which is to be examined. In this way, it is not neces- sary to look directly through the coils, and thus the coils can be made condiderably smaller and the number of coils possibly increased, the result being that a greater resolution is achieved than with the coil con¬ figuration shown in fig. 3. Moreover, magnification effect can be achieved by inserting an optical magnify- ing element, e.g. a lens or a lens-system K at the dis¬ play, e.g. between the display and the circuit U 1 which is being examined. With this construction, which is intended particularly for printed circuits U 1 without components, it is also possible to reduce the distance between the coils Sp. and Sp 2 and the circuit U.. to a minimum. Z merely indicates a plate on which the circuit U 1 to be examined is placed. Fig. 4 is a block diagram showing the electronic circuit placed on the printed circuits X and W shown in figs. 5 and 6. The signal generator 2 generates a sinusoidal signal with a frequency which is regulated from the com¬ puter 7 to a value of around 3 kHz, corresponding to the middle frequency of an active bandpass filter built into the detector 3. The detector 3 also contains the coil sets Sp 1 and Sp 2 from the current sensor, and transfers all signals from from all coils to an analogue multi¬ plexer 4, so that the computer 7 can select a certain current sensor coil set. The sinusoidal signal from the generator 2 passes through a driver circuit 1 and is sent further to the two test leads E and F, which are connected to the two leads or circuits on the printed circuit to be examined. From the driver circuit 1, a reference signal and an output signal are fed back to the analogue multiplexer 4, with which the computer 7 selects that signal which is permitted to pass to the phase decoder 5 and the amplitude decoder 6. The phase decoder 5 and the amplitude decoder 6 are connected via a databus 8 to the computer 7, which via a second data- bus 9 is coupled to the generator 2 and via a third databus 10 to the display G. On the basis of the measur¬ ed phase and amplitude values, the computer 7 produces a picture which is shown instantaneously and continuously on the display G.

Claims: C L A I M S 1. Method for the localization of an electrical con¬ ductor, preferably a short-circuit between electrical circuits or conductors, where it is known beforehand which circuits or conductors are mutually connected, in that a an electric current is applied to the circuits or the conductors, the electromagnet fields of which are scanned with a measuring element, and where the scanned values measured are data-processed and the result is shown on a display, c h a r a c t e r i z e d in that there is used a display or an arrangement which is transparent or substantially transparent and which is positioned immediately over the circuit or the conduc¬ tors to be scanned. 2. Method according to claim 1, c h a r a c t e r i - z e in that an alternating current is applied to the circuits or the conductors to be examined, preferably a sinusoidal alternating current, and in that the measur¬ ing element and the data processing are arranged in such a manner that there is also carried out a calculation of the phase differences between current and voltage in the circuits or the conductors which are scanned. 3. Apparatus for the localization of an electrical conductor, preferably a short-circuit between electrical circuits or conductors, where it is known beforehand which circuits or conductors are mutually connected, said apparatus comprising means (1,2,3,E,F) for applying an electric current to the circuits or the conductors (U,U. ) being examined, at least one inductive scanning element (Sp., Sp 2 ) for the scanning of the electromagne- tic field from the conductors or the circuits, means (4,5,6,7) for the data-processing of the scanning ele¬ ment's signals, and a display (G) for showing the result of the data processing, c h a r a c t e r i z e d in that the display (G) is a transparent or substantially transparent display and is arranged to be positioned immediately above the circuit or the conductor which is to be scanned. 4. Apparatus according to claim 3, c h a r a c t e ¬ r i z e d in that the means for applying an electric current to the circuits or the conductors (U,U 1 ) to be examined comprise a signal generator (2) for alternat¬ ing, preferably sinusoidal alternating current. 5. Apparatus according to claim 3 or 4, c h a r a c ¬ t e r i z e d in that the scanning element (Sp 1 , Sp 2 ) comprises a number of coil pairs (Sa.., Sb 1 ; Sa 2 , Sb 2 • • * ) • 6. Apparatus according to claim 5, c h a r a c t e ¬ r i z e d in that the coils are arranged in a holder (Sp 1 , Sp 2 ) of transparent material, and in such a manner that the coils are placed in a number, preferably two, of parallel planes. 7. Apparatus according to any of the claims 3-6, c h a r a c t e r i z e d in that the coils and the display (G) are arranged at the end of an elongated tube construction (M). 8. Apparatus according to claim 7, c h a r a c t e ¬ r i z e d in that the tube construction is configured as a telescope (M,N), in that the coils (Sp,, Sp 2 ) are arranged at the end of a tube (M) and the display (G) is placed at a short distance from here in the direction of the viewer (Z ), and in that the apparatus is arranged to be directed towards that circuit or that conductor (U) which is examined, so that this can be viewed through the display and the coils (fig. 5). 9. Apparatus according to claim 7, c h a r a c t e ¬ r i z e d in that the tube construction is configured as a telescope, in that the display (G) is placed at the end of a tube (M), and that the coils (Sp, , Sp ) are arranged at a distance herefrom, so that the circuit or the conductor to be examined can be inserted between the coils and the display and be viewed through the display (fig- 6). 10. Apparatus according to claim 9, c h a r a c t e ¬ r i z e d in that at the display (G) there is placed an optical magnification element, e.g. a lens or a lens- system (K) .

Inventors: LARSEN MARTIN, LARSEN, MARTIN
Applicants: LARSEN MARTIN, LARSEN, MARTIN
Application year: 1990
Main classification: G01R31
IPC codes: G01R31