Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
  • G01R31/28—Testing of electronic circuits, e.g. by signal tracer
  • G01R31/302—Contactless testing
  • G01R31/315—Contactless testing by inductive methods

Definitions

• 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.
• 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.
• a conductor e.g. a short-circuit
• 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.
• a conductor signature for instance a line, im ⁇ mediately above the pysical conductor
• 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.
• 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.
• 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.
• 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.
• the apparatus according to the invention 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 devisve both the display and the underlying circuit being measured at one and the same time.
• the apparatus according to the invention 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.
• 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.
• 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.
• fig. 6 shows a second embodiment of a measuring apparatus according to the invention.
• 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.
• 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.
• 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.
• 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.
• a current sensor system consisting of seven sets of coils Sa., Sb 1 ; Sa 2 , Sb 2 ; ... Sa convention, 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.
• three lamps 0 which serve to illuminate the area immediately under the coils.
• 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.
• the signals are analysed and this results in a drawing on the display G, e.g.
• 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 .
• 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.
• an optical magnify- ing element e.g. a lens or a lens-system K
• 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.
• 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.
• the computer 7 produces a picture which is shown instantaneously and continuously on the display G.

Landscapes

• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Measurement And Recording Of Electrical Phenomena And Electrical Characteristics Of The Living Body (AREA)
• Tests Of Electronic Circuits (AREA)
• Measuring Instrument Details And Bridges, And Automatic Balancing Devices (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=8134988

Family Applications (1)

Country Status (5)

Cited By (1)

Citations (3)

• 1989
  • 1989-09-18 DK DK459789A patent/DK459789A/da not_active Application Discontinuation
• 1990
  • 1990-09-18 JP JP51354990A patent/JPH05500564A/ja active Pending
  • 1990-09-18 WO PCT/DK1990/000239 patent/WO1991004497A1/en not_active Application Discontinuation
  • 1990-09-18 AU AU64400/90A patent/AU6440090A/en not_active Abandoned
  • 1990-09-18 EP EP19900914513 patent/EP0493477A1/en not_active Withdrawn

Patent Citations (3)

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