WO2000022375A1 - Method and device for measuring cross-section of wires - Google Patents
Method and device for measuring cross-section of wires Download PDFInfo
- Publication number
- WO2000022375A1 WO2000022375A1 PCT/SE1999/001835 SE9901835W WO0022375A1 WO 2000022375 A1 WO2000022375 A1 WO 2000022375A1 SE 9901835 W SE9901835 W SE 9901835W WO 0022375 A1 WO0022375 A1 WO 0022375A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- frequency
- section
- wire
- cross
- elongated element
- Prior art date
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/12—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring diameters
Definitions
- wires e.g. copper wires for electrical windings in e.g. electrical motors or transformers
- One particular such need is to measure the thickness of insulation coatings applied to the wire during the manufacturing. Control of the insulation thickness and uniformity is a very important quality factor where inconsistencies can cause short circuit failures in electrical machines or devices being manufactured using a faulty copper wire.
- Prior art wire diameter or strip cross-section dimensions measuring devices such as purely mechanical or laser-based apparatuses, all measure the total outside diameter or dimensions. This is a drawback, because when being produced the wire or strip will have a surface covered by grease, oil or contamination that will pollute a metal cross-section measurement.
- An object of the invention is to provide a device, which can measure the metal cross-section ignoring the insulation coating. Using then this information in the coating thickness can readily be obtained by simple subtraction calculus.
- a well-known phenomena in relation to AC electrical signals at high frequencies in electrical conductors is the so-called skin-depth which describes the fact that the high-frequency conduction takes place in a skin layer of the conductor. The penetration depth of the skin is related to the AC signal frequency as well as the electrical resisitivity and magnetic permeability of the conductor itself.
- ⁇ is the so called skin depth, it corresponds to the thickness from the surface to the center of the wire which the electromagnetic field can penetrate; ⁇ and ⁇ are the magnetic permeability and the electric conductivity of the wire material, respectively; and f is the frequency of the ac electric current. According to this formula, when the frequency increases the skin depth decreases thus reducing the actual cross section of the wire through which the current can flow. This effect produces an increase of the impedance of the wire that can be measured.
- the effective resistance of the conductor is therefore related to the skin layer cross-section (in product with the resisitivity of the conductor material) which then will vary with the AC signal frequency.
- a simply measurement of the voltage drop, or resistance at the ac frequency will show a value which is related to the AC frequency.
- the effective resistance of a conductor is therefore greater than the d.c. or ohmic resistance when carrying alternating current.
- This relation is basically an inverse square root relation until the frequency when the skin depth reaches and equals the conductor radius (or minimum cross-section dimension for a rectangular conductor). At this point the AC resistance of the conductor will stop to decrease as the AC frequency decreases further. This point is therefore a discontinuity point in the AC resistance to AC frequency relationship.
- the frequency at which the skin depth equals the radius of the wire will be referred to as the Saturation Frequency (SFr).
- SFr Saturation Frequency
- the frequency range close to saturation, where the impedance begins to increase with the frequency, is important for determining the diameter of the wire through the value of its SFr.
- the Saturation Frequency (SFr) is the lowest frequency of an AC current for which the impedance of the wire behaves linearly (in relation to the frequency).
- the AC frequency value at the point of the discontinuity will allow the calculation of the conductor diameter according to the skin depth calculation formula.
- Fig. 1 schematically shows a circular cross section wire conductor with a skin depth part at three different AC frequencies
- Fig. 2 is a schematic diagram showing a frequency response over a time period from a wire according to Fig. 1
- Fig. 3 schematically shows two rectangular cross section wire conductors with skin depth parts
- Fig. 4 is a schematic diagram showing the frequency responses from the wires in Fig. 3,
- Fig. 5 shows an embodiment of the wire conductor and Fig. 6 is a schematic view of an experimental arrangement.
- One practical implement of the method is to apply a frequency modulated (eg sine or triangular modulation) sine wave AC signal along a section of the wire conductor while simultaneously measuring the voltage drop within this section of the conductor. As the AC signal frequency decreases the voltage drop along the conductor will reach a plateau or flat region representing the AC frequency interval during which the skin depth exceeds the conductor radius.
- a frequency modulated (eg sine or triangular modulation) sine wave AC signal along a section of the wire conductor while simultaneously measuring the voltage drop within this section of the conductor.
- Fig. 1 a cross section of an electrical conductor 10 is shown at three different frequencies F1 , F2 and F3 of an AC current fed through the conductor.
- F1 there is a first skin depth d1 that is substantially smaller than the radius R of the conductor.
- REFF effective conductor resistance
- the frequency decreases to F2 the corresponding skin depth d2 increases and as a result the effective conductor resistance REFF decreases.
- the decrease of the effective conductor resistance R E FF is continuous.
- a decrease of the frequency to F3 will result in a skin depth d3 that is equal to the radius R of the conductor.
- the effective conductor resistance REFF varies in dependence of the frequency of the applied AC current.
- the applied AC current signal is frequency modulated.
- Fmod a sine wave modulation signal
- the modulation signal is indicated with dashed lines.
- Different electronic or digital signal processing techniques can be utilised to precisely determine the AC frequency at the amplitude modulation (voltage drop) discontinuity related to the applied frequency modulated AC signal.
- One such technique is an amplitude demodulation of the AC voltage drop signal followed by subtraction of the FM reference signal and derivations to detect the discontinuity point.
- the conductor radius detection criteria is a discontinuity in the measuring signal - which easily can be distinguished from continuously varying features in the measuring signal resulting from e.g. frequency related changes in inductance, reflections, capacitive couplings etc.
- the minimum dimension can be measured by the discontinuity point. Taking the rectangular cross-sections as an example the thickness would be measured through the discontinuity point, remains then however the width.
- a secondary effect of the skin-depth can be used as shown in Fig. 3 and Fig. 4.
- ⁇ d which relates to a certain ⁇ f
- ⁇ REFF the corresponding change in effective resistance
- Fig. 5 shows one embodiment according to which the wire has been folded.
- the wire is also wound to reduce effects from inductance.
- the determination of the SFrs has been carried out by measuring the voltage drop along the Cu wires when they are connected to a constant voltage generator that produces an ac signal with frequencies varying according to a controlled sweep amplitude.
- FIG. 6 An experimental setup is schematically shown in Fig. 6.
- a first function generator 13 is used to produce the voltage signal which controls the frequency sweep, and a second function generator 14 is used to feed the wire 10.
- the available frequency range of both generators is from below 1 Hz up to 13 MHz.
- the generator that feeds the wire is driven by the signal of the first generator through a VCO connection.
- An oscilloscope 15 is used to represent the time dependence of the voltage drop across the wire 10 and the voltage signal which controls the frequency sweep.
- the oscilloscope needs a peak detection function. The possibilities of saving the traces in the internal memory of the oscilloscope have been used although they are not essential for these measurements.
- the diameters shown in the table were measured using a Digital Micrometer.
- the coating of the wires was removed chemically before doing the measurements.
- the dispersion errors arising from 5 measurements in each wire and the systematic error of the Micrometer have been considered.
- the set of copper wires of different diameters have been measured using the skin-depth effect by the methods described formerly.
- the SFr of each wire has been measured 10 times using both methods.
- the following table sums up the values of the SFr and the error bars obtained by taking into account the dispersion of the ten measurements.
- the diameter values have been obtained from the SFr through the skin depth calculation formula.
- the absolute and relative errors appended to the diameter values have been calculated from the dispersion errors of the frequencies. As it is seen in the former table, the relative errors in diameters (coming from the errors in frequencies) do not reach the 10 % in any case.
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)
- Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
Abstract
Description
Claims
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP99956453A EP1151239A1 (en) | 1998-10-11 | 1999-10-11 | Method and device for measuring cross-section of wires |
AU13061/00A AU1306100A (en) | 1998-10-11 | 1999-10-11 | Method and device for measuring cross-section of wires |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
SE9803506A SE9803506D0 (en) | 1998-10-11 | 1998-10-11 | Method for measuring cross-section geometry based on AC signal skin-depth penetration |
SE9803506-6 | 1998-10-11 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO2000022375A1 true WO2000022375A1 (en) | 2000-04-20 |
Family
ID=20412947
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/SE1999/001835 WO2000022375A1 (en) | 1998-10-11 | 1999-10-11 | Method and device for measuring cross-section of wires |
Country Status (4)
Country | Link |
---|---|
EP (1) | EP1151239A1 (en) |
AU (1) | AU1306100A (en) |
SE (1) | SE9803506D0 (en) |
WO (1) | WO2000022375A1 (en) |
Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4593244A (en) * | 1982-08-06 | 1986-06-03 | Australian Wire Industries Pty. Ltd. | Determination of the thickness of a coating on a highly elongated article |
US4947132A (en) * | 1986-11-25 | 1990-08-07 | Battelle Memorial Institute | Method for detecting thickness variations in the wall of a tubular body which conducts electricity |
WO1990015965A1 (en) * | 1989-06-22 | 1990-12-27 | Benoit De Halleux | Process and device for measuring the cross-section or the diameter of long cylindrical products made of conductive material |
EP0629837A1 (en) * | 1993-06-15 | 1994-12-21 | Tokyo Gas Co., Ltd. | Method of measuring inner diameter of pipe |
CA2232348A1 (en) * | 1997-03-24 | 1998-09-24 | Centro Automation Spa | Method to measure the variations in section of a rolled bar |
-
1998
- 1998-10-11 SE SE9803506A patent/SE9803506D0/en unknown
-
1999
- 1999-10-11 EP EP99956453A patent/EP1151239A1/en not_active Withdrawn
- 1999-10-11 AU AU13061/00A patent/AU1306100A/en not_active Abandoned
- 1999-10-11 WO PCT/SE1999/001835 patent/WO2000022375A1/en not_active Application Discontinuation
Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4593244A (en) * | 1982-08-06 | 1986-06-03 | Australian Wire Industries Pty. Ltd. | Determination of the thickness of a coating on a highly elongated article |
US4947132A (en) * | 1986-11-25 | 1990-08-07 | Battelle Memorial Institute | Method for detecting thickness variations in the wall of a tubular body which conducts electricity |
WO1990015965A1 (en) * | 1989-06-22 | 1990-12-27 | Benoit De Halleux | Process and device for measuring the cross-section or the diameter of long cylindrical products made of conductive material |
EP0629837A1 (en) * | 1993-06-15 | 1994-12-21 | Tokyo Gas Co., Ltd. | Method of measuring inner diameter of pipe |
CA2232348A1 (en) * | 1997-03-24 | 1998-09-24 | Centro Automation Spa | Method to measure the variations in section of a rolled bar |
Also Published As
Publication number | Publication date |
---|---|
EP1151239A1 (en) | 2001-11-07 |
AU1306100A (en) | 2000-05-01 |
SE9803506D0 (en) | 1998-10-11 |
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