WO2004057358A1

WO2004057358A1 - Non-contact current detection device

Info

Publication number: WO2004057358A1
Application number: PCT/IL2003/001043
Authority: WO
Inventors: Jonathan Devor; Scott Kirkpatrick
Original assignee: Yissum Research Development Company Of The Hebrew University Of Jerusalem
Priority date: 2002-12-20
Filing date: 2003-12-09
Publication date: 2004-07-08
Also published as: AU2003286403A1

Abstract

Apparatus (10) and method for determining electromagnetic field strength about a field source (30), comprises: vibrating a coil (12) with a predetermined amplitude and a predetermined frequency at a location about the field source (30), measuring emf induced in the coil (12), and deducing a field strength from the induced emf. The field source (30) may typically be a current bearing wire (30), and the method provides a way of non-contact measurement of the current (I) in the wire (30) as well as a way of locating the wire (30) if concealed. An alternative mode involves using the coil (12, 34) as a scanning device for obtaining distribution information of a magnetic field.

Description

Non-Contact Current Detection Device

FIELD AND BACKGROUND OF THE INVENTION The present invention relates to a non-contact current detection device and method and, more particularly, but not exclusively to a device and method that both measures the current and uses the current as a means of locating a hidden current carrier.

One of the great difficulties in trying to diagnose any electric circuit is the fact that the measuring equipment itself always has some impact on the electrical properties of circuit. This can cause deviations in the properties being measured and in some cases, can even cause the circuit to behave very differently from how it would behave without the measuring equipment attached. Of all the common electrical measurements, one of the most intrusive and problematic is the measurement of the current flow in a wire. At present, this measurement can only be carried out directly by physically severing the wire and connecting the ends to a regular ammeter. Accordingly, the circuit requires repair after the measurement of the current. In addition the ammeter always adds resistance to the wire, which lowers the current flow in it. In cases where the voltage is low, the value measured will have a significant systematic deviation from the real value. It is possible to detect current on the basis of induction in a surrounding coil.

The magnetic field produced around the current carrying wire induces current in the surrounding coil. However, whilst this overcomes the need for physical contact with the wire and a change in the circuit path, the current in the wire is still affected by the process. By the principle of conservation of energy, induction of current in the surrounding coil appears as a load to the originating current, again reducing the current that it is intended to measure. Furthermore, the actual current induced in the surrounding coil is a function of the distance from the current bearing wire. As the distance is difficult to define in the non-contact case the device has to be calibrated each time it is used in order to obtain an accurate measurement. The measurement of current, by measurement of the magnetic field about a single wire is nevertheless a well established measurement procedure. Indirectly, the procedure also involves measurement of power too, as the voltage is often fixed. Equipment for such measurements are often referred to as clamp-on or snap-on current measurement meters. As they clamp around the circuit being measured, the geometry of the problem is defined and thus the calibration problem is overcome.

Such equipment is manufactured by many companies, for example Hewlett-Packard,

Fluke, Amprobe, Philips, & others. For alternating current (a.c.) measurements, a coil wound around a ferromagnetic core is commonly used as a sensor or pickup device to detect the current flow. The ferromagnetic core is then snapped closed about the single current carrying wire so that the current induces a magnetic field in the ferromagnetic core.

The core acts as a transformer to produce a voltage in the coil wound about the core. The voltage is then amplified or attenuated to give a calibrated meter reading of the current.

A related system is presently manufactured, which measures both direct current (d.c.) and a.c. currents and power. In that system, transformer coupling is generally not utilized. The magnetic field of the current carrying wire is employed to operate upon a hall effect device, and the hall effect device provides a voltage which is proportional to the current in the current carrying wire. The voltage is, once again, amplified or attenuated to provide a meter reading giving the current in the wire, or alternatively, when the voltage is known, the power carried by the wire. Direct contact methods are utilized to pick up voltages and currents from low intensity sources such as printed circuit traces, the human body, and telephone systems.

It is noted that the use of a surrounding coil is not possible if the wire is embedded within a wall or the like, as is often the case.

US5,473,244 discloses a method and apparatus for performing non-contact measurements of the voltage, current and power levels of conductive elements such as wires, cables and the like. A non-contacting voltage measurement system includes an arrangement of capacitive sensors for generating a first current in response to variation in voltage of a conductive element. Each sensor is positioned in an electric field of the conductive element, and is thereby coupled to the conductive element through a coupling capacitance. A reference source drives the capacitive sensor arrangement at a reference frequency so as to induce the flow of a reference current therethrough. A measurement network is disposed to calculate the coupling capacitance based on a measurement of the reference current, and to then determine the voltage in the conductive element based on the first current and the coupling capacitance. Measurements of a composite current through single or multiple-element conductors may be effected using a similar procedure, wherein the composite current induces a measurement current to flow within a set of coils positioned in a predetermined manner proximate the conductor. In both current and voltage measurements a balancing procedure may be employed, in which a measurement signal is balanced by a feedback signal so as to improve accuracy and reduce the effects of stray coupling. Again the device is not free of influence on the circuit being measured, and necessarily requires the ability to induce the flow in the wire being measured of a reference current. EP 0748451 discloses a current sensor for non-contacting measurement of current in a line. Current is sensed by a circuit which provides a high frequency reversing voltage to a sensing winding on a current transformer, for driving the transformer into its linear region at least once per high frequency cycle. Current through the sensing winding is sampled while the transformer is in that linear region. Preferably, the current is sampled approximately at the instants of reversal of the voltage being applied to the sensing winding, and the sample having the lower absolute value is selected as a sample proportional to the line current

The above citations both provide non-contact methods for measuring current. However they fail to adequately solve the problems of minimizing influence on the current being measured and dealing with concealed wires and the like. There is a widely recognized need for, and it would be highly advantageous to have, a non- contact current measurement system devoid of the above limitations.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided a non- contact electromagnetic flux measuring apparatus comprising: a vibratable magnetic-flux sensitive unit, suitable for voltage induction in the presence of magnetic flux, for placing in non-contact proximity with a flux source and for vibrating at a predetermined rate, a voltage measurement unit connected to the vibratable magnetic-flux sensitive unit, for producing an output comprising measurements of voltages induced in the vibratable flux-sensitive unit, and a processing unit for using the measurements, together with data of the predetermined vibration rate, to deduce strength information of a field due to the flux source.

Preferably, the vibratable magnetic-flux sensitive unit comprises a coil.

Preferably, the vibratable magnetic-flux sensitive unit comprises a flux- concentrating core within the coil.

Preferably, the vibratable magnetic-flux sensitive unit further comprises a vibratable mounting.

Preferably, the vibratable mounting is controllable to permit setting of the predetermined rate.

Preferably, the voltage measurement unit is controllable such that the output comprises an average over a predetermined number of the measurements.

In one embodiment, the predetermined number is user determinable.

The flux source may be a current bearing member such as a wire, and a particular advantage of the present embodiments is that they are applicable to wires which are embedded beneath a surface, and for which an exact location may not be known.

Preferably, the processing unit is arranged to deduce from the information of the field, information of a current within the current bearing member. The information may be the size of the current in amperes, or it may be location information, indicating where the current is flowing. As explained herein, if the location is known and the wire can be accessed, then a calibration can be carried out and the current can be measured more accurately. In one embodiment the location is firstly determined, then the wire is accessed and calibration is carried out and then an accurate measurement of the current is carried out.

In one embodiment, the processing unit is operable to deduce the information of the current by analysis of a graph of detected voltage with respect to time.

Additionally, the processing unit may be able to deduce by analysis of the graph, information of location of the current bearing member.

As explained, the information of the current is deduced by comparison with a calibration current.

In an alternative embodiment, the flux source is not a current carrying member but a magnet. Preferably, the magnetic flux sensitive unit is configured to scan a region about the magnet to provide distribution information of the field.

Preferably, the scan is a two-dimensional scan.

In an alternative embodiment, the scan is a three-dimensional scan.

According to a second aspect of the present invention there is provided a method of determining electromagnetic field strength about a field source, comprising: vibrating a coil with a predetermined amplitude and a predetermined frequency at a location about the field source, measuring electromotive force, or emf, induced in the coil, deducing a field strength from the induced emf.

Preferably, the field source is a current bearing member, the method further comprising determining the current within the current bearing member from the induced emf.

Preferably, the deducing comprises analysis of the measured emf as a function of time.

In one embodiment, deducing comprises comparing the measured emf with a previously measured emf of a calibration stage.

The method may comprise analyzing the measured emf to deduce location information of the current bearing member.

The method may comprise scanning the coil about the field source to generate distribution information of the field.

The scanning may be two-dimensional or three-dimensional scanning.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The materials, methods, and examples provided herein are illustrative only and not intended to be limiting. Implementation of the method and system of the present invention involves performing or completing certain selected tasks or steps such as signal processing or scanning manually, automatically, or a combination thereof. Moreover, according to actual instrumentation and equipment of preferred embodiments of the method and system of the present invention, several selected steps could be implemented by hardware or by software on any operating system of any firmware or a combination thereof. For example, as hardware, selected steps of the invention could be implemented as a chip or a circuit. As software, selected steps of the invention could be implemented as a plurality of software instructions being executed by a computer using any suitable operating system. In any case, selected steps of the method and system of the invention could be described as being performed by a data processor, such as a computing platform for executing a plurality of instructions.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

In the drawings: Fig. 1 is a simplified diagram showing a non-contact current measuring apparatus suitable for measuring current in a current-carrying member, according to a first preferred embodiment of the present invention;

Fig. 2 is a simplified diagram illustrating the apparatus of Fig. 1 in the proximity of a current bearing member; Fig. 3 is a schematic diagram illustrating the motion of the vibrating flux sensitive unit of Fig. 1, compared to the current carrying member;

Fig. 4 is a graph showing an example of an ideal curve of epsilon as a function of time;

Fig. 5 is a graph of actual results obtained of the curve of Fig. 4 whilst testing a prototype embodiment of a dynamic ammeter according to the present invention;

Fig. 6 is a simplified flow chart showing use of the device of Fig. 1 according to a current-calibrated mode; and Fig. 7 is a simplified flow chart illustrating use of the device of Fig. 1 for two or three dimensional magnetic field tracing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present embodiments provide a non-contact dynamic ammeter which measures the current within a current bearing member, without any physical contact with the current bearing member, and it is able to do this through a barrier. An additional benefit of the device is that it can also give a pinpoint three-dimensional location of a wire hidden behind such a barrier. The device measures magnetic field strength and as such can also be used to study magnetic fields that are not caused by current, such as magnetic fields surrounding a magnet.

The principles and operation of a dynamic ammeter according to the present invention may be better understood with reference to the drawings and accompanying description.

Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.

Reference is now made to Fig. 1, which is a simplified block diagram illustrating a non-contact current measuring apparatus suitable for measuring current in a current-carrying member. Apparatus 10 comprises a vibratable magnetic-flux sensitive unit 12, suitable for voltage induction in the presence of a magnetic field, and which can be placed in non-contact proximity with the current bearing member. The flux sensitive unit 12 is typically a coil with an iron core, and is designed for maximum sensitivity to flux. The flux sensitive unit is mounted such as to be vibrated by a vibrating driver 14. The vibrating driver is preferably controllable to vibrate at a predetermined rate, and/or at a predetermined amplitude. In a preferred embodiment, the predetermined rate coincides with a resonant frequency mechanically designed into the flux sensitive unit 12. Such an arrangement reduces the amount of power that the device has to expend on vibrations.

A voltage measurement unit 16 is connected to the magnetic- flux sensitive unit. The voltage measurement unit typically comprises an A/D converter, which samples the output of the flux sensitive units at a desired rate. Subsequent processing may then be carried out digitally. It is however possible to design an analog system. Subsequent to the voltage measurement unit is an averager 18. The averager 18 takes an average, over a predetermined time frame, of the readings at the voltage measurement unit 16. Averaging helps in particular with noise reduction. Processing unit 20 obtains the averaged measurements from the averager 18 and uses data of the vibrations being applied to the coil, whether the vibration rate, the amplitude or any other parameter applying to the vibration, to deduce information of the current in the current bearing member.

Preferably the vibration driver is user controllable to permit setting of the vibration rate or amplitude. Different vibration rates are appropriate for different circumstances.

A signal generator 22 provides a timing signal which can be used for controlling the vibrations and for controlling the averager 18.

Construction of a simple working embodiment is as follows. It will be appreciated that exact specifications for each component will vary depending on the sensitivity, cost and task specialization requirements. Nevertheless some general rules apply. The vibrating coil of flux sensitive unit 12 preferably has a relatively large cross-section, a ferric core and a relatively large number of loops, so as to produce a strong signal. The coil is preferably light enough to vibrate rapidly and small enough to be able to resolve as separate signals, fluxes from two wires that are placed close together. That is to say the size of the coil is chosen for the geometry of the situation it is intended to measure, and it is noted that whilst increasing the cross-section increases the signal, it also decreases the resolution, so that a tradeoff is preferably found for a given application. Thus a device for locating wires in a wiring duct in a domestic building does not require the same geometry as a device intended for testing of connecting wires inside a computer, or indeed for a device intended for detecting currents flowing within an integrated circuit. In order to maximize the measured signal, specialized parts may be necessary, but cheap off-the-shelf parts such as tape or hard disk reader heads have proved to give remarkably good results, clearly detecting currents as low as 100mA without the use of a pre-amp. Similarly, a household speaker can be used as the vibration driver, providing a full range of vibration amplitudes and frequencies to make the device effective. There is a disadvantage to using a speaker, in that it produces a strong magnetic field of its own, which may interfere with the field being measured. In order to minimize such magnetic interference, the speaker is preferably provided with magnetic shielding and/or is placed as far away from the coil as possible. Preferably, the speaker is both remotely located and provided with shielding. A further disadvantage of using a speaker is that the speaker may require a bulky power supply, as a result causing the device to be too large and heavy to be handheld.

Other approaches for the vibration driver include the use of a piezoelectric driver or specialized electromechanical materials. In any case, the power requirements can be greatly reduced if the coil is designed to be in resonance with the frequency of the vibrations.

As briefly mentioned above, the signal processing may in one embodiment be carried out using analog technology, but it is generally more practical to convert the coil's signal to a digital format immediately after amplification. A simple analog to digital (A2D) converter can easily sample the signal from the coil at a rate far higher than the vibration frequency, in order to obtain an accurate description of the signal curve. The sampled array values are then preferably aligned using a trigger signal from signal generator 22, to achieve signal averaging, as described above. By averaging over N cycles, all non-systematic noise can be reduced by a factor of the square root of N. The optimal number of cycles in the averaging process is preferably set in light of the expected rate of change of the current being measured. In the case of a device intended for engineers or technicians the issue is best handled manually. The final result is preferably extracted, as described in the following section, from the exact shape of the signal curve obtained by measuring the coil output over time.

In contrast with previous stages, the analysis of the output curve need not be carried out in real-time, although real time results are perfectly feasible if desired. State of the art floating-point based digital signal processors (DSP) are able to perform the required analysis within a fraction of a second. Reference is now made to Fig. 2, which is a simplified diagram illustrating apparatus 10 in the proximity of current bearing member 30. The current bearing member 30, which is perpendicular to the plane of the paper, is surrounded by field lines 32, into which flux sensitive unit 12 is extended. It will be noticed that the field lines are circular, apart from an aberration caused by the flux sensitive unit itself.

Considering the measurement procedure, the induced magnetic field (B) in a coil with effective permeability (μ) at a distance from an electric wire (r), through which a current (I) is flowing, can be approximated as:

2πr

The above approximation assumes circular magnetic field lines, despite the aberration referred to above. The aberration is in fact caused by the coil's ferric core.

The magnetic flux passing through the detector cross section (S) is defined as:

≡ Ϊ BdS

Assuming the detector cross section is small, the flux value can simply be approximated to be proportional to the perpendicular amplitude of the magnetic field. Since calculating the ratio analytically is difficult, it is simply marked hereinbelow as a positive constant (k). Thus:

= kB perp

The electromotive force (emf) induced by the change of flux over time is equal to:

₌ dΦ ~ _l: ^dBp _P dt dt

Now let us solve the above equation using the assumption that the motion of the detector has a constant amplitude (A) and frequency (f), and can be described as:

Reference is now made to Fig. 3, which is a schematic diagram illustrating the motion of the vibrating flux sensitive unit compared to the current carrying member. The current carrying member 30 is surrounded by magnetic field lines 32 as in the previous figure. The vibrating coil is represented by small gray square 34 which moves along solid line segment 36 which has length (2A). The coil 34 is at a distance of x(t) relative to the center of line 36 and the wire is located at a position (b,h) relative to the same center. The distance of the detector from the wire, may be expressed as:

r(t) = ,J(x + h)² + b² = {Asm(2πft) + h)² + b²

Now, let us make a simplification that the current (I) remains constant, over the time period of a vibration cycle (1/f). The simplification provides the following solution:

— dl « I _τ-f , => dt

^Bperp (0 = B = ^~ r 2π r dBperp kμl d x + h ε(t) = -k- dt 2π dt r 2

Ikμlf cos(2πft)cos(4πft) + 2 sin(4πft)(sm(2πft) + (*)) - (1 +2(^)² - 2(^)²)cos(2.τ/t) ^~ ^4 (2(A)² + ₄( )sm(2πft) + l + 2( )² - cos(4^t))²

The above result has two components. The left hand side is a constant that describes the physical units of the problem, while the right hand side is unitless and describes the geometry of the problem. When trying to fit the measured values to the above curve, one needs to find the value of the left hand side as well as the two free parameters in the right hand side, which are the ratios (h/A) and (b/A). Given that the vibration parameters are known, then if the geometry-based values are known it is possible to find the current. If the current is known, then it is possible to find the geometry values, that is to say it is possible to obtain an accurate location of the current carrying member. Reference is now made to Fig. 4, which is a graph showing an example of an ideal curve of epsilon as a function of time resulting from the above equation when setting (h/A) = 0.5 and (b/A) = 2. Fig. 5, set alongside, shows actual results obtained whilst testing a prototype embodiment of a dynamic ammeter according to the present invention.

Examples of operation:

Three fundamental and one hybrid mode of use for a dynamic ammeter according to the present embodiments are presented here. The list is merely exemplary and modes of use for a variety of tasks will be apparent to the skilled person.

A current & location ammeter probe.

In the default case no information is known about the location of the wire being measured or of the current it is carrying. That is to say, all three free parameters of the curve of Fig. 4, namely current, and two location parameters are unknown and need to be found. The probe is placed in the electrical field of the wire and the graph of Fig. 5 obtained. The parameters may be extracted from the curve using a "best fit" procedure. Such a "best fit" can be achieved by minimizing the sum of the differences squared, or more crudely, by measuring key features of the curve such as height, width, slope, etc.

In general, for three non-degenerate parameters, one may use an off-the-shelf algorithm. One preferred algorithm for such tasks is the "Downhill Simplex Method" or the "Downhill Simplex Method with Simulated Annealing". Another preferred algorithm is "Powell's Method", which is considered more powerful, but is also more complex. All of these algorithms are described in chapter 10 of "Numerical Recipes in C++" by W.H. Press et al. the contents of which are hereby incorporated by reference and are well known in the field. In any given case, the algorithm that works best with depends principally on two factors, one being the speed or computational limitation of the DSP selected and the other being the amount of noise in the measurements. Using the values of the three parameters one can calculate the amount of current in the wire as well as the vertical and horizontal offset of the wire compared to the mid position of the vibrating coil. In the current and location approach it is assumed that the amplitude of vibration (A), the frequency of the vibrations (f), the effective permeability (μ) and the flux ratio (k) are all fixed. For this reason, it may be necessary to manually recalibrate the device from time to time to preserve accuracy.

A current-calibrated ammeter probe.

Reference is now made to Fig. 6, which is a simplified flow chart showing use of the ammeter according to a current-calibrated mode. The mode shown in Fig. 6 uses calibration rather than the curve fitting or like procedures as described above, in order to give a more precise result. The mode requires more work from the user than the location and current mode above, and requires access to the current carrying member itself, typically a wire. The mode only finds the amount of current in the wire and does not determine the position, but it achieves a far more accurate value for the current. The calibrated mode of the embodiment of Fig. 6 does not assume anything about any of the parameters and does not attempt any kind of fitting. Instead, in a first stage S50, the user is asked to turn off, or deactivate, the circuit to be probed. In a stage S52 the user electrically accesses the circuit wires, preferably over a short section including the area of interest but as little as possible beyond that. In a stage S54 the user passes a known calibration current through the selected wire. That is to say a short section of the wire is accessed and a current passed therethrough. Next, in a stage S56, the induction in the coil as a result of the calibration current is measured. Then, the user turns off the calibration current and in a stage S58, reactivates the circuit, without making any changes to the position of the measuring device. In a stage S60 the induction due to the actual circuit current is measured. In stage S62 the ratio between the voltages in the two phases is read and used, together with the known calibration current, to infer the actual current in the second phase, as follows:

Provided that all the factors in the equation apart from the current remain unaltered, then it is not necessary to obtain absolute values for these factors, and they may remain unknown. Rather the value measured by the Dynamic Ammeter is exactly proportional to the current in the wire, and thus the ratio between the values measured equals the ration between the currents in the two phases. Thus, for example, if we measure a value of lOOμV in the calibration phase with a calibration current of 100mA, then in the second phase, if we measure 35μV then it may be inferred that there was 35mA of current in the wire.

Besides the operational complexity, an additional drawback with the calibration mode is that stage S52 thereof involves making electrical contact with the circuit being measured during the current calibration phase. This drawback is usually not serious since contact need only be made once, whilst the circuit is disconnected.

After calibration any number of measurements can be made, so long as the circuit and the measuring device are not moved. In addition, there is no danger of causing damage to the circuit during the calibration phase, since all that calibration involves is to insert a very small voltage potential across a conductive wire. Assuming that the wire has negligible resistance, the laws of electricity guarantee that almost none of the current will pass through any other part of the circuit.

Lastly, even if the wire is entirely sealed in, with no points of contact at its ends, one can still access it using small pins inserted into the wall or the like in which the wire is embedded. Pin insertion may cause a small amount of damage, but it is far less damaging that any conventional approach.

Mixed Location and calibration mode for embedded wires

It is appreciated that the calibration approach requires the positions of embedded wires to be known so that they can be accessed. It is possible to use the location and current approach to locate the embedded wire. The located wire is then accessed by penetrating the wall etc concealing the wire with contact pins or the like, and then the calibration approach may be used to provide an accurate measurement of current.

Magnetic field probe

Reference is now made to Fig. 7, which is a simplified diagram showing a mode of use of the present embodiments which allows for scanning in two or three dimensions of a magnetic field, so as to map the magnetic field. The mode may be used for analyzing magnetic fields due to permanent magnets or electromagnets, or even for providing field shape information for a current carrying member as before. That is to say the mode is equally applicable to any magnetic field since the properties of the magnetic fields they emit are the same. The probe is used to systematically scan points near the magnet, S70. Scanning may be manual but in a preferred embodiment is carried out using a robot arm making it easier to know the exact location of each measured point, and to ensure that the points are evenly distributed. The scan may be a two-dimensional scan about a wire or a two or three-dimensional scan about a magnet or shaped body of interest. During the scan, a recording is made of the measured values at the different points. Preferably the orientation of the vibration axis of the flux-sensitive unit is altered during the scanning of individual points. The measured values themselves provide an analysis of the magnetic field strength at the various points in the scan, and vibration axis reorientation provides directional information of the field being measured. A vector array of field direction and orientation for the selected points can then be constructed S72 and used to generate an image for display on a screen or for printing out, S74.

The conventional approach to measuring the strength of the magnetic fields is by utilizing the Hall effect. Though Hall effect devices are very accurate, they tend to be relatively large, giving poor resolution. Experimental analysis of magnetic fields is not an easy task and embodiments of the present invention may be cheaper and easier to use, particularly in conditions of space limitation. Thus it may be desired to study the magnetic field between two relatively closely packed components in order to find a source for suspected interference. A prior art Hall effect device may be too large to insert into the available space, or even if it can be inserted, it may not give the necessary resolution to be able to determine which component is the source of the measured field.

It is expected that during the life of this patent many relevant imaging devices and systems will be developed and the scope of the terms herein, particularly of the terms "camera" and "imaging system", is intended to include all such new technologies a priori.

Additional objects, advantages, and novel features of the present invention will become apparent to one ordinarily skilled in the art upon examination of the following examples, which are not intended to be limiting. Additionally, each of the various embodiments and aspects of the present invention as delineated hereinabove and as claimed in the claims section below finds experimental support in the following examples. It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination.

Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention.

Claims

WHAT IS CLAIMED IS:

1. Non-contact electromagnetic flux measuring apparatus comprising: a vibratable magnetic-flux sensitive unit, suitable for voltage induction in the presence of magnetic flux, for placing in non-contact proximity with a flux source and for vibrating at a predetermined rate, a voltage measurement unit connected to said vibratable magnetic-flux sensitive unit, for producing an output comprising measurements of voltages induced in said vibratable flux-sensitive unit, and a processing unit for using said measurements, together with data of said predetermined vibration rate, to deduce strength information of a field due to said flux source.

2. Apparatus according to claim 1, wherein said vibratable magnetic-flux sensitive unit comprises a coil.

3. Apparatus according to claim 2, wherein said vibratable magnetic- flux sensitive unit comprises a flux-concentrating core within said coil.

4. Apparatus according to claim 3, wherein said vibratable magnetic-flux sensitive unit further comprises a vibratable mounting.

5. Apparatus according to claim 4, wherein said vibratable mounting is controllable to permit setting of said predetermined rate.

6. Apparatus according to claim 1, wherein said voltage measurement unit is controllable such that said output comprises an average over a predetermined number of said measurements.

7. Apparatus according to claim 6, wherein said predetermined number is user determinable.

8. Apparatus according to claim 1, wherein said flux source is a current bearing member.

9. Apparatus according to claim 8, wherein said processing unit is arranged to deduce from said information of said field, information of a current within said current bearing member.

10. Apparatus according to claim 8, wherein said processing unit is operable to deduce said information of said current by analysis of a graph of detected voltage with respect to time.

11. Apparatus according to claim 10, wherein said processing unit is further operable to deduce by analysis of said graph, information of location of said current bearing member.

12. Apparatus according to claim 8, wherein said information of said current is deduced by comparison with a calibration current.

13. Apparatus according to claim 1 , wherein said flux source is a magnet.

14. Apparatus according to claim 13, wherein said magnetic flux sensitive unit is configured to scan a region about said magnet to provide distribution information of said field.

15. Apparatus according to claim 14, wherein said scan is a two- dimensional scan.

16. Apparatus according to claim 14, wherein said scan is a three- dimensional scan.

17. A method of determining electromagnetic field strength about a field source, comprising: vibrating a coil with a predetermined amplitude and a predetermined frequency at a location about said field source, measuring emf induced in said coil, deducing a field strength from said induced emf.

18. The method of claim 17, wherein said field source is a current bearing member, the method further comprising determining the current within said current bearing member from said induced emf.

19. The method of claim 18, wherein said deducing comprises analysis of said measured emf as a function of time.

20. The method of claim 18, wherein said deducing comprises comparing said measured emf with a previously measured emf of a calibration stage.

21. The method of claim 19, further comprising analyzing said measured emf to deduce location information of said current bearing member.

22. The method of claim 18, further comprising scanning said coil about said field source to generate distribution information of said field.

23. The method of claim 22, wherein said scanning is two-dimensional scanning.

24. The method of claim 22, wherein said scanning is three-dimensional scanning.