NZ619291B2 - Sensors - Google Patents
Sensors Download PDFInfo
- Publication number
- NZ619291B2 NZ619291B2 NZ619291A NZ61929112A NZ619291B2 NZ 619291 B2 NZ619291 B2 NZ 619291B2 NZ 619291 A NZ619291 A NZ 619291A NZ 61929112 A NZ61929112 A NZ 61929112A NZ 619291 B2 NZ619291 B2 NZ 619291B2
- Authority
- NZ
- New Zealand
- Prior art keywords
- component
- sensor
- coil
- coils
- separation
- Prior art date
Links
- 239000000758 substrate Substances 0.000 claims abstract description 25
- 239000000696 magnetic material Substances 0.000 claims abstract description 15
- 239000004020 conductor Substances 0.000 claims description 57
- 238000000926 separation method Methods 0.000 claims description 47
- 210000000887 Face Anatomy 0.000 claims description 24
- 229910000529 magnetic ferrite Inorganic materials 0.000 claims description 6
- 229910000859 α-Fe Inorganic materials 0.000 claims description 6
- 230000001419 dependent Effects 0.000 claims description 3
- 230000035945 sensitivity Effects 0.000 description 22
- 239000000463 material Substances 0.000 description 17
- 230000035699 permeability Effects 0.000 description 16
- 239000010410 layer Substances 0.000 description 14
- 230000000694 effects Effects 0.000 description 12
- 230000001965 increased Effects 0.000 description 9
- 238000004519 manufacturing process Methods 0.000 description 6
- 230000001788 irregular Effects 0.000 description 5
- 239000012141 concentrate Substances 0.000 description 4
- 230000000875 corresponding Effects 0.000 description 4
- 230000005611 electricity Effects 0.000 description 4
- 238000005259 measurement Methods 0.000 description 4
- 238000009413 insulation Methods 0.000 description 3
- PNEYBMLMFCGWSK-UHFFFAOYSA-N AI2O3 Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- 230000001808 coupling Effects 0.000 description 2
- 238000010168 coupling process Methods 0.000 description 2
- 238000005859 coupling reaction Methods 0.000 description 2
- 238000011065 in-situ storage Methods 0.000 description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 229910001369 Brass Inorganic materials 0.000 description 1
- 229910000976 Electrical steel Inorganic materials 0.000 description 1
- 229910000990 Ni alloy Inorganic materials 0.000 description 1
- 238000004026 adhesive bonding Methods 0.000 description 1
- 229910052790 beryllium Inorganic materials 0.000 description 1
- ATBAMAFKBVZNFJ-UHFFFAOYSA-N beryllium(0) Chemical compound [Be] ATBAMAFKBVZNFJ-UHFFFAOYSA-N 0.000 description 1
- 239000010951 brass Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 238000010292 electrical insulation Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000001939 inductive effect Effects 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 229920000515 polycarbonate Polymers 0.000 description 1
- 239000004417 polycarbonate Substances 0.000 description 1
- 238000007639 printing Methods 0.000 description 1
- 238000009420 retrofitting Methods 0.000 description 1
- 239000002356 single layer Substances 0.000 description 1
- 239000007779 soft material Substances 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/18—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using inductive devices, e.g. transformers
- G01R15/181—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using inductive devices, e.g. transformers using coils without a magnetic core, e.g. Rogowski coils
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/18—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using inductive devices, e.g. transformers
- G01R15/186—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using inductive devices, e.g. transformers using current transformers with a core consisting of two or more parts, e.g. clamp-on type
Abstract
Disclosed is a current sensor (200) with a sensing volume formed by a first component including plural coils (202). Each coil includes one or more turns printed on at least one planar surface of a respective substrate, and the planes of the coils are parallel to one another and are perpendicular to a longitudinal axis of the first component. A second component is included and has a soft magnetic material and having first and second planar faces that are at opposite ends of the first component and are arranged perpendicularly to and are intersected by the longitudinal axis of the first component. a longitudinal axis of the first component. A second component is included and has a soft magnetic material and having first and second planar faces that are at opposite ends of the first component and are arranged perpendicularly to and are intersected by the longitudinal axis of the first component.
Description
Sensors
Description
This invention relates to sensors.
Current sensors are well known. A current sensor can be used for measurement of
current in a conductor through which the current flowing is so high that the direct
application of measuring instruments is undesirable or impossible.
One well known form of current sensor is a Rogowski coil. These typically comprise a
toroid of wire wound around a non-magnetic core that encircles the conductor of
interest. A correctly formed Rogowski coil, with equally spaced windings and a regular
shape, is quite insensitive to external magnetic fields whilst being sensitive to magnetic
fields generated by the encircled conductor. However, it can be difficult to achieve
correctly formed Rogowski coils, especially if they are required to be configured such
that they can be retrofitted around a conductor of interest.
A number of sensors based on the Rogowski principle but absent of toroidal coils have
been proposed. US 5521572 discloses a sensor that is included within an electricity
meter and includes material to define two air gaps in which secondary coils are located.
US 6313727 discloses a sensor that is retrofittable onto a three phase system and
includes helical sensing coils with low coercivity bars. US 5617019 discloses a sensor
that is designed to fit a busbar and is not retrofittable. Most of the embodiments
incorporate shielding, to improve rejection of external fields. All three disclose
magnetic circuits with a sensing coil in an air gap between two soft magnetic
components.
Sentec Limited has produced a number of different sensors based on the principle of
the Rogowski sensor but using coils printed onto circuit boards, which simplifies
manufacture and improves accuracy of manufactured product. Examples include US
6414475 and . An example of an easily retrofittable sensor
incorporating coils printed onto circuit boards is .
Sensor design incorporates many considerations, including ease and cost of
manufacture, sensitivity to external fields, uniformity of sensitivity within a sensing
zone and physical dimensions. Some of the sensors with the best performance are too
large to be accommodated easily in some environments, an example of which is an
electricity substation in which conductors of interest are closely packed together within
a cabinet or other container.
The invention was made in this context.
It is an object of preferred embodiments of the present invention to address some of the
aforementioned disadvantages. An additional or alternative object is to at least provide
the public with a useful choice.
According to a first aspect of the invention there is provided a current sensor
comprising a sensing volume formed by:
a first component comprising plural coils, wherein:
each coil comprises one or more turns printed on at least one planar
surface of a respective substrate, and
the planes of the coils are parallel to one another and are perpendicular
to a longitudinal axis of the first component; and
a second component comprising soft magnetic material and having first and
second planar faces that are at opposite ends of the first component and are arranged
perpendicularly to and are intersected by the longitudinal axis of the first component.
The term ‘comprising’ as used in this specification means ‘consisting at least in part of’.
When interpreting each statement in this specification that includes the term
‘comprising’, features other than that or those prefaced by the term may also be
present. Related terms such as ‘comprise’ and ‘comprises’ are to be interpreted in the
same manner.
The second component may comprise only soft magnetic material or it may include
other components. In some embodiments, the second component comprises one or
more other components including coils. In the embodiments, the components
including coils are absent of magnetic material.
A separation between adjacent coils may be approximately the same for all coils of the
first component. The separation may be exactly the same. Separations may instead
vary, at a cost of reduced performance.
The coils of the first component may each include the same number of turns and have
the same area on the substrate. They may instead be different and indeed this may be
preferred if the regular coil separation cannot be achieved.
The second component may comprise a U-shaped soft magnetic component and the
first and second faces may be parallel faces within the mouth of the U. Here, the
second component may be separable from the first component so as to allow a
conductor to be introduced into the U before the second component is placed within
the mouth of the U of the second component. Alternatively or in addition, a separation
between adjacent coils may approximately the same for all coils of the first component
and a separation between a coil closest to the first end and the first contact face may be
substantially equal to a separation between a coil closest to the second end and the
second contact face and may be equal or approximately equal to half of the separation
between adjacent coils.
Although providing an optimal arrangement, irregular spacing may instead be
provided, in which case the effects of irregular spacing can be mitigated by varying the
turn area product on appropriate ones of the substrates.
The sensor may comprise means for causing the second component to be maintained
within the mouth of the U of the second component.
The second component may also include a third component comprising plural coils,
wherein: each coil of the third component comprises one or more turns printed on at
least one planar surface of a respective substrate, and the coils of the third component
are parallel to one another and lie on a longitudinal axis of the third component; and
wherein the second component comprises third and fourth planar faces that are
arranged perpendicularly to and are intersected by the longitudinal axis of the third
component.
Here, the second component may comprise first and second I-shaped components, the
first I-shaped component including the first and third faces and the second I-shaped
component including the second and fourth faces.
A separation between adjacent coils may be approximately the same for all coils of the
first and third components and wherein a separation between a coil closest to the first
end of the first component and the first face is the same as a separation between a coil
closest to the second end of the first component and the second face, which is the same
as a separation between a coil closest to the first end of the third component and the
third face and is the same as a separation between a coil closest to the second end of the
third component and the fourth face, and is approximately half the separation between
adjacent coils.
Although providing an optimal arrangement, irregular spacing may instead be
provided, in which case the effects of irregular spacing can be mitigated by varying the
turn area product on appropriate ones of the substrates.
The second component may comprise one or more further components each including
plural coils, wherein: each coil of each further component comprises one or more turns
printed on at least one planar surface of a respective substrate, and the coils of each
further component are parallel to one another and lie on a longitudinal axis of the
further component.
Adjacent substrates may be mechanically separated by spacers.
An end substrate in the first component may be separated from the first component by
a spacer.
The sensor may comprise a circuit board configured to connect the coils in a circuit.
The sensor may comprise one or more shielding components configured to at least
partially surround the first component and, if present, the third component.
The sensor may comprise a current-carrying conductor extending through a central
portion of the sensor.
The soft magnetic material may be a ferrite.
Each coil may comprise one or more turns printed on at least two parallel surfaces of a
respective substrate.
The first component may comprise first and second coils printed respectively on first
and second parallel surfaces of a first substrate. Here, the second component may also
include a third component comprising third and fourth coils printed on first and second
parallel surfaces of a second substrate respectively, wherein the coils of the third
component are parallel to one another and lie on a longitudinal axis of the third
component; and wherein the second component comprises third and fourth planar
faces that are arranged perpendicularly to and are intersected by the longitudinal axis
of the third component. The first and second substrates may be of the same thickness
and a separation the third coil and the fourth component may be the same as a
separation between the first coil and the second component.
The first and third components may be formed of a single multilayer printed circuit
board having formed therein a slot or cutaway configured to receive a conductor.
The sensor may contain an insulating and/or weatherproof housing.
Embodiments of the invention will now be described, by way of example, with reference
to the accompanying drawings in which:
Figure 1 is a perspective view of a first embodiment of a sensor according to the
invention;
Figure 2 are side and end views of the first embodied sensor;
Figure 3 is a perspective view of part of a coil stack forming part of the first embodied
sensor;
Figures 4a and 4b are views of different sides of a printed circuit board forming part of
the first embodied sensor;
Figure 5 is a perspective view of the first embodied sensor with a connecting printed
circuit board and shielding cans in place;
Figure 6 is a perspective view of a second embodiment of a sensor according to the
present invention in a closed position;
Figures 7a and 7b are side and end views of the second embodied sensor;
Figure 8 is a perspective view of the second embodied sensor in an open position;
Figure 9 is a side view of a sensor according to a third embodiment of the invention;
Figure 10 is a side view of a sensor according to a fourth embodiment of the invention;
Figure 11 is a side view of a sensor according to a fifth embodiment of the invention;
Figures 12a, 12b and 12c show a double-sided printed circuit board that provides a coil
stack that is used in some embodiments of the invention;
Figure 13 is a perspective view of a sensor according to a sixth embodiment; and
Figures 14a to 14d represent different aspects of a sensor according to a seventh
embodiment of the invention.
A sensor 10 according to a first embodiment of the invention will now be described with
reference to Figures 1 to 5.
As can best be seen in Figure 1, a sensor 10 includes first and second components 11, 12,
each including plural coils, and third and fourth components 13, 14, each comprising
soft magnetic material. The first and second components 11, 12 will hereafter be
termed coil stacks. The third and fourth components 13, 14, will hereafter be referred
to as soft magnetic bars or just magnetic bars. The magnetic bars are formed of a
material with low coercivity. Iron is a suitable material, although other materials also
are suitable. The material may be a ferrite. The material may be for instance an alloy of
Nickel. The material may for instance be laminated electrical steel. Here, the laminates
preferably lie in the plane perpendicular to the axis of the conductor that is the subject
of measurement, e.g. the plane of Figure 2b.
Each of the coil stacks 11, 12 includes a number of circuit boards 15, each of which has
printed thereon a number of coils, and a number of spacers 16 in between the circuit
boards.
As can be seen best from Figures 2a and 2b, the first coil stack 11 includes first to sixth
circuit boards 27 to 32 and first to seventh spacers 20 to 26. The second spacer 21 is
located between the first and second circuit boards 27, 28, and so on. The first spacer
is located at the uppermost end of the first coil stack 11 and its lowermost face abuts
the uppermost surface of the first circuit board 27. The sixth spacer 26 is located at the
lowermost end of the coil stack 11 and it’s uppermost face abuts the lowermost face of
the circuit board 32. An end or lowermost face 31 of the sixth spacer 26 is parallel to an
end or uppermost face 43 of the first spacer 20 and is perpendicular to a longitudinal
axis of the first coil stack 11.
In this embodiment, the circuit boards 27 to 32 are relatively thin and the spacers 20 to
26 are relatively thick compared to the circuit boards. Each of the circuit boards 27 to
32 is substantially rectangular in shape. Each is the same size as all of the other circuit
boards of the first coil stack 11. Each of the spacers 20 to 26 also is rectangular. The
spacers 20 to 26 are the same as one another except that the first and sixth spacers 20,
26 are thinner than the second to fifth spacers 21 to 25, as is described in more detail
below. The dimensions of the spacers 20 to 26 apart from the thicknesses of the
spacers are approximately the same as the dimensions of the circuit boards 27 to 32.
Moreover, the spacers 20 to 26 and the circuit boards 27 to 32 are coupled to one
another, for instance by gluing. Coupling is provided whilst the spacer is 20 to 26 and
the circuit boards 27 to 32 are in alignment, so the overall shape of the first coil stack 11
is of a rectangular cuboid. Because the second to fifth spacers 21 to 25 each have the
same thickness, the separation between adjacent ones of the first to fifth circuit boards
27 to 32 is the same.
The key function of the spacers 20 to 26 is to maintain the printed circuit boards 27 to
32 at the desired separation and as such the spacers may instead take some other form
without compromising the sensor 10.
Figure 3 is an alternative view of the first coil stack 11. Here, the first spacer 20 is
omitted from the Figure, allowing the uppermost surface of the first circuit board 27 to
be visible.
As can be seen most clearly in Figure 3, each of the circuit boards 27 to 32 is provided
with a number of tabs at three of its edges. In particular, on the edge that is externally
facing (leftwards in Figure 2b), first and second tabs 80 and 81 are provided
approximately one quarter and three quarters of the distance along the edge of the
circuit board. Tabs 85, 86 are provided at corresponding locations on the opposite side
of each circuit board 27 to 32. On the edge of the circuit boards 27 to 32 that are viewed
face on in Figure 2b, are three tabs, referenced as 82, 83 and 84. The tab 83 is formed
approximately centrally along the edge of the circuit board and the tabs 82 and 84 are
located on either side. Between the central tab 83 and each of the tabs 82 and 84 are
formed recesses.
The purpose of the tabs 82 to 86 is described in more detail below.
Referring again to Figures 1 and 2, it will be seen that the second coil stack 12 is
identical in form to the first coil stack 11. The second coil stack 12 includes first to sixth
circuit boards 57 to 62 and first to seventh spacers 50 to 56, corresponding to the
circuit boards 27 to 32 in the spacers 20 to 26 of the first stack 11 respectively.
At the lowermost end of the second coil stack 12 is a face 71 that is parallel to a face 73
at the uppermost end of the second coil stack 12. Both faces are perpendicular to a
longitudinal axis of the second coil stack 12
The first and second coil stacks 11, 12 are aligned so that the uppermost faces 43, 73 of
the first and second coil stack respectively are formed in a common plane. Similarly,
the lowermost faces, 41, 71 of the first and second coil stacks 11, 12 respectively are also
in a common plane.
The first and second magnetic bars 13, 14 each generally have the form of a rectangular
cuboid. However, each of the soft magnetic bars 13, 14 is bevelled along two edges
thereof.
On one face of the first soft magnetic bar 13, which is facing downwards in Figure 2, is a
face 42 that abuts the uppermost end face of 43 the first coil stack 11. It also includes a
face 72 that abuts the uppermost end face 73 of the second coil stack 12.
Similarly, the second soft magnetic bar 14 has on the face that is facing uppermost in
Figure 2 a face 40 that abuts the lowermost end face 41 of the first coil stack and a face
70 that abuts the lowermost face 71 of the second coil stack 12.
The cuboid shape of each bar 13, 14 has three dimensions. A height dimension extends
in the same direction as the longitudinal axes of the coil stacks 11, 12. Ends of the
length dimension of the magnetic bars 13, 14 are substantially aligned with the cross
section of the coil stacks 11, 12. The width dimension of the magnetic bars 13, 14 is
generally the same as the corresponding dimension of the coil stacks 11, 12. As such,
the soft magnetic bars 13, 14 and the coil stacks 11, 12 together provide a generally
rectangular annulus.
The bevelling of the first and second soft magnetic bars 13, 14 is provided at the ends of
the bars but on the opposite side to the face of the bar that contacts the first and second
coil stacks 11, 12. This provides some rounding-off of the rectangular annulus shape
without reducing the maximum current before saturation of the magnetic bars 13, 14.
Because the spacers 20 to 26 of the first coil stack 11 are of uniform thickness, the
circuit boards 27 to 32 lie on a common straight axis. Moreover, because the first and
second spacers 20 to 26 are of uniform thickness, the lengthwise axes and the faces 42,
72 of the magnetic bars 13, 14 are formed at right angles to the longitudinal axis of the
first coil stack 11 and parallel to the planes of the circuit boards 27 to 32.
The same applies to the second coil stack 12 and the second magnetic bar 14, by virtue
of the arrangements of the spacers 50 to 56 and the resulting arrangement of the circuit
boards 57 to 62.
The first magnetic bar 13 is operable to concentrate magnetic field present at the
uppermost end of the first coil stack 11 and to link it directly to the uppermost face 73 of
the second coil stack 12. Similarly, the second soft magnetic bar 14 concentrates on
magnetic fields between the lowermost end 41 of the first coil stack 11 and lowermost
end 71 of the second coil stack 12.
Because the faces 40, 42, 70 72 of the first and second soft magnetic bars 13, 14 are
perpendicular to the longitudinal axes of the first and second coil stacks 11, 12, and the
end gaps are half the intermediate gaps, (or equal in the case of a single, double-sided
board) the sensor 10 can be considered to be equivalent to an infinite solenoid. This is
discussed in more detail below.
Each printed circuit board 27 to 32 has formed thereon a coil having plural turns.
Figure 4 illustrates surface patternisation on the printed circuit boards 27 to 32 and 57
to 62. On one surface thereof, the pattern shown in Figure 4a is provided. It will be
seen that this comprises plural turns 87 of a coil 88 between innermost and outermost
ends. On the other side of the printed circuit board 27 to 32 and 57 to 62, shown in
Figure 4b, plural turns 87 of the coil 88 extend between innermost and outermost ends.
Although the direction of the coil 88 appears to be different sides to the printed circuit
board, because Figures 4a and 4b in different views, the turns are actually in the same
direction. Thus, the turns on each side of the printed circuit board are constructive
with one another.
A via through the printed circuit board 27 to 32 and 57 to 62 connects the innermost
end of the patternisation on each side. As such, a single coil 88 is formed between the
outermost end on one side of the printed circuit board 27 to 32 and 57 to 62 and the
uppermost end of the other side of the printed circuit board. The number of turns of
the coil 88 is equal to the sum of the number of turns on each side of the printed circuit
board 27 to 32 and 57 to 62.
In this example, the turns 87 are generally rectangular in shape. This allows the turns
87 to have a large diameter having regard to the size of the printed circuit board 27 to
The printed circuit boards 27 to 32 and 57 to 62 may be made of FR4, for instance.
The coils of the two coil stacks 11, 12 are connected in opposite directions, i.e. clockwise
in one and anti-clockwise in the other direction when viewed from above. As such, they
are connected in the same direction in the sense of a circuit comprising the coils and
the magnetic bars 1, 14.
The coils of the printed circuit board 27 to 32 to 57 to 62 are connected together in
series by a circuit provided on a further circuit board 90, which is best seen in Figure 5.
The circuit board 90 is a thin, flexible board.
Also shown in Figure 5 are first to fourth shielding cans 91 to 94. These comprise
perforated metallic plates. Each shielding can 91 to 94 includes slots that are
configured to receive the tabs 80, 81, 85 and 86 provided on the printed circuit boards
27 to 32 and 57 to 62. The slots in the shielding cans 91 to 94 engage with the tabs 80,
81, 85 and 86 and result in the shielding cans 91 to 94 being secured to the coil stacks
11, 12.
The shielding cans 91 to 94 each shield the whole of one major face of one of the coil
stacks 11, 12. Front and back faces of the coil stacks 11, 12 are not shielded in this
embodiment.
An effect of the shielding cans 91 to 94 is to remove electrostatic coupling both from
within and from without the sensing volume. If relatively thick conductive material,
e.g. 0.3 mm beryllium, copper or brass, is used for the shielding case 91 to 94, it is
useful not to complete a shorted turn about the coil stacks 11, 12 if accurate harmonic
response (e.g. to 5 kHz and beyond) is desired.
Part of the reason for the sensor 10 being equivalent to an infinite solenoid is the choice
of spacer thickness. In particular, the thickness of the first spacer 20 of the first coil
stack 11 and the thickness of the first spacer 50 of the second coil stack 12 are chosen
such that the sum of the thicknesses is equal to the thickness of the second to fifth
spacers 21 to 25 and 51 to 55 of the first and second coil stacks 11, 12. The presence of
the first magnetic bar 13 connecting the end face 43 of the first spacer 20 of the first coil
stack 11 to the face 73 of the first spacer 50 of the second coil stack 12 has the effect
that, magnetically, the distance between the first printed circuit board 27 of the first
coil stack 11 and the first printed circuit board 57 of the second coil stack 12 is equal to
the separation between adjacent printed circuit boards in either of the first and second
coil stacks. As such, the second coil stack 12 appears, magnetically, as an extension of
the first coil stack 11.
Because the sixth spacer 26 of the first coil stack 11 and the sixth spacer 56 of the
second coil stack 12 are the same thickness and the thickness of each is equal to half of
the thickness of the second to fifth spacers 21 to 25 and 51 to 55 of the first and second
coil stacks 11, 12 and because the second magnetic bar 14 directly connects the end face
41 of the sixth spacer 26 of the first coil stack to the end face 71 of the sixth spacer 56 of
the second coil stack 12, the same effect is experienced at the lowermost ends of the
first and second coil stacks 11, 12. As such, the first coil stack 11 can be considered to be
a continuation of the second coil stack 12 also at the other end. This contributes to the
infinite solenoid effect.
In the above-described embodiments, each of the printed circuit boards 27 to 32 and 57
to 62 is substantially identical. As such, each of the printed circuit boards has the same
number of coil turns and the same average turn radius. Also, the separation between
adjacent printed circuit boards is the same for all of the circuit boards, which is the
same as the effective separation between printed circuit boards that a separated by one
of the first and second magnetic bars, 13, 14. This highly symmetrical arrangement has
a number of advantages. One advantage is ease of manufacture. In particular, only one
circuit board design is required and only two spacer designs are required. Another
advantage is sensitivity, in that this highly regular arrangement has a uniform
sensitivity to magnetic fields originating from within the volume defined by the sensor
whilst providing good rejection of externally applied magnetic fields. However,
alternative arrangements will be envisaged by the skilled person. Many alternatives
have almost as good performance, although may be of greater complexity and thus
more expensive to manufacture.
The spacers 20 to 26 and 50 to 56 are made of a non magnetic material. For instance,
the spacers 20 to 26 and 50 to 56 are made of a polycarbonate. The printed circuit
boards 27 to 32 and 57 to 62 also are made of non-magnetic materials. The shielding
cans 91 to 96 are also made of non magnetic materials. As such, the coil stacks 11, 12 are
absent of magnetic material. The coil stacks 11, 12 constitute air gaps between the soft
magnetic bars.
Dimensions of components of a prototype of the sensor 10 constructed by the inventors
will now be provided for the purposes of illustration. In the prototype, the printed
circuit boards are 0.4 mm thick, 10 mm wide and 25 mm long. The thickness of the
second to fifth spacers is 3.95 mm, giving a separation between the centres of adjacent
printed circuit boards (taking into account board thickness) of 4.35 mm. The overall
length of each coil stack 11, 12, which defines the separation between the innermost
surfaces of the soft magnetic bars, is 26 mm. The soft magnetic bars 13, 14 have
dimensions of 27 mm deep by 60 mm long and 9 mm high. When the coil stacks 11, 12
are in place, the separation between their longitudinal axes is 48 mm. Each printed
circuit board is provided with 13 coil turns on each side. Considering that there are six
double-sided printed circuit boards in each coil stack 11, 12, each coil stack has 156
turns, so there are 312 turns in total. The average area of each turn is 1.2 square
centimetres (clearly different turns on a given side of a printed circuit board have
different areas). The initial relative permeability of the soft magnetic bars is
approximately 2000. Medium power ferrite with saturation at ~0.4 Tesla gives a
current handling capability of approaching 1000 Arms for the sensor 10.
The sensor 10 is operable as a Rogowski-type sensor. The sensor 10 is able to be used
to measure currents flowing through a conductor that passes into the volume between
the first and second coil stacks 11, 12 and the first and second magnetic bars 13, 14,
which is hereafter referred to as the sensing volume.
Sensitivity of the sensor within the sensing volume is determined by the area turns
product per metre length of the coil stacks 11, 12. This is a generally applicable
statement and does not apply only to the sensor 10
In the prototype sensor 10 referred-to above, the theoretical sensitivity is calculated as
follows. The mutual inductance between the measured current and the sense coil is
calculated as 6 (printed circuit boards in the coil stack) * 26 (turns per printed circuit
board) * (0.00012 (average area of the turns)/0.026 (coil stack length)) * U0
(permeability of vacuum, 4pi10^-7, or ~1.25e-6) is 0.9 µH. This represents 0.9 micro
volt seconds per amp. Multiplying this by the angular frequency to get provides
sensitivity in Volts/amp. For 50 Hz (mains frequency in many countries), the
sensitivity is 0.28mV/A.
However, actual sensitivity is reduced by two small factors, namely the finite
permeability of the soft magnetic bars and due to the finite overlap of the soft magnetic
bars beyond the coil stacks. It is envisaged by the inventors that sensitivity due to the
finite permeability of the magnetic bars is reduced by between 0.1 % and 1% and
reduction in sensitivity due to the finite overlap of the magnetic bars beyond the coil
stacks (assuming gaps formed by spacers at the end of the stacks) is between 0.05% and
0.5%. For example, in the sensor 10 as described, the finite permeability of the bars
reduces the sensitivity by ~0.4%. As such, if the permeability doubles (e.g. due to
increasing current and/or increasing temperature), the gain of the sensor will increase
by 0.2%.
The limited projection of the flat surface of the soft magnetic bars 13, 14 beyond the
outline of the coils gives a gain reduction of ~0.1%.
The gain reduction due to permeability can be altered by using a different permeability
material for the soft magnetic bars 13, 14 and/or choosing a different thickness for the
soft magnetic bars. For instance, the gain reduction due to permeability (0.4%) can be
reduced by a factor of 5 to ~0.08% by increasing the ferrite permeability to 10,000 (e.g.
by using Ferroxcube 3E6 material). The gain reduction can be halved again to 0.04%
by doubling the thickness of the soft magnetic bars 13, 14 to ~16 mm.
The reduction in gain due to the limited projection of the soft magnetic bars 13, 14 can
be reduced if desired by increasing the length and/or width of the magnetic bars. The
reduction in gain can be reduced by a significant amount by increasing the length and
width of the magnetic bars 13, 14 as described above by a few millimetres, although this
is at the expense of increased overall size.
Generally, the sensor 10 is insensitive to uniform field (fields generated distant from
the sensing volume are uniform at the sensor) provided that the sensor 10 is
symmetrically built. Sensitivity to gradient field is limited by the limited permeability
of the soft magnetic bars. For a given permeability, the shorter and thicker they are the
better. Typical sensitivity of the sensor 10 to an external current carrying conductor
immediately adjacent the exterior of the sensor is about ~1/500 compared to the
conductor in the sensing volume. The sensitivity to such externally generated fields can
be improved by approximately ten times by providing the magnetic bars with a
permeability of 10000 and increasing the thickness of the magnetic bars to
approximately 16mm high. If ferrite is used as the soft material, increasing
permeability tends to be balanced with lower maximum values of magnetic induction
before saturation; the extra thickness of the magnetic bars 13, 14 provides extra
capability whilst maintaining good current handling capability.
As mentioned above, sensitivity is given by turn area product per unit length. As such,
the sensitivity can be increased by providing coils with greater areas, by providing more
turns on the coils, by providing more layers of coils in each board, and/or by reducing
the separation between adjacent printed circuit boards. Reducing the separation
between adjacent boards requires smaller first spacers 20, 50, which can provide
limitations when the sensor is provided in an openable housing, as is discussed below
with reference to Figure 2.
In the above description, each printed circuit board 27 to 32 and 57 to 62 is described
as comprising one coil with turns on both sides of the board. Alternatively, the printed
circuit boards 27 to 32 and 57 to 62 can be considered to comprise two coils, one on
each side of the board. Here, each coil has 13 turns, although of course the total
number of turns in the coil stack 11, 12 is unchanged.
In this case, the distance between the two coils on the board is equal to the thickness of
the printed circuit board 27 to 32 and 57 to 62. Also, the distance from a coil to the
next coil in the stack is equal to the thickness of the spacer that separates the adjacent
printed circuit board. In this case, the coils in each coil stack 11, 12 are not equally
spaced. Instead, the separation between coils alternates between the thickness of the
spacer and the thickness of the printed circuit board along the length of the printed
circuit board.
To allow the sensor 10 to be used to measure current flowing in a conductor, the
conductor is passed in a direction through the plane of the page in Figure 2b, or from
left to right, or vice versa, in Figure 2a. It will be appreciated that current flowing
through such a conductor results in magnetic field lines forming concentric circles
around the conductor, which lines of magnetic field therefore extend along the axis of
each of the first and second coil stacks 11, 12. The magnetic bars 13, 14 serve to
concentrate the magnetic field such as to focus the field through the first and second
coil stacks 11, 12. It will be understood that Rogowski-type sensors conventionally do
not include magnetic material.
There are a number of different options for providing the sensor 10 around a
conductor. In a first option, the sensor 10 remains complete and the conductor is
inserted into the hole formed by the first and second coil stacks 11, 12 and first and
second magnetic bars 13, 14. With this method, however, the sensor 10 is not able to be
retrofitted to a conductor that is in situ.
In a second option, once the magnetic bars 13, 14, for instance the first magnetic bar,
13, is separated from the ends 43, 73 of the first and second coil stacks 11, 12. Once the
first magnetic bar 13 has been removed, the conductor can be inserted into the centre of
the U shape formed by the first and second coil stacks 11, 12 and the second magnetic
bar 14. The first magnetic bar 13 may then be reconnected to the faces 43, 73 of the first
and second coil stacks 11, 12, and secured in place. The result of this is that the
conductor is contained by the form main components 11 to 14 of the sensor 10, i.e.
extends through the sensing volume.
Alternatively, the sensor 10 may be provided in a housing that is constructed so as to
allow the sensor 10 to be retrofitted to a conductor that is located in situ. A second
embodiment of a sensor 10, which can be retrofitted particularly easily, is shown in
Figures 6, 7 and 8, which will now be described. The sensor 10 includes all of the
components of the first embodied sensor 10 except the first spacers 20, 50. The above
description of the first embodied sensor should be considered to be present in this
description of the second embodied sensor but is omitted here for conciseness and
clarity.
The sensor 10 in this second embodiment comprises two main parts. A U-shaped part
100 is provided with a gate 101. In the U-shaped part 100, as shown in Figures 1 to 5,
the circuit board 90 shown in Figure 5 may also be present. Alternatively, some other
means for connecting the turns of the coils on the circuit boards may be provided. The
U-shaped part 100 may also include the shielding components 91 to 94 that are shown
in Figure 5.
The gate 101 is hinged at one end to one end of the U-shaped part 100. The other end
of the gate 101 abuts the other end of the U-shaped part 100 but is not permanently
secured thereto. The hinge connection between the U-shaped part 100 and the gate 101
allows the gate to be opened such as to allow a conductor to be inserted into the sensing
volume, which is defined by the U-shaped part 100. Once the conductor is in place, the
gate 101 may again be closed such that it abuts each to the two ends of the U-shaped
part 100. The gate 101 includes the first magnetic bar 13, thereby acting as a magnetic
field concentrator between the uppermost ends of the first and second coil stacks 11, 12.
The gate 101 and the U-shaped part 100 are configured so as to allow the sensor 10 to
be semi-permanently fixed in the closed position. This may be achieved using a
resilient clip, for instance. This allows the gate to be opened by a user when needed but
causes the gate to remain closed otherwise, even if knocked or subjected to vibration.
It is shown in Figure 8 that the hinge is such that the gate 101 pivots in the plane of the
first magnetic bar 13. However, the gate 101 may instead pivot in some other way, for
instance around an axis that extends perpendicular, rather than parallel to, an axis of
the first and second coil stacks 11, 12.
In the embodiment shown in Figures 6 to 8, a gap between the first printed circuit
boards 27, 57 of the first and second coil stacks 11, 12 and the magnetic bar 13 is
provided by the thickness of the material of the U-shaped part 100 at the uppermost
ends of the first and second coil stacks 11, 12 and the thickness of the material of the
gate 101, that houses the first magnetic bar 13. The gate 101 and the U-shaped part 100
are configured such that the separation between the first printed circuit board 27 of the
first coil stack 11 and the magnetic bar 17 and the separation between the first printed
circuit board 57 of the second coil stack and bar 13 is equal, or approximately equal, to
half the separation between adjacent printed circuit boards in the first coil stack 11.
This may be achieved, for instance, by selecting the thickness of the material forming
the parts of the U-shaped part and the gate 101 that lie between the magnetic bar and
the ends of the coil stacks 11, 12 to correspond to the thicknesses of the spacers 20, 50
of Figures 1 to 5 and configuring the U-shaped part 100 and the gate 101 such that the
two components are abutting when the sensor 10 is in the closed position shown in
Figure 6.
As mentioned above, the sensor 10 provides the equivalent of an infinite solenoid.
Alternative arrangements also can provide the same affect, and some such alternatives
will now be described with reference to Figures 9, 10 and 11.
Referring firstly to Figure 9, a third embodiment of a sensor 200 is shown. Here the
sensor 200 comprises a U-shaped soft magnetic component 201 and a single coil stack
202. The coil stack 202 is very similar to the first and second coil stacks 11, 12 of the
Figures 1 to 5 embodiments, and the above description of those coil stacks should be
considered to be part of this description of the third embodiment, although is omitted
here for clarity and conciseness. Very briefly, the coil stack 202 has a number of
printed circuit boards 209 which are separated by spacers 205 to 208. The coil stack
202 is provided at its end with spacers 203 and 204 which are approximately half the
thickness of the spacers 205 to 208 that are located between the printed circuit boards
209. The spacers 203 to 208 and the printed circuit boards 209 are aligned such that
the first coil stack 202 has a generally rectangular cuboid shape. An uppermost end
face 213 of the first spacer 203 is parallel to an end face 212 of the lowermost spacer
204.
An inside face 210 of one end of the U-shaped soft magnetic component 201 abuts the
uppermost end face 213 of the coil stack 202. The inside face 211 of the other end of the
U shape component 201 abuts the end face 212 at the bottom end of the coil stack 202.
As such, the faces 210 and 211 of the soft magnetic component 201 are parallel to one
another and are perpendicular to the longitudinal axis of the coil stack 202. Although
not shown, the sensor 200 is three dimensional in that it extends into the direction of
the page of the Figure.
As with the first embodiment, the soft magnetic component 201 serves to concentrate
magnetic fields such as to cause one end of the coil stack 202 to link directly,
magnetically, to the other end of the coil stack. Thus, the infinite solenoid effect is
again provided.
A conductor (not shown) extending into the sensing volume defined by the U-shaped
soft magnetic component 201 and the coil stack 202 is the subject of the sensor 200. A
current flowing through the conductor generates a magnetic field around the
conductor, which magnetic field extends generally longitudinally along the coil stack
202 and is concentrated through the U-shaped soft magnetic component 201. A
changing current flowing in the conductor thus generates a corresponding emf in the
coils of the coil stack 202, which can be used to measure the current flowing through
the conductor.
To fit the sensor 200 to a conductor, either the conductor needs to be inserted into the
volume between the U-shaped soft magnetic component 201 and the coil stack 202 or
the coil stack 202 needs to be removed before the U-shaped component 201 is placed
over the conductor and the coil stack 202 then reintroduced into the volume between
the ends of the U-shaped soft magnetic component 201. These two methods assume
that the U-shaped component 201 is a unitary piece that is relatively rigid.
Alternatively, the U-shaped soft magnetic component 201 may not be rigid and may in
some way allow the introduction of a conductor into the sensing volume. A housing
(not shown) may be provided to facilitate this.
A fourth embodiment will now be described with reference to Figure 10. Here, first to
fourth coil stacks 301 to 304 are arranged in a rectangle, in particular a square. Each of
the coil stacks is as described above in relation to the first or third embodiments. As
such, each of the coil stacks 301 to 304 has ends that are generally parallel to one
another. First to fourth soft magnetic parts 305 to 308 are provided. The soft magnetic
parts 305 to 308 each connect the ends of two adjacent coil stacks. Faces of the soft
magnetic parts 305 to 308 that contact an end of a coil stack 301 to 304 are flat and are
arranged generally perpendicular to the longitudinal axis of the respective coil stack.
As such, each soft magnetic component 305 to 308 includes two faces that are generally
perpendicular to one another so as to result in adjacent coil stacks 301 to 304 being
supported at a 90˚ angle to each another.
In Figure 10, the soft magnetic components 305 to 308 are shown as having generally
triangular cross sections. However, alternative shapes are conceived. For instance, the
soft magnetic parts 305 to 308 may have a square cross section or they may have a
cross section of a quarter of a circle. A main requirement is that faces of the soft
magnetic components 305 to 308 are flat and extend perpendicular to the relevant axis
of the coil stacks 301 to 304. Although not shown, the sensor 300 is three dimensional
in that it extends into the direction of the page of the Figure.
The fourth embodied sensor 300 also provides the effect of an infinite solenoid. The
sensor is capable of allowing measurement of a current flowing through a conductor
provides in the sensing volume that is defined between the coil stacks 301 to 304.
The above-described sensors 10, 200, 300 provide sensing volumes that are generally
rectangular in cross-section. The sensors 10, 200, 300 can be used to measure currents
flowing in any conductor that can be accommodated in the sensing volumes.
In some embodiments, the sensors 10, 200, 300 are installed around conductors of
electricity substations, particularly low-voltage or distribution substations. Here, the
conductors at the inputs of the substation tend to be circular or a circular segment in
cross-section and have a diameter, including the insulation sheath, of tens of
millimetres. Using a sensor 10, 200, 300 having a minimum internal dimension only
slightly larger than the external diameter of the conductor, the overall size of the sensor
installed onto the conductor can be relatively small. The sensors 10, 200, 300 thus can
be installed even where plural conductors are relatively tightly packed, as is
increasingly common in modern substations. Moreover, this is achieved even though
the sensors provide relatively good performance in terms of accuracy and sensitivity. A
contributory factor in the compactness of the sensors is the provision of the longest side
of the printed circuit boards in the direction along the axis of the sensing volume. This
allows the shortest side to be radial to the axis of the sensing volume, thereby
minimising the additional diameter added to the conductor when the sensor is installed
thereon.
When the sensor is provided within an openable housing, such as is shown in Figures 6,
7 and 8, a separation between a printed circuit board at the end of a coil stack that is
included in the main body 100 and the magnetic bar 13, 14 that is included in the gate
101 of the housing is dependent on mechanical features that provide insulation and/or
weatherproofing to the housing. In general, greater sensitivity is provided by a greater
number of turns per unit length of the coil stack. The minimum separation that can be
achieved between the end printed circuit board and the magnetic bar 13, 14 also defines
the separation between adjacent boards in the coil stack. For a given length coil stack,
this defines the number of boards that are present in the stack.
A sensor 400 constructed according to a fifth embodiment is shown in Figure 11.
The sensor is similar to the third embodied sensor 200 in that it includes a U-shaped
soft magnetic component 402 and a coil stack. The coil stack includes three printed
circuit boards 403 to 405. The printed circuit boards 403 to 405 are regularly spaced.
Other features from the first and second embodiments are included in the sensor 400
but are omitted from the Figure and this description for clarity and conciseness.
Also shown in Figure 11 is a conductor 401, in the form of a busbar. The busbar 401
extends through the sensing volume that is defined between the three sides of the U-
shaped soft magnetic component 402 and the coil stack. It will be seen also that there
is relatively little separation between the busbar 401 and the nearest surfaces of the
sensor 400. This allows the overall volume of the sensor to be relatively small, and
indeed smaller than many prior art sensors used for similar purposes. The sensor 400
certainly is smaller than prior art sensors that may have similar ease of manufacture
and/or similar performance.
The sensor 400 may be provided with a housing (not shown) with which to insulate the
sensor 400 from the busbar 401. However, if the materials of the relevant parts of the
sensor 400 are chosen carefully, the parts of the sensor 400 that can contact the busbar
401 may be sufficiently electrically insulating that no additional housing or other
insulation is required. Additionally, if the relative positions of the sensor 400 and the
busbar 401 can be correctly maintained, as for instance can be provided in
embodiments in which the sensor 400 in incorporated in a switchboard, electricity
substation, distribution board or meter, no precautions need be made to provide
electrical insulation between the sensor and the busbar 401.
In other embodiments, the coil stacks 11, 12 can also be made as a single part using
multilayer printed circuit board technology. The multilayer printed circuit board may
or may nor include spacers provided by layers of the board at the ends of the coil stacks
11, 12. In a multilayer printed circuit board, each layer comprises a substrate.
One such coil stack is illustrated in Figure 12. Figure 12a shows the single part stack,
Figure 12b shows the layout of printed circuit board layers, and Figure 12c shows a side
perspective view that illustrates placement of the layers within the height of the printed
circuit board.
In this example, twelve printed circuit board layers are provided. These include a
screen layer at the top and another screen layer at the bottom. A screening track
extends around the outside of each of layers 2 to 11.
Each pair of the non-screening layers 2,3; 4,5; 6,7; 8,9; 10,11 forms a coil with
connections to the exterior surface of the printed circuit board, as shown on the right of
Figure 12a. In this embodiment, these are connected in the same way as the boards in
the stack in the sensor 10 as described above, but in other embodiments they are
interconnected together in series within the multilayer printed circuit board.
Two coil stacks may alternatively be provided from a single printed circuit board, as will
now be described with reference to Figure 13. Here, a sensor 600 comprises first and
second magnetic bars 601, 602 that are separated by a multilayer printed circuit board
603. The printed circuit board 603 includes a slot or cutaway 604 into which a
conductor 605 is located. The slot 604 extends between a front and back of the sensor
600. A bend 605 in the conductor 605 allows the conductor 605 to depart from the
plane of the printed circuit board 603, although a part 607 of the conductor extends
along the plane of the printed circuit board 603. Coil stacks 608, 609 are formed
within the printed circuit board 603 either side of the slot 604 and between the
magnetic bars 601, 602. The coil stacks are connected together by the part of the
printed circuit board that extends around the end of the slot 604.
This can be extended to make a multiphase transducer, as will now be described with
reference to Figure 14. In Figure 14a, four coil stacks are provided from a single printed
circuit board. A sensor 700 comprises first and second magnetic bars 701, 702 that are
separated by a multilayer printed circuit board 703. The printed circuit board 703
includes three slots or cutaway portions 704 to 706 into each of which a respective
conductor 711 to 713 is located. Each slot 704 to 706 extends between a front and back
of the sensor 700. A bend in each conductor 704 to 706 allows it to depart from the
plane of the printed circuit board 703, although a part of each conductor extends along
the plane of the printed circuit board 703. Four coil stacks 707 to 710 are formed
within the printed circuit board 703. Each pair of coil stacks 707 to 710 is formed either
side of a slot 704 to 706 and between the magnetic bars 701, 702. The coil stacks 707 to
710 are connected together by the part of the printed circuit board that extends around
the end of the slots 704 to 706.
Figures 14a and 14b show patterns on opposite sides of one layer within the printed
circuit board 703. Here, it can be seen that the coil stacks 707 to 710 include turns on
each side of the board layer that are connected by a respective through-layer via. These
figures also show how the patterns are connected to terminals T1 to T5. These can for
instance be connected to the differential current inputs on a polyphase metering chip.
An alternative coil pattern includes an individual pair of coils on either side of each
conductor 711, 712, 713. This provides independent isolated outputs, although at the
expense of a larger overall sensor, a greater number of layers in the printed circuit
board or lower sensitivity.
Figure 14d illustrates an circuit formed by the printed circuit board 703 and shows
terminals T1 to T5 that provide signals from the coil stacks 707 to 710.
Figure 14 shows how a three phase current may be measured using a small number of
coil stacks, in this case equal to the number of conductors plus one. This is possible
because of the coil stack sharing that results from the relative locations of the
conductors and the coil stacks.
In other embodiments, the same effect is achieved using independent coil stacks, i.e.
coil stacks that are not formed within a common printed circuit board.
All of the above-described sensors 10, 200, 300, 400, 600, 700 have the advantage of
being relatively simple to manufacture reliably with the desired properties, and at
relatively low cost. This is an effect in particular of the printing of the turns of the coils
and the locating of the substrates supporting the coils in relation to one another and to
the soft magnetic material. Moreover, the sensors also are susceptible to retrofitting
onto existing conductors whilst maintaining their original form or configuration, and
thus maintaining their desirable properties, except for where otherwise stated.
Some general comments about the different configurations will now be provided.
The greater the number of coil stacks in a sensor, the greater is the symmetry of the
sensor, and the lower is the effect of limited permeability of the soft magnetic
components. However, this is achieved at the expense of higher complexity of the
sensor assembly.
For a lowest negative effect from limited permeability, the sensors of the first, second
and fourth embodiments, i.e. those embodiments not using U-shaped soft magnetic
components, are preferred. However, a U-shaped soft magnetic component provides a
dipole moment, which is sensitive to uniform fields. When using U-shaped soft
components in multiple sets of sensors measuring polyphase current or a pair of +/-
phases for power monitoring or fiscal measurement (metering) purposes, it is preferred
to have all the U shapes facing the same direction, or less preferably generally the same
direction, so that the common sensitivity to uniform field cancels out when multiplied
by the out of phase voltages in the power calculation. A dual coil stack sensor, such as
the sensor 10 of the first and second embodiments, provides a quadrupole moment,
which has sensitivity to first order gradient fields. A quad coil stack sensor in a square,
such as the fourth embodied sensor 300, is sensitive only to higher order field
gradients.
Alterative arrangements will be envisaged by the skilled person.
For instance, the printed circuit boards may be made of FR4 or some other suitable
material, such as alumina or a paper-based material. Each of these materials allows the
construction of double-sided boards incorporating vias. Other embodiments utilise
single-sided boards. Because the printed circuit boards are relatively small and have a
relatively simple shape, it can be advantageous for the boards to be made of a material
that can be stamped. Some types of FR4 are suitable for stamping, as are paper-based
boards. Alumina boards can be laser cut.
In some embodiments the spacers are omitted from the coil stacks. In the embodiments
above the spacers serve a purpose of maintaining the printed circuit boards, and thus
the coils, in the desired position. However, this may be achieved instead in some other
manner, for instance using a frame or housing that is mechanically coupled to the
printed circuit boards so as to fix them in position.
Additionally, in some embodiments there are different numbers of coils on different
printed circuit boards. Alternatively or in addition there may be irregular spacing
between adjacent printed circuit boards. Such embodiments may be satisfactory in
many applications, although regular sensors have the best performance. Varying the
turns area product on boards can be used to compensate to some extent for variations
in spacing between printed circuit boards and magnetic bars 13, 14 that may be
unavoidable in sensor design, for instance because of a minimum that can be achieved
between components when using a body and openable gate-type housing.
In some embodiments, each coil stack in a sensor includes only one single layer,
double-sided circuit board, each circuit board having a coil printed on each side
thereof. As such, the circuit board provides two coils. The sensor may include one or
two such coil stacks, or in other embodiments more coil stacks. Placement of the
printed circuit board in the sensor is chosen so as to achieve a suitable separation
between adjacent coils. For instance, in a dual core stack sensor the printed circuit
boards may be located centrally between two magnetic bars such as the bars 13, 14 of
Figure 1.
It will be appreciated that the above-described embodiments are purely illustrative and
not limiting on the scope of protection, which is defined only by the appended claims
and their equivalents.
Claims (24)
1. A current sensor comprising a sensing volume formed by: a first component comprising plural coils, wherein: 5 each coil comprises one or more turns printed on at least one planar surface of a respective substrate, and the planes of the coils are parallel to one another and are perpendicular to a longitudinal axis of the first component; and a second component comprising soft magnetic material and having first and 10 second planar faces that are at opposite ends of the first component and are arranged perpendicularly to and are intersected by the longitudinal axis of the first component.
2. A sensor as claimed in claim 1, wherein a separation between adjacent coils is approximately the same for all coils of the first component.
3. A sensor as claimed in claim 1 or claim 2, wherein the coils of the first component each include the same number of turns and have the same area on the substrate. 20
4. A sensor as claimed in any preceding claim, wherein the second component comprises a U-shaped soft magnetic component and wherein the first and second faces are parallel faces within the mouth of the U.
5. A sensor as claimed in claim 4, wherein the second component is separable 25 from the first component so as to allow a conductor to be introduced into the U before the second component is placed within the mouth of the U of the second component.
6. A sensor as claimed in claim 4 or claim 5, wherein a separation between adjacent coils is approximately the same for all coils of the first component and wherein 30 a separation between a coil closest to the first end and the first contact face is substantially equal to a separation between a coil closest to the second end and the second contact face and is equal or approximately equal to half of the separation between adjacent coils.
7. A sensor as claimed in claim 6 when dependent on claim 5, comprising means for causing the second component to be maintained within the mouth of the U of the second component. 5
8. A sensor as claimed in any of claims 1 to 3, wherein the second component also includes a third component comprising plural coils, wherein: each coil of the third component comprises one or more turns printed on at least one planar surface of a respective substrate, and the coils of the third component are parallel to one another and lie on a longitudinal axis of the third component; and wherein the second 10 component comprises third and fourth planar faces that are arranged perpendicularly to and are intersected by the longitudinal axis of the third component.
9. A sensor as claimed in claim 8, wherein the second component comprises first and second I-shaped components, the first I-shaped component including the first and 15 third faces and the second I-shaped component including the second and fourth faces.
10. A sensor as claimed in claim 9, wherein a separation between adjacent coils is approximately the same for all coils of the first and third components and wherein a separation between a coil closest to the first end of the first component and the first 20 face is the same as a separation between a coil closest to the second end of the first component and the second face, which is the same a separation between a coil closest to the first end of the third component and the third face and is the same as a separation between a coil closest to the second end of the third component and the fourth face, and is approximately half the separation between adjacent coils.
11. A sensor as claimed in claim 8, wherein the second component comprises one or more further components each including plural coils, wherein: each coil of each further component comprises one or more turns printed on at least one planar surface of a respective substrate, and the coils of each further component are parallel to one 30 another and lie on a longitudinal axis of the further component.
12. A sensor as claimed in any preceding claim, wherein adjacent substrates are mechanically separated by spacers. 35
13. A sensor as claimed in any preceding claim, wherein an end substrate in the first component is separated from the first component by a spacer.
14. A sensor as claimed in any preceding claim, comprising a circuit board configured to connect the coils in a circuit. 5
15. A sensor as claimed in any preceding claim, comprising one or more shielding components configured to at least partially surround the first component and, if present, the third component.
16. A sensor as claimed in any preceding claim, comprising a current-carrying 10 conductor extending through a central portion of the sensor.
17. A sensor as claimed in any preceding claim, wherein the soft magnetic material is a ferrite. 15
18. A sensor as claimed in any preceding claim, each coil comprises one or more turns printed on at least two parallel surfaces of a respective substrate.
19. A sensor as claimed in claim 1, wherein the first component comprises first and second coils printed respectively on first and second parallel surfaces of a first 20 substrate.
20. A sensor as claimed in claim 19, wherein the second component also includes a third component comprising third and fourth coils printed on first and second parallel surfaces of a second substrate respectively, wherein the coils of the third component are 25 parallel to one another and lie on a longitudinal axis of the third component; and wherein the second component comprises third and fourth planar faces that are arranged perpendicularly to and are intersected by the longitudinal axis of the third component. 30
21. A sensor as claimed in claim 20, wherein the first and second substrates are of the same thickness and wherein a separation the third coil and the fourth component is the same as a separation between the first coil and the second component.
22. A sensor as claimed in any of claims 8 to 11 or any claim dependent thereon, 35 wherein the first and third components are formed of a single multilayer printed circuit board having formed therein a slot or cutaway configured to receive a conductor.
23. A sensor as claimed in any preceding claim, containing an insulating and/or weatherproof housing. 5
24. A current sensor comprising a sensing volume, substantially as herein described with reference to the accompanying figures.
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GBGB1110825.5A GB201110825D0 (en) | 2011-06-27 | 2011-06-27 | Sensors |
GB1110825.5 | 2011-06-27 | ||
PCT/GB2012/051508 WO2013001298A1 (en) | 2011-06-27 | 2012-06-27 | Sensors |
Publications (2)
Publication Number | Publication Date |
---|---|
NZ619291A NZ619291A (en) | 2014-09-26 |
NZ619291B2 true NZ619291B2 (en) | 2015-01-06 |
Family
ID=
Similar Documents
Publication | Publication Date | Title |
---|---|---|
EP2724167B1 (en) | Sensors | |
EP1264188B1 (en) | High precision rogowski coil | |
US6624624B1 (en) | Electrical current sensor | |
US6965225B2 (en) | Coreless current sensor | |
US6680608B2 (en) | Measuring current through an electrical conductor | |
JPS63500961A (en) | Current transformation device for static integration electric meter | |
US8890509B2 (en) | Current sensor | |
RU2646592C2 (en) | Flux sensor with magnetic core | |
US6441605B1 (en) | Current sensor for an electrical device | |
CN101178417A (en) | High-precision rogowski current transformer | |
EP2860535B1 (en) | Hall effect sensor core with multiple air gaps | |
WO2018143122A1 (en) | Balance-type electric current sensor | |
US20130002236A1 (en) | Device for measuring the electric current flowing in an electric apparatus, said device enabling power measurement, and an electric apparatus comprising same | |
EP2948779B1 (en) | Flexible magnetic field sensor | |
CN104237591A (en) | Designing method and achievement for single PCB closed rogowski coil resisting magnetic field interference | |
NZ619291B2 (en) | Sensors | |
CN205317833U (en) | Three -phase current transformer's magnetism shield assembly | |
JP3344526B2 (en) | Zero-phase current transformer | |
JP7536374B1 (en) | Power Line Mounted Current Sensor | |
JP6832520B2 (en) | Current sensor, current sensor manufacturing method, and distribution board | |
US20230008422A1 (en) | Reduction of ac resistive losses in planar conductors | |
IE59537B1 (en) | Current-transformer arrangements | |
WO2011003977A1 (en) | A current sensor assembly | |
IE20100423U1 (en) | A current sensor assembly |