Rogowski coil

Abstract

The current sensor comprises a single piece of rigid printed circuit board, PCB 102. The PCB comprises first and second sides 104, 106, wherein a length of the PCB extends between the first and second sides, and a plurality of first areas 108, with a first thickness and a plurality of second areas 110, with a second thickness. The first and second areas are arranged alternately along the length of the PCB. The first thickness t1, is greater than the second thickness t2, and the second thickness is configured such that the plurality of second areas of the PCB are non-resiliently deformable. The current sensor further comprises coil windings (108, figure 1B) located in each of the plurality of first areas of the PCB, wherein at least some of the coil windings are connected via the plurality of second areas.

Description

FIELD This relates to a Rogowski coil. In particular, this relates to a non-flexible Rogowski 5 coil current sensor comprising a single piece of rigid PCB. BACKGROUND There is a need for small, cheap, precise, and repeatable current sensors. It is also desirable to have linear current sensors which do not saturate and can be used for 10 high current applications (e.g., detecting short circuit conditions or arc faults). Moreover, modern devices favour miniaturization of sensors. Flat board current sensors cannot be easily miniaturized, as smaller boards have a lower sensitivity because of their smaller winding area. However, flexible sensors can 15 provide a bigger windings area, are scalable, and can effectively utilize space within a device. Examples of flexible current sensors are discussed in US 9,448,258 B2, which discloses a Rogowski coil formed of one or more pieces of rigid PCB that are joined to each other by means of flexible zones which can be bent in a hinge-like manner. In some examples, the portions of PCB are alternated with portions having a reduced 20 thickness; the reduced thickness portions bend in the manner of hinges to provide the flexible zones. It is desirable to provide a robust current sensor which provides the above-described benefits and overcomes some of the disadvantages with the arrangement of US 25 9,448,258 B2. SUMMARY Disclosed herein is a Rogowski coil current sensor. In particular, there is disclosed herein a semi-rigid PCB based Rogowski coil current sensor. The current sensor 30 comprises a single piece of rigid printed circuit board, PCB. The PCB comprises first and second sides, wherein a length of the PCB extends between the first and second sides, and a plurality of first areas with a first thickness and a plurality of second areas with a second thickness. The first and second areas are arranged alternately along the length of the PCB. The first thickness is greater than the second thickness, and 35 the second thickness is configured such that the plurality of second areas of the PCB are non-resiliently deformable. The current sensor further comprises coil windings located in each of the plurality of first areas of the PCB, wherein at least some of the coil windings are connected via the plurality of second areas. In this way, a semi-rigid PCB based Rogowski coil sensor can be provided. The second areas are non-resiliently deformable, meaning they can be bent and will stay in their bent shape in the absence of force. This is in contrast to an arrangement where the 5 rigid areas or portions are joined by flexible portions, as in US 9,448,258 B2. Such flexible portions cannot withstand bending on multiple occasions and are not suitable for repeated use. By providing a non-resiliently deformable portion instead of a flexible portion, a more robust current sensor can be provided which provides the advantages of a small size and easy installation and which can be reused without risk of wear to io any flexible portions. The current sensor described herein can thus be installed more easily than rigid designs, and is more robust than flexible designs. "Semi-rigid" as used herein means that there is some flex within the PCB fibre, but the component is not flexible by form / material. Instead, the material is thinned 15 (optionally milled) so that it can be bent (non-resiliently deformed) under the application of a force. Any movement of the non-resiliently deformable areas comes from utilising movement between the fibre glass and PPE within the PCB. In some examples, the PCB is bent at each of the plurality of second areas until the 20 first and second sides of the PCB are adjacent, thereby to form the Rogowski coil. Optionally, the PCB is bent to a predetermined angle at each of the plurality of second areas, the predetermined angle based on the number of first areas. In some examples, there are six first areas and the PCB forms a hexagonal Rogowski 25 coil. The second areas can be bent to a predetermined angle of 60 degrees or substantially 60 degrees. In other examples, there are four first areas and the PCB forms a square Rogowski coil. The second areas can be bent to a predetermined angle of 90 degrees or substantially 90 degrees. 30 In some implementations, the current sensor further comprises a plurality of conductive pads arranged along the length of the PCB. The plurality of conductive pads can be disposed in the plurality of first areas and arranged between the coil windings and an edge of the PCB. In some examples, the plurality of conductive pads can be disposed on or at the edge of the PCB (the edge meaning here the long edge 35 which extends between the first and second sides). Optionally, the plurality of conductive pads are surface mount pads. Optionally, the plurality of conductive pads are solder mask defined, SMD, pads. In some examples, the coil windings comprise a single coil comprising a forward path, the forward path winding in a first winding direction and extending from the first side of the PCB to the second side of the PCB. In some particular examples the single coil further comprises a return path. Use of a return path can help to reduce the influence 5 of (conductive) noise from external magnetic fields, on the output / measured signal from the current sensor. The return path can wind in the first winding direction and extending from the second side of the PCB to the first side of the PCB, wherein windings of the forward path and the return path are alternately arranged, and wherein the forward and return paths are connected at the second side of the PCB. In 10 some other examples, there is no return path. In other examples, the coil windings comprise first and second coils, each comprising a forward path and a return path. For the first coil, the forward path winds in a first winding direction and extends from a centre of the PCB to the first side of the PCB and 15 the return path winds in the first winding direction and extends from the first side of the PCB to the centre of the PCB, wherein windings of the forward path and the return path are alternately arranged. For the second coil, the forward path winds in a second winding direction and extends from the centre of the PCB to the second side of the PCB and the return path winds in the second winding direction and extends from the 20 second side of the PCB to the centre of the PCB, wherein windings of the forward path and the return path are alternately arranged. The second winding direction is opposite the first winding direction. Optionally, the first and second coils are arranged symmetrically around a centre of the PCB; this can help to improve robustness and reduce the influence from external magnetic fields, as well as to decrease the 25 influence of misalignment in the measured current line / conductor. Also disclosed herein is a system comprising, a mounting (or base) printed circuit board, PCB, and a Rogowski coil current sensor as described herein. The Rogowski coil current sensor is mounted on and soldered to the mounting PCB. This 30 arrangement can facilitate provision of a robust current monitoring sensor which is easily installed. Optionally, there are a plurality of Rogowski coil sensors, each of the plurality of Rogowski coil sensors mounted on and soldered to the mounting PCB. In this way, a 35 multi-phase current monitoring system can be provided in a compact manner. Also described herein is a method of forming a Rogowski coil current sensor from a rigid printed circuit board, PCB, having first and second sides, wherein a length of the PCB extends between the first and second sides. The method comprises forming coil windings in the PCB and milling the PCB to form a plurality of first areas with a first thickness and a plurality of second areas with a second thickness, wherein the first and second areas are arranged alternately along the length of the PCB and wherein 5 the first thickness is greater than the second thickness, wherein the second thickness is configured such that the plurality of second areas are non-resiliently deformable. The milling is configured so that the coil windings are arranged in each of the plurality of first areas of the PCB, wherein at least some of the coil windings are connected via the plurality of second areas. 10 In some examples, the method of forming the Rogowski coil current sensor further comprises, for each of the plurality of second areas of the PCB, in turn, until the first and second sides of the PCB are adjacent: applying heat at the second area and bending the PCB at the second area. Heat can be applied to the second area directly 15 and / or the apparatus used for bending the PCB can be heated so as to indirectly heat the second area during the bending process. Optionally, bending the PCB at the second area comprises bending the PCB at the second area to a predetermined angle, the predetermined angle based on the number of first areas. 20 The above-described features can be provided in any suitable combination. LIST OF FIGURES The description is with reference to the following Figures. Figure 1A shows a schematic illustration of a side view of a current sensor as 25 described herein, and Figure IB shows a schematic illustration of a plan or top view of the current sensor of Figure 1A. Figures 2A, 2B and 2C are perspective views of a first example current sensor at different stages of assembly. Figures 3A, 3B and 3C are perspective views of a second example current 30 sensor at different stages of assembly, and Figure 3D is a perspective view of the coil winding of the second example current sensor. Figure 4 a perspective view of the coil winding of a third example current sensor. Figure 5 is a perspective view of a system comprising one or more current 35 sensors as described herein and a mounting or base PCB. Figure 6 is a flow diagram showing an example method of forming a current sensor as described herein. Figures 7A, 7B and 7C are perspective views of components of a vice used for assembling the current sensor. DETAILED DESCRIPTION 5 With reference to Figures 1A and IB, there is described herein a current sensor 100. The current sensor comprises a single piece of rigid printed circuit board 102, also referred to herein as a PCB, and coil windings 112. The PCB 102 has first 104 and second 106 sides, wherein a length (L) of the PCB io extends between the first and second sides. A plurality of first areas 108 and a plurality of second areas 110 are arranged alternately along the length of the PCB. The coil windings 112 are located in each of the plurality of first areas of the PCB, wherein at least some of the coil windings are connected via the plurality of second areas. 15 The first areas 108 have a first thickness (tl) and the second areas 110 have a second thickness (t2). The first thickness is greater than the second thickness, as shown in Figure 1A. In other words, the PCB is thicker in the first areas 108 than in the second areas 110. The second thickness (t2) is selected or configured such that the plurality 20 of second areas of the PCB are non-resiliently deformable. In this way, the PCB can be bent in each of the second areas to provide a semi-rigid Rogowski coil current sensor 100 which can be disposed around a cable or conductor. For example, the PCB can be bent at each of the plurality of second areas until the first and second sides of the PCB are adjacent, thereby to form the Rogowski coil. The first and second ends 25 can then be glued in place. The PCB can be bent under the application of force and / or heat, as discussed below with reference to Figures 6 and 7. By reducing the thickness in the second areas, the PCB can be bent more easily than if the PCB was a single thickness, whilst still providing thicker, robust, areas in which the 30 coil windings 112 can be disposed. The thinner second areas can be produced by e.g., milling the rigid PCB 102. The specific thickness of the first and second areas is dependent on properties of the PCB, as well as the minimum bending radius of the PCB. In some examples, the thickness Tl of the first areas is configured to be a standard PCB thickness (i.e., no milling of the PCB is performed in the first areas) 35 which can help to reduce manufacturing costs. Optionally, the PCB thickness Tl is a standard PCB thickness of 3.2mm and the thickness T2 of the second areas can vary between 0.1mm and 0.4mm, optionally between 0.15mm and 0.3mm, optionally between 0.2mm and 0.3mm. The PCB 102 can be provided in a flat configuration, to be bent by a consumer / purchaser, or may be provided in a pre-bent state, as required by a given application or use case. In some specific examples, the PCB is bent to a predetermined angle at each of the 5 plurality of second areas. The predetermined angle is based on the number of first areas, thereby providing a regular shaped Rogowski coil. In other examples, the PCB can be bent by any suitable angle in each of the second areas. The shape, size, and number of first and second areas can be determined by the specific application of the current sensor. 10 In one example illustrated in Figure 2 (Figures 2A, 2B, 2C), there are there are four first areas; the PCB is bent 90 degrees in each second area so that the first and second sides are adjacent and the PCB forms a square Rogowski coil current sensor 100. Figure 2A shows a plan view of the PCB 102 illustrating the alternating first and 15 second areas 108, 110. Figure 2B shows the PCB 102 during the bending process, and Figure 2C shows the square current sensor 100. The coil windings 112 in the plurality of first areas 108 are also shown, including the connections 112a arranged in the second areas 110. Once bent into the arrangement shown in Figure 2C, the PCB can be mounted to a mounting or base board (not shown) and a current line or 20 conductor to be measured can be placed through a centre of the bent PCB 102 (illustrated by example current line 200). In this example, the coil windings 112 comprises a single coil with a forward path and a return path. The coil start and end is placed at the same PCB edge, and the forward 25 and return paths are interconnected at the second PCB edge. There is a closed condition between the forward and return path. In particular, the forward path winds in a first winding direction and extends from the first side 104 of the PCB to the second side 106 of the PCB, whilst the return path winds in the first winding direction and extends from the second side 106 of the PCB to the first side 104 of the PCB. In 30 other words, the forward and return path windings are in the same direction. Looking edge on from the first side, the first winding direction is in a counter clockwise direction. The windings of the forward path and the return path are alternately arranged, and the forward and return paths are connected at the second side 106 of the PCB. Use of a return path can help to reduce the influence of noise from external 35 magnetic fields on the output / measured signal from the current sensor. In other examples, the single coil may not have a return path; in arrangements with no return path, the coil starts from one edge of PCB, and is uniformly wound to the second edge or side (where the coil ends). In another example illustrated in Figure 3 (Figures 3A, 3B, 3C, 3D), there are there are six first areas; the PCB is bent 60 degrees in each second area so that the first and second sides are adjacent and the PCB forms a hexagonal Rogowski coil current 5 sensor 100. Figure 3A shows a plan view of the PCB 102 illustrating the alternating first and second areas 108, 110. Figure 3B shows the PCB 102 during the bending process, and Figure 3C shows the hexagonal current sensor 100. Once bent into the arrangement shown in Figure 3C, the PCB can be mounted to a mounting or base board (not shown) and a current line or conductor to be measured can be placed io through a centre of the bent PCB 102 (illustrated by example current line 200). The coil windings in the plurality of first areas 108 are also shown, including examples of the connections 112a arranged in the second areas 110. In this example, the coil windings 112 comprise first 112' and second 112" coils, each comprising a forward 15 and a return path. The return paths are interconnected on a separate mounting or base board (not shown), and on the forward paths there is a differential signal which is related to the measured current through a current line passing through the centre of the bent PCB 102. 20 For the the first coil 112', the forward path winds in a first winding direction and extends (in a direction) from a centre of the PCB to the first side of the PCB and the return path winds in the first winding direction and extends (in a direction) from the first side of the PCB 104 to the centre of the PCB. Looking edge on from the first side, the first winding direction is in a counter clockwise direction. Windings of the forward 25 path and the return path are alternately arranged. In this way, the start and end contacts 350 of the first coil is disposed proximate the centre of the PCB (see e.g. Figure 3D). For the second coil 112", the forward path winds in a second winding direction and 30 extends (in a direction) from the centre of the PCB to the second side of the PCB and the return path winds in the second winding direction and extends (in a direction) from the second side 106 of the PCB to the centre of the PCB, wherein windings of the forward path and the return path are alternately arranged. The second winding direction is opposite the first winding direction. Looking edge on from the first side, 35 the second winding direction is in a clockwise direction. In this way, the start and end contacts 360 of the second coil is disposed proximate the centre of the PCB (see e.g. Figure 3D). With reference to Figure 3, each coil is described as extending in a direction starting from a "centre" of the PCB; the centre here is defined as mid-way between the first and second sides 104, 106, which is illustrated by the dashed line, C. The start of the first and second coils may not be disposed actually at or on the centre line C, but can 5 be arranged either side of it, each extending away from the centre line and towards a respective side of the PCB. In some examples the first and second coils are arranged symmetrically around the centre of the PCB. Depending on the number of first areas, the start of each of the first and second coils may be arranged on a single first area, disposed symmetrically around the centre line of the PCB, or on different first areas. io Where there are an even number of first areas, as in Figure 3, the first and second coils 112', 112" are disposed symmetrically around the centre line (which in this case is positioned in a second area 110), but the coils are located on / in different first areas which are adjacent to (either side of) the central second area. There are no connections in this central second area through which the centre line C passes. 15 This differential coil winding arrangement with two coils having return paths is shown further in Figure 3D, in which the windings are arranged as they would be for the bent PCB of Figure 3C (only the windings are shown, no PCB). The centre line C of the PCB is shown for illustrative purposes only. 20 Figures 2 and 3 show specific examples of particular coil arrangements. However, it will be understood that any suitable coil winding arrangement can be implemented in the PCB arrangement of this Figures. For example, for any given PCB shape and configuration there may a single coil with only a forward path (no return path), a 25 single coil with a forward and return path, or there may be two coils. Any other winding arrangement is possible, as will be understood by the skilled person. Any coil arrangement is advantageously arranged with windings which are symmetric and uniform (as illustrated in the coil arrangements of Figures 2 and 3); the use of symmetric and uniform windings can help to improve robustness and reduce the 30 influence from external magnetic fields, as well as to decrease the influence of misalignment in the measured current line / conductor. With further reference to Figures 2 and 3, it can be seen that comprising a plurality of conductive pads or soldering points 250 are arranged along the length of the PCB. 35 The plurality of conductive pads are disposed in the plurality of first areas 108 and arranged between the coil windings 112 and an edge of the PCB. In some arrangements the conductive pads 250 are proximate the edge, or they can be disposed on the edge as shown in Figures 2 and 3. The pads or points 250 can be placed on the edge using edge-metallisation, and optionally can be formed as a castellated hole. The conductive pads 250 can be surface mount pads, and in some examples can be solder mask defined SMD pads. In other examples the conductive pads are NSMD pads. In other examples, particularly where the PCB is to be used 5 without a mounting or base pad, the conductive pads / points 250 can comprise holes configured to receive external wiring, for connecting the PCB 102 to e.g. a sensing or measuring device and reading the output from the current sensor 100. In another example, described in Figure 4, the coil winding for a square Rogowski coil io current sensor can be implemented with a differential dual coil winding having a return path. In this arrangement, there is a first coil 112' and a second coil 112". For the first coil 112'the forward path winds in a first winding direction and extends (in a direction) from the first side of the PCB to the centre of the PCB and the return path winds in the first winding direction and extends (in a direction) from the centre of the 15 PCB to the first side of the PCB. Windings of the forward path and the return path are alternately arranged. In this way, contrary to Figure 3D, the start and end contacts 350 of the first coil are disposed proximate the first side of the PCB. The forward and return paths are connected proximate the centre, or centre line C. 20 For the second coil 112", the forward path winds in a second winding direction and extends (in a direction) from the second side of the PCB to the centre of the PCB and the return path winds in the second winding direction and extends (in a direction) from the centre of the PCB to the second side of the PCB, wherein windings of the forward path and the return path are alternately arranged. The second winding 25 direction is opposite the first winding direction. In this way, the start and end contacts 360 of the second coil is disposed proximate the second side of the PCB. The forward and return paths are connected proximate the centre, or centre line C. With reference to Figure 5, a system 500 is described. The system comprises a 30 mounting PCB 570 and one or more Rogowski coil current sensors 100 as described herein. The sensor 100 can be bent and mounted to the mounting (or base) board 570 and then soldered or otherwise electrically connected in place. There can be any number of current sensors mounted on the PCB 570, in any suitable shape and configuration. In this specific example, there are three current sensors 100: two 35 square and one hexagonal. Such a mounting arrangement allows to provide monitoring of three phase currents within a small device, since the Rogowski coil current sensors 100 have a good volume utilisation. The one or more sensors 100 can also be glued / adhered to the board 570 with any suitable compound, so as to minimise any vibrational effects. The mounting or base PCB 570 can be a main PCB, which the current sensors 100 are 5 soldered to. The main board 570 may comprise an MCU and metering chip for monitoring and sensing current through current lines 200 when the system 500 is installed. An additional power board (not shown) may also be provided. The power board may comprise a switching AC-DC convertor and any other electronics. The main PCB 570 can be connected to the power board using e.g. pin-headers, with an optional io board-board stacking distance of 10mm. Any suitable PCB size and thickness may be used, depending on the signal conditioning path, measuring or metering ranges for which the sensor is to be used, and other factors such as the PCB material and desired shape / configuration. 15 With reference to Figure 6, a method of forming a Rogowski coil current sensor 100 from a rigid PCB is now described. Firstly, the PCB is manufactured and the windings are provided. This PCB manufacturing process, as the skilled person would understand, can comprise: printing 20 and etching core; drilling; via copper coating; soldering mask cover. In this way, by the use of any suitable drilling / coating / masking, the coil windings can be formed in the PCB in accordance with step 680. Once the coil windings are formed, the PCB can be milled in accordance with step 682. 25 In particular, milling 682 the PCB comprising milling the PCB to form a plurality of first areas with a first thickness and a plurality of second areas with a second thickness. The first and second areas are arranged alternately along the length of the PCB. The first thickness is greater than the second thickness, wherein the second thickness is configured such that the plurality of second areas are non-resiliently deformable. The 30 milling is also configured such that the coil windings formed at step 680 are arranged in each of the plurality of first areas of the PCB, wherein at least some of the coil windings are connected via the plurality of second areas. The milling can be by controlled depth milling. Any other method of reducing the thickness of certain areas of the PCB can also be used. Optionally, a compound can be placed in the partial 35 depth milled corners between the first and second areas to strengthen the PCB. After the manufacturing of the current sensor 100, the sensor can be assembled. Assembly can comprise for each of the plurality of second areas of the PCB, in turn, heating 686 the second area and bending the PCB at the second area. This can be repeated 684 for each of the second areas in turn until the first and second sides of the PCB are adjacent. Optionally, bending the PCB at the second area comprises bending the PCB at the second area to a predetermined angle, the predetermined 5 angle based on the number of first areas. The second area can be heated directly (optionally before being bent) and / or indirectly by heating the apparatus used to bend the PCB. In the latter case where the apparatus is heated, the heating and bending are understood to optionally occur simultaneously or substantially simultaneously. io In more detail, the assembly stage can comprise positioning and clamping the edge part of the PCB 102 in a mechanical vice 790, an example of which is shown in Figure 7A. Each respective second area can be heated, for example with a flow of hot air from below (see exemplary direction of heat, H, in Figure 7A). Optionally, the PCB is heated to its glass temperature before being bent or non-resiliently deformed. 15 The (heated) second area can be bent using the vice, as shown in Figure 7B. The vice 790 can be optionally implemented as a platform with a slot 792 for exact edge board positioning and a polygonal tube 794 which is configured based on the angles and distances between PCB faces (as is required for the given current sensor 20 arrangement). A pinion 796 can be used to bend the PCB, as shown in Figure 7B. In some optional examples (not shown here), the pinion can be heated by any suitable heat source; this heat is then transferred to the second area during the bending process. In other words, the PCB is heated indirectly via the heated pinion. This heating can be instead of or as well as the direct heating of the second area by the 25 exemplary heat H shown in Figure 7A. Heating the pinion can help to bend the PCB to the correct angle and with the proper or appropriate bending radius. The pinion 796 pinion is pressed into the tube 794 with the PCB 102 between the pinion and the tube (see direction offeree, F, in Figure 7B). The pinion can be 30 pressed by a plunger (not shown) with a predefined shape, the plunger size and shape configured in accordance with the desired PCB arrangement. The force exerted on the PCB causes it to non-resiliently deform, or bend. The pinion and tube can be configured with a predetermined angle so as to bend the PCB by the corresponding predetermined angle, the angle depending on the number of first areas. An example 35 of the pinion 796 is shown in Figure 7C. This pinion is configured to bend each second area by 60 degrees. Any other suitable vice arrangement may be used. After being bent, the pinion can be pulled out of the vice in a direction substantially perpendicular to the direction in which the force F was applied, and the PCB can be left pressed and fixed within the vice 790 by the plunger (not shown). The PCB can then be cooled down again using the same apparatus which was used for applying heat (for 5 example by applying compressed air in the same direction as the heat H was applied). The process can then be repeated for each of the second areas. In other words, for each second area in turn until the PCB first and second sides are substantially adjacent, the following steps can be performed: heating with hot air from io direction H shown in Figure 7A and / or heating the pinion; pressing down on the second area with (the optionally heated) pinion and plunger (in other examples, the pinion can be heated after it is pressed onto the PCB); pulling out the pinion from the vice (PCB left pressed and fixed in vice 790 with plunger); and cooling-down the PCB (for example, with compressed air using same apparatus as was used for heating). 15 Once the PCB is bent at each of the second areas, it can be wrapped around a central post or placed in a mould and fixed in the final position. A compound can be placed in the slot between the adjacent first and second PCB sides or edges. As example, glue or adhesive for SMD component fixation can be used. The compound can then be 20 polymerised (by placing in a high temperature oven or with UV, depending on the compound used). The sensor 100 is thus assembled for use. The sensor can be used as it is, or mounted to a board 570. Soldering to a board 570 can be performed by way of the conductive pads 250 on the 25 PCB edges, which are connected to each other with edge metallization. In some examples, the conductive pads are provided with a repeatable footprint, and a regular soldering process with soldering paste can be used. After soldering, to improve vibration stability, the PCB 102 can also be secured to the board 570 with SMD glue. Depending on the coil winding being used, return-path ends can be interconnected on 30 the external mounting board 570.

Claims

1.

1. A Rogowski coil current sensor (100), comprising:a single piece of rigid printed circuit board (102), PCB, the PCB comprising:5 first (104) and second (106) sides, wherein a length (L) of the PCB extendsbetween the first and second sides; anda plurality of first areas (108) with a first thickness (tl) and a plurality of second areas (110) with a second thickness (t2), wherein the first and second areas are arranged alternately along the length of the PCB and wherein the first thickness is io greater than the second thickness; andcoil windings (112) located in each of the plurality of first areas of the PCB, wherein at least some of the coil windings are connected via the plurality of second areas,wherein the second thickness is configured such that the plurality of second15 areas of the PCB are non-resiliently deformable.

2. The current sensor of claim 1, wherein the PCB is bent at each of the plurality of second areas until the first and second sides of the PCB are adjacent, thereby to form the Rogowski coil.

203. The current sensor of claim 2, wherein the PCB is bent to a predetermined angle at each of the plurality of second areas, the predetermined angle based on the number of first areas.25 4. The current sensor of any of claims 1 to 3, wherein:there are six first areas and the PCB forms a hexagonal Rogowski coil; or there are four first areas and the PCB forms a square Rogowski coil.

5. The current sensor of any preceding claim, further comprising a plurality of30 conductive pads arranged along the length of the PCB, the plurality of conductive pads disposed in the plurality of first areas and arranged between the coil windings and an edge of the PCB.

6. The current sensor of claim 5, wherein the plurality of conductive pads are 35 surface mount pads, optionally wherein the plurality of conductive pads are solder mask defined, SMD, pads.

7. The current sensor of any preceding claim, wherein the coil windings comprise a single coil comprising a forward path, the forward path winding in a first winding direction and extending from the first side of the PCB to the second side of the PCB.5 8. The current sensor of claim 7, wherein the single coil further comprises areturn path, the return path winding in the first winding direction and extending from the second side of the PCB to the first side of the PCB, wherein windings of the forward path and the return path are alternately arranged, and wherein the forward and return paths are connected at the second side of the PCB.io9. The current sensor of any of claims 1 to 6, wherein the coil windings comprise first and second coils, each comprising a forward path and a return path, wherein:for the first coil, the forward path winds in a first winding direction and extends from a centre of the PCB to the first side of the PCB and the return path winds in the 15 first winding direction and extends from the first side of the PCB to the centre of the PCB, wherein windings of the forward path and the return path are alternately arranged; andfor the second coil, the forward path winds in a second winding direction and extends from the centre of the PCB to the second side of the PCB and the return path20 winds in the second winding direction and extends from the second side of the PCB to the centre of the PCB, wherein windings of the forward path and the return path are alternately arranged,wherein the second winding direction is opposite the first winding direction.25 10. The current sensor of claim 9, wherein the first and second coils are arrangedsymmetrically around a centre of the PCB.

11. A system comprising,a mounting printed circuit board, PCB; and30 the Rogowski coil current sensor of any preceding claim,wherein the Rogowski coil current sensor is mounted on and soldered to the mounting PCB.

12. The system of claim 11, further comprising a plurality of Rogowski coil sensors35 in accordance with any of claims 1 to 10, each of the plurality of Rogowski coil sensors mounted on and soldered to the mounting PCB.

13. A method of forming a Rogowski coil current sensor from a rigid printed circuit board, PCB, having first and second sides, wherein a length of the PCB extends between the first and second sides, the method comprising:forming (680) coil windings in the PCB;5 milling (682) the PCB to form a plurality of first areas with a first thickness anda plurality of second areas with a second thickness, wherein the first and second areas are arranged alternately along the length of the PCB and wherein the first thickness is greater than the second thickness, wherein the second thickness is configured such that the plurality of second areas are non-resiliently deformable; andio wherein the milling is configured so that the coil windings are arranged in eachof the plurality of first areas of the PCB, wherein at least some of the coil windings are connected via the plurality of second areas.

14. The method of claim 13, further comprising, for each of the plurality of second 15 areas of the PCB, in turn, until the first and second sides of the PCB are adjacent(684):heating (686) the second area; and bending the PCB at the second area.20 15. The method of claim 14, wherein bending the PCB at the second areacomprises bending the PCB at the second area to a predetermined angle, the predetermined angle based on the number of first areas.16