Rogowski current sensor including a printed circuit board
Patent Information
- Application Number
- EP2024791403
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-11-03
- Filing Date
- 2024-10-21
- Publication Date
- 2026-09-09
AI Technical Summary
Rogowski type current sensors are highly susceptible to electromagnetic disturbances due to external electromagnetic fields interfering with the sensor's operation, affecting the measurable voltage.
A Rogowski type current sensor is designed with a printed circuit configuration featuring upper and lower tracks arranged in a specific offset pattern, with vias connecting them, to minimize electromagnetic interference by blocking external fields perpendicular to the sensor's plane.
The sensor's design effectively reduces electromagnetic sensitivity, allowing for accurate current measurement while minimizing disruptions from external electromagnetic fields.
Smart Images
Figure EP2024079696_08052025_PF_FP_ABST
Abstract
Description
DESCRIPTION Title of the invention: Rogowski current sensor comprising a printed circuit
[0001] The invention relates to the field of current measurement at the level of an electrical element, in particular to that of Rogowski type sensors or coils.
[0002] As is known, current measurement through an electrical element can be done in different ways. This can be done, for example, using a measuring shunt adapted to measure the current passing through said electrical element. It is also possible to use a Hall effect measuring sensor inserted in a magnetic circuit or coupled to a magnetic flux concentrator or a Neel effect measuring sensor consisting of a super-paramagnetic circuit, a measuring coil and electronics allowing spectral analysis of this measurement.
[0003] Another way to measure current in an electrical element is to use a Rogowski-type measuring sensor, which consists of a winding and a high-impedance load to measure the variation in current flowing through the sensor. A Rogowski sensor consists of a helical winding of conductive wire wound, for example, around an annular tube. One end of the conductive wire returns through the center of the winding to the other end of the conductive wire, so that the two ends of the winding are adjacent. The Rogowski-type measuring sensor is positioned around the electrical conductor, i.e., the electrical element, whose current is to be measured.
[0004] The Rogowski type measuring sensor has many advantages, such as its low weight and wide frequency band.
[0005] Alternatively, the Rogowski sensor's annular tube can be replaced by a printed circuit board. The sensor's winding is deposited on the faces of the printed circuit board through holes through the printed circuit board.
[0006] If the section of the sensor is crossed by a current variation perpendicular to the plane formed by all the turns of the sensor, then this current variation generates an electromagnetic field parallel to the plane formed by all the turns of the conductive wire. This electromagnetic field generates a measurable voltage at the terminals or ends of the Rogowski sensor.
[0007] However, any electromagnetic field outside the Rogowski sensor that is perpendicular to the electromagnetic field generated by the current variation becomes disruptive for the Rogowski current sensor. Indeed, this external electromagnetic field is superimposed on the electromagnetic field specific to the sensor and generated by the current variation passing through the sensor and modifies the measurable voltage at the sensor terminals. Such a Rogowski-type current sensor is therefore very susceptible to electromagnetic disturbances from its environment.
[0008] The invention aims to propose a Rogowski type current sensor produced on a printed circuit or PCB ("Printed Circuit Board") which is little or not sensitive to electromagnetic disturbances.
[0009] To this end, the invention relates to a Rogowski type sensor configured to measure an electric current passing through an electrical element, the sensor comprising a printed circuit, said printed circuit comprising: - at least two upper tracks extending along a first plane; - at least one lower track extending along a second plane parallel to the first plane, the upper tracks and said at least one lower track being configured to surround the electrical element; and - vias connecting the upper tracks to said at least one lower track, the sensor further comprising a conductive wire comprising several turns, each turn comprising an upper portion, a lower portion and an intermediate portion connecting the upper portion to the lower portion, the upper portion of each turn extending on an upper face of an upper track among the upper tracks, the lower portion of each turn extending on a lower face of a lower track among the at least one lower track, and the intermediate portion passing through one of the vias connecting said upper track to said lower track, the sensor being characterized in that each lower track among the at least one lower track comprises a first portion facing an upper track among said at least two upper runways, and a second portion facing an upper runway adjacent to said upper runway.
[0010] This arrangement of the lower and upper tracks has the advantage of allowing a lower track to be covered by an upper track and vice versa, so as to limit any electromagnetic disturbance oriented perpendicular to the upper and lower tracks.
[0011] According to one aspect of the invention, the sensor comprises a return track between said at least two upper tracks and said at least one lower track, the return track extending along a third plane parallel to the first plane and to the second plane, the return track being configured to surround the electrical element, the conductive wire passing through the return track.
[0012] According to one aspect of the invention, the first portion of the at least one lower track represents two thirds of the at least one lower track and the second portion of the at least one lower track represents one third of the at least one lower track.
[0013] According to one aspect of the invention, the first portion and the second portion each represent one half of the at least one lower track.
[0014] According to one aspect of the invention, the at least one lower track and the upper tracks are identical to each other.
[0015] According to one aspect of the invention, the first portion of the at least one lower track comprises a first via among said vias and the second portion of the at least one lower track comprises a second via among said vias.
[0016] According to one aspect of the invention, the at least one lower track comprises four vertices, the first via and the second via being positioned near two vertices not adjacent to each other.
[0017] According to one aspect of the invention, a lower track comprises four sides, two of the four sides being straight and two of the four sides being curved, one curved side connecting the two straight sides.
[0018] According to one aspect of the invention, the at least two upper tracks are spaced from the at least one lower track by a distance of less than 5 millimeters, and preferably equal to 1.5 millimeters.
[0019] According to one aspect of the invention, the at least two upper tracks and the at least one lower track are made of copper.
[0020] The invention will be better understood and other advantages will appear on reading the detailed description of an embodiment given by way of example, a description illustrated by the attached drawing in which:
[0021] Figure 1 represents a schematic top view of a Rogowski type sensor according to one embodiment of the invention;
[0022] Figure 2 is a simplified side schematic view of Figure 1 showing a coil passing through a printed circuit of the sensor;
[0023] Figure 3 shows a view similar to Figure 2 in which a sensor return track is shown;
[0024] Figure 4 shows a schematic top view of part of the sensor showing the coil passing through the printed circuit;
[0025] Figure 5 shows an exploded schematic view of part of the sensor showing the coil passing through the printed circuit;
[0026] Figure 6 shows an exploded schematic view of the part of the sensor of Figure 5 repeated twice; and
[0027] Figure 7 represents a schematic side view of Figure 6.
[0028] For the sake of clarity, the same elements will have the same references in the different figures.
[0029] Figure 1 represents a schematic top view of a Rogowski-type current sensor 1 configured to measure a current flowing through an electrical element. The current sensor 1 at least partially surrounds the electrical element. The current sensor 1 is preferably in contact with the electrical element. In a preferred configuration, the current sensor 1 surrounds the electrical element so that the surface surrounded by the measurement sensor 1 in a first plane P1 corresponds to a current measurement section 2 of the electrical element. In other words, the measuring section 2 is a surface bordered by the current measuring sensor 1 in the first plane P1 parallel to the measuring sensor 1.
[0030] The current measurement sensor 1 comprises a printed circuit 10 shown more precisely in FIG. 2. The printed circuit 10 is configured to surround the electrical element so as to delimit the measurement section 2.
[0031] The printed circuit 10 comprises at least two upper tracks, namely at least a first upper track 12' and a second upper track 12”, extending along the first plane P1 and at least one lower track 14' extending along a second plane P2 parallel to the first plane P1, the upper tracks 12' and 12” and said at least one lower track 14' being configured to surround the electrical element.
[0032] The printed circuit 10 then extends from the first plane P1 to the second plane P2. The upper tracks 12' and 12” are thus superimposed on said at least one lower track 14'.
[0033] The printed circuit 10 also comprises at least one via 16 connecting the upper tracks 12' and 12” to said at least one lower track 14'. The at least one via 16 takes the form of an opening in one track among the at least two upper tracks 12' and 12” and the at least one lower track 14' extending towards the other track among the at least two upper tracks 12' and 12” and the at least one lower track 14'. The printed circuit 10 is crossed by the at least one via 16.
[0034] The current measurement sensor 1 comprises a conductive wire 18 comprising several turns 19. Each turn 19 comprises an upper portion 182, a lower portion 186 and an intermediate portion 184 connecting the upper portion 182 to the lower portion 186. The upper portion 182 extends on an upper face 122 of the upper track, as shown in FIG. 2, among the at least two upper tracks 12' and 12” such as for example the first upper track 12'. The lower portion 186 extends on a lower face 142 of the lower track among the at least one lower track 14'. And the intermediate portion 184 passes through one of the vias 16.
[0035] The turns 19 surround the printed circuit 10 and each turn is adjacent to at least one other turn 19 so that the turns 19 form a winding 20 around the printed circuit 10.
[0036] Therefore, when an electric current passes through the electrical element and in particular the measuring section 2 perpendicular to the plane P1, an electromagnetic field CE is generated in the winding 20 perpendicular to the plane formed by each turn 19.
[0037] In a preferred configuration, the at least two upper tracks 12' and 12” comprise a defined number, greater than or equal to 2, of upper tracks in the plane P1. And, the at least one lower track 14' comprises a defined number, greater than or equal to 1, of lower tracks in the second plane P2 parallel to the plane P1.
[0038] Each lower track of the at least one lower track 14' comprises a first portion 146 facing an upper track among said at least two upper tracks such as for example the first upper track 12', and a second portion 148 facing an upper track adjacent to said upper track, such as for example the second upper track 12”.
[0039] In other words, the first lower track 14' is arranged between the first upper track 12' and the second upper track 12”. Thus, the projection of the first lower track 14' is between the first upper track 12' and the second upper track 12” in the first plane P1. The first lower track 14' is therefore offset relative to the first upper track 12' by means of a rotation whose center is substantially close to the center of the section to be measured 2.
[0040] And, similarly, the printed circuit 10 may comprise, in addition to the first lower track 14', a second lower track 14”. The first lower track 14' and the second lower track 14” are included in the second plane P2 parallel to the plane P1 coincident with the lower track 14. And, similarly, each upper track of the at least two upper tracks 12' and 12” comprises a first portion 126 facing a lower track among said at least one lower track, and a second portion 128 facing a lower track adjacent to said at least one lower track.
[0041] In other words, the second upper track 12” is arranged between the first lower track 14' and the second lower track 14”, as shown in figure 1. And, a first portion 126 of the second upper track 12” is opposite the first lower track 14' while a second portion 128 of the second upper track 12” is opposite the second lower track 14”.
[0042] Thus, the projection of the second upper track 12” is between the first lower track 14' and the second lower track 14” in the second plane P2. The second upper track 12” is therefore offset relative to the second lower track 14” by means of a rotation whose center is substantially close to the center of the section to be measured 2.
[0043] And, in an identical manner, the printed circuit 10 may comprise a third upper track 12'” included with the first upper track 12' and the second upper track 12” in the first plane P1. And, the second lower track 14” may then be arranged between the second upper track 12” and the third upper track 12'”. And, as indicated previously, a first portion of the second lower track 14” is opposite the second upper track 12” while a second portion of the second lower track 14” is opposite the third upper track 12'”.
[0044] So the projection of the second lower track 14” can be between the second upper track 12” and the third upper track 12'” so that there is the offset.
[0045] The first upper runway 12' is distant from the second upper runway 12”. In other words, there is a spacing 13 between the first upper runway 12' and the second upper runway 12”.
[0046] The printed circuit 10 may also comprise, as shown in FIG. 3, a return track 17 extending along a third plane P3 parallel to the first plane P1 and to the second plane P2. The return track 17 is configured to surround the electrical element. The third plane P3 is between the first plane P1 and the second plane P2 along a fourth plane P4 perpendicular to the first plane P1, to the second plane P2 and to the third plane P3. The conductive wire 18 passes through the return track 17.
[0047] The return track 17 is a layer of the printed circuit 10 in which the conductive wire 18 extends. The return track 17 is also crossed by the conductive wire 18 so that an intermediate portion 188 of conductive wire 18 is positioned between the upper portion 182 and the lower portion 186 of conductive wire according to the fourth plane P4. The winding 20 comprises two ends 202 and 204, a first end 202 being connected to a turn 19. The second end 204 is connected to the return track 17. The return track 17 allows for a return of the conductive wire 18 so as to allow the measurement of a voltage and a current in the measurement sensor 1.
[0048] In the plane P4 shown in figure 3, the return track 17 is less wide than the at least two upper tracks 12' and 12” and the at least one lower track 14'. The vias 16 are thus on either side of the return track 17, which thus makes it possible to pass the conductive wire 18 into the printed circuit 10 without crossing the return track 17.
[0049] Generally, each lower track of the at least one lower track 14' is arranged opposite a spacing 13. And, each upper track of the at least two upper tracks 12' and 12” is arranged opposite a spacing 13.
[0050] Advantageously, the first portion 146 of the at least one lower track 14' represents one half of the at least one lower track 14' and the second portion 148 of the at least one lower track 14' represents the other half of the at least one lower track 14'. Alternatively, the first portion 146 of the at least one lower track 14' may represent two thirds of the at least one lower track 14' and the second portion 148 of the at least one lower track 14' may represent one third of the at least one lower track 14'.
[0051] The at least two upper tracks 12' and 12” and the at least one lower track 14' then have the advantage of magnetically isolating the printed circuit 10 from any electromagnetic field external to the current measurement sensor 1. More precisely, any disturbing magnetic flux CEP passing through the printed circuit 10 and perpendicular to the first plane P1, i.e. orthogonal to the electromagnetic field CE, is blocked by one of the upper tracks of the at least two upper tracks 12' and 12” if this disturbing electromagnetic flux CEP must pass through one of the upper tracks of the at least two upper tracks 12' and 12” before crossing the printed circuit 10 or by the at least one lower track 14' if this disturbing electromagnetic flux CEP must cross the at least one lower track 14' before crossing the printed circuit 10. The at least two upper tracks 12' and 12” and the at least one lower track 14' thus ensure a magnetic isolation function in the fourth plane P4.
[0052] More precisely, the disturbing electromagnetic flux CEP crossing perpendicularly the plane P1 at the level of the current measurement sensor 1, is blocked at least by an upper track of the at least two upper tracks 12' or 12” or by the at least one lower track 14' so as not to be able to disturb the measurement sensor 1. This offset architecture also has the advantage of reducing the dimensions of the at least two upper tracks 12 and of the at least one lower track 14'.
[0053] The at least two upper tracks 12 and / or the at least one lower track 14 may also be an electrically conductive track so as to facilitate the electrical connection between each via 16. It may thus be envisaged that the at least two upper tracks 12 and / or the at least one lower track 14 is obtained from a material comprising copper which is an excellent magnetic insulator and a good electrical conductor, thus allowing the at least two upper tracks 12' and 12” and / or the at least one lower track 14' to ensure the two functions of magnetic insulation with respect to the electromagnetic field external to the current measurement sensor 1 and electrical conduction around the printed circuit 10. The printed circuit 10 may also comprise an electrical insulator between the at least two upper tracks 12' and 12” and the at least one lower track 14'.
[0054] As shown in Figure 4, the offset of the first upper track 12' relative to the first lower track 14' causes misalignment of the upper portion 182 disposed against the first upper track 12' and of the lower portion 186 disposed against the first lower track 14'.
[0055] As shown in Figure 5, each upper track 12', 12” or 12'” of the at least two upper tracks 12' and 12” such as the first upper track 12' or the second upper track 12” of the upper track 12 and each lower track of the at least one lower track 14' such as the first lower track 14' or the second lower track 14” comprises two vias 16 of so as to allow the turns 19 to be connected together. It is thus possible to repeat the same elementary pattern, namely the turn 19 of conductive wire 18 as shown in figure 6.
[0056] As stated previously, the measuring sensor 1 surrounds the electrical element. Preferably, the measuring sensor 1 has an annular shape.
[0057] Further, each track of the at least one lower 14' track, such as the first lower 14' track or the second lower 14” track, and each track of the at least two upper tracks, such as the first upper 12' track or the second upper 12” track, are identical.
[0058] In a configuration of a measurement sensor 1 of annular shape, the first upper track 12' may have the shape of a trapezoid or a solid arc in the first plane P1. The first lower track 14' may also have the shape of a trapezoid or an arc in the first plane P1. Alternatively, the measurement sensor 1 may have an elliptical or bar shape. However, any other geometric shape may be considered, such as a triangle for example.
[0059] By a full arc, it is meant that the at least one lower track 14' comprises four sides 1400, 1401, 1402 and 1403 in the second plane P2, as shown in Figure 1. Two sides 1400 and 1402 of the four sides 1400, 1401, 1402 and 1403 are straight and two sides 1401 and 1403 of the four sides 1400, 1401, 1402 and 1403 are curved. And, one curved side, for example the first curved side 1401 is adjacent to the two straight sides 1400 and 1402.
[0060] And similarly, the at least two lower tracks 12' or 12” comprise four sides 1200, 1201, 1202 and 1203 in the first plane P1. Two sides 1200 and 1202 of the four sides 1200, 1201, 1202 and 1203 are straight and two sides 1201 and 1203 of the four sides 1200, 1201, 1202 and 1203 are curved. And, one curved side, for example the first curved side 1201 is adjacent to the two straight sides 1200 and 1202.
[0061] As stated previously, each track of the at least two upper tracks 12' or the at least one lower track 14' comprises two vias 16. The first portion of the at least one lower track 14' may comprise a first via 16' and the second portion of the at least one lower track 14' comprises a second via 16”. And, similarly, the first portion of an upper track of the at least two upper tracks 12' may comprise a first via and the second portion of the upper track of the at least two upper tracks 12' comprises a second via.
[0062] The via of the first portion of the at least one lower track 14', i.e. the first via 16', is arranged next to a first straight side 1400 of the two straight sides and a first curved side 1401 of the two curved sides and the via of the second portion of the at least one lower track 14', i.e. the second via 16”, is arranged next to the other straight side 1402 of the two straight sides, i.e. the second straight side 1402, and the other curved side 1403 of the two curved sides, i.e. the second curved side 1403.
[0063] In other words, each track among the at least one lower track 14' comprises four vertices 1410, 1412, 1414, 1416. The first via 16' and the second via 16” are positioned near two vertices that are not adjacent to each other. As an indicative example, the first via 16' can be positioned near a first side 1410 and the second via 16” is then positioned near a third side 1414 that is not adjacent to the first side 1410. By non-adjacent, we mean that the two vertices are not consecutive.
[0064] And similarly, each track among the at least two upper tracks comprises four vertices. The first via of said upper track and the second via of said upper track are positioned near two vertices not adjacent to each other.
[0065] As shown in Figure 7, the first upper track 12' is in contact, along the first right side 1200, with a spacing 13 and, along the second right side 1202, at another spacing 13'. And, the first lower track 14' is in contact, along the first right side 1400, with a third spacing 13” and, along the second right side 1402, at a fourth spacing 13'”.
[0066] In other words, each track of the upper track of the at least two upper tracks 12' and 12” is arranged between two spacings 13 in the first plane P1 and each track of the lower track of the at least one lower track 14' is arranged between two spacings 13 in the second plane P2.
[0067] Now, as stated previously, the surface area of the first portion and the surface area of the second portion are identical.
[0068] In other words, each spacing 13 is arranged opposite the center of an upper track of the at least two upper tracks 12' or 12” such as the first upper track 12' or opposite the center of a lower track of the at least one lower track 14' such as the first lower track 14'.
[0069] Thus, the second spacing 13' disposed between the first upper track 12' and the second upper track 12” faces the center of the first lower track 14'. And, the fourth spacing 13'” disposed between the first lower track 14' and the second lower track 14” also faces the center of the second upper track 12” in the first plane P1. The at least one lower track 14' as well as the at least two upper track 12' comprises an average angular length la mwhich is defined as the average length of the sum of the two curved sides 1402 and 1404. Therefore, the offset between the at least two upper tracks 12' such as the first upper track 12' or the second upper track 12” and the at least one lower track such as the first lower track 14' or the second lower track 14” is of a length equal to
[0070] The first lower track 14' is offset from the first upper track 12' by an arc of a circle of length equal to Any other offset along an arc of a circle of defined length, such as — or — can be considered.
[0071] Advantageously, the distance separating the first plane P1, and therefore the at least two upper tracks 12' and 12”, from the second plane P2, and therefore from the at least one lower track 14' is less than 5 millimeters so that the thickness of the measurement sensor 1, defined by this distance between the first plane P1 and the second plane P2, is small. Very advantageously, the distance separating the first plane P1 from the second plane P2 is less than 2 millimeters and preferably equal to 1.5 millimeters so that the thickness of the measurement sensor 1 is small.
[0072] The measuring sensor 1, surrounding the electrical element, can advantageously comprise an internal diameter R1 of between 20 millimeters and 200 millimeters, defining the measuring section 2 and an external diameter R2 of between 40 millimeters and 400 millimeters so that the measuring sensor is suitable for wide ranges of dimensions of the electrical element.
[0073] The first upper track 12', the second upper track 12”, the first lower track 14' or the second lower track 14” advantageously comprises an average angular length m between 10 millimeters and 1.5 millimeters so that the number of turns 19 surrounding the printed circuit 10 can be defined.
[0074] The diameter of the at least one via 16 can also be between 0.3 millimeters and 5 millimeters.
[0075] Advantageously, it can be envisaged that each track of the at least one lower track 14' and each track of the at least two upper tracks 12' and 12” are identical. The machining of each track is then facilitated.
[0076] The offset arrangement of the upper track 12 and the lower track 14 thus has the advantage of having one track overlap the other so as to reduce the electromagnetic sensitivity of the measuring sensor 1.
Claims
CLAIMS 1. Rogowski type sensor (1) configured to measure an electric current passing through an electrical element, the sensor (1) comprising a printed circuit (10), said printed circuit (10) comprising: - at least two upper tracks (12', 12”) extending along a first plane (P1): - at least one lower track (14') extending along a second plane (P2) parallel to the first plane (P1), the upper tracks (12', 12”) and said at least one lower track (14') being configured to surround the electrical element; and - vias (16, 16', 16”) connecting the upper tracks (12', 12”) to said at least one lower track (14'), the sensor (1) further comprising a conductive wire (18) comprising several turns (19), each turn (19) comprising an upper portion (182), a lower portion (186) and an intermediate portion (184) connecting the upper portion (182) to the lower portion (186), the upper portion (182) of each turn (19) extending on an upper face (122) of an upper track (12', 12”) among the upper tracks (12', 12”), the lower portion (186) of each turn (19) extending on a lower face (142) of a lower track (14') among the at least one lower track (14'), and the intermediate portion (184) passing through one of the vias (16, 16', 16”) connecting said upper track (12', 12”) to said lower track (14'),the sensor (1) being characterized in that each lower track among the at least one lower track (14') comprises a first portion (146) facing an upper track (12') among said at least two upper tracks (12', 12”), and a second portion (148) facing an upper track adjacent (12”) to said upper track (12')., 2. Rogowski type current sensor (1) according to claim 1, comprising a return track (17) between said at least two upper tracks (12', 12”) and said at least one lower track (14), the return track (17) extending along a third plane (P3) parallel to the first plane (P1) and to the second plane (P2), the return track (17) being configured to surround the electrical element, the conductive wire (18) passing through the return track (17).
3. Rogowski type current sensor (1) according to one of claims 1 or 2, wherein the first portion (146) of the at least one lower track (14') represents two thirds of the at least one lower track (14') and the second portion (148) of the at least one lower track (14') represents one third of the at least one lower track (14').
4. Rogowski type current sensor (1) according to one of claims 1 or 2, in which the first portion (146) and the second portion (148) each represent a half of the at least one lower track (14').
5. Rogowski type current sensor (1) according to one of claims 1 to 4, in which the at least one lower track (14') and the upper tracks (12', 12”) are identical to each other.
6. Rogowski type current sensor (1) according to one of claims 1 to 5, wherein the first portion (146) of the at least one lower track (14') comprises a first via (16') among said vias (16, 16', 16”) and the second portion (148) of the at least one lower track (14') comprises a second via (16”) among said vias (16, 16', 16”).
7. Rogowski type current sensor (1) according to one of claims 1 to 6, wherein the at least one lower track (14') comprises four vertices, the first via (16') and the second via (16”) being positioned near two vertices not adjacent to each other.
8. Rogowski type current sensor (1) according to claim 5, wherein the at least one lower track (14') comprises four sides (1400, 1401, 1402, 1403), two sides (1400, 1402) among the four sides being straight and two sides (1401, 1403) among the four sides being curved, one curved side (1401) connecting the two straight sides (1400, 1402).
9. Rogowski type current sensor (1) according to one of the preceding claims, in which the at least two upper tracks (12', 12”) are spaced from the at least one lower track (14') by a distance of less than 5 millimeters, and preferably equal to 1.5 millimeters.
10. Rogowski type current sensor (1) according to one of the preceding claims, in which the at least two upper tracks (12', 12”) and the at least one lower track (14') are made of copper.