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EP-4065751-B1 - ELECTRIC FIELD GRADIENT SENSOR

EP4065751B1EP 4065751 B1EP4065751 B1EP 4065751B1EP-4065751-B1

Inventors

  • DORRESTIJN, Igor Konrad

Dates

Publication Date
20260506
Application Date
20201126

Claims (14)

  1. An electric field gradient sensor (1), comprising: - a sensor body (2) having an outer surface; and - a plurality of electrodes (4) distributed over said surface, each electrode having an electrode surface facing outward from said surface; wherein said plurality of electrodes (4) are arranged forming a plurality of electrode pairs, each electrode pair comprising a first electrode and a second electrode located on opposite sides of said sensor body (2), wherein for each electrode pair an imaginary interconnecting line is formed interconnecting the first electrode and the second electrode, and wherein said electrodes (4) are distributed over said surface such that said imaginary interconnecting lines intersect at one single point of intersection (6) within the sensor body (2), wherein the electric field gradient sensor (1) further comprises sensor electronics (10) for measuring a voltage over each of said electrode pairs, said sensor electronics (10) comprising electrical contacts to each of said plurality of electrodes (4), characterized in that : the electric field gradient sensor (1) further comprises a bias electrode (8) arranged for setting a bias voltage for said sensor electronics (10), wherein said bias electrode (8) is arranged at said single point of intersection (6).
  2. Sensor (1) according to claim 1, wherein each electrode is provided with a non-conductive tube (34), a first end of said tube (34) enclosing said electrode, preferably wherein said non-conductive tubes (34) extend in a substantially radial direction outwards from said sensor body (2) and/or wherein said non-conductive material comprises a plastic material, a flexible polymer or rubber.
  3. Sensor (1) according to any preceding claim, wherein said single point of intersection (6) substantially corresponds to a geometrical center of said sensor body (2), and/or wherein said sensor body (2) has a substantially spherical shape, preferably wherein said sensor body (2) has an oblate spheroid shape or a prolate spheroid shape, or wherein said sensor body (2) has a substantially cylindrical shape.
  4. Sensor (1) according to any one of the preceding claims, wherein said sensor electronics (10) is arranged within said sensor body (2) or at a vehicle to which the sensor (1) is mounted, more preferably wherein said sensor electronics (10) further comprises a microcontroller for sampling a differential voltage over each electrode pair, preferably wherein said sensor electronics (10) further comprises one or more of the following: amplifiers (26) for amplifying measured voltages, a power source, and a communication unit (28) for communicating said measured voltages to a receiver arranged remote from said sensor (1).
  5. Sensor (1) according to any one of the preceding claims, wherein said sensor body (2) comprises a plastic material and/or a composite material, and/or wherein said electrode surfaces comprise gold, carbon, platinum, titanium or stainless steel, or wherein said electrodes (4) are formed by gold plated circuit boards, gold plated circuit boards printed with carbon; or by metal plated with gold or platinum.
  6. Sensor (1) according to any one of the preceding claims, wherein said plurality of electrodes (4) comprises between 6 to 40 electrodes (4), preferably between 20 to 34, more preferably 24 or 32 electrodes (4), and/or wherein the sensor further comprises a mounting component coupled to said sensor body (2) for mounting said sensor (1) to a vehicle, in particular to an unmanned underwater vehicle (16), and/or wherein said sensor body (2) is hollow and is provided with a plurality of holes (14) in its outer surface.
  7. System for measuring an electric field gradient at a structure located in an electrically conductive medium, the system comprising: - the electric field gradient sensor (1) according to any of claims 1-6,; - an unmanned underwater vehicle (16), wherein the electrical field gradient sensor (1) is mounted to the unmanned underwater vehicle (16); and - sensor electronics (10) for measuring a voltage over each of said electrode pairs, said sensor electronics (10) comprising electrical contacts to each of said plurality of electrodes (4); wherein said plurality of electrodes (4) are arranged forming a plurality of electrode pairs, each electrode pair comprising a first electrode and a second electrode located on opposite sides of said sensor body (2).
  8. System according to claim 7, wherein said sensor electronics (10) is arranged within said sensor body (2) or in said vehicle, and/or wherein said single point of intersection (6) substantially corresponds to a geometrical center of said sensor body (2), and/or wherein said sensor electronics (10) further comprises a microcontroller for sampling a differential voltage over each electrode pair, preferably wherein said sensor electronics (10) further comprises one or more of the following: amplifiers (26) for amplifying measured voltages, a power source, and a communication unit (28) for communicating said measured voltages to a receiver arranged remote from said sensor (1) .
  9. System according to claim 7 or 8, wherein said sensor body (2) comprises a plastic material and/or a composite material, and/or wherein said sensor body (2) is hollow and is provided with a plurality of holes (14) in its outer surface.
  10. Method for manufacturing an electric field gradient sensor (1), comprising the steps of: - providing sensor electronics (10); - forming a sensor body (2) around said sensor electronics (10), said sensor body (2) having an outer surface; and - forming a plurality of electrodes (4) distributed over said surface, each electrode having an electrode surface facing outward from said surface and being electrically connected to said sensor electronics (10); wherein said plurality of electrodes (4) are arranged such as to form a plurality of electrode pairs, each electrode pair comprising a first electrode and a second electrode located on opposite sides of said sensor body (2), wherein for each electrode pair an imaginary interconnecting line is formed interconnecting the first electrode and the second electrode, and wherein said electrodes (4) are distributed over said surface such that said imaginary interconnecting lines intersect at one single point of intersection (6) within the sensor body , characterized in that : the electric field gradient sensor (1) further comprises a bias electrode (8) arranged for setting a bias voltage for said sensor electronics (10), wherein said bias electrode (8) is arranged at said single point of intersection (6).
  11. Method according to claim 10, wherein said single point of intersection (6) substantially corresponds to a geometrical center of said sensor body (2), and/or wherein said sensor body (2) is formed by 3D printing, or wherein said sensor body (2) is formed by molding or machining, preferably wherein said sensor body (2) comprises a plastic material or a composite material, or wherein said step of forming said plurality of electrodes (4) comprises providing electrodes (4) having the outward facing electrode surface comprising gold, carbon, platinum, titanium or stainless steel, more preferably wherein said electrode surface is formed by plating gold or platinum onto a metal.
  12. Method according to claim 10 or 11, wherein said step of forming said plurality of electrodes (4) comprises plating circuit boards with gold, and/or wherein said step of forming said plurality of electrodes (4) comprises printing carbon onto gold plated circuit boards, and/or wherein the method further comprises attaching a nonconducting tube (34) to each of said electrodes (4) such that a first end of said tube (34) encloses said electrode, said tube (34) extending radially outwards from said sensor body (2).
  13. Method of performing electric field gradient measurements of a structure located in an electrically conducting medium, comprising the steps of: - providing an electric field gradient sensor (1) according to any one of claims 1 to 6; - mounting said sensor to an unmanned underwater vehicle (16); and - moving said vehicle along at least a part of said structure, while sampling differential voltages over said electrode pairs of said sensor at a plurality of sampling locations.
  14. Method according to claim 13, wherein said sensor (1) is maintained substantially fixed with respect to said vehicle, and/or wherein said differential voltages are combined to form an electric field gradient vector at each of said plurality of sampling locations, and/or wherein the method further comprises registering the position of each sampling location.

Description

Field of the invention The present invention relates to an electric field gradient sensor for measuring the electric field around and/or along a structure located in an electrically conducting medium. The electric field gradient sensor is in particular useful for assessing the state of cathodic protection of pipelines, marine and/or subsea structures. Background art Structures, such as pipelines, marine structures, etc., located under water, e.g. in sea, are often provided with cathodic protection for preventing corrosion of the structure. However, the cathodic protection may become damaged or degrade with time, or be otherwise defective. Therefore, there exists a need to assess and/or monitor the status of the cathodic protection. Measurements of the status of cathodic protection have conventionally been performed by contact measurements using a stab or probe stepped over the structure. This is however a rather time consuming procedure. Faster measurements can be achieved by sensors configured for performing non-contact measurements while being moved along the structure. WO 2017/126975 A1 presents a method and a sensor for detection of electric fields around a structure in an electrically conducting medium while moving the sensor along the structure. This sensor comprises two electrodes located on a rotating disc, enabling measuring the electrical field in the rotation plane of the disc. For measuring the electric field in three dimensions two sensors are required, arranged at a 90° angle to one another. This leads to a complex instrument, relying on rotating parts and having complex electronics inside. The instrument further has a relatively large weight, which has to be taken into account when using the sensor. EP3163288A2 discloses a set for the inspection of the cathodic protection conditions of subsea pipelines, including: a device or probe with two reference electrodes for measuring a potential difference or electrical potential gradient in close proximity to a subsea pipeline to be inspected; and a probe for the execution of contact potential measurements and of resistivity measurements of the seabed where a subsea pipeline to be inspected is buried. The device or probe, with the reference electrodes, and the probe, with a contact tip, are separated and can be separately arranged and positioned. US2010/185348A1 discloses an autonomous underwater vehicle for monitoring underwater fluid currents by detecting electrical currents induced by the flow of a conductive liquid through the Earth's magnetic field and to the gathering of data related to underwater fluid currents and the control of vehicle motion during data gathering. WO2009/067015A1 discloses an underwater measurement system for monitoring an underwater region. The system includes a sensor assembly operable to sense at least one physical variable in the region for generating at least one sensor signal, and a data processing arrangement for processing the at least one sensor signal to generating processed data for presentation or logging. The sensor assembly includes one or more voltage sensors configured to sense electric fields present in the underwater region and provide information in the at least one signal indicative of the electric fields. JP2000304533A discloses electrodes for detecting electric potential differences under water, which are arranged on two points on a first and a second line perpendicularly crossing to each other and on two points on a third line perpendicular to them and further discloses differential amplifier circuits, a depth indicator measuring the depth in water with the electric field sensor, a position displacement calculation circuit calculating the position displacement of the ship from the output of the differential amplifier circuits and the depth measured with the depth indicator, and a data recorder. JP2016060451A discloses an underwater information measuring device capable of detecting an underwater electric field. The device comprises pairs of electrodes formed on the surface of a spherical shell and being arranged at positions opposite to each other, i.e. positions that are point-symmetrical with respect to the centre of the spherical shell. WO2015/177499A1 discloses a detection apparatus and method arranged to detect defects within a flexible pipe at least partially surrounded by seawater, comprising a seawater electrode, arranged to be in contact with seawater surrounding at least part of a flexible pipe, an impedance monitor, arranged to measure the impedance between a metallic structural component of the flexible pipe, and a processor, arranged to determine the distance from the seawater electrode to a pipe defect electrically connecting the metallic structural component to seawater using the measured impedance. CN108614163A discloses a three-dimensional electric field sensor comprising a packaging structure, an electric field sensitive unit, packaged in the packaging structure, and a plurality of di