An Eddy Current Based Non-contact Displacement Sensor
25 May 2020-pp 1-6
TL;DR: A signal conditioning circuit is presented in this paper which measures the difference in inductance between two coils and a suitable algorithm has been developed to calculate the displacement using the corresponding inductance values.
Abstract: This paper presents a novel, non-contact displacement sensor based on the eddy current sensing technique. The moving part of the sensor is a conductive sheet with a simple surface groove. This part is easy to fabricate as the machining process required is simple. The moving part is not electrically connected to the measurement system, like the eddy current proximity sensor. The displacement of the moving part is determined by the change in the inductance of four identical stationary planar coils kept underneath the moving part. A signal conditioning circuit is presented in this paper which measures the difference in inductance between two coils. A suitable algorithm has been developed to calculate the displacement using the corresponding inductance values. A prototype has been fabricated in the laboratory to evaluate the performance. The test result shows that the maximum error is less than 1.65%. The output of the prototype sensor was linear for the full range, as expected. It is well suited for application where the vertical space available for the installation is limited. The overall thickness of the developed sensor is less than 5 mm.
Citations
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TL;DR: In this paper, an open-source tool that allows for fast and precise analytical calculation of multi-layer planar coils self-inductance, without any geometry limitation is proposed.
Abstract: An open-source tool that allows for a fast and precise analytical calculation of multi-layer planar coils self-inductance, without any geometry limitation is proposed here. The process of designing and simulating planar coils to achieve reliable results is commonly limited on accuracy and or geometry, or are too time-consuming and expensive, thus a tool to speed up this design process is desired. The model is based on Grover equations, valid for any geometry. The validation of the tool was performed through the comparison with experimental measurements, Finite Element Model (FEM) simulations, and the main analytical methods usually used in literature, with errors registered to be below 2.5%, when compared to standard FEM simulations, and when compared to experimental measurements they are below 10% in the case of the 1-layer coils, and below 5% in the 2-layer coils (without taking into consideration the coil connectors). The proposed model offers a new approach to the calculation of the self-inductance of planar coils of several layers that combines precision, speed, independence of geometry, easy interaction, and no need for extra resources.
8 citations
TL;DR: Wang et al. as discussed by the authors proposed a novel temperature compensation approach for ECS problem using an improved sparrow search algorithm (ISSA) and radial basis function neural network (RBFNN).
Abstract: Eddy-current displacement sensor (ECS) has been applied widely to the production of modern industry by reason of its characteristics of high sensitivity, good reliability, powerful anti-interference capacity, and noncontact measurement. However, it cannot be used when severe temperature drift occurs at high temperature. Some traditional compensation methods are difficult to achieve good performance with neglecting the nonlinearity. Hence, it is essential to propose a better method for temperature compensation. A novel temperature compensation approach for ECS problem using an improved sparrow search algorithm (ISSA) and radial basis function neural network (RBFNN) is proposed in this article. In the ISSA, a chaos strategy is introduced in the algorithm for avoiding local optimal point, and an elite opposition-based learning strategy is integrated to promote global search ability of ISSA with high efficiency. RBFNN is elected to model the temperature drift, and its parameters are determined by the proposed ISSA. The proposed method compensates the significant deterministic errors caused by temperature variation within a wide temperature range. The experimental schemes were designed to the effectiveness of the proposed method according to data fusion technology. The various test results obtained confirm the potential and effectiveness of the proposed approach compared to some other traditional temperature compensation methods presented in the literatures.
3 citations
10 Mar 2021
TL;DR: In this article, a tool based on Grover equations was developed to calculate the self-inductance of planar coils with a general geometry, and the results achieved using this method, considering different coil geometries and dimensions, were compared with the main analytical methods that can be found in the literature.
Abstract: This paper presents a versatile tool for the self-inductance calculation of planar coils. Due to the growing interest in planar coils in the past few years, the possibility of using an analytical model as a valid alternative to FEM simulations, regarding versatility and result reliability, would be of great interest. The ideal scenario would be to combine speed, precision, easy interaction and understanding, while adding versatility in terms of geometry. To achieve that, a tool, based on Grover equations, that calculates the self-inductance of planar coils with a general geometry has been developed. The results achieved using this method, considering different coil geometries and dimensions, were compared with the main analytical methods that can be found in the literature, proving the reliability of the proposed method. This model has the novelty of not having any limitation on the coil geometry or dimension, which is not the case for the other existing methods.
DOI•
TL;DR: In this article , a thin eddy-current-based angle sensor is realized by converting the shaft, whose rotation angle is to be measured, into the sensing element, and the modification to the shaft is minimal; a small surface groove is introduced without affecting the mechanical strength.
Abstract: Eddy current sensors are an attractive choice due to their high resolution, reliability, and durability in harsh environments while being able to measure in a noncontact manner. This article presents a novel design to realize a thin eddy-current-based angle sensor. It is realized by converting the shaft, whose rotation angle is to be measured, into the sensing element. The modification to the shaft is minimal; a small surface groove is introduced without affecting the mechanical strength. The stationary part of the sensor consists of two layers of flexible square-planar coils. Depending on the angular position of the shaft, the inductances of the planar coils get modified. These are measured using a specially designed circuitry, optimized for this sensor. The output for the entire circle range (360°) is derived from the inductance values of each coil using a successive approximation algorithm developed for this purpose. Finite-element analysis was employed to design the sensor and analyze the axial/radial misalignment of the rotor. A sensor prototype was built and tested. The output showed a resolution of 0.1° and the worst case linearity error of 0.9%. The prototype sensor dimensions are designed to fit in a standard steering column. The proposed sensor is thin, easy to manufacture at low cost, tolerant to axial vibration by design, and has a 360° sensing range.
30 Oct 2022
TL;DR: In this article , a planar-electrode sensor was developed with relatively large electrodes that was capable of measuring low electrical conductivity values on sand samples collected near a sea turtle nesting site, requiring only 2 g of dried sand from each sample collection location.
Abstract: Even though sea turtles have worldwide distribution, many species are classified as endangered. To help ensure their survival, an important research topic is how sea turtles select their nesting sites along beaches. Several beach parameters have been suggested as possible factors for nesting site selection, including sand salinity, which is determined by measuring the electrical conductivity (EC) of an aqueous solution prepared from mixing a precise mass of the dried sand into a known volume of deionized water, since salinity is proportional to electrical conductivity when adjusted for temperature. Typically, 50 g of dried sand is mixed into 50 mL of deionized water, yielding an evaluation solution. However, this quantity of sand could limit the number of measurements made at a site to avoid disturbing the nest. In this work, a low-cost printed circuit board based planar-electrode EC sensor was developed with relatively large electrodes that was capable of measuring low EC values. Using this sensor, EC measurements were made on sand samples collected near a sea turtle nesting site, requiring only 2 g of dried sand from each sample collection location. This much smaller quantity of sand required for each EC measurement could allow for additional testing samples near a nesting site without adversely affecting it.
References
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TL;DR: This paper presents a review of the latest advances in the field of capacitive, inductive (eddy current), and magnetic sensors, for measurement of absolute displacement, based on both theoretical analysis and experimental results.
Abstract: This paper presents a review of the latest advances in the field of capacitive, inductive (eddy current), and magnetic sensors, for measurement of absolute displacement. The need for accurate displacement and position measurement in the micrometer, nanometer, and subnanometer scales has increased significantly over the last few years. Application examples can be found in high-tech industries, metrology, and space equipment. Besides measuring displacement as a primary quantity, absolute displacement sensors are also used when physical quantities such as pressure, acceleration, vibration, inertia, etc., have to be measured. A better understanding of the commonalities between capacitive, inductive, and magnetic displacement sensors, as well as the main performance differences and limitations, will help one make the best choice for a specific application. This review is based on both theoretical analysis and experimental results. The main performance criteria used are: sensitivity, resolution, compactness, long-term stability, thermal drift, and power efficiency.
87 citations
05 Jun 2005
TL;DR: In this paper, a capacitive displacement sensor is designed and fabricated for measurement of a large displacement with very high accuracy, which is a kind of linear encoder with an array of micro electrodes made by micromachining processes, and two patterned electrodes on the sensor substrates are assembled facing each other after being coated with thin dielectric film.
Abstract: A new capacitive displacement sensor is designed and fabricated for measurement of a large displacement with very high accuracy. This sensor is a kind of linear encoder with an array of micro electrodes made by micromachining processes. The two patterned electrodes on the sensor substrates are assembled facing each other after being coated with thin dielectric film. Due to the thin dielectric film, it is highly sensitive to displacement but minimizes expected misalignments such as a tilting error. The sensor fabricated as a sample has a grating of electrodes with a width of 100 /spl mu/m, which is coated with a diamond-like carbon (DLC) film 0.8 /spl mu/m thick. The proposed sensor was tested to conclude that its resolution is 9.07 nanometers for the measuring range of 15 millimeters and that the linearity error is expected to be less than 0.02% throughout the measurable range.
84 citations
TL;DR: A contact-type linear encoder-like capacitive displacement sensor (CLECDS) is proposed in this paper, which consists of two substrates with a series of conducting grating in identical size.
Abstract: In this paper, a contact-type linear encoder-like capacitive displacement sensor (CLECDS) is proposed. It is based on the linear encoder capacitive displacement sensor that consists of two substrates with a series of conducting grating in identical size and it is used as a contact sensor of which the two substrates assembled faced to each other after coated with thin dielectric film. It was confirmed that the prototype of this sensor has resolution of about 126nm and measuring range of 20 mm in the test.
46 citations
"An Eddy Current Based Non-contact D..." refers background in this paper
...Although noncontact sensors based on capacitive [1], [2], and optical [3] techniques are available, their output is sensitive to dust and humidity....
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TL;DR: In this article, a planar spiral coil-based inductive displacement sensor is presented, which employs a fixed planar coil and a movable $U$ -shaped magnetic core.
Abstract: A new, non-contact, planar spiral coil-based inductive displacement sensor is presented in this paper. The proposed sensor employs a fixed planar coil and a movable $U$ -shaped magnetic core. The sensor is designed such a way that the shape of inductance versus displacement $x$ is sinusoidal. Due to this feature, the value of $x$ is obtained easily from the inductance measured without the need of a look-up table, which is not the case for most of the planar coil-based sensors. The proposed sensor has very low sensitivity to vertical misalignment of the core. A phase-sensitive detector-based measurement scheme is employed to measure the inductance. The inductance characteristic of the proposed sensor is symmetric with respect to the center of the coil. A simple capacitive detection scheme to distinguish the position of the core between the two halves of the coil is proposed in this paper. This method enables to extend the sensor range with multiple coils connected in series. A prototype of the proposed sensor has been developed and tested. The sensor has a worst case error of 0.6%. A modified sensor using two coil sets has been developed. The modified sensor has high sensitivity over its entire range, unlike the first prototype. It has a worst case error of 0.2% and a resolution of 6.5 $\mu \text{m}$ . The low-cost sensor developed will be useful for many industrial linear position sensing applications.
40 citations
"An Eddy Current Based Non-contact D..." refers background in this paper
...Non-contact inductive displacement sensors have been reported but they require specially fabricated shapes having high relative permeability [6], [7]....
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TL;DR: Each inductive coil shape has its own advantages and disadvantages and is proposed to be the pattern that can achieve good sensing performance of a linear displacement sensor.
Abstract: This paper discusses the effect of inductive coil shape on the sensing performance of a linear displacement sensor. The linear displacement sensor consists of a thin type inductive coil with a thin pattern guide, thus being suitable for tiny space applications. The position can be detected by measuring the inductance of the inductive coil. At each position due to the change in inductive coil area facing the pattern guide the value of inductance is different. Therefore, the objective of this research is to study various inductive coil pattern shapes and to propose the pattern that can achieve good sensing performance. Various shapes of meander, triangular type meander, square and circle shape with different turn number of inductive coils are examined in this study. The inductance is measured with the sensor sensitivity and linearity as a performance evaluation parameter of the sensor. In conclusion, each inductive coil shape has its own advantages and disadvantages. For instance, the circle shape inductive coil produces high sensitivity with a low linearity response. Meanwhile, the square shape inductive coil has a medium sensitivity with higher linearity.
38 citations
"An Eddy Current Based Non-contact D..." refers background in this paper
...Non-contact inductive displacement sensors have been reported but they require specially fabricated shapes having high relative permeability [6], [7]....
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