CN1356546A - Array-type flexible electric eddy sensor - Google Patents

Abstract

The invention relates to an array type flexible eddy current sensor, which belongs to the technical field of sensors. It includes a sensitive coil array distributed in a certain way on a film substrate made by a flexible printed circuit board process, a lead-out cable composed of a lead-out signal line and a ground wire connected to each sensitive coil, a multi-way selector switch, and a multi-way selector. A clapp oscillator circuit with a pass switch and said signal line connected to ground. The invention has a thin structure, is not easily deformed, has good temperature performance, good consistency, and the base is in a flexible state, and is especially suitable for gap measurement between metal curved surfaces and non-metal curved surfaces.

Description

Array type flexible eddy current sensor

technical field

The invention belongs to the technical field of sensors, in particular to the structural design of an eddy current sensor.

Background technique

Eddy current testing technology is a non-destructive, non-contact measurement testing technology. The eddy current sensor has the advantages of simple structure, high sensitivity, large measurement linear range, no influence of oil and other media, and strong anti-interference ability. It is widely used in machinery, electric power, petroleum, chemical, textile, aviation, atomic energy and other industrial sectors. application. For example, it is used to measure displacement, size, thickness, vibration, speed, pressure, conductivity, temperature and other parameters and detect metal parts defects.

The sensitive element of the traditional eddy current sensor is a coil made of enameled wire. Coil size is greatly affected by temperature, therefore, its temperature performance is poor. At the same time, the parameters of the wound coils are quite different, which is not suitable for array application or mass production. Due to the limitations of the manufacturing process, this type of coil has a large structural size, is easy to deform, has poor temperature performance, and poor consistency, and is not suitable for curved surface measurement occasions, nor is it suitable for rapid measurement occasions in a large area. There are also some studies that use printed circuit board technology to process sensitive coils on the circuit board, or use photolithography and other micro-fabrication processes to process micro-coils on silicon substrates. These eddy-current sensor substrates are in a rigid state and can only be used in planar measurement applications.

The traditional eddy current sensor frequency modulation circuit generally adopts the clapper circuit. As shown in Figure 1, the circuit consists of triodes, resistors, capacitors, and sensitive coils. The triode is the core component of the oscillating circuit. Four resistors Rb1, Rb2, Rc, and Re determine the DC operating point of the triode. Capacitors Cb, C1, and C2 are connected to the triode of the triode, and together with the capacitor C3 and the sensitive coil, form a capacitive three-point oscillation circuit. . The disadvantage of this circuit is that it is difficult to start oscillation when the quality factor of the sensitive coil is small.

Contents of the invention

The purpose of the present invention is to propose an array type flexible eddy current sensor in order to overcome the shortcomings of the prior art. It has a thin structure, not easy to deform, good temperature performance, good consistency, and the substrate is in a flexible state, especially suitable for gap measurement between metal curved surfaces and non-metal curved surfaces.

An array type flexible eddy current sensor proposed by the present invention is characterized in that it includes an array of sensitive coils distributed in a certain way on a film substrate made by flexible printed circuit board technology (FPCB), and an output signal connected to each sensitive coil Line and the lead-out cable that ground wire is formed, multi-way selector switch, and the Clapp oscillating circuit that is connected with ground wire by multi-way selector switch and said signal line.

The present invention selects materials and designs according to measurement conditions and requirements. The film base can be made of flexible materials suitable for FPCB technology, such as polyimide film, polyester film and the like.

The distribution mode and shape of the coil array can also be designed arbitrarily. Said sensitive coil can be made into single layer, double layer or even multiple layers, and the shape of sensitive coil can be circular, square or other shapes. Each coil array has two lead wires: signal wire and ground wire. The ground wire and signal wire of each sensitive coil are brought together to form a close-packed cable, and the ground wires of each coil can also be connected in parallel. The other end of the cable is made into a FPC (Flexible Printed Circuit) plug, which is connected to a multi-channel strobe switch.

Said oscillating circuit is based on the traditional clapper circuit, and an inductance L connected in parallel with the sensitive coil is set. The inductance value of the inductance L is more than 10 times the inductance value of the sensitive coil, and the resistance value is smaller than the resistance value of the coil. The improved circuit is more suitable for sensitive coils with small quality factors.

The working mode and principle of the array sensor of the present invention are shown in Fig. 2, and are described as follows:

The sensitive coil array is attached to the non-metallic curved surface (including the plane) 2, and the sinusoidal alternating current I1 is passed through the coil ₁ through the oscillating circuit. The current I ₁ will generate a sinusoidal alternating magnetic field H ₁ , and the metal curved surface 2 in the alternating magnetic field H ₁ will induce an eddy current I ₂ , and I ₂ will also generate an alternating magnetic field H ₂ , the direction of H ₂ and H ₁ in the opposite direction. Due to the reaction of the magnetic field H ₂ , the inductance and resistance parameters of the coil change, so that the output frequency of the oscillation circuit changes. Fix other parameters so that the output frequency of the circuit is only related to the gap x between the coil and the metal surface, so that the gap between the coil and the metal surface can be determined according to the output frequency value. In actual work, the sensitive coils are scanned in a rapid cycle through the multi-channel strobe switch, and the distance from each coil to the metal surface is measured. Since the distribution of these coils is known, the gap between the metal curved surface and the non-metal curved surface can be obtained by performing data processing on the measurement results.

Features of the present invention:

1. In the present invention, the base material of the sensitive coil array and its lead-out cables is in a flexible state, so the sensitive coil can be attached to any non-metallic surface for measurement. However, traditional eddy current sensors cannot be installed on curved surfaces for measurement.

2. It can perform rapid measurement in a large area. Due to the adoption of the FPCB process, the sensitive coil array can be distributed in a large area (1000mm×500mm or even larger), thereby realizing the measurement of a large area. However, other processes, such as photolithography and other microfabrication processes, cannot fabricate large-area flexible sensor arrays, so it is also difficult to achieve large-area measurement. If a single sensor is used to measure a large area, it is necessary to use a mechanical device to control the sensor or the measured target to move regularly, which will inevitably affect the speed and accuracy of the measurement. However, in the present invention, a multiplex switch is used to realize fast cycle scanning of the sensor array. Scanning a channel takes only 20 milliseconds.

3. Ultra-thin. The minimum thickness of the sensitive coil array and its outgoing cables can be 0.11mm, which is suitable for installation in a narrow space for measurement.

4. Closely packed cables. The lead wires of the sensitive coil array and the common ground wire are brought together to form a densely packed long cable, which makes the structure more compact. Due to the circular scanning measurement method, at any time, only one channel of the cable has signal transmission, so the signals transmitted by the cable do not interfere with each other.

5. Improved circuit. In the flexible coil of the present invention, the inductance value is small and the resistance value is relatively large, so the quality factor of the coil is small. Aiming at this characteristic of the sensor, the traditional Clapp circuit is improved, and the quality factor of the circuit is improved. At the same time, the improved circuit improves the consistency among the channels of the sensitive coil array.

6. Compared with the traditional eddy current sensor, the present invention can be applied to more measurement occasions, such as curved surface measurement, rapid measurement in a large area, and measurement in a narrow space. If the base material is polyimide, the sensor array can also be used in high temperature (300-400° C.), radiation and other measurement occasions.

7. The present invention adopts a flexible printed circuit board processing technology, and the coil inductance parameter is not affected by temperature, so the system has good temperature performance. The processing technology also greatly improves the consistency among the coils, making the present invention more suitable for mass production.

The invention can achieve excellent performance index.

Resolution: 1μm

Sensitivity: 100Hz/μm

Measurement accuracy: ±1%FS

Temperature drift: -84Hz/℃

Measuring range: 0-5mm or higher.

Description of drawings

Figure 1 is the schematic diagram of the clapp oscillation circuit of the traditional eddy current sensor

Fig. 2 is a schematic diagram of the working mode and principle of the present invention.

Fig. 3 is a structural schematic diagram of several sensitive coil embodiments of the present invention.

Fig. 4 is a schematic structural diagram of Embodiment 1 of the array type flexible eddy current sensor of the present invention.

Fig. 5 is a circuit diagram of the improved Clapper circuit of Embodiment 1 and Embodiment 2 of the present invention.

Fig. 6 is a schematic structural diagram of embodiment 2 of the array type flexible eddy current sensor of the present invention.

Detailed ways

The structure of several sensitive coil embodiments designed by the present invention is shown in Figure 3. The sensitive coil is made on a flexible material film substrate suitable for the process by using the FPCB process, wherein: the coil 11 is a single-layer spiral circle in Figure 3 (a) Coil, the front lead-out line 113 is a signal line, the back lead-out line (reverse line is indicated by a dotted line, the same below) 112 is a ground wire, and the front and back windings are connected through the central via hole 111; the coil 12 in Fig. 3 (b) is a double Layer spiral circular coil, its front lead-out line 123 is a signal line, the back lead-out line 122 is a ground wire, and the front and back windings are connected through the central via hole 121; the coil 13 in Fig. 3 (c) is a single-layer spiral square coil, and its front The lead-out line 133 is a signal line, the lead-out line 132 on the back is a ground wire, and the front and back windings are connected through the central via hole 131; the coil 14 in FIG. 3( d ) is a double-layer square coil. The lead-out line 143 on the front side is a signal line, the lead-out line 142 on the back side is a ground wire, and the winding lines on the front and back sides are connected through the central via hole 141 .

The structure of Embodiment 1 of the array type flexible eddy current sensor designed by the present invention is shown in Figure 4. In the figure, the sensor array flexible substrate 3 is made of polyimide film, and its shape is three horizontal arms and a connecting one On the central vertical arm, on the three horizontal arms of the film substrate 3, three groups of 12 double-layer sensitive square coils 1 with a side length of 10 mm are fabricated by FPCB technology. The center distance of each coil in each group is 62.5mm. The distance between groups was 280mm. The lead wires of each sensitive coil and the common ground wire are collected and fabricated on the central vertical arm of the film 3 to form a cable 4 with a width of 10 mm. The end of the cable 4 is made into an FPC plug, which is connected to the improved Clapper circuit through a multi-channel strobe switch. , and then set an inductance L connected in parallel with the sensitive coil. The value of inductance L in this circuit is 22μH. The total size of the sensitive coil array and its outgoing cables is 1000mm×250mm.

The inner diameter parameters of long steel pipes can be measured by using the array type flexible eddy current sensor of this embodiment. When in use, attach the sensitive coil array of the sensor to a non-metallic rod with an outer diameter of 79.6mm, and send it into the steel pipe through a mechanical device, so that the axis of the non-metallic rod and the steel pipe to be tested (about 85mm in diameter and 2.5m in length) are basically coincide. The 12-way sensor is cyclically scanned to obtain the output frequency of the 12-way sensor, and according to the pre-calibrated data, the output frequency is converted into the gap between the coil and the inner wall of the metal pipe. Since the 4 coils of each group are symmetrically arranged on the non-metallic rod, the inner diameters of the steel pipe at these three positions can be obtained by simply processing the three sets of data. By turning the steel pipe around, you can measure the inner diameter values at three positions at the other end of the steel pipe.

The structure of Embodiment 2 of the array type flexible eddy current sensor designed by the present invention is shown in Figure 6, in the figure: the sensor array flexible base 3 is made of polyester film, and its shape is like a round fan, and the diameter on the fan base is Six single-layer circular coils 1 with a diameter of 15 mm are evenly produced on a circumference of 240 mm by FPCB technology, and at the same time, a coil with the same parameters is also produced on the center of the circle. Lead wires (solid lines) and common ground wires (dotted lines) of these 7 coils are brought together to form a cable 3 with a width of 8 mm and a length of 450 mm. The cable 3 is made on the elongated fan handle base 3 . The other end of the cable is made into an FPC plug, and is connected to the improved Clapper circuit through a multiplex switch, as shown in Figure 5. The total size of the sensitive coil array and its outgoing cables is 750mm×300mm.

In some harsh environments, it is necessary to monitor a small gap (0-2 mm) between a large metal plane (circle) and a non-metal plane, which can be solved by using this embodiment. During measurement, the sensor array is attached to the non-metallic plane, and the distance between each sensor and the metal plane can be measured by cyclic scanning of the sensor array, and the gap relationship between the metal plane and the non-metal plane can be determined through data processing .

Claims (5)

1. An array type flexible eddy current sensor is characterized in that it includes a sensitive coil array distributed in a certain way on a film substrate made by a flexible printed circuit board process, and consists of an outgoing signal line connected to each sensitive coil and a ground wire The lead-out cable, the multiplex switch, and the Clapp oscillation circuit connected to the ground through the multiplex switch and said signal line. 2. The array type flexible eddy current sensor according to claim 1, characterized in that said film substrate is made of polyimide film, polyester film and other flexible materials suitable for flexible printed circuit board technology. 3. The array type flexible eddy current sensor according to claim 1, characterized in that, the sensitive coil is one of single layer, double layer, or multilayer, and the shape of the coil is circular, square or other shapes . 4. The array type flexible eddy current sensor as claimed in claim 1, characterized in that each of said sensitive coils has a signal wire and two ground wires; the ground wire and signal wire of each sensitive coil are brought together , to form an outgoing densely packed cable, the other end of which is provided with a plug connected to a multi-way strobe switch. 5. The array type flexible eddy current sensor as claimed in claim 1, characterized in that, said oscillating circuit is based on the traditional clapper circuit, and an inductance L connected in parallel with the sensitive coil is set again; the inductance L The inductance value is more than 10 times the inductance value of the sensitive coil, and its resistance value is smaller than the resistance value of the coil.

Images