Low-frequency vibration sensor and method based on time difference measurement

Abstract

The invention belongs to the technical field of vibration measurement, and particularly provides a low-frequency vibration sensor and method based on time difference measurement, and the sensor comprises a sensor pedestal, the sensor pedestal is provided with an upper supporting plate, a waveguide wire is fixed between the sensor pedestal and the upper supporting plate, and a control module is connected with two points of the waveguide wire through wires to form a closed loop. The part, connected into the closed loop, of the waveguide wire is an access loop section, the control module sends out pulse current to flow in the closed loop and excites a pulse excitation magnetic field in the circumferential direction of the access loop section, and the access loop section of the waveguide wire penetrates through the permanent magnet ring; the upper end of the waveguide wire is provided with a first detection coil, the first detection coil is fixed on the sensor base through a reed, the first detection coil is connected to the control module through a cable, and the control module is provided with a leading-out cable connected to the plug. The low-frequency vibration sensor and method based on time difference measurement can directly measure the amplitude of vibration, and have the characteristics of high reliability and high precision.

Description

Technical Field

[0001] The present invention belongs to the technical field of vibration measurement, and in particular, relates to a low-frequency vibration sensor and method based on time difference measurement. Background Art

[0002] The vibration parameters of the frames, top covers and other parts of large hydro-turbine generator sets during operation are characterized by vibration amplitude according to industry standards. The existing technology uses magnetoelectric vibration sensors to measure the vibration velocity and calculates the vibration amplitude by integration. The defects and shortcomings of the existing technology are as follows: First, the sensor does not directly measure the vibration amplitude, but indirectly measures it by integral calculation, which is easy to cause errors and reduce the accuracy of vibration measurement; second, the vibration of the frames, top covers and other parts of large hydro-turbine generator sets is mainly low-frequency vibration, with a lower frequency limit of 0.02Hz. At low-frequency vibration, the measurement signal of the magnetoelectric vibration sensor is distorted and the signal is small and is greatly interfered by environmental noise.

[0003] The detection principle of magnetostrictive displacement / liquid level sensor is to use the Widman effect between the magnetostrictive waveguide wire and the vernier magnetic ring, which are the core detection elements of the sensor. The general method is as follows. During measurement, the excitation module applies a query pulse at both ends of the waveguide wire. The pulse forms a circular magnetic field around the waveguide wire at the speed of light. When the circular magnetic field interacts with the magnetic field of the vernier magnetic ring, a Widman effect torsional stress wave is formed on the surface of the waveguide wire. The stress wave propagates from the generation point to both ends of the waveguide wire at the speed of sound. The stress wave transmitted to the end is absorbed by the damping device, and the signal transmitted to the head end is received by the detection device. The calculation module calculates the time difference between the query pulse and the stress wave reception signal, and then multiplies it by the propagation speed of the torsional stress wave in the waveguide material to calculate the distance between the receiving point and the vernier magnetic ring, thereby realizing real-time and accurate measurement of displacement / liquid level. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a low-frequency vibration sensor and method based on time difference measurement, which can directly measure the vibration amplitude of an object.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a low-frequency vibration sensor based on time difference measurement, including a sensor base, an upper support plate is provided on the sensor base, a waveguide wire is fixed between the sensor base and the upper support plate and is vertically non-disturbance-free, a control module is connected to two points on the waveguide wire through a wire to form a closed loop, the part where the waveguide wire is connected to the closed loop is an access loop section, the control module sends a pulse current to flow in the closed loop, and excites a pulse excitation magnetic field in the circumferential direction of the access loop section, a lower support plate is provided on the sensor base, and a waveguide wire is provided on the lower support plate. The waveguide wire passes through a through hole, the permanent magnetic ring is fixed on the lower support plate and is sleeved on the outside of the waveguide wire, the access loop section of the waveguide wire passes through the permanent magnetic ring, the magnetic field of the permanent magnetic ring interacts with the circumferential pulse excitation magnetic field of the access loop section, and an axial stress pulse wave is generated in the waveguide wire; a first detection coil is provided at the upper end of the waveguide wire, the first detection coil is sleeved on the outside of the waveguide wire and fixed to the sensor base through a spring leaf, the first detection coil can slide up and down relative to the waveguide wire, the first detection coil is connected to the control module through a cable, the control module is provided with a lead-out cable connected to a plug, and the plug is used to be electrically connected to the acquisition system.

[0006] In a preferred solution, a second detection coil is arranged at the upper end of the waveguide wire. The second detection coil is arranged above the first detection coil and is sleeved on the outer side of the upper end of the waveguide wire and fixed on the upper support plate. The second detection coil is connected to the control module via a cable.

[0007] In a preferred solution, the sensor base is a cylindrical structure, and the waveguide wire, the control module, the first detection coil, the second detection coil and the reed are all arranged in the cylindrical structure of the sensor base.

[0008] In a preferred solution, a fixing bolt is provided at the bottom of the sensor base for connecting with the object to be measured.

[0009] The present invention also provides a method for measuring low-frequency vibration based on time difference, using the above-mentioned low-frequency vibration sensor based on time difference measurement to perform vibration measurement, comprising the following steps: Step 1: Fix the sensor base to the object to be measured by fixing bolts. When the object vibrates, the sensor base, waveguide wire, permanent magnet ring and the second detection coil vibrate synchronously. The first detection coil is softly connected to the sensor base through the reed. Under the action of inertia, it does not vibrate synchronously with the sensor base, and relative sliding and displacement occur between it and the waveguide wire. Step 2: When the control module is working, a pulse current is sent to the access loop section of the waveguide wire. When the pulse current passes through the access loop section, a pulse excitation magnetic field is excited in its circumferential direction. This pulse excitation magnetic field interacts with the magnetic field of the permanent magnet ring, and a twist occurs in the axial position of the waveguide wire, generating a stress pulse wave, which propagates along the waveguide wire and passes through the first detection coil and the second detection coil. Step three, the first detection coil dynamically slides on the waveguide wire as the object under test vibrates, and transmits the real-time induced stress pulse wave signal to the control module. The control module synchronously measures the time of the stress pulse wave signal, calculates the time difference between the induced stress pulse wave signals in dynamic and static states and the sliding displacement of the first detection coil, and reflects the vibration amplitude of the object under test.

[0010] In the preferred solution, in step 3, after calculating the sliding displacement of the first detection coil relative to the waveguide wire caused by the vibration of the measured object, the vibration amplitude value can be directly obtained by using the inertial vibration amplitude-frequency characteristic and the vibration test bench calibration method. The calculation formula is: S=V×(T 测 -T0); (1) ; (2) In the above formula, S represents the sliding displacement of the first detection coil relative to the waveguide wire; V represents the propagation speed of the stress pulse wave in the waveguide wire; T 测 Indicates the time when the first detection coil senses the stress pulse wave signal in the dynamic state of vibration; T0 indicates the time when the first detection coil senses the stress pulse wave signal in the static state; Y represents the vibration amplitude of the object under test; ω represents the vibration frequency of the object under test; c represents the damping coefficient of the sensor; m represents the mass of the first detection coil assembly; and k represents the elastic stiffness of the reed.

[0011] In a preferred embodiment, the calculation formula for the propagation speed V of the stress pulse wave in the waveguide wire is: ; (3) In the above formula, G represents the shear modulus; ρ Indicates the waveguide filament density.

[0012] In a preferred solution, in step 3, the real-time propagation speed V of the stress pulse wave is calculated by measuring the difference between the time when the second detection coil (6) induces the stress pulse wave and the time when the known pulse current is emitted. 校 , real-time propagation speed of stress pulse wave V 校 The calculation formula is: V 校 =L / (T 校 -T); (4) In the above formula, V 校 represents the measured speed; L represents the distance between the second detection coil and the permanent magnet ring, which is a constant value; T 校 It indicates the time when the second detection coil senses the stress pulse wave; T indicates the time when the pulse current is emitted.

[0013] In a preferred solution, the correction vibration amplitude of the measured object is calculated by the formula: S校 =V 校 ×(T 测 -T0); (5) ; (6) In the above formula, S 校 It represents the sliding displacement of the first detection coil relative to the waveguide wire after correction, Y 校 Indicates the corrected vibration amplitude of the measured object.

[0014] The present invention provides a low-frequency vibration sensor and method based on time difference measurement, which has the following beneficial effects: 1. Utilizing the Wiedemann effect and the Villari effect, the first detection coil dynamically slides on the waveguide wire as the object under test vibrates, and transmits the real-time induced stress pulse wave signal to the control module. The control module synchronously measures the time of the stress pulse wave signal, calculates the time difference between the induced stress pulse wave signal in the dynamic and static states and the sliding displacement of the first detection coil (5), and reflects the vibration amplitude of the object under test.

[0015] 2. In the present invention, the vibration amplitude measurement accuracy is determined by the time measurement accuracy, which changes the way in which the vibration amplitude measurement accuracy is determined by the electrical signal measurement accuracy in the traditional measurement method, avoids the problems of electrical signals being easily distorted and easily disturbed by environmental noise in low-frequency vibration situations, and improves the measurement accuracy of the sensor.

[0016] 3. In the present invention, the position of the permanent magnetic ring relative to the waveguide wire is fixed, and the waveguide wire will not be repeatedly magnetized due to movement, thereby eliminating the displacement hysteresis effect caused by the hysteresis effect of the material and improving the measurement accuracy of the sensor.

[0017] 4. The distance between the second detection coil and the permanent magnet ring is fixed. By measuring the time when the stress pulse wave is induced by the second detection coil and the difference between the time when the known pulse current is emitted, the real-time propagation speed of the stress pulse wave is calculated. This method can correct and compensate in real time the influence of factors such as ambient temperature on the shear modulus of the waveguide wire, thereby causing the propagation speed of the stress pulse wave in the waveguide wire to be unstable, thereby improving the measurement accuracy of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will be further described below in conjunction with the accompanying drawings and embodiments: Figure 1 It is a structural schematic diagram of the low-frequency vibration sensor of the present invention; In the figure: sensor base 1, waveguide wire 2, access loop section 201, permanent magnet ring 3, control module 4, first detection coil 5, second detection coil 6, reed 7, upper support plate 8, lower support plate 9, plug 10, fixing bolt 11. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0020] Embodiment 1: like Figure 1 As shown, a low-frequency vibration sensor based on time difference measurement includes a sensor base 1. In this embodiment, the measuring base 1 is a cylindrical structure, an upper support plate 8 is provided on the sensor base 1, a waveguide wire 2 is fixed between the sensor base 1 and the upper support plate 8, and the waveguide wire 2 is vertically arranged without vertical disturbance. The control module 4 is connected to the lower end and one point in the middle of the waveguide wire 2 through a wire to form a closed loop. The part of the waveguide wire 2 connected to the closed loop is the access loop section 201. The control module 4 sends a pulse current to flow in the closed loop and excites a pulse excitation magnetic field in the circumferential direction of the access loop section 201. The lower end of the waveguide wire 2 is covered with a permanent magnet ring 3, and the access loop section 201 of the waveguide wire 2 passes through the permanent magnet ring 3. The magnetic field of the permanent magnet ring 3 interacts with the circumferential pulse excitation magnetic field of the access loop section 201 to generate an axial stress pulse wave in the waveguide wire 2; a first detection coil 5 is provided at the upper end of the waveguide wire 2, the first detection coil 5 is covered on the outside of the waveguide wire 2 and fixed on the sensor base 1 through a reed 7, the first detection coil 5 can slide up and down relative to the waveguide wire 2, the first detection coil 5 is connected to the control module 4 through a cable, and the control module 4 is provided with a lead-out cable connected to a plug 10, the plug 10 is used to be electrically connected to the acquisition system, specifically, the plug 10 is electrically connected to the acquisition system through a cable, and the acquisition system is connected to the PC control terminal.

[0021] Preferably, the sensor base 1 is provided with a lower support plate 9, the lower support plate 9 is provided with a through hole for the waveguide wire 2 to pass through, and the permanent magnetic ring 3 is fixed on the lower support plate 9. The permanent magnetic ring 3 and the waveguide wire 2 do not produce relative motion, so as to avoid the hysteresis effect caused by the waveguide wire 2 being repeatedly magnetized by the permanent magnetic ring 3, thereby improving the vibration amplitude measurement accuracy and the response frequency.

[0022] Preferably, a fixing bolt 11 is provided at the bottom of the sensor base 1 for connecting with the object to be measured.

[0023] The first detection coil 5 can slide dynamically and change position on the waveguide wire 2 with the vibration of the measured object, and sense stress pulse wave signals at different positions. The control module 4 measures the time when the stress pulse wave signals are sensed in the dynamic and static states, and calculates the time difference to reflect the vibration amplitude of the measured object. The time measurement accuracy determines the vibration amplitude measurement accuracy. This changes the traditional way that the electrical signal measurement accuracy determines the vibration amplitude measurement accuracy. It avoids the problems of electrical signal distortion in low-frequency vibration situations and interference of environmental noise on the signal, and improves the sensor measurement accuracy.

[0024] Embodiment 2: Using a low-frequency vibration sensor based on time difference measurement in Example 1, vibration measurement is performed based on time difference, including the following steps: Step 1: Fix the sensor base 1 on the object to be measured. When the object vibrates, the sensor base 1, the waveguide wire 2, the permanent magnet ring 3 and the second detection coil 6 vibrate synchronously. The first detection coil 5 is softly connected to the sensor base 1 through the reed 7. Under the action of inertia, it does not vibrate synchronously with the sensor base 1, and relative motion and displacement occur between it and the waveguide wire 2.

[0025] Step 2: When the control module 4 is working, a pulse current is emitted to the access loop section 201 of the waveguide wire 2. When the pulse current passes through the access loop section 201, a pulse excitation magnetic field is excited in its circumferential direction. This pulse excitation magnetic field interacts with the magnetic field of the permanent magnet ring 3, and twists the waveguide wire 2 in the axial position, generating a stress pulse wave, which propagates along the waveguide wire 2 and passes through the first detection coil 5 and the second detection coil 6.

[0026] Step three, the first detection coil 5 dynamically slides on the waveguide wire 2 with the vibration of the object under test, and transmits the real-time induced stress pulse wave signal to the control module 4. The control module 4 synchronously measures the time of the stress pulse wave signal, calculates the time difference between the induced stress pulse wave signal in dynamic and static states and the sliding displacement of the first detection coil 5, and reflects the vibration amplitude of the object under test.

[0027] After calculating the sliding displacement of the first detection coil 5 relative to the waveguide wire 2 caused by the vibration of the measured object, the vibration amplitude value can be directly obtained by using the inertial vibration amplitude-frequency characteristic and the vibration test bench calibration method. The calculation formula is: S=V(T 测 -T0); (1) Y = f (S, ω, c, m, k); (2) In formula (1), S represents the sliding displacement of the first detection coil 5 relative to the waveguide wire; V represents the propagation speed of the stress pulse wave in the waveguide wire; T 测 It indicates the time when the first detection coil 5 senses the stress pulse wave signal in the dynamic vibration state; T0 indicates the time when the first detection coil 5 senses the stress pulse wave signal in the static state.

[0028] In formula (2), Y represents the vibration amplitude of the object under test; ω represents the vibration frequency of the object under test; c represents the damping coefficient of the sensor; m represents the mass of the first detection coil 2 component; and k represents the elastic stiffness of the reed.

[0029] f(S,ω,c,m,k) represents a function, and the specific expression is: .

[0030] In a preferred solution, in step 3, the calculation formula for the propagation speed V of the stress pulse wave in the waveguide wire is: ; (3) In formula (3), G represents the shear modulus; ρ Indicates the waveguide filament density.

[0031] Embodiment 3: Different from the second embodiment, in the step 3, the real-time propagation speed V of the stress pulse wave is calculated by measuring the difference between the time when the second detection coil 5 induces the stress pulse wave and the time when the known pulse current is emitted. 校 , real-time propagation speed of stress pulse wave V 校 The calculation formula is: V 校 =L / (T 校 -T); (4) In formula (4), V 校 represents the measured speed; L represents the distance between the second detection coil 5 and the permanent magnet ring 3, which is a constant value; T 校 It indicates the time when the second detection coil 5 senses the stress pulse wave; T indicates the time when the pulse current is emitted.

[0032] The correction vibration amplitude of the measured object is calculated as follows: S 校 =V 校 ×(T 测 -T0); (5) Y 校 =f(S 校 ,ω,c,m,k); (6) ; In formula (5), S 校 represents the sliding displacement of the first detection coil 5 relative to the waveguide wire 2 after correction. In formula (6), Y 校 Indicates the corrected vibration amplitude of the measured object.

[0033] By using the Wiedemann effect and the Villari effect, the first detection coil 5 can slide dynamically and change position on the waveguide wire 2 with the vibration of the object under test, and induce stress pulse wave signals at different positions. The control module 4 measures the time when the stress pulse wave signal is induced in the dynamic and static conditions; measures the time when the stress pulse wave is induced by the second detection coil 6, and the difference between the time when the known pulse current is emitted, and calculates the real-time propagation speed of the stress pulse wave; Through the time difference of the induced stress pulse wave signal in dynamic and static state and the real-time propagation speed of the stress pulse wave, the sliding displacement of the first detection coil 5 is calculated to reflect the vibration amplitude of the object under test. In this example, first, the vibration amplitude measurement accuracy is determined by the time measurement accuracy, which changes the way in which the vibration amplitude measurement accuracy is determined by the electrical signal measurement accuracy in the traditional measurement method, avoids the problem that the electrical signal is easily distorted and easily disturbed by environmental noise in low-frequency vibration occasions, and improves the sensor measurement accuracy; second, the position of the permanent magnet ring 3 relative to the waveguide wire is fixed, eliminating the displacement hysteresis effect caused by the material hysteresis effect, and improving the sensor measurement accuracy; third, the real-time propagation speed of the stress pulse wave is calculated by the second detection coil 6, and the influence of the shear modulus of the waveguide wire due to factors such as ambient temperature is corrected and compensated in real time, thereby causing the propagation speed of the stress pulse wave in the waveguide wire to be unstable, and improving the sensor measurement accuracy.

[0034] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A low-frequency vibration sensor based on time difference measurement, characterized in that: The invention comprises a sensor base (1), an upper support plate (8) is provided on the sensor base (1), a waveguide wire (2) is fixed between the sensor base (1) and the upper support plate (8) and is vertically free of disturbance, a control module (4) is respectively connected to two points on the waveguide wire (2) through a wire to form a closed loop, the portion of the waveguide wire (2) connected to the closed loop is an access loop section (201), the control module (4) emits a pulse current flowing in the closed loop and excites a pulse excitation magnetic field in the circumferential direction of the access loop section (201), a lower support plate (9) is provided on the sensor base (1), a through hole is provided on the lower support plate (9) for the waveguide wire (2) to pass through, and a permanent magnetic ring (3) is fixed on the lower support plate ( 9) and is sleeved on the outside of the waveguide wire (2), the access loop section (201) of the waveguide wire (2) passes through the permanent magnet ring (3), the magnetic field of the permanent magnet ring (3) interacts with the circumferential pulse excitation magnetic field of the access loop section (201), and an axial stress pulse wave is generated in the waveguide wire (2); a first detection coil (5) is provided at the upper end of the waveguide wire (2), the first detection coil (5) is sleeved on the outside of the waveguide wire (2) and is fixed to the sensor base (1) through a reed (7), the first detection coil (5) can slide up and down relative to the waveguide wire (2), the first detection coil (5) is connected to the control module (4) through a cable, and the control module (4) is provided with a lead-out cable connected to the plug (10).

2. A low-frequency vibration sensor based on time difference measurement according to claim 1, characterized in that: A second detection coil (6) is arranged at the upper end of the waveguide wire (2); the second detection coil (6) is arranged above the first detection coil (5) and is sleeved on the outer side of the upper end of the waveguide wire (2) and fixed on the upper support plate (8); the second detection coil (6) is connected to the control module (4) via a cable.

3. A low-frequency vibration sensor based on time difference measurement according to claim 2, characterized in that: The sensor base (1) is a cylindrical structure, and the waveguide wire (2), the control module (4), the first detection coil (5), the second detection coil (6) and the reed (7) are all arranged in the cylindrical structure of the sensor base (1).

4. A low-frequency vibration sensor based on time difference measurement according to claim 1, characterized in that: A fixing bolt (11) is provided at the bottom of the sensor base (1) for connecting with the object to be measured.

5. A method for measuring low-frequency vibration based on time difference, characterized in that: Using a low-frequency vibration sensor based on time difference measurement as described in any one of claims 1 to 4 to perform vibration measurement comprises the following steps: Step 1: fix the sensor base (1) to the object to be measured by means of fixing bolts (11); when the object vibrates, the sensor base (1), the waveguide wire (2), the permanent magnetic ring (3) and the second detection coil (6) vibrate synchronously; the first detection coil (5) is softly connected to the sensor base (1) via the reed (7); under the action of inertia, it does not vibrate synchronously with the sensor base (1), and relative sliding and displacement occur between it and the waveguide wire (2); Step 2: When the control module (4) is in operation, a pulse current is emitted to the access loop section (201) of the waveguide wire (2). When the pulse current passes through the access loop section (201), a pulse excitation magnetic field is excited in its circumferential direction. The pulse excitation magnetic field interacts with the magnetic field of the permanent magnet ring (3), causing a twist in the axial position of the waveguide wire (2), generating a stress pulse wave, which propagates along the waveguide wire (2) and passes through the first detection coil (5) and the second detection coil (6); Step 3: The first detection coil (5) dynamically slides on the waveguide wire (2) as the object under test vibrates, and transmits the real-time induced stress pulse wave signal to the control module (4). The control module (4) synchronously measures the time of the stress pulse wave signal, calculates the time difference between the induced stress pulse wave signal in the dynamic state and the static state and the sliding displacement of the first detection coil (5), and reflects the vibration amplitude of the object under test.

6. The method for measuring low-frequency vibration based on time difference according to claim 5, characterized in that: In the step 3, after calculating the sliding displacement of the first detection coil (5) relative to the waveguide wire (2) caused by the vibration of the measured object, the vibration amplitude value can be directly obtained by using the inertial vibration amplitude-frequency characteristic and the vibration test bench calibration method. The calculation formula is: S=V×(T 测 -T0);(1) ；（2） In the above formula, S represents the sliding displacement of the first detection coil relative to the waveguide wire; V represents the propagation speed of the stress pulse wave in the waveguide wire; T 测 Indicates the time when the first detection coil senses the stress pulse wave signal in the vibration dynamics; T0 represents the time when the first detection coil senses the stress pulse wave signal in static state; Y Indicates the vibration amplitude of the object being measured; ω represents the vibration frequency of the object under test; c represents the damping coefficient of the sensor; m represents the mass of the first detection coil assembly; and k represents the elastic stiffness of the reed.

7. The method for measuring low-frequency vibration based on time difference according to claim 6, characterized in that: The calculation formula for the propagation speed V of the stress pulse wave in the waveguide wire is: ；（3） In the above formula, G represents the shear modulus; ρ Indicates the waveguide filament density.

8. The method for measuring low-frequency vibration based on time difference according to claim 5, characterized in that: In step 3, the real-time propagation speed V of the stress pulse wave is calculated by measuring the difference between the time when the second detection coil (6) induces the stress pulse wave and the time when the known pulse current is emitted. 校 , real-time propagation speed of stress pulse wave V 校 The calculation formula is: V 校 =L / (T 校 -T);(4) In the above formula, V 校 represents the measured speed; L represents the distance between the second detection coil and the permanent magnet ring, which is a constant value; T 校 Indicates the time when the second detection coil senses the stress pulse wave; T represents the time when the pulse current is emitted.

9. The method for measuring low-frequency vibration based on time difference according to claim 8, characterized in that: The correction vibration amplitude of the measured object is calculated as follows: S 校 =V 校 ×(T 测 -T0);(5) ；（6） In the above formula, S 校 It represents the sliding displacement of the first detection coil relative to the waveguide wire after correction, Y 校 Indicates the corrected vibration amplitude of the measured object.

Images