PVDF target embedded stress sensor working characteristics calibration system and method

Abstract

The present invention is a system and method for calibrating the working characteristics of a stress sensor embedded in a PVDF target. It comprises a pressure-generating oil cylinder arranged on a working platform of an excitation load application device, a calibration piston rod connected to the interior of the oil cylinder arranged at the upper end of the pressure-generating oil cylinder, a PVDF stress sensor to be calibrated rigidly connected to the upper surface of the mounting platform of the calibration piston rod, a force-transmitting mass block having the same cross-section as the sensitive surface of the PVDF stress sensor to be calibrated rigidly connected to the sensitive surface of the PVDF stress sensor to be calibrated; an acceleration sensor is mounted on the lower surface of the mounting platform of the calibration piston rod, and a standard pressure sensor mounting hole connected to the interior of the pressure cylinder is provided on the side of the pressure-generating oil cylinder. The present invention installs the sensor on the upper end face of the piston rod of the pressure-generating oil cylinder, applies a load to the sensor by striking the force-transmitting mass block on the sensor, relies on a standard pressure sensor installed on the side of the oil cylinder to monitor the pressure amplitude generated inside the oil cylinder, calculates the equivalent stress generated in the stress sensor, and realizes the working characteristics detection of the PVDF stress sensor.

Description

Technical Field

[0001] The present invention belongs to the technical field of sensor detection, and in particular relates to a system and method for calibrating the working characteristics of a PVDF target embedded stress sensor. Background Art

[0002] Measuring the dynamic changes in internal stress within concrete targets under implosion, penetration, or external blast loads is crucial for assessing their vulnerability. Using embedded PVDF stress sensors with excellent dynamic characteristics is a common method for testing internal stress within concrete targets. Accurately obtaining the operating characteristic parameters of PVDF stress sensors is crucial for ensuring accurate stress measurement.

[0003] PVDF stress sensors generally have poor static characteristics. Due to charge leakage, static calibration is not suitable for PVDF sensors. Currently, calibration of PVDF sensor operating characteristic parameters is mostly performed using quasi-static calibration, a common calibration method for stress sensors. Quasi-static calibration typically requires mounting the sensitive surface of the sensor being tested inside a pressure-generating cylinder to ensure that a quasi-static pressure load can be applied to the sensor. This requires the cylinder to have a mounting interface compatible with the sensor being tested. PVDF stress sensors are typically secured to the mounting bracket using adhesive bonding and lack fastening features such as mounting threads. Furthermore, due to the lack of a unified standard, the size and shape of PVDF stress sensors vary. Most common PVDF stress sensors are not round due to the presence of wire connectors. This makes it difficult to directly install PVDF stress sensors inside a pressure-generating cylinder. Installation tooling, or even the entire pressure-generating cylinder assembly, must be designed and manufactured specifically for the sensor's dimensions and structure. This significantly inconveniences the testing and calibration of PVDF stress sensors, resulting in a waste of manpower and resources, and significantly increases the time and difficulty required for sensor calibration. Summary of the Invention

[0004] The object of the present invention is to provide a system and method for calibrating the working characteristics of a PVDF target embedded stress sensor.

[0005] The technical solution for achieving the objectives of the present invention is as follows: a PVDF target embedded stress sensor working characteristic calibration system, comprising a pressure-generating oil cylinder arranged on a working platform of an excitation load applying device, a calibration piston rod connected to the interior of the oil cylinder provided at the upper end of the pressure-generating oil cylinder, a PVDF stress sensor to be calibrated rigidly connected to the upper surface of the mounting platform of the calibration piston rod, a force-transmitting mass block having the same cross-section as the sensitive surface of the PVDF stress sensor to be calibrated rigidly connected to the upper surface of the mounting platform of the calibration piston rod, the force-transmitting mass block being a cylinder; an acceleration sensor being installed on the lower surface of the mounting platform of the calibration piston rod, the interior of the pressure-generating oil cylinder being filled with a pressure-generating medium, and a standard pressure sensor mounting hole connected to the interior of the pressure-generating oil cylinder being provided on the side of the pressure-generating oil cylinder for mounting a standard pressure sensor;

[0006] The excitation load applying device applies nearly half-sine force loads of different amplitudes to the upper surface of the force-transmitting mass block.

[0007] Furthermore, the area of ​​the mounting platform of the calibration piston rod is larger than the area of ​​the sensitive surface of the PVDF stress sensor to be calibrated.

[0008] Furthermore, the PVDF stress sensor to be calibrated is mounted on the mounting platform at the upper end of the calibration piston rod by gluing.

[0009] Furthermore, the operating frequency band of the standard pressure sensor is larger than the effective frequency band of the pressure signal in the pressure-generating oil cylinder.

[0010] Furthermore, multiple standard pressure sensors are set up at the same time, and the average of the test results of the multiple standard pressure sensors is used as the final measurement result.

[0011] Furthermore, the excitation load applying device is a pendulum-type hydraulic generating device. During calibration, the installed pressure-generating cylinder is placed on the working platform of the pendulum-type hydraulic generating device; and the landing point of the hammer head of the pendulum-type hydraulic generating device is ensured to be on the central axis of the calibration piston rod; the pendulum-type hydraulic generating device controls the hammer head installed on the connecting rod to fall at different heights, thereby applying a nearly half-sine force load of different amplitudes to the upper surface of the force-transmitting mass block.

[0012] A method for calibrating the working characteristics of a PVDF target embedded stress sensor using the above system includes the following steps:

[0013] Step (1): The connecting rod is rotated to a specified angle by a pendulum hydraulic generating device and the hammer is released; the hammer head will swing freely under the action of gravity and eventually hit the force transmission mass block, generating a nearly semi-sinusoidal stress load on the sensitive surface of the PVDF sensor to be calibrated. At the same time, the downward pressure is transmitted to the calibration piston rod through the PVDF sensor to be calibrated. The calibration piston rod compresses the pressure medium inside the pressure cylinder, generating a nearly semi-sinusoidal pressure signal in the pressure cylinder;

[0014] Step (2): The acceleration sensor monitors the acceleration a(t) of the calibration piston rod, reads the pressure monitoring pressure value p(t) of the standard pressure sensor, and solves the equivalent stress curve of the PVDF stress sensor to be calibrated and the output curve of the PVDF stress sensor to be calibrated based on the dynamic model of the calibration system;

[0015] Step (3): adjusting the angle of the connecting rod and the hammer head to adjust the magnitude of the load generated in the PVDF stress sensor to be calibrated; obtaining the output curve of the PVDF stress sensor to be calibrated under stress load excitation of different amplitudes through multiple tests using the method of step (2);

[0016] Step (4): Relying on the least squares method to fit the equivalent stress and output value of the PVDF stress sensor to be calibrated to obtain the working characteristic curve of the PVDF stress sensor to be calibrated, and calculate the working characteristic parameter index of the PVDF stress sensor to be calibrated to achieve the calibration of the working characteristics of the PVDF stress sensor.

[0017] Furthermore, the kinetic model in step (2) is:

[0018] S2σ(t)-S1p(t)-f=(m1+m2+m3)(a(t)-g)

[0019] Where S2 is the sensitive surface area of ​​the PVDF stress sensor, S1 is the cross-sectional area of ​​the calibration piston rod, σ(t) is the stress load on the PVDF stress sensor, p(t) is the internal pressure of the pressure cylinder measured by the standard pressure sensor, f is the resistance encountered by the calibration piston rod during movement, m1 is the mass of the calibration piston rod, m2 is the mass of the PVDF stress sensor, m3 is the mass of the acceleration sensor, a(t) is the test result obtained by the acceleration sensor, and g is the acceleration due to gravity.

[0020] Ignoring the influence of resistance f under ideal lubrication conditions, the relationship between the stress load σ(t) applied to the PVDF stress sensor 4 to be calibrated, the pressure value p(t) monitored by the standard pressure sensor 2, and the acceleration a(t) monitored by the acceleration sensor 6 is:

[0021]

[0022] The equivalent stress curve of the PVDF stress sensor 4 and the output curve of the PVDF stress sensor are calculated by the above formula.

[0023] Compared with the prior art, the present invention has the following significant advantages:

[0024] The PVDF stress sensor is installed on the precision piston rod, and a standard pressure sensor is used to monitor the pressure generated inside the pressure cylinder when the PVDF stress sensor is subjected to force. An acceleration sensor is installed on the calibration piston rod to monitor the piston rod acceleration, thereby further calculating the equivalent stress on the PVDF stress sensor, thereby realizing a comparative calibration of the stress sensor. In this calibration method, the installation of the PVDF stress sensor is flexible and convenient, and is closer to the installation method of PVDF sensors in actual use. It avoids the need to redesign the pressure cylinder with corresponding mounting interfaces for PVDF stress sensors of different specifications during calibration, making the calibration of PVDF stress sensors more convenient. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the pressure-generating cylinder and its components of the PVDF target embedded stress sensor calibration system.

[0026] Figure 2 Schematic diagram of the installation of the pressure-generating cylinder on the pendulum-type hydraulic generating device.

[0027] Figure 3 Equivalent stress curve of PVDF stress sensor.

[0028] Figure 4 Output of PVDF strain sensor under equivalent stress.

[0029] Figure 5 Working characteristic curve of PVDF stress sensor.

[0030] Description of reference numerals:

[0031] 1-pressure-generating cylinder, 2-standard pressure sensor, 3-calibration piston rod, 4-PVDF stress sensor to be calibrated, 5-force-transmitting mass block, 6-acceleration sensor, 7-hammer, 8-connecting rod, 9-pendulum hydraulic generating device. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below with reference to the accompanying drawings.

[0033] The present invention proposes a method for calibrating the working characteristics of a stress sensor embedded in a PVDF target. This method designs a calibration piston rod with a sensor mounting platform for the PVDF stress sensor, replacing the pressure-generating cylinder piston rod in the original quasi-static calibration equipment. During calibration, the PVDF stress sensor is attached to the mounting platform at the upper end of the calibration piston rod, and an acceleration sensor is mounted on the piston rod to monitor the piston rod acceleration. A force-transmitting mass block is designed above the PVDF stress sensor. The force-transmitting mass block is a cylinder with a cross-section identical to the sensitive surface of the PVDF stress sensor and is used to ensure uniform force on the PVDF stress sensor during calibration. During calibration, a pendulum or drop-weight hydraulic generator strikes the upper end face of the force-transmitting mass block, generating a downward force, thereby producing an approximately half-sinusoidal stress load in the PVDF stress sensor. When the calibration piston rod is subjected to force, it compresses the pressure-generating medium within the cylinder, generating a corresponding pressure signal within the cylinder. A standard pressure sensor is mounted on the side of the cylinder to monitor the pressure signal within the cylinder. An accelerometer is mounted on the calibration piston rod to monitor its acceleration during movement. The pressure curve within the cylinder is used to calculate the stress load on the PVDF stress sensor. By comparing the PVDF stress sensor output with the calculated stress load, the sensor's operating characteristic parameters can be determined, enabling comparative calibration of the PVDF stress sensor.

[0034] The present invention proposes a method for calibrating the working characteristic parameters of a stress sensor embedded in a PVDF target. The system composition of the detection method is as follows: Figure 1 As shown, it includes a pressure-generating cylinder 1, a standard pressure sensor 2, a calibration piston rod 3, a PVDF stress sensor 4, a force-transmitting mass block 5 and an acceleration sensor 6;

[0035] The pressure-generating cylinder 1 has a cavity filled with a pressure-generating medium, and a calibration piston rod 3 is installed on the pressure-generating cylinder 1. The upper end of the calibration piston rod 3 has a large mounting surface for installing the PVDF stress sensor 4. The area of ​​this mounting surface is larger than the sensitive surface area of ​​the PVDF stress sensor to be calibrated. The PVDF stress sensor is mounted on the mounting surface at the upper end of the calibration piston rod 3 by gluing. During installation, the sensitive surface of the sensor faces upward. During installation, the sensitive surface of the PVDF stress sensor remains coaxial with the piston rod. There is an acceleration sensor mounting hole under the mounting platform of the calibration piston rod 3 for installing the acceleration sensor 6 to monitor the acceleration change a(t) of the calibration piston rod 3 during the calibration process. The calibration piston rod 3 is connected to the inside of the cylinder. When the calibration piston rod 3 is forced to move downward, it compresses the pressure-generating medium in the pressure-generating cylinder 1, thereby generating a corresponding pressure signal in the pressure-generating cylinder 1. The side of the pressure-building cylinder 1 has a standard pressure sensor mounting hole connected to the inside of the pressure-building cylinder 1, which is used to install a standard pressure sensor 2 to monitor the pressure p(t) inside the pressure-building cylinder 1 to obtain the equivalent stress σ(t) exerted on the PVDF stress sensor 4 during calibration.

[0036] Assume that the calibration piston rod 3 and PVDF stress sensor 4, and the PVDF stress sensor and force-transmitting mass block 5, are rigidly connected. The calibration piston rod 3 and force-transmitting mass block 5 are rigid bodies. Considering the calibration piston rod 3 and PVDF stress sensor 4 as a whole, their dynamic model can be expressed using formula (1).

[0037] S2σ(t)-S1p(t)-f=(m1+m2+m3)(a(t)-g) (1)

[0038] Where S2 is the sensitive surface area of ​​the PVDF stress sensor, S1 is the cross-sectional area of ​​the piston rod, σ(t) is the stress load on the PVDF stress sensor, p(t) is the internal pressure of the pressure-generating cylinder 1 detected by the standard pressure sensor 2, f is the friction and other resistance encountered by the piston rod when it moves, m1 is the mass of the piston rod, m2 is the mass of the PVDF stress sensor, m3 is the mass of the acceleration sensor, a(t) is the test result of the acceleration sensor, and g is the acceleration due to gravity.

[0039] Standard pressure sensor 2 is mounted on the side of the pressure-generating cylinder 1 to monitor pressure changes within the cylinder, thereby indirectly measuring the force acting on the piston rod. Standard pressure sensor 2 must accurately measure the pressure generated within the cylinder 1. This requires that its operating frequency band be larger than the effective frequency band of the pressure signal within the cylinder. To improve pressure monitoring accuracy, multiple standard pressure sensors can be installed simultaneously, with the average of their test results serving as the final measurement result. This improves the accuracy of pressure monitoring within the cylinder 1.

[0040] like Figure 2 As shown, a pendulum-type hydraulic generator 9 is used as an excitation load applying device. During calibration, the installed pressure-generating cylinder is placed on the working platform of the pendulum-type hydraulic generator 9. Ensure that the landing point of the hammer head of the pendulum-type hydraulic generator 9 is on the central axis of the piston rod. The pendulum-type hydraulic generator 9 controls the hammer head 7 installed on the connecting rod 8 to fall at different heights, thereby applying an approximately half-sine force load of different amplitudes to the upper surface of the force-transmitting mass block 5. The force-transmitting mass block 5 converts the force load it receives into a uniform stress load σ(t) applied to the sensitive surface of the PVDF stress sensor 4. Under good lubrication conditions, the friction force in formula (1) is very small, and the influence of the friction force f can be ignored during calculation. At this time, according to formula (1), the relationship between the stress load σ(t) on the PVDF stress sensor 4 and the pressure value p(t) monitored by the standard pressure sensor 2 and the acceleration a(t) monitored by the acceleration sensor 6 is:

[0041]

[0042] When calibrating the operating characteristic parameters of the PVDF sensor using this method, the control link 8 is rotated to a specified angle via the pendulum hydraulic generator 9 and the hammer is released. The hammer head 7 will swing freely under the action of gravity and will eventually strike the force-transmitting mass 5, thereby generating an approximately semi-sinusoidal stress load on the sensitive surface of the PVDF sensor 4. At the same time, the downward pressure is transmitted through the PVDF sensor 4 to the calibration piston rod 3, which compresses the pressure-generating medium inside the pressure-generating cylinder 1, thereby generating an approximately semi-sinusoidal pressure signal in the pressure-generating cylinder 1, as shown in Figure 2. Figure 4 As shown. At the same time, the acceleration sensor 6 installed on the calibration piston rod 3 can monitor the acceleration a(t) of the piston rod during this process. According to the pressure monitoring result p(t) of the standard pressure sensor 2 and the acceleration a(t) of the calibration piston rod 3, the equivalent stress curve of the PVDF sensor 4 and the output curve of the PVDF stress sensor can be calculated by formula (2), as shown in the figure below: Figure 3 Figure 4 As shown. By properly adjusting the angle of the connecting rod 8 and the falling angle of the hammer head 7, the magnitude of the force applied to the force-transmitting mass block 5 can be adjusted. Thus, the magnitude of the load generated in the PVDF stress sensor 4 can be adjusted. By using the above method and multiple tests, the output value of the PVDF sensor 4 under stress load excitation of different amplitudes can be obtained. By fitting the equivalent stress and output value of the PVDF sensor 4 with the least squares method, the working characteristic curve of the PVDF sensor 4 can be obtained as shown below. Figure 5 As shown, the working characteristic parameter indicators such as sensitivity and linearity of the PVDF sensor 4 can be calculated to achieve the calibration of the working characteristics of the PVDF stress sensor.

Claims

1. A method for calibrating the working characteristics of a PVDF target embedded stress sensor using a PVDF target embedded stress sensor working characteristics calibration system, characterized in that: The working characteristic calibration system of the PVDF target embedded stress sensor comprises a pressure-generating oil cylinder (1) arranged on a working platform of an excitation load applying device, a calibration piston rod (3) connected to the inside of the oil cylinder is arranged at the upper end of the pressure-generating oil cylinder (1), a PVDF stress sensor (4) to be calibrated is rigidly connected to the upper surface of the mounting platform of the calibration piston rod (3), a force transmission mass block (5) having the same cross section as the sensitive surface of the PVDF stress sensor (4) to be calibrated is rigidly connected to the sensitive surface of the PVDF stress sensor (4), and the force transmission mass block (5) is a column; an acceleration sensor (6) is installed on the lower surface of the mounting platform of the calibration piston rod (3), the inside of the pressure-generating oil cylinder (1) is filled with a pressure medium, and a standard pressure sensor mounting hole connected to the inside of the pressure-generating oil cylinder (1) is provided on the side of the pressure-generating oil cylinder (1) for mounting a standard pressure sensor (2); the excitation load applying device applies a nearly half-sine force load of different amplitudes to the upper surface of the force transmission mass block (5); the calibration piston rod (3) The area of ​​the mounting platform is larger than the area of ​​the sensitive surface of the PVDF stress sensor (4) to be calibrated; the PVDF stress sensor (4) to be calibrated is mounted on the mounting platform at the upper end of the calibration piston rod (3) by gluing; the working frequency band of the standard pressure sensor (2) is larger than the effective frequency band of the pressure signal in the pressure-generating oil cylinder (1); a plurality of standard pressure sensors are set at the same time, and the average value of the test results of the plurality of standard pressure sensors is used as the final measurement result; the excitation load applying device is a pendulum-type hydraulic generating device (9); during calibration, the installed pressure-generating oil cylinder is placed on the working platform of the pendulum-type hydraulic generating device (9); and it is ensured that the landing point of the hammer head (7) of the pendulum-type hydraulic generating device (9) is on the central axis of the calibration piston rod (3); the pendulum-type hydraulic generating device (9) controls the hammer head (7) mounted on the connecting rod (8) to fall at different heights, thereby applying nearly half-sine force loads of different amplitudes to the upper surface of the force-transmitting mass block (5); The method comprises the following steps: Step (1): The connecting rod (8) is rotated to a specified angle by a pendulum-type hydraulic generating device (9) and the hammer is released; the hammer head (7) will swing freely under the action of gravity and eventually hit the force transmission mass block (5), generating a nearly half-sine stress load on the sensitive surface of the PVDF stress sensor (4) to be calibrated. At the same time, the downward pressure is transmitted to the calibration piston rod (3) through the PVDF stress sensor (4) to be calibrated. The calibration piston rod (3) compresses the pressure medium inside the pressure cylinder (1), generating a nearly half-sine pressure signal in the pressure cylinder (1); Step (2): The acceleration sensor (6) monitors the acceleration a(t) of the calibration piston rod (3), reads the pressure monitoring pressure value p(t) of the standard pressure sensor (2), and solves the equivalent stress curve of the PVDF stress sensor (4) to be calibrated and the output curve of the PVDF stress sensor (4) to be calibrated according to the dynamic model of the calibration system; Step (3): adjusting the angle at which the connecting rod (8) and the hammer head (7) fall, thereby adjusting the magnitude of the load generated in the PVDF stress sensor (4) to be calibrated; obtaining the output curve of the PVDF stress sensor (4) to be calibrated under stress load excitation of different amplitudes through multiple tests using the method of step (2); Step (4): using the least squares method to fit the equivalent stress and output value of the PVDF stress sensor to be calibrated (4) to obtain a working characteristic curve of the PVDF stress sensor to be calibrated (4), and calculating the working characteristic parameter index of the PVDF stress sensor to be calibrated (4), thereby achieving calibration of the working characteristics of the PVDF stress sensor; The kinetic model in step (2) is: S2σ(t)-S1p(t)-f=(m1+m2+m3)(a(t)-g) Where S2 is the sensitive surface area of ​​the PVDF stress sensor, S1 is the cross-sectional area of ​​the calibration piston rod, σ(t) is the stress load on the PVDF stress sensor, p(t) is the internal pressure of the pressure cylinder measured by the standard pressure sensor, f is the resistance encountered by the calibration piston rod during movement, m1 is the mass of the calibration piston rod, m2 is the mass of the PVDF stress sensor, m3 is the mass of the acceleration sensor, a(t) is the test result obtained by the acceleration sensor, and g is the acceleration due to gravity. Ignoring the influence of resistance f under ideal lubrication conditions, the relationship between the stress load σ(t) on the PVDF stress sensor (4) to be calibrated, the pressure value p(t) monitored by the standard pressure sensor (2), and the acceleration a(t) monitored by the acceleration sensor (6) is: The equivalent stress curve of the PVDF stress sensor (4) and the output curve of the PVDF stress sensor are calculated by the above formula.

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