A PVDF piezoelectric sensor strain measurement circuit conditioning device

Abstract

The present application discloses a PVDF piezoelectric sensor strain measurement circuit conditioning device, comprising a PVDF intelligent sensing module (I) attached to a structure to be measured, and an input signal conditioning module (II), a charge-to-voltage module (III), a post-stage electrical signal amplification and denoising module (IV), and an output signal protection module (V) integrated into the same printed circuit board and sequentially connected. When the PVDF intelligent sensing module (I) generates an input charge signal, the signal passes through the input signal conditioning module (II), then through the charge-to-voltage module (III), and then into the post-stage electrical signal amplification and denoising module (IV). The signal then passes through the output signal protection module (V) and enters other data acquisition equipment or devices. The present invention aims to accurately measure strain information in the quasi-static and low-frequency ranges of the structure to be measured, thereby enabling health monitoring of key structural parts.

Description

Technical Field

[0001] The present application relates to the field of piezoelectric sensor measurement technology, and in particular to a PVDF piezoelectric sensor strain measurement circuit conditioning device. Background Art

[0002] PVDF (polyvinylidene fluoride) piezoelectric sensors, due to their excellent piezoelectric effect, anti-aging, chemical resistance, weather resistance, and UV resistance, are suitable for use in harsh environments and currently show great application prospects in strain measurement. PVDF piezoelectric sensors have fast response times and a wide measurement frequency range, and are primarily used in dynamic high-frequency strain measurement. However, the short retention time of the output charge of PVDF piezoelectric sensors limits their application in strain measurement within low-frequency or quasi-static frequency ranges. Therefore, a PVDF piezoelectric sensor strain measurement circuit conditioning device is needed to enable PVDF strain measurement in a quasi-static state. Currently, such conditioning circuit devices on the market and even in laboratories are mostly charge amplifiers with large time constants.

[0003] Currently available charge amplifiers generally have problems such as poor measurement signal quality, high noise, and low output sensitivity, resulting in large errors in the measurement results. For example, Emad Alnasser proposed a charge amplifier with low bias current influence that can be used at lower frequencies, but its minimum cutoff frequency can only reach 0.2Hz, which is far from enough for quasi-static measurement of structures. In addition, there is not much consideration for noise reduction performance (E.Alnasser, "A Novel Low Output Offset Voltage Charge Amplifier for Piezoelectric Sensors," in IEEE Sensors Journal, vol. 20, no. 10, pp. 5360-5367, 15 May 15, 2020, doi: 10.1109 / JSEN.2020.2970839.). The charge amplifier used by Zhou Lingbo et al. in the experiment can achieve basic static measurement by adjusting the time constant, but the general-purpose charge amplifier used has low output sensitivity and does not consider noise reduction processing (Zhou Lingbo, Hu Zhikuan, Sun Yudong, Duan Yong & Wu Jianghai. (2021). Quasi-static measurement method and uncertainty analysis of water hammer impact process. (eds.) Proceedings of the 18th Academic Symposium on Ship Underwater Noise (pp.1127-1134).). Summary of the Invention

[0004] The present invention aims to provide a strain measurement circuit conditioning device for a PVDF piezoelectric sensor, designed to accurately measure strain information within the quasi-static and low-frequency ranges of the structure being measured, enabling health monitoring of key structural components. Specifically, four operational amplifiers are used to condition the charge signal. The first stage circuit primarily consists of two charge amplifiers, whose primary purpose is to convert the PVDF output charge signal into a voltage signal suitable for measurement and acquisition. Due to its symmetrical design, its output sensitivity is twice that of a conventional single-charge amplifier conditioning circuit with the same configuration, improving measurement sensitivity. Two small-capacitance capacitors are connected in series at the PVDF input terminals, reducing voltage drift caused by insufficient PVDF insulation resistance. The second stage voltage amplifier circuit utilizes a symmetrical negative feedback voltage amplifier design. Adjusting the feedback resistor value allows the output voltage gain to be adjusted to meet the strain measurement requirements of different engineering materials. The symmetrical design suppresses common-mode noise and power-frequency noise entering the circuit, significantly improving the quality of the acquired signal. By adjusting the capacitance of the feedback capacitors at both ends of the charge amplifier, weak charge detection can be achieved.

[0005] To achieve the above objectives, the present invention provides the following technical solutions.

[0006] The present application discloses a PVDF piezoelectric sensor strain measurement circuit conditioning device, comprising a PVDF intelligent sensing module (I) attached to a structure to be measured, and an input signal conditioning module (II), a charge-to-voltage module (III), a post-stage electric signal amplification and denoising module (IV), and an output signal protection module (V) integrated into the same printed circuit board and sequentially connected. When the PVDF intelligent sensing module (I) generates an input charge signal, the signal passes through the input signal conditioning module (II), then through the charge-to-voltage module (III), and then into the post-stage electric signal amplification and denoising module (IV). The signal then passes through the output signal protection module (V) and into other data acquisition equipment or devices.

[0007] The PVDF intelligent sensing module (I) includes a PVDF sensor attached to the frame structure (1) and the cantilever beam (2). When the structure is affected by the outside world, the PVDF piezoelectric sensor generates a charge signal representing structural strain information. The generated charge signal enters the input signal conditioning module (II).

[0008] The input signal conditioning module (II) includes resistors R1 and R2 and capacitors C1 and C2. The resistor R1 is connected in series between the positive charge interface generated by the PVDF piezoelectric sensor and the capacitor C1. The resistor R2 is connected in series between the negative charge interface generated by the PVDF piezoelectric sensor and the capacitor C2. The ends of the capacitors C1 and C2 facing away from the resistors R1 and R2 are respectively connected to the charge-to-voltage module (III).

[0009] The charge-to-voltage module (III) includes touch switches SW1 and SW2, a resistor R 11 and R 12 , operational amplifiers N1 and N2, feedback resistors R3 and R4, feedback capacitors C3 and C4, touch switch SW1 is connected in parallel across the feedback resistor R3 and feedback capacitor C3, touch switch SW2 is connected in parallel across the feedback resistor R4 and feedback capacitor C4, feedback capacitor C3 is connected in parallel between the output terminal and the inverting input terminal of the operational amplifier N1 to form a circuit negative feedback, feedback capacitor C4 is connected in parallel between the output terminal and the inverting input terminal of the operational amplifier N2 to form a circuit negative feedback, feedback resistor R3 is connected in parallel across the feedback capacitor C3, feedback resistor R4 is connected in parallel across the feedback capacitor C4, resistor R 11 Connected in series between the inverting input terminal of operational amplifier N1 and capacitor C2, resistor R 12 Connected in series between the port of the reverse input terminal of the operational amplifier N2 and the capacitor C1,

[0010] The post-stage electrical signal amplification and denoising module (IV) includes input resistors R5 and R6, negative feedback resistors R7 and R8, and operational amplifiers N3 and N4. The input resistor R5 is connected in series between the output end of the operational amplifier N1 and the inverting input end of the operational amplifier N8. The input resistor R6 is connected in series between the output end of the operational amplifier N2 and the inverting input end of the operational amplifier N4. The negative feedback resistor R7 is connected in parallel between the output end and the negative feedback input end of the operational amplifier N3. The negative feedback resistor R8 is connected in parallel between the output end and the negative feedback input end of the operational amplifier N4.

[0011] The output signal protection module (V) includes resistors R9, R 10 , resistor R9 is connected in series to the output of operational amplifier N3, resistor R 10 Connected in series to the output terminal of operational amplifier N4.

[0012] Preferably, in the above-mentioned PVDF piezoelectric sensor strain measurement circuit conditioning device, the resistance values ​​of the resistors R3 and R4 are at the TΩ level.

[0013] Preferably, in the above-mentioned PVDF piezoelectric sensor strain measurement circuit conditioning device, the feedback capacitors C3 and C4 have the same specifications, and the feedback resistors R3 and R4 have the same specifications.

[0014] Preferably, in the above-mentioned PVDF piezoelectric sensor strain measurement circuit conditioning device, the negative feedback resistors R7 and R8 have the same or different resistance values, and their resistance range is 1-100KΩ.

[0015] Preferably, in the above-mentioned PVDF piezoelectric sensor strain measurement circuit conditioning device, the touch switches SW1 and SW2 are programmable analog switches or touch switches or normally open switches.

[0016] Preferably, in the above-mentioned PVDF piezoelectric sensor strain measurement circuit conditioning device, the feedback capacitors C3 and C4 are CB14 polystyrene precision capacitors whose capacitance is adjustable through analog switches.

[0017] Compared with existing technologies, the advantages of this invention include: a PVDF piezoelectric sensor strain measurement circuit conditioning device designed to measure structural strain information using a PVDF piezoelectric sensor. The output sensitivity of this PVDF piezoelectric sensor strain measurement circuit conditioning device is twice that of a conventional single charge amplifier conditioning circuit, improving measurement sensitivity; reducing voltage drift caused by insufficient PVDF insulation resistance, thereby enhancing the accuracy of the acquired signal; suppressing common-mode noise and power-frequency noise entering the circuit, significantly improving the quality of the acquired signal; and preventing equipment damage caused by output short circuits, thereby enhancing the reliability and safety of the device's operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 The figure shows a circuit schematic diagram of a PVDF piezoelectric sensor strain measurement circuit conditioning device in a specific embodiment of the present invention;

[0020] Figure 2 The figure shows a signal acquisition test flow chart of a PVDF piezoelectric sensor strain measurement circuit in a specific embodiment of the present invention;

[0021] Figure 3 The figure shows the framework structure of the PVDF piezoelectric sensor strain measurement circuit signal acquisition test used in the experiment.

[0022] Figure 4 Shown is the cantilever beam used in the signal acquisition test of the PVDF piezoelectric sensor strain measurement circuit used in the experiment. DETAILED DESCRIPTION

[0023] The following is a detailed description of the technical solutions in the embodiments of the present invention, with reference to the accompanying drawings. Obviously, the described embodiments are only a portion of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0024] Combine Figure 1-3 As shown, the entire PVDF piezoelectric sensor strain measurement circuit conditioning device consists of five components: a PVDF intelligent sensing module I, an input signal conditioning module II, a charge-to-voltage module III, a post-stage electrical signal amplification and denoising module IV, and an output signal protection module V. After the charge signal is generated by the PVDF piezoelectric sensor, it passes through resistors R1 and R2 and capacitors C1 and C2, respectively, to a certain extent suppressing the voltage drift caused by the PVDF piezoelectric sensor's insufficient insulation resistance. The charge signal then enters the charge-to-voltage module, where it is converted into a voltage signal by a charge amplifier consisting of TL034CN operational amplifiers labeled N1 and N2, along with feedback capacitors and resistors. After the conversion is complete, the voltage signal enters the post-stage circuit. The symmetrical negative feedback circuit design of the TL034CN operational amplifier achieves signal denoising and voltage amplification. At this point, the entire PVDF piezoelectric sensor strain measurement circuit conditioning device has completed the purpose of conditioning the collected sensor electrical signal. Finally, when connected to standard signal acquisition equipment, the corresponding structural strain signal can be acquired.

[0025] The equipment and settings required for the entire test process consist of a resistance strain gauge attached to the frame structure 1 and cantilever beam 2, a PVDF piezoelectric sensor, a programmable strain amplifier, a strain measurement circuit conditioning device for the PVDF piezoelectric sensor, an oscilloscope, and host computer data processing software. First, a piece of PVDF and a resistance strain gauge are attached to the frame structure 1 and cantilever beam 2 at the location where the maximum strain is generated, respectively. The resistance strain gauge is attached to the same location as the PVDF piezoelectric sensor. The charge signal generated by the PVDF is conditioned by the strain measurement circuit conditioning device of the piezoelectric sensor, and then the signal is collected by the oscilloscope; the signal generated by the resistance strain gauge is modulated by the programmable strain amplifier, and then the signal is collected by the oscilloscope at the same time. The stored data is input into the host computer software for signal quality analysis, thereby respectively testing the quality assessment of the signal collected by the PVDF piezoelectric sensor strain measurement circuit conditioning device for simple and complex structures.

[0026] The specific contents are as follows:

[0027] The PVDF piezoelectric sensor strain measurement and conditioning device comprises a PVDF intelligent sensing module (I) attached to a structure to be measured, an input signal conditioning module (II) integrated into the same printed circuit board and sequentially connected, a charge-to-voltage module (III), a post-stage electrical signal amplification and denoising module (IV), and an output signal protection module (V). When the PVDF intelligent sensing module (I) generates an input charge signal, it passes through the input signal conditioning module (II), the charge-to-voltage module (III), and then into the post-stage electrical signal amplification and denoising module (IV). The signal then passes through the output signal protection module (V) and enters other data acquisition equipment or devices.

[0028] The strain measurement circuit conditioning device for PVDF piezoelectric sensors utilizes four operational amplifiers to condition the charge signal. The first stage, consisting primarily of two charge amplifiers, primarily converts the PVDF output charge signal into a voltage signal suitable for measurement and acquisition. Due to its symmetrical design, its output sensitivity is double that of a conventional single-charge amplifier conditioning circuit with the same configuration, improving measurement sensitivity. Two small-capacitance capacitors are connected in series at the PVDF input to reduce voltage drift caused by insufficient PVDF insulation resistance. The second stage, the voltage amplifier circuit, employs a symmetrical negative feedback design. Adjusting the feedback resistor value allows the output voltage gain to be adjusted to meet the strain measurement requirements of various engineering materials. The symmetrical design suppresses common-mode noise and power-frequency noise entering the circuit, significantly improving the quality of the acquired signal. By adjusting the capacitance of the feedback capacitors at both ends of the charge amplifier, the detection of weak charges can be achieved.

[0029] The PVDF intelligent sensing module I is mainly composed of a PVDF sensor attached to an aluminum cantilever beam. Due to the external influence of the structure, the PVDF piezoelectric sensor generates a charge signal representing the structural strain information. The generated input charge signal enters the signal conditioning module II, where the signal conditioning module II is composed of small resistance resistors R1 and R2 and small capacity capacitors C1 and C2. Resistors R1 and R2 are connected in series after the positive and negative charge interfaces of the PVDF piezoelectric sensor and before capacitors C1 and C2, respectively, acting as a damping agent in the circuit and can suppress circuit oscillations to a certain extent. Capacitors C1 and C2 are connected in series after resistors R1 and R2 and before charge-to-voltage module III, respectively, to reduce the zero-point drift caused by the insufficient insulation resistance of the piezoelectric sensor and absorb overvoltage in the spike state to prevent voltage mutations.

[0030] The signal is converted from charge signal to voltage signal in the charge-to-voltage module III. It consists of two touch switches SW1 and SW2, two small resistance resistors R 11 and R 12The system consists of two precision operational amplifiers, N1 and N2; two high-precision feedback resistors, R3 and R4, with values ​​in the TΩ range; and two high-precision, high-leakage-resistance feedback capacitors, C3 and C4. Tactile switches, SW1 and SW2, are connected in parallel across feedback resistors R3 and R4 and capacitors C3 and C4, respectively. They can be closed before measurement begins to discharge any residual charge in the circuit. They can be programmable analog switches, tactile switches, or normally open switches. Their function is to form a short circuit at the start of each measurement to discharge any residual charge in feedback capacitors C3 and C4, eliminating measurement errors. Feedback capacitors C3 and C4, as one of the core components of the entire circuit conditioning device, are connected in parallel between the output and reverse input terminals of charge amplifiers N1 and N2 to form a negative feedback circuit, so that the charge generated by the PVDF piezoelectric sensor is converted into voltage information. It is necessary to ensure that its accuracy is high enough and the leakage resistance is large enough. At the same time, in order to ensure that this circuit conditioning module has a large time constant to meet its application in the field of quasi-static strain measurement, a large-capacitance CB14 polystyrene precision capacitor or other similar precision capacitors with the same function is required. Feedback resistors R3 and R4, as channels for charge discharge in feedback capacitors C3 and C4, are connected in parallel at both ends of capacitors C3 and C4. It is necessary to ensure that their resistance is large enough. High-precision resistors with a resistance above TΩ level are selected to make the time constant large enough to meet the application requirements of quasi-static strain measurement. It should be noted that the feedback capacitors C3 and C4 in the circuit are strictly symmetrical with the feedback resistors R3 and R4, and their resistance and capacitance should be strictly consistent. Resistor R 11 and R 12 The ports connected in series to the reverse input terminals of operational amplifiers N1 and N2 respectively prevent the charge amplifier from being burned out by excessive current. 11 and R 12 Before the subsequent electrical signal amplification and denoising module IV, it is necessary to ensure that it is less affected by temperature, has high enough stability, and has a large enough input impedance.

[0031] The post-stage electrical signal amplification and denoising module IV is composed of input resistors R5 and R6, negative feedback resistors R7 and R3, and two precision op amps N3 and N4. R6 and R6 are connected in series after the charge-to-voltage module III and before the reverse input terminals of the op amps N3 and N4, respectively. Resistors R7 and R8 are connected in parallel to the output terminals and negative feedback input terminals of the op amps N3 and N4, respectively. The combination of input resistors R5, R6, and negative feedback resistors R7 and R8 realizes adjustable amplification of the voltage output by the charge-to-voltage module III, and the resistance range should be selected within the range of 1-100KΩ. Due to the strict symmetrical design of this part, the common-mode noise signal in the external environment can be eliminated. Resistors R7 and R8 can be matched with different resistance values ​​to realize the voltage amplification factor selection of the post-stage amplifier circuit. Finally, the output signal protection module V is composed of small resistance resistors R9, R 10Resistors R9, R 10 They are respectively connected in series after the post-stage electrical signal amplification and denoising module IV to prevent external device failure or output line short circuit from causing burnout of the PVDF piezoelectric sensor strain measurement circuit conditioning device.

[0032] This invention is a PVDF piezoelectric sensor strain measurement circuit conditioning device designed to measure structural strain information using a PVDF piezoelectric sensor. The output sensitivity of this PVDF piezoelectric sensor strain measurement circuit conditioning device is twice that of a conventional single charge amplifier conditioning circuit, improving measurement sensitivity. It also reduces voltage drift caused by insufficient PVDF insulation resistance, enhancing the accuracy of the acquired signal. It also suppresses common-mode noise and power-frequency noise entering the circuit, significantly improving the quality of the acquired signal. It also prevents equipment damage caused by output short circuits, improving the reliability and safety of the device's operation.

[0033] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element.

[0034] The above is only a specific implementation method of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A PVDF piezoelectric sensor strain measurement circuit conditioning device, characterized in that: The invention comprises a PVDF intelligent sensing module (I) attached to a structure to be measured, and an input signal conditioning module (II), a charge-to-voltage module (III), a post-stage electric signal amplification and denoising module (IV), and an output signal protection module (V) integrated in the same printed circuit board and sequentially connected. When the PVDF intelligent sensing module (I) generates an input charge signal, the signal passes through the input signal conditioning module (II), then passes through the charge-to-voltage module (III), and then enters the post-stage electric signal amplification and denoising module (IV). The signal then passes through the output signal protection module (V) and enters other data acquisition equipment or devices. The PVDF intelligent sensing module (I) includes a PVDF sensor attached to the frame structure (1) and the cantilever beam (2). When the structure is affected by the outside world, the PVDF piezoelectric sensor generates a charge signal representing structural strain information. The generated charge signal enters the input signal conditioning module (II). The input signal conditioning module (II) includes resistors R1 and R2 and capacitors C1 and C2. The resistor R1 is connected in series between the positive charge interface generated by the PVDF piezoelectric sensor and the capacitor C1. The resistor R2 is connected in series between the negative charge interface generated by the PVDF piezoelectric sensor and the capacitor C2. The ends of the capacitors C1 and C2 facing away from the resistors R1 and R2 are respectively connected to the charge-to-voltage module (III). The charge-to-voltage module (III) includes touch switches SW1 and SW2, a resistor R 11 and R 12 , operational amplifiers N1 and N2, feedback resistors R3 and R4, feedback capacitors C3 and C4, touch switch SW1 is connected in parallel across the feedback resistor R3 and feedback capacitor C3, touch switch SW2 is connected in parallel across the feedback resistor R4 and feedback capacitor C4, feedback capacitor C3 is connected in parallel between the output terminal and the inverting input terminal of the operational amplifier N1 to form a circuit negative feedback, feedback capacitor C4 is connected in parallel between the output terminal and the inverting input terminal of the operational amplifier N2 to form a circuit negative feedback, feedback resistor R3 is connected in parallel across the feedback capacitor C3, feedback resistor R4 is connected in parallel across the feedback capacitor C4, resistor R 11 Connected in series between the inverting input terminal of operational amplifier N1 and capacitor C2, resistor R 12 Connected in series between the port of the reverse input terminal of the operational amplifier N2 and the capacitor C1, The post-stage electrical signal amplification and denoising module (IV) includes input resistors R6 and R6, negative feedback resistors R7 and R8, operational amplifiers N3 and N4, input resistor R5 is connected in series between the output end of operational amplifier N1 and the inverting input end of operational amplifier N3, and input resistor R ∈ It is connected in series between the output terminal of the operational amplifier N2 and the inverting input terminal of the operational amplifier N4. The negative feedback resistor R7 is connected in parallel between the output terminal and the negative feedback input terminal of the operational amplifier N3. The negative feedback resistor R8 is connected in parallel between the output terminal and the negative feedback input terminal of the operational amplifier N4. The output signal protection module (V) includes resistors R9, R 10 , resistor R9 is connected in series to the output of operational amplifier N3, resistor R 10 Connected in series to the output terminal of operational amplifier N4.

2. The PVDF piezoelectric sensor strain measurement circuit conditioning device according to claim 1, characterized in that: The resistance values ​​of the resistors R3 and R4 are at the TΩ level.

3. The PVDF piezoelectric sensor strain measurement circuit conditioning device according to claim 1, characterized in that: The feedback capacitors C3 and C4 have the same specifications, and the feedback resistors R3 and R4 have the same specifications.

4. The PVDF piezoelectric sensor strain measurement circuit conditioning device according to claim 1, characterized in that: The negative feedback resistors R7 and R8 can be of the same or different resistance values, and their resistance range is 1-100KΩ.

5. The PVDF piezoelectric sensor strain measurement circuit conditioning device according to claim 1, characterized in that: The tact switches SW1 and SW2 are programmable analog switches or tact switches or normally open switches.

6. The PVDF piezoelectric sensor strain measurement circuit conditioning device according to claim 1, characterized in that: Feedback capacitors C3 and C4 are CB14 polystyrene precision capacitors whose capacitance can be adjusted through analog switches.

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