Method for determining explosion pressure in current mode of PVDF piezoelectric sensor

Abstract

The application is suitable for the technical field of explosion pressure measurement, and provides a method for determining explosion pressure of a PVDF piezoelectric sensor in a current mode, comprising: discretely sampling a voltage signal output by an oscilloscope to obtain a plurality of sampling voltage signals; filtering the sampling voltage signals by using a filter to filter out low-frequency trend items, drift noise and background noise introduced by sampling, and calculating explosion pressure corresponding to a sampling point based on the filtered voltage signals; generating an explosion pressure curve based on explosion pressure corresponding to a plurality of sampling points, and judging whether the explosion pressure curve satisfies a preset filter termination condition; if yes, explosion pressure corresponding to each sampling point is taken as explosion pressure of the explosive at a time corresponding to the sampling point; if not, the filter frequency of the filter is adjusted, and the sampling voltage signals corresponding to the sampling points are continuously filtered by using the filter until the filter termination condition is satisfied. The application can improve the measurement accuracy of explosion pressure of the explosive.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of explosion pressure measurement, and particularly relates to a method for determining explosion pressure in a current mode of a PVDF piezoelectric sensor. BACKGROUND

[0002] Polyvinylidene fluoride (PVDF) piezoelectric sensors have been widely used in transient high-pressure testing scenarios such as explosion mechanics, impact loading, and structural dynamic response due to their good flexibility, fast response, and impact resistance. In particular, in explosion load measurement, PVDF sensors convert the force process into a charge signal through the positive piezoelectric effect, and then convert it into current or voltage form through a circuit to identify the pressure process of detonation wave and blast gas. With the improvement of sensor integration and measurement frequency, the current mode has gradually become a common means of high-bandwidth and high-sensitivity measurement. However, in actual explosion testing, due to strong environmental electromagnetic interference, wide signal frequency coverage, and difficulty in system impedance matching, low-frequency trend items, drift noise and background noise are easily introduced in the process of discrete sampling and processing of the voltage signal recorded by the oscilloscope, which seriously affects the accuracy of the pressure curve obtained by subsequent integral calculation.

[0003] Most existing methods directly integrate the voltage to restore the pressure, but when facing voltage signals with low-frequency trend items, drift noise and background noise, integral error accumulation will occur, causing distortion of the pressure curve, and even the peak pressure and sustained pressure stages cannot be accurately identified. Although some studies introduce sliding window, envelope analysis and other algorithms for trend item suppression, there are still problems such as peak loss and signal distortion in high dynamic and transient processes, resulting in low measurement accuracy of explosive explosion pressure. SUMMARY

[0004] The embodiments of the application provide a method for determining explosion pressure in a current mode of a PVDF piezoelectric sensor, which can solve the problem of low measurement accuracy of explosive explosion pressure.

[0005] The embodiments of the application provide a method for determining explosion pressure in a current mode of a PVDF piezoelectric sensor, which can solve the problem of low measurement accuracy of explosive explosion pressure.

[0006] Discretely sampling the voltage signal output by the oscilloscope to obtain a plurality of sampling voltage signals corresponding to a plurality of sampling points;

[0007] The filter is used to filter out low-frequency trend items, drift noise and background noise introduced by discrete sampling.

[0008] The explosion pressure curve is generated based on the explosion pressures corresponding to the plurality of sampling points, and it is determined whether the explosion pressure curve satisfies a preset filter termination condition.

[0009] If the explosion pressure curve satisfies the filter termination condition, the explosion pressure corresponding to each sampling point is taken as the explosion pressure of the explosive at the time corresponding to the sampling point.

[0010] If the explosion pressure curve does not satisfy the filter termination condition, the filter frequency of the filter is adjusted, and the step of filtering the sampling voltage signal corresponding to each sampling point by using the filter and calculating the explosion pressure corresponding to the sampling point based on the filtered voltage signal is returned.

[0011] Optionally, the calculation of the explosion pressure corresponding to the sampling point based on the filtered voltage signal comprises:

[0012] The explosion pressure corresponding to the sampling point is calculated by using a pressure calculation formula.

[0013] ;

[0014] wherein, represents the explosion pressure corresponding to the i th sampling point, represents the explosion pressure corresponding to the j th sampling point, is 0, represents the resistance value of the parallel resistor, represents the sampling interval of the discrete sampling, represents the effective area of the PVDF piezoelectric sensor, represents the piezoelectric constant, represents the voltage value of the filtered voltage signal corresponding to the i th sampling point, represents the voltage value of the filtered voltage signal corresponding to the j th sampling point. Optionally, the explosion pressure curve is a curve of the explosion pressure of the explosive versus time. The filter termination condition comprises:

[0015] The explosion pressure curve contains the explosion pressure corresponding to a first time period in which a detonation wave is generated by the explosion of the explosive.

[0016] The explosion pressure curve contains the explosion pressure corresponding to a first time period in which a detonation wave is generated by the explosion of the explosive.

[0017] The explosion pressure curve contains the explosion pressure corresponding to a first time period in which a detonation wave is generated by the explosion of the explosive. ​​

[0018] The explosion pressure curve includes the explosion pressure during the second time period when the explosive gases are generated during the explosion.

[0019] The rate of decrease in explosion pressure after the second time period satisfies: ;

[0020] The explosion pressure curve satisfies: ;

[0021] in, Indicates the first The rate of decrease of explosion pressure at each sampling point, Indicates the descent rate threshold. Indicates the first The explosion pressure corresponding to each sampling point Indicates the residual fluctuation noise threshold. Indicates the moment in the explosion pressure curve The corresponding explosion pressure, This indicates the preset explosion test time. This represents the average pressure calculated based on the voltage signal output by the oscilloscope during a preset time period before the explosive detonation.

[0022] Optionally, the duration of the first time period is 200 microseconds to 500 microseconds, and the duration of the second time period is 20 milliseconds to 100 milliseconds.

[0023] Optionally, the thickness of the PVDF piezoelectric sensor is 10 μm to 50 μm, and the diameter of the PVDF piezoelectric sensor is less than or equal to 5 mm.

[0024] Optionally, the sampling frequency of discrete sampling is greater than or equal to 10 MHz.

[0025] Optionally, the filter is a Butterworth high-pass filter.

[0026] Optionally, the diameter of the explosion hole is greater than 50mm.

[0027] The above-mentioned solution in this application has the following beneficial effects:

[0028] In the embodiments of this application, after discrete sampling processing of the voltage signal output by the oscilloscope, the original voltage signal is iteratively filtered using a filter to suppress the low-frequency trend term, drift noise and background noise introduced by discrete sampling, while retaining the high-frequency effective signal generated during the action of the explosion shock wave and explosive gas. As a result, the explosion pressure of the explosive calculated based on the iteratively filtered voltage signal is more accurate than the explosion pressure determined by the traditional current mode, thus achieving the effect of improving the measurement accuracy of the explosive explosion pressure.

[0029] Other benefits of the present application will be described in the following detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.

[0031] Figure 1 It is a schematic diagram of explosion pressure measurement circuit in the related art;

[0032] Figure 2 It is a flow chart of the method for determining explosion pressure of PVDF piezoelectric sensor in current mode provided by an embodiment of the present application;

[0033] Figure 3 It is a schematic diagram of original voltage signal in an example of the present application;

[0034] Figure 4 It is a schematic diagram of explosion pressure curve in an example of the present application. DETAILED DESCRIPTION

[0035] In the following description, for the purpose of explanation and not limitation, specific details are set forth, such as particular system configurations, techniques, etc., in order to provide a thorough understanding of the embodiments of the present application. However, it will be apparent to those skilled in the art that the present application can be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present application with unnecessary detail.

[0036] It should be understood that the term "comprising" as used in the specification and in the following claims indicates the presence of the recited features, integers, steps, operations, elements, and / or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0037] It should also be understood that the term "and / or" as used herein refers to any combination of associated listed items, and all possible combinations, and includes these combinations.

[0038] As used in the specification and the appended claims, the term "if' can be interpreted as meaning "when" or "upon" or "in response to determining" or "in response to detecting" depending on the context. Similarly, the phrase "if it is determined" or "if [the described condition or event] is detected" can be interpreted to mean "upon determining" or "in response to determining" or "upon detecting [the described condition or event]" or "in response to detecting [the described condition or event]" depending on the context.

[0039] In addition, in the description of the present application and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0040] Reference in the specification to "one embodiment" or "some embodiments" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the application. The appearances of the phrase "in one embodiment" or "in some embodiments" in various places in the specification are not necessarily all referring to the same embodiment, although it can. The terms "comprising", "including", "having" and their variants are meant to be construed as "including but not limited to", unless otherwise indicated.

[0041] In view of the low measurement accuracy of the current explosive explosion pressure, the present application provides a method for determining the explosion pressure of a PVDF piezoelectric sensor in current mode. After the voltage signal output by the oscilloscope is discretely sampled and processed, the original voltage signal is iteratively filtered by using a filter to suppress the low-frequency trend item, drift noise and background noise introduced by discrete sampling, and the high-frequency effective signal generated during the action of the explosion shock wave and the explosion gas is retained. Thus, the explosion pressure of the explosive calculated based on the voltage signal after iterative filtering has higher accuracy than the explosion pressure determined by the traditional current mode, and the effect of improving the measurement accuracy of the explosion pressure of the explosive is achieved.

[0042] The method for determining the explosion pressure of a PVDF piezoelectric sensor in current mode provided by the present application will be described below in conjunction with specific embodiments.

[0043] In the related art, the measurement of the explosion pressure of an explosive in the current mode of a PVDF piezoelectric sensor is achieved, and the structure of the explosion pressure measurement circuit composed of the PVDF piezoelectric sensor, the related parallel resistance and the oscilloscope is as shown in Figure 1 Figure 1 ​In the formula, PVDF represents the PVDF piezoelectric sensor, R represents the parallel resistance of the PVDF piezoelectric sensor, and U represents the voltage signal measured by the oscilloscope. The charge signal output by the PVDF piezoelectric sensor corresponds to the current.

[0044] It can be understood that, in the explosion pressure measurement of the explosive, the PVDF piezoelectric sensor is arranged on the inner wall of the explosion hole in which the explosive (i.e. the explosive to be measured for explosion pressure) is arranged, and the output end of the PVDF piezoelectric sensor is connected in parallel with the parallel resistance and the oscilloscope in sequence. During the explosion of the explosive, the output end of the PVDF piezoelectric sensor outputs a charge signal, and the output charge signal is converted into a current signal through the parallel resistance and is recorded as a voltage signal through the high-impedance oscilloscope.

[0045] In some optional embodiments, the above-mentioned PVDF piezoelectric sensor can be attached to the inner wall of the explosion hole, and specifically can be installed on the inner wall of the explosion hole containing water or air medium. Specifically, the thickness of the PVDF piezoelectric sensor can be 10 μm to 50 μm, and the diameter of the PVDF piezoelectric sensor is less than or equal to 5 mm, so as to meet the constraint conditions of hole wall attachment and curvature, and thus be suitable for explosion pressure measurement.

[0046] In order to facilitate the development of explosion test, the hole diameter of the above-mentioned explosion hole is greater than 50 mm, so as to be suitable for the test of the explosion charge structure with a hole diameter greater than 50 mm. It can be understood that the charge form can be an air uncoupling or water uncoupling structure, and the attachment part of the PVDF piezoelectric sensor is the inner wall surface of the hole wall.

[0047] Based on the foregoing explosion pressure measurement circuit, as shown in Figure 2 The determination method of the explosion pressure of the PVDF piezoelectric sensor in the current mode provided by the embodiments of the present application includes the following steps:

[0048] Step 21, discrete sampling is performed on the voltage signal output by the oscilloscope to obtain a sampling voltage signal corresponding to a plurality of sampling points.

[0049] Each sampling point corresponds to a time point in the explosion test process, and the sampling voltage signal corresponding to each sampling point is the voltage signal output by the oscilloscope at the corresponding time point. In some embodiments of the present application, the input impedance of the above-mentioned oscilloscope is greater than 1 MΩ, and the sampling frequency of the above-mentioned discrete sampling is greater than or equal to 10 MHz, so as to ensure the transient response capability of voltage sampling. At the same time, due to the high sampling frequency, the explosion pressure corresponding to all sampling points in the subsequent steps can be regarded as covering the explosion pressure at each time point (i.e. each time point in the explosion test process), so as to ensure the accuracy of the explosion pressure of the explosive.

[0050] In step 22, for each sampling point in the plurality of sampling points, a filter is used to filter the sampling voltage signal corresponding to the sampling point, and the explosion pressure corresponding to the sampling point is calculated based on the filtered voltage signal; the filter is used to filter out the low-frequency trend item, drift noise and background noise introduced by discrete sampling.

[0051] The low-frequency trend item, the drift noise and the background noise are introduced when the voltage signal output by the oscilloscope is discretely sampled. For the i th sampling point, the sampling voltage signal corresponding to the sampling point includes: represents the actual sampling voltage signal (i.e., the voltage signal excluding noise) corresponding to the i th sampling point, represents the slowly changing trend (i.e., the low-frequency trend item, the drift noise and the background noise) corresponding to the i th sampling point. The low-frequency trend item specifically refers to a slowly changing non-periodic offset component in the pressure signal, which is manifested as a slow upward or downward trend of the entire curve over time, rather than a true fluctuation from the explosion physical process; the drift noise refers to non-zero mean slowly varying random noise caused by stability defects of the explosion pressure measurement circuit, which is different from the “deterministic” slow change of the low-frequency trend item, and is more irregular and unstable; and the background noise specifically refers to a non-target noise component in the voltage signal that is unrelated to the explosion but widely exists, and has characteristics such as high frequency, low amplitude, approximate white noise or narrowband noise.

[0052] To improve the accuracy of the explosion pressure, in the present application, a filter is used to perform noise reduction processing on the sampling voltage signal to suppress the low-frequency trend item, the drift noise and the background noise introduced by discrete sampling, and to retain the high-frequency effective signal generated in the explosion shock wave and the action process of the explosion gas. To effectively filter out the low-frequency trend item, the drift noise and the background noise and retain the high-frequency effective component, the filter cutoff frequency is set to be higher than 10 kHz.

[0053] It should be noted that the filter can be a Butterworth high-pass filter, and specifically can be a fourth-order IIR filter, which adopts a bidirectional zero-phase filter design to avoid phase distortion. In some optional embodiments, a filter function can be implemented by using Python language, fourth-order filter coefficients are generated, and a filtfilt function (the filtfilt function is a bidirectional zero-phase filter function, which is a tool for implementing zero-phase shift filtering) is used to implement bidirectional filtering.

[0054] In some embodiments of the present application, the specific implementation manner of calculating the explosion pressure corresponding to the sampling point based on the filtered voltage signal can be:

[0055] ​​​​​The explosion pressure corresponding to the sampling point is calculated using the following pressure calculation formula:

[0056] ;

[0057] in, Indicates the first The explosion pressure corresponding to each sampling point Indicates the first The explosion pressure corresponding to each sampling point =0, This indicates the resistance value of the parallel resistors. This represents the sampling interval for discrete sampling. This indicates the effective area of ​​the PVDF piezoelectric sensor (usually referring to the force-bearing area of ​​the piezoelectric element). This represents the piezoelectric constant (a constant related to the material of a piezoelectric sensor, measured in picocoulons per newton (pC / N)). Indicates the first The voltage value of the filtered voltage signal corresponding to each sampling point. Indicates the first The voltage value of the filtered voltage signal corresponding to each sampling point.

[0058] It is worth mentioning that in the above pressure calculation formula, the voltage signal is integrated using the midpoint method approximation, and the voltage in the integration interval is taken as the average of two adjacent points. Therefore, the calculation accuracy can be improved and the sampling error can be reduced.

[0059] Step 23: Generate an explosion pressure curve based on the explosion pressure corresponding to multiple sampling points, and determine whether the explosion pressure curve meets the preset filtering termination condition. If the explosion pressure curve meets the filtering termination condition, proceed to step 24; if the explosion pressure curve does not meet the filtering termination condition, proceed to step 25.

[0060] As mentioned earlier, since the frequency of discrete sampling is high enough, it is entirely possible to generate an explosion pressure curve based on the explosion pressure corresponding to multiple sampling points (this curve can be generated using common plotting tools). This explosion pressure curve is the relationship curve between the explosion pressure of the explosive and time, recording the explosion pressure corresponding to each moment during the explosion test.

[0061] In some embodiments of this application, the above-mentioned filtering termination conditions include:

[0062] The explosion pressure curve includes the explosion pressure corresponding to the first time period of the detonation wave generated by the explosive explosion; the explosion pressure curve includes the explosion pressure corresponding to the second time period of the explosive explosion generating propellant gases; the rate of decrease of the explosion pressure after the second time period satisfies: The explosion pressure curve satisfies: .

[0063] wherein, represents the drop rate of the explosion pressure at the i-th sampling point (approximately the pressure difference between two adjacent sampling points divided by the time interval, in units of MPa / ms), represents a drop rate threshold, such as 5 MPa / ms, represents the i-th sampling point, represents the explosion pressure corresponding to the i-th sampling point, represents a residual fluctuation noise threshold, such as 2 MPa, represents the explosion pressure at time corresponding to the explosion pressure, represents a preset explosion test time (the preset time is usually greater than the total duration of the explosive explosion, and can be set according to actual conditions), represents a pressure average value calculated based on the voltage signal output by the oscilloscope within the preset period before the explosive explosion. It should be noted that before the explosive explosion, the PVDF piezoelectric sensor will also output a current, so the oscilloscope will output a corresponding voltage. The calculation method of the pressure within the preset period before the explosive explosion is the same as the methods of steps 21 and 22 described above, that is, first, the voltage signal output by the oscilloscope within the preset period is discretely sampled, then the pressure corresponding to each discrete sampling point is calculated, and finally the average value of these pressures is taken as .

[0064] The duration of the first time period is 200 microseconds to 500 microseconds, and the duration of the second time period is 20 milliseconds to 100 milliseconds.

[0065] In related technologies, based on the explosion crushing mechanism, the explosive will generate a detonation wave and an explosion gas in the explosion process. Therefore, the explosion pressure curve must contain the detonation wave stage (i.e. the first time period and the explosion pressure corresponding to the first time period described above) and the explosion gas stage (i.e. the second time period and the explosion pressure corresponding to the second time period described above).

[0066] The detonation wave stage has the following characteristics: voltage rises sharply, explosion pressure jumps instantaneously, and reflects the shock wave characteristics in the initial stage of explosive initiation. That is: at a certain time T1 after initiation, a transient high-amplitude peak pressure P1 is generated, representing the detonation wave loading; generally, the first explosion pressure peak is around 50 microseconds, and the entire stage can be up to 500 microseconds, and the result is not unique, which is related to the properties and amount of explosive.

[0067] ​The above explosion gas stage has the following characteristics: the explosion pressure starts to appear a second significant platform segment at T2 moment (T2 moment is after the detonation wave stage), the explosion pressure reaches P2, and the duration is significantly longer than the detonation wave stage, which can be judged as the explosion gas expansion loading effect. In this stage, the voltage is smooth but significant, and the explosion pressure is platform-like, reflecting the dominant sustained loading effect of gas expansion.

[0068] It should be noted that when the explosion pressure curve satisfies the following condition on the second time period: , it means that there is no significant explosion pressure signal, and the curve is in the natural decay stage, and the integral can be terminated. The explosion pressure curve satisfies: , it means that the baseline shift does not appear after the filtering process, and the residual low-frequency trend item, drift noise and background noise are completely removed.

[0069] Step 24, taking the explosion pressure corresponding to each sampling point as the explosion pressure of the explosive at the time corresponding to the sampling point.

[0070] Step 25, adjusting the filtering frequency of the filter, and returning to the step of filtering the sampling voltage signal corresponding to each sampling point in the plurality of sampling points using the filter, and calculating the explosion pressure corresponding to the sampling point based on the filtered voltage signal.

[0071] In some embodiments of the present application, the above-mentioned filter is implemented based on Python language, and usually needs to be filtered several times to determine the explosion pressure of the explosive at each time.

[0072] Specifically, when the explosion pressure curve does not satisfy the filtering termination condition after one filtering process, the filtering frequency of the filter is adjusted (specifically, the filtering frequency needs to be adjusted up or down according to the explosion pressure curve), and the adjusted filter is returned to execute step 22 until the explosion pressure curve satisfies the filtering termination condition, and the explosion pressure of the explosive at the time corresponding to each sampling point is obtained.

[0073] It can be understood that in order to facilitate the user to view the explosion pressure, the determined explosion pressure can be presented to the user in the form of an explosion pressure curve.

[0074] It is worth mentioning that the determination method of the present application processes the original voltage signal by using a fourth-order Butterworth high-pass filter to remove low-frequency trend items, drift noise and background noise, and constructs a pressure calculation formula according to the piezoelectric effect and the physical model under the current mode, realizes the high-precision reconstruction of the explosion pressure signal, therefore, the present application can effectively suppress noise interference, improve the precision and stability of the explosion pressure measurement, and is suitable for explosion load test scenes in water or air medium hole wall, especially for processing and identification of transient high-frequency impact signals.

[0075] More notably, after accurately obtaining the full-time blast pressure response curve (i.e., the aforementioned blast pressure curve) without drift and with high signal-to-noise ratio, the pressure peak characteristics of the explosive can be regulated, the action time of the detonation wave and the detonation gas can be reasonably allocated, and the time-domain optimization control of the explosion energy can be realized, thereby significantly improving the fine level of the blasting parameter design, and helping to improve the blasting effect, reduce the rock mass disturbance, and enhance the precision of the controlled explosion.

[0076] For ease of understanding, the origin of the above pressure calculation formula is exemplarily described below.

[0077] Suppose that in a certain explosion event, the PVDF piezoelectric sensor is subjected to force , and free surface charge density is generated in the polarization direction, which satisfies:

[0078] ;

[0079] In the above formula, represents the piezoelectric constant, with the unit of picocoulomb per Newton (pC / N), represents the effective area of the PVDF piezoelectric sensor, represents the instantaneous normal stress / pressure in the time domain, represents the time-varying charge quantity. The output charge of the PVDF piezoelectric sensor is converted into a current signal through an external parallel resistor:

[0080] ;

[0081] In the above formula, represents the current output by the PVDF piezoelectric sensor, with the unit of A, represents the derivative of stress with respect to time, with the unit of Pa / s. The oscilloscope collects signals in a high-impedance input mode and records the equivalent voltage , which is related to the current flowing through the resistor as follows:

[0082] ;

[0083] In the above formula, represents the voltage recorded by the oscilloscope, with the unit of V, represents the resistance value of the parallel resistor.

[0084] The above formula is rearranged to obtain the relationship between the original pressure and the voltage as follows:

[0085] ;

[0086] In the above formula, represents the integral constant, which can be taken as 0 under ideal noiseless conditions. However, in practice, due to The presence of baseline drift and low-frequency errors causes trend errors in the integration results, resulting in explosive pressure. The estimate is inaccurate.

[0087] Next, a discrete integral model is established: the sampling frequency is fs, the time step is Δt = 1 / fs, and the voltage signal is at discrete times... Let Vn be the value of the pressure, and let Vn be the value of the numerical integral.

[0088] ;

[0089] In the above formula, This represents the explosion pressure value corresponding to the nth sampling point, in Pa. Indicates the sequence number of the sampling point. Indicates the first The voltage signal corresponding to each sampling point Indicates the first The voltage signal corresponding to each sampling point, where Δt represents the sampling time interval in seconds.

[0090] It should be noted that the pressure calculation formula mentioned above is a variation of the above formula, one using a summation operation and the other using an accumulation operation.

[0091] To facilitate understanding of the determination method provided in this application, a specific example is provided below to illustrate the determination method of this application.

[0092] In this example, a PVDF piezoelectric sensor was attached to the inner wall of a test blast borehole with a diameter of 90 mm and a depth of 4 m, fixed in place and kept in close contact with the borehole wall. The sensor thickness was 30 μm to ensure it did not affect the borehole wall curvature and pressure propagation. A coaxial cable was used to complete the transmission channel setup, and the signal entered an oscilloscope with a sampling frequency set to 10 MHz and a sampling time window of 100 ms. The detonating charge was a 32 mm diameter rock emulsion explosive, approximately 0.25 m from the measuring point, using a decoupled charge structure. After setting up the blast pressure measurement circuit, the raw voltage data in PVDF current mode was acquired. Due to the presence of a strong low-frequency trend term, drift noise, and background noise in the system, the raw voltage signal (i.e., the voltage signal output by the oscilloscope) was as follows: Figure 3 As shown, direct integration will produce baseline drift error. Figure 3 The horizontal axis represents time in milliseconds (ms), and the vertical axis represents the test voltage (i.e., the voltage value of the original voltage signal) in volts (V). Therefore, this application uses Python to implement a fourth-order Butterworth high-pass filter, setting the cutoff frequency to above 10 kHz. The filter coefficients are generated using Python, and the `filtfilt` function is used to implement bidirectional zero-phase filtering, resulting in the filtered voltage signal sequence.

[0093] Then, according to the PVDF piezoelectric model and the integral relationship of the current mode, the pressure-time response curve is calculated. The differential integral expression is adopted:

[0094]

[0095] Wherein: = 50 Ω, , d = 10 pC / N, Δt = 0.1 μs. The integrated explosion pressure curve is shown in Figure 4 , which is obviously divided into a detonation wave stage and a detonation gas stage. As shown in Figure 4 , the detonation wave stage is a steep rising area dominated by the detonation wave, and the pressure peak P1 = 165 MPa appears near the time T1 = 0.12 ms, which has a typical impact response characteristic; the detonation gas stage is a detonation gas loading stage, and the platform pressure peak P2 = 157 MPa appears at T2 = 9.80 ms, which presents a steady and continuous state. Figure 4 The horizontal axis represents time in ms, and the vertical axis represents explosion pressure in MPa.

[0096] In summary, the method for determining the explosion pressure of the PVDF piezoelectric sensor in the current mode has the following advantages:

[0097] I. The original voltage signal of the PVDF piezoelectric sensor in the current mode is processed by using a fourth-order Butterworth high-pass filter, which can effectively remove low-frequency trend items, drift noise and background noise, significantly improve the signal-to-noise ratio of the pressure signal, and solve the baseline drift problem caused by cumulative error in the existing integral method.

[0098] II. A termination judgment mechanism based on integral expression and physical segmentation recognition is proposed, which can accurately identify the peak pressure and stable pressure interval of the detonation wave stage and the detonation gas stage.

[0099] III. The proposed method is based on a strict piezoelectric physical model and mathematical integral relationship, and has good portability and universality, which can be adapted to PVDF piezoelectric sensors of different sizes and thicknesses, and is suitable for explosion load test scenarios of air medium or water-containing medium hole wall.

[0100] IV. The method has good dynamic response capability for the whole process of explosion pressure, and can accurately capture the detonation wave peak (microsecond level) and the detonation gas pressure platform (millisecond level) at the same time, which provides a reliable data basis for blasting energy distribution analysis, charge structure optimization and rock mass response evaluation.

[0101] ​Five、Compared with the existing noise reduction means based on moving average, empirical window, etc., the application retains the high-frequency effective signal, filters out the noise without excessively weakening the peak, effectively balances the signal integrity and processing stability, and is suitable for integrated in the data acquisition and real-time processing module of the explosion mechanics test system.

[0102] The above is the preferred embodiment of the application. It should be pointed out that for ordinary skilled in the art, without departing from the principles described in the application, a number of improvements and refinements can be made, which should be considered as the protection scope of the application.

Claims

1. A method for determining the explosion pressure in current mode of a PVDF piezoelectric sensor, characterized in that, A PVDF piezoelectric sensor is installed on the inner wall of an explosive hole containing explosives. A parallel resistor and an oscilloscope are connected in parallel to the output of the PVDF piezoelectric sensor. During the explosive detonation, the output of the PVDF piezoelectric sensor outputs a charge signal. The method for determining the explosion pressure in the current mode of the PVDF piezoelectric sensor includes: The voltage signal output by the oscilloscope is discretely sampled to obtain sampled voltage signals corresponding to multiple sampling points; For each of the plurality of sampling points, a filter is used to filter the sampling voltage signal corresponding to the sampling point, and the explosion pressure corresponding to the sampling point is calculated based on the filtered voltage signal; the filter is used to filter out low-frequency trend terms, drift noise and background noise introduced by the discrete sampling. An explosion pressure curve is generated based on the explosion pressure corresponding to the multiple sampling points, and it is determined whether the explosion pressure curve meets the preset filtering termination condition. If the explosion pressure curve satisfies the filtering termination condition, then the explosion pressure corresponding to each sampling point is taken as the explosion pressure of the explosive at the time corresponding to that sampling point. If the explosion pressure curve does not meet the filtering termination condition, the filtering frequency of the filter is adjusted, and the process returns to the steps of filtering the sampling voltage signal corresponding to each of the plurality of sampling points using the filter, and calculating the explosion pressure corresponding to the sampling point based on the filtered voltage signal. The calculation of the explosion pressure corresponding to the sampling point based on the filtered voltage signal includes: The explosion pressure corresponding to the sampling point is calculated using a pressure calculation formula; the pressure calculation formula is: ； in, Indicates the first The explosion pressure corresponding to each sampling point Indicates the first The explosion pressure corresponding to each sampling point =0, This indicates the resistance value of the parallel resistor. This represents the sampling interval of the discrete sampling. This indicates the effective area of ​​the PVDF piezoelectric sensor. Represents the piezoelectric constant. Indicates the first The voltage value of the filtered voltage signal corresponding to each sampling point. Indicates the first The voltage value of the filtered voltage signal corresponding to each sampling point; The explosion pressure curve is the relationship curve between the explosion pressure of the explosive and time. The filtering termination conditions include: The explosion pressure curve includes the explosion pressure during the first time period when the detonation wave is generated by the explosion of the explosive; The explosion pressure curve includes the explosion pressure during the second time period when the explosive gases are generated during the explosion. After the second time period, the rate of decrease in explosion pressure satisfies: ; The explosion pressure curve satisfies: ; in, Indicates the first The rate of decrease of explosion pressure at each sampling point, Indicates the descent rate threshold. Indicates the first The explosion pressure corresponding to each sampling point Indicates the residual fluctuation noise threshold. Indicates the moment in the explosion pressure curve The corresponding explosion pressure, This indicates the preset explosion test time. This represents the average pressure calculated based on the voltage signal output by the oscilloscope during a preset time period before the explosive detonation.

2. The method for determining the explosion pressure in current mode using a PVDF piezoelectric sensor according to claim 1, characterized in that, The duration of the first time period is 200 microseconds to 500 microseconds, and the duration of the second time period is 20 milliseconds to 100 milliseconds.

3. The method for determining the explosion pressure in current mode using a PVDF piezoelectric sensor according to claim 1, characterized in that, The thickness of the PVDF piezoelectric sensor is 10μm to 50μm, and the diameter of the PVDF piezoelectric sensor is less than or equal to 5mm.

4. The method for determining the explosion pressure in current mode using a PVDF piezoelectric sensor according to claim 1, characterized in that, The sampling frequency of the discrete sampling is greater than or equal to 10 MHz.

5. The method for determining the explosion pressure in current mode using a PVDF piezoelectric sensor according to claim 1, characterized in that, The filter is a Butterworth high-pass filter.

6. The method for determining the explosion pressure in current mode using a PVDF piezoelectric sensor according to claim 1, characterized in that, The diameter of the explosion hole is greater than 50 mm.

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