Piezoelectric acceleration sensor

Abstract

The invention discloses a piezoelectric acceleration sensor, which relates to the technical field of vibration monitoring and is characterized in that a composite piezoelectric unit is formed by positive temperature coefficient piezoelectric ceramics and negative temperature coefficient piezoelectric ceramics with the same polarization direction; the volume ratio of the positive temperature coefficient piezoelectric ceramic to the negative temperature coefficient piezoelectric ceramic is set according to different influences of the temperature on the two piezoelectric ceramics, so that when the environment temperature changes, the charge changes of the positive temperature coefficient piezoelectric ceramic and the negative temperature coefficient piezoelectric ceramic caused by the environment temperature change can be mutually counteracted, and therefore, in a relatively wide temperature range, the charge change of the positive temperature coefficient piezoelectric ceramic and the negative temperature coefficient piezoelectric ceramic can be greatly reduced. The performance of the piezoelectric material is kept stable, and the stability of the sensitivity of the piezoelectric acceleration sensor in the nuclear power station environment is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of vibration monitoring, and particularly relates to a piezoelectric acceleration sensor. BACKGROUND

[0002] At present, the vibration state of key rotating equipment (such as a main pump, a fan) and structures (such as a pipeline, a support) in a nuclear power station is directly related to the safe and stable operation of the power station. It is crucial to realize high-precision and long-term reliable monitoring of them. Generally, the piezoelectric effect of piezoelectric material can be utilized to monitor the vibration state of the equipment and the structure through a piezoelectric acceleration sensor. Specifically, when the piezoelectric acceleration sensor is subjected to vibration, an inertial force is generated in an internal mass block, which acts on a piezoelectric element to make it generate an electric charge or voltage signal proportional to the acceleration.

[0003] In the prior art, a conventional piezoelectric acceleration sensor is a commonly used device in the field of vibration monitoring, and its core composition and structure follow the working principle of classical piezoelectric effect. The structural composition includes a base, a shell, a pre-tightening screw, a mass block and a piezoelectric unit.

[0004] However, the conventional piezoelectric acceleration sensor faces severe challenges in the harsh application environment of the nuclear power station, especially the drastic change of environmental temperature, which can cause the performance drift of the piezoelectric unit and the serious instability of the sensitivity, thereby reducing the measurement accuracy. SUMMARY

[0005] Therefore, it is necessary to provide a piezoelectric acceleration sensor aiming at the above technical problems.

[0006] The present application adopts the following technical solutions: The present application provides a piezoelectric acceleration sensor, which comprises a shell, a base, a pre-tightening screw, a mass block, an insulating gasket, a composite piezoelectric unit and a wire. The pre-tightening screw is used to tightly press the mass block and the composite piezoelectric unit on the base based on a target pre-tightening force. The insulating gasket is arranged between the mass block and the composite piezoelectric unit and between the composite piezoelectric unit and the base. The shell buckles the pre-tightening screw and its penetrating part in the shell to isolate the pre-tightening screw from the outside. The wire is connected with the upper electrode and the lower electrode of the composite piezoelectric unit respectively to lead out the electric signal of the composite piezoelectric unit. The composite piezoelectric unit comprises a positive temperature coefficient piezoelectric ceramic, a negative temperature coefficient piezoelectric ceramic and an electrode sheet. The positive temperature coefficient piezoelectric ceramic and the negative temperature coefficient piezoelectric ceramic are stacked in the same polarization direction and sandwich the electrode sheet to form a laminated structure. The upper surface and the lower surface of the laminated structure are both provided with the electrode sheet as the upper electrode and the lower electrode of the composite piezoelectric unit. The volume ratio of the positive temperature coefficient piezoelectric ceramic to the negative temperature coefficient piezoelectric ceramic is a negative number of the ratio of the first product to the second product; when the ambient temperature changes, the charge changes of the positive temperature coefficient piezoelectric ceramic and the negative temperature coefficient piezoelectric ceramic caused by the ambient temperature change offset each other; The first product is the product of the piezoelectric constant of the negative temperature coefficient piezoelectric ceramic at a reference temperature and the temperature coefficient of the piezoelectric constant of the negative temperature coefficient piezoelectric ceramic, and the second product is the product of the piezoelectric constant of the positive temperature coefficient piezoelectric ceramic at a reference temperature and the temperature coefficient of the piezoelectric constant of the positive temperature coefficient piezoelectric ceramic.

[0007] Optionally, the positive temperature coefficient piezoelectric ceramic is a rare earth doped bismuth layer structure ceramic, and the negative temperature coefficient piezoelectric ceramic is a Z-cut lithium niobate single crystal, and the volume ratio of the rare earth doped bismuth layer structure ceramic to the Z-cut lithium niobate single crystal is 0.3:1.

[0008] Optionally, a plurality of composite piezoelectric units are included, and the positive charge ends of each composite piezoelectric unit are adjacently stacked or the negative charge ends of each composite piezoelectric unit are adjacently stacked to form a series structure. The positive charge ends of each composite piezoelectric unit are connected in series through a first electrode sheet, the negative charge ends of each composite piezoelectric unit are connected in series through a second electrode sheet, and the conductive wire is connected with the first electrode sheet and the second electrode sheet respectively to lead out the electrical signals of the plurality of composite piezoelectric units.

[0009] Optionally, the inner surface of the shell is coated with a boron-containing polyethylene coating for absorbing thermal neutrons in the external environment.

[0010] Optionally, the shell is filled with an inert gas.

[0011] Optionally, the connection between the positive temperature coefficient piezoelectric ceramic, the negative temperature coefficient piezoelectric ceramic and each electrode sheet in the composite piezoelectric unit is sintered by gold paste or platinum paste.

[0012] The above-mentioned at least one technical solution adopted by the present application can achieve the following beneficial effects: The present application forms a composite piezoelectric unit with positive temperature coefficient piezoelectric ceramics and negative temperature coefficient piezoelectric ceramics with the same polarization direction, and sets the volume ratio of the positive temperature coefficient piezoelectric ceramic to the negative temperature coefficient piezoelectric ceramic according to the different effects of temperature on the two, so that when the ambient temperature changes, the charge changes of the positive temperature coefficient piezoelectric ceramic and the negative temperature coefficient piezoelectric ceramic caused by the ambient temperature change can offset each other, thereby keeping the performance of the piezoelectric material stable in a wider temperature range, and improving the stability of the sensitivity of the piezoelectric acceleration sensor in the nuclear power plant environment. BRIEF DESCRIPTION OF DRAWINGS

[0013] The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the application. In the drawings:

[0014] Figure 1 A schematic diagram of a piezoelectric acceleration sensor provided by the present application; Figure 2 A schematic diagram of a parallel laminated structure and electrical connection provided by the present application; Figure 3 A schematic diagram of four composite piezoelectric units in series and electrode sheet arrangement provided by the present application; Figure 4 An iterative design process for ratio calculation and optimization provided by the present application. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be described below in conjunction with specific embodiments of the present application and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0016] At present, conventional piezoelectric acceleration sensors face severe challenges in nuclear power plant environments, such as performance drift of piezoelectric materials due to drastic changes in environmental temperature (-20°C to +320°C or even higher), serious instability of sensitivity, material degradation of sensors due to long-term strong radiation, and influence of complex electromagnetic interference on extraction of weak charge signals.

[0017] The core limitation of traditional conventional piezoelectric acceleration sensors lies in the inherent defects of single-material piezoelectric units and the insufficient adaptation of structural design to extreme environments. The piezoelectric units of the sensors are made of a single material, and there is no temperature self-compensation mechanism, which leads to serious drift of piezoelectric constant and performance degradation in the wide temperature and strong radiation environment of nuclear power plants. At the same time, the overall structure lacks radiation protection, intelligent pre-tightening compensation, and efficient sealing design, further amplifying the instability of performance.

[0018] The environment of nuclear power plants has very high requirements for sealing, corrosion resistance, and long-term mechanical reliability. The present application is based on "composite piezoelectric units" and "intelligent thermal elastic structure", and provides a sensing solution that can provide accurate and reliable vibration data throughout the life cycle of nuclear power plants through the synergistic innovation of material system, mechanical structure, and manufacturing process.

[0019] For the design index of piezoelectric acceleration sensor: Core indexes include: Sensitivity: 10 PC / g ± 5%.

[0020] Frequency response range: 1 Hz ~ 10000 Hz.

[0021] Temperature stability: within the full operating temperature range, the sensitivity change is ≤ ± 5%.

[0022] Radiation resistance: after a cumulative absorbed dose of 500 kGy (50 Mrad), the sensitivity change is < ± 8%.

[0023] Protection level: IP68.

[0024] Standard compliance, design and testing comply with or refer to the following standards: JJG 233-2008 Piezoelectric Accelerometer Verification Regulation, JB / T 6822-2018 Piezoelectric Accelerometer.

[0025] The technical solutions provided by the embodiments of the present application are described in detail below in combination with the drawings.

[0026] Sensor principle: the sensor of the present application is based on the forward working principle of piezoelectric effect. When the sensor base bears vibration acceleration, the internal mass block exerts an inertial force on the piezoelectric unit. The force makes the piezoelectric unit deform, and generates an electric charge signal on its surface proportional to the force (proportional to acceleration).

[0027] The core is to suppress the negative effects of temperature: The piezoelectric constant (d) and insulation resistance of the piezoelectric material (such as PZT) of the traditional piezoelectric accelerometer change with temperature, resulting in sensitivity drift and low frequency response distortion. This scheme actively counteracts the negative effects of temperature inside the sensor through electrical compensation of the composite piezoelectric unit and mechanical compensation of the intelligent thermal elastic structure, thereby realizing high stability of the output.

[0028] Figure 1 is a schematic view of a piezoelectric accelerometer in the present application. It comprises Figure 1 It can be seen that the piezoelectric accelerometer comprises a shell, a base, a pre-tightening screw, a mass block, an insulating gasket, a composite piezoelectric unit and a wire.

[0029] The pre-tightening screw is used to penetrate and press the mass block and the composite piezoelectric unit on the base based on the target pre-tightening force; the insulating gasket is clamped between the mass block and the composite piezoelectric unit and between the composite piezoelectric unit and the base; the shell buckles the pre-tightening screw and its penetrating part in the shell, which is isolated from the outside world; the wire is connected with the upper electrode and the lower electrode of the composite piezoelectric unit respectively, which is used to lead out the electric signal of the composite piezoelectric unit.

[0030] The outer shell serves to isolate and shield the internal components. The inner surface of the outer shell is coated with a boron-containing polyethylene coating to effectively absorb thermal neutrons. The interior of the outer shell is filled with an inert gas to provide a stable environment for the sensor.

[0031] Preload screws: Used to apply preload to internal components such as composite piezoelectric units to ensure structural stability and normal operation of the composite piezoelectric units.

[0032] Mass block: Under the action of acceleration, it generates inertial force, causing the composite piezoelectric unit to deform, thereby realizing force-to-electricity conversion.

[0033] Insulating gaskets: They serve to insulate against short circuits between electrode plates or between electrode plates and other components.

[0034] Base: This is the basic supporting component of the entire piezoelectric accelerometer, used to fix the piezoelectric accelerometer and connect it to the object being measured, transmitting acceleration signals.

[0035] Figure 1 Terminals are used to bring out wires, which are used to bring out the electrical signals generated by the composite piezoelectric unit for signal processing and measurement.

[0036] The composite piezoelectric unit is the core sensing element. When subjected to the inertial force of a mass block, it generates an electrical signal due to the piezoelectric effect. Its performance directly affects the sensor's sensitivity and other indicators.

[0037] The composite piezoelectric unit includes a positive temperature coefficient piezoelectric ceramic, a negative temperature coefficient piezoelectric ceramic, and an electrode sheet. The positive temperature coefficient piezoelectric ceramic and the negative temperature coefficient piezoelectric ceramic are stacked in the same polarization direction and sandwiched with an electrode sheet to form a stacked structure. The upper and lower surfaces of the stacked structure are provided with electrode sheets as the upper and lower electrodes of the composite piezoelectric unit.

[0038] The electrode sheet is used to collect the electrical signals generated by the piezoelectric ceramic unit and to extract the signals.

[0039] The volume ratio of a positive temperature coefficient piezoelectric ceramic to a negative temperature coefficient piezoelectric ceramic is the negative of the ratio of the first product to the second product. When the ambient temperature changes, the charge changes of the positive and negative temperature coefficient piezoelectric ceramics caused by the change in ambient temperature cancel each other out.

[0040] The first product is the product of the piezoelectric constant of the negative temperature coefficient piezoelectric ceramic at the reference temperature and the temperature coefficient of the piezoelectric constant of the negative temperature coefficient piezoelectric ceramic. The second product is the product of the piezoelectric constant of the positive temperature coefficient piezoelectric ceramic at the reference temperature and the temperature coefficient of the piezoelectric constant of the positive temperature coefficient piezoelectric ceramic.

[0041] In one or more embodiments of the present application, the positive temperature coefficient piezoelectric ceramic can be a rare earth doped bismuth layer-structured ceramic, the negative temperature coefficient piezoelectric ceramic can be a Z-cut lithium niobate single crystal, and the volume ratio of the rare earth doped bismuth layer-structured ceramic to the Z-cut lithium niobate single crystal is 0.3:1. The present application does not limit the positive temperature coefficient piezoelectric ceramic and the negative temperature coefficient piezoelectric ceramic, which are only used as examples here.

[0042] The design idea is described below. The main purpose of the present application is to construct a temperature-insensitive piezoelectric sensitive core, so that the output charge signal and the mechanical vibration stress remain a stable proportional relationship in a wide temperature range. The temperature drift is actively offset from the source of the signal (the piezoelectric material itself), rather than being passively corrected in the subsequent circuit. Table 1 shows the selection and characteristics of a material in the present application.

[0043] Table 1. Selection and characteristics of materials Figure 2 A parallel stacked structure and electrical connection diagram in the present application is shown in Figure 2 It can be seen that the order of the stacked structure is: upper electrode (platinum / gold) → positive temperature coefficient bismuth layer ceramic → middle electrode (platinum / gold) → negative temperature coefficient lithium niobate single crystal → lower electrode (platinum / gold). All connections are sintered with high-temperature gold paste or platinum paste to ensure conductivity and bonding strength at high temperatures.

[0044] Electrical connection (parallel): the upper electrode of the rare earth doped bismuth layer-structured ceramic and the lower electrode of the Z-cut lithium niobate single crystal are respectively led out as the total positive electrode and the total negative electrode of the composite unit. The middle electrode is not led out as an internal common connection point. Ensure that the polarization directions of the two are consistent, so that the polarity of the generated electric charge is the same when subjected to pressure, and the output is superimposed.

[0045] Further, when only one composite piezoelectric unit is provided, the generated electric signal can be small, and the monitoring effect on the vibration state can be poor. In order to improve the monitoring effect, in one or more embodiments of the present application, the piezoelectric acceleration sensor can include a plurality of composite piezoelectric units, the positive charge ends of the composite piezoelectric units are adjacently stacked or the negative charge ends of the composite piezoelectric units are adjacently stacked to form a series structure. Among them, the positive charge ends of each composite piezoelectric unit are connected in series through a first electrode sheet, the negative charge ends of each composite piezoelectric unit are connected in series through a second electrode sheet, and a lead wire can be connected with the first electrode sheet and the second electrode sheet respectively, for leading out the electric signal of the plurality of composite piezoelectric units. As shown in Figure 1 or Figure 3 As shown, Figure 1 two composite piezoelectric units in series, Figure 3 a four-composite-piezoelectric-unit-in-series and electrode sheet setting diagram in the present application.

[0046] Figure 4 For the iterative design process of ratio calculation and optimization in this invention, the following is demonstrated through an example: Objective: Achieve optimal compensation within the range of 200°C to 350°C.

[0047] Known parameters (assumptions): Rare earth doped bismuth layer-structured ceramic d (@25°C) = 16 pC / N, temperature coefficient α_H = +0.00008 pC / N / °C.

[0048] Z-cut lithium niobate single crystal d (@25°C) = 8 pC / N, temperature coefficient α_L = -0.00003 pC / N / °C.

[0049] Ratio formula: V_H / V_L = - (α_L / α_H) Calculation: V_H / V_L = - (-0.00003 / +0.00008) = 0.375 Geometric implementation: Case A (equal diameter): If the diameters are the same, the thickness of the rare earth doped bismuth layer-structured ceramic should be 0.375 times the thickness of the Z-cut lithium niobate single crystal. Case B (equal thickness): If the thicknesses are the same, the area of the rare earth doped bismuth layer-structured ceramic should be 0.375 times the area of the Z-cut lithium niobate single crystal. The final ratio needs to be determined through the iterative process in the figure above, through simulation and experiment.

[0050] Working principle of temperature self-compensation: Basic principle and mathematical model: The charge output of a piezoelectric acceleration sensor follows the basic formula: Q=d 33 ×F Where Q is the output charge, d 33 is the piezoelectric constant, and F is the force applied to the piezoelectric crystal.

[0051] When the temperature changes, d 33 will change, causing sensitivity drift. The goal of a composite piezoelectric unit is to make the derivative of the total output charge Q total with respect to temperature approach zero:

[0052] ≈0 Composite piezoelectric unit output model: Assume that the composite piezoelectric unit is composed of two types of piezoelectric crystals: Crystal A (positive temperature coefficient): QA = (T)×F Crystal B (negative temperature coefficient): Q B = (T)×F Due to the parallel connection, the total output charge is: Q total =Q A +Q B =[ (T)+ (T)]×F Temperature coefficient definition and linearization process: Within a limited temperature range, it can be assumed that the piezoelectric constant has a linear relationship with temperature: (T)= ×[1+α A ×(T−T0)] (T)= ×[1+α B ×(T−T0)] where, and are the piezoelectric constants at the reference temperature T0, α A and α B are the temperature coefficients of the piezoelectric constant (% / °C), T0 is the reference temperature (usually 25°C).

[0053] Temperature dependence of total output charge: Substitute the linearization expression into the total output formula: Q total ={ ×[1+α A (T−T0)]+ ×[1+α B (T−T0)]}×F After rearrangement: Q total =[ + +( α A + α B )(T−T0)]×F Temperature compensation condition: To achieve temperature self-compensation, it is necessary to satisfy: ≈0 This means: αA + α B =0 or: = A concrete calculation example: Using the material parameters determined earlier: Crystal A (bismuth layer ceramic): = 16 pC / N; α A = +0.05% / °C = 1 / (5x10−4°C) Crystal B (lithium niobate): = 8 pC / N; α B = -0.03% / °C = 1 / (3x10−4°C) Verification of compensation condition: α A + α B = (16x5x10−4) + (8x(-3x10−4)) = 5.6x10−3≠ 0 Calculate the optimal volume / area ratio: Let the volume ratio of crystal A to crystal B be γ = V A / V B , then the compensation condition becomes: γx α A + α B = 0 γ= Therefore, the volume of bismuth layer ceramic should be 0.3 times the volume of lithium niobate.

[0054] Evaluation of compensation effect: Using the optimal volume ratio r = 0.3, calculate the sensitivity drift when the temperature changes: Total sensitivity at reference temperature T0: S0= γx + = 0.3x16 + 8 = 12.8 pC / N Total sensitivity at temperature T: S(T)= γx x[1+α A (T−T0)]+ x[1+α B (T−T0) = 0.3 x 16 x [1 + 5 x 10-4ΔT] + 8 x [1 - 3 x 10-4ΔT] = 12.8 + (2.4 x 10-3- 2.4 x 10-3)ΔT = 12.8 pC / N The results show that after the optimal volume ratio is adopted, the sensitivity is completely unaffected by temperature in theoretical calculation.

[0055] Practical considerations and high-order effects: In practical applications, the following factors also need to be considered: Nonlinear effects: The temperature dependence of the piezoelectric constant may not be completely linear, especially in a wide temperature range: d 33 (T) = d 33,0 [1 + a(T - T0) + b(T - T0)2+...] Thermal expansion effect: The difference in thermal expansion coefficients of different materials will cause the pre-tightening force to change, which is both a mechanical compensation mechanism and needs to be considered in the design of electrical compensation.

[0056] Material dispersion: The parameters of actual materials will have batch-to-batch differences, which need to be accurately measured and paired in production.

[0057] As can be seen from the above, by accurately selecting two piezoelectric materials with complementary temperature characteristics and calculating their optimal volume ratio, a composite piezoelectric unit with stable sensitivity in a wide temperature range can be constructed. This self-compensation mechanism is completely based on the physical properties of the material and does not require external circuit intervention, providing an extremely reliable solution for vibration monitoring in extreme environments such as nuclear power plants.

[0058] The calculations show that when the volume ratio of rare earth doped bismuth layer structure ceramic to Z-cut lithium niobate single crystal is 0.3:1, the sensitivity change in the temperature range of 200-350°C can be completely compensated in theory. In actual manufacturing, the performance in the whole temperature range can be optimized by fine-tuning this ratio.

[0059] Further, for the thermal expansion effect described above, in one or more embodiments of the present invention, mechanical structures can also be used for compensation, thereby being combined with the composite piezoelectric unit to further improve the stability of the piezoelectric acceleration sensor in high temperature sensitivity.

[0060] Design idea: Take advantage of the natural difference in thermal expansion coefficients of different materials to build a passive mechanical system that can automatically adjust the pre-tightening force of the piezoelectric crystal stack with temperature changes. When the temperature rises and the piezoelectric material sensitivity decreases, the structure can automatically increase the pre-tightening force to increase the charge output, thereby offsetting the sensitivity decrease and achieving stable mechanical compensation.

[0061] Structure and material selection: The structure mainly consists of three key components, whose material selection is based on the precise matching of the coefficient of thermal expansion. Table 2 shows the coefficient of thermal expansion of a key component in the present invention.

[0062] Table 2 Coefficient of thermal expansion of key components Compensation principle and working mechanism: The compensation mechanism is entirely dependent on the CTE difference between the washer and the shell / bolt system.

[0063] Compensation displacement difference calculation: ΔL = L _ washer ×ΔT×(α _ washer - α _shell ) Assuming the effective thickness of the washer L _ washer = 12 mm, the temperature rise ΔT = 300°C (from 20°C to 320°C).

[0064] ΔL = 12 mm × 300°C × (18.5 - 14.5) × 10 / °C = 0.0144 mm = 14.4 μm.

[0065] Pre-tightening force increment calculation: Pre-tightening force increment ΔF = k _bolt ×ΔL.

[0066] Bolt stiffness k _bolt = (A × E) / L _bolt (A: cross-sectional area of the bolt; E: Young's modulus) Assuming an Inconel718 bolt with a diameter of 3mm and an effective length of 20mm, the Young's modulus E = 200 GPa.

[0067] A = π × (1.5e-3)² ≈ 7.07e-6 m² k _bolt = (7.07e-6 × 200e9) / 0.02 = 70700 N / m = 70.7 N / mm.

[0068] ΔF = 70.7 N / mm × 0.0144 mm ≈ 1.02 N.

[0069] This pre-tightening force increment may seem small, but for a piezoelectric stack already in a high pre-tightening state, it is a significant percentage change, sufficient to produce a considerable adjustment effect on the charge output.

[0070] Collaborative compensation process: Temperature rise → Z-cut lithium niobate single crystal d decreases, and rare earth doped bismuth layer-structured ceramic d increases (electrical compensation begins to work).

[0071] At the same time, temperature rise → compensation gasket expansion is greater than the shell → displacement difference is generated → pre-tightening force increases (mechanical compensation begins to work).

[0072] Final output: the increased pre-tightening force and the changed d are multiplied together to make the output charge (Q = d x F) stable.

[0073] Shell and sealing design: all metal (stainless steel) laser welding sealing, internal filling of normal pressure inert gas (nitrogen or argon), to ensure internal gas pressure stability and long-term sealing, prevent moisture and corrosive medium from entering.

[0074] The signal is led out through high-temperature ceramic insulating terminals, which provides excellent electrical insulation and high-temperature stability.

[0075] Technical advantages and applications: the present application selects Z-cut lithium niobate single crystal and rare earth doped bismuth layer-structured ceramic as an innovative "high-temperature piezoelectric material pair", which successfully raises the upper limit of the working temperature of the composite piezoelectric unit to 320°C. Through precise ratio design and the cooperation of the intelligent thermal elastic structure composed of Inconel-310S material system, the temperature self-compensation is realized completely and passively.

[0076] The present application can be a top-level vibration sensor that can work long-term in the extreme environment of the primary side of a nuclear power plant without maintenance, which has great strategic value and market prospect.

[0077] It should be further noted that the terms "include", "contain" or any other variants thereof in the present application are intended to cover non-exclusive inclusion, that is, in addition to the elements listed in the present application, other elements not explicitly listed can also be included.

[0078] Each embodiment in the present application is described in a progressive manner, and the same and similar parts between each embodiment can be referred to each other, and each embodiment mainly explains the difference from other embodiments.

[0079] The above only describes the embodiments of the present application and is not used to limit the present application. The present application can have various changes and variations for those skilled in the art. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the scope of the claims of the present application.

Claims

1. A piezoelectric accelerometer, characterized in that, include: Housing, base, preload screws, mass block, insulating gasket, composite piezoelectric unit, and wires; The preload screw is used to press the mass block and the composite piezoelectric unit through and tightly onto the base based on the target preload force; the insulating gasket is sandwiched between the mass block and the composite piezoelectric unit, and between the composite piezoelectric unit and the base; the housing holds the preload screw and its through portion inside the housing, isolating them from the outside; the wire is connected to the upper and lower electrodes of the composite piezoelectric unit respectively, for leading out the electrical signal of the composite piezoelectric unit; The composite piezoelectric unit includes a positive temperature coefficient piezoelectric ceramic, a negative temperature coefficient piezoelectric ceramic, and an electrode sheet. The positive temperature coefficient piezoelectric ceramic and the negative temperature coefficient piezoelectric ceramic are stacked in the same polarization direction and sandwiched with an electrode sheet to form a stacked structure. The upper and lower surfaces of the stacked structure are provided with electrode sheets as the upper electrode and lower electrode of the composite piezoelectric unit. The volume ratio of the positive temperature coefficient piezoelectric ceramic to the negative temperature coefficient piezoelectric ceramic is the negative of the ratio of the first product and the second product; when the ambient temperature changes, the charge changes of the positive temperature coefficient piezoelectric ceramic and the negative temperature coefficient piezoelectric ceramic caused by the ambient temperature change cancel each other out. The first product is the product of the piezoelectric constant of the negative temperature coefficient piezoelectric ceramic at the reference temperature and the temperature coefficient of the piezoelectric constant of the negative temperature coefficient piezoelectric ceramic. The second product is the product of the piezoelectric constant of the positive temperature coefficient piezoelectric ceramic at the reference temperature and the temperature coefficient of the piezoelectric constant of the positive temperature coefficient piezoelectric ceramic.

2. The piezoelectric accelerometer sensor as described in claim 1, characterized in that, The positive temperature coefficient piezoelectric ceramic is a rare earth-doped bismuth layered structure ceramic, and the negative temperature coefficient piezoelectric ceramic is a Z-tangential lithium niobate single crystal. The volume ratio of the rare earth-doped bismuth layered structure ceramic to the Z-tangential lithium niobate single crystal is 0.3:

1.

3. The piezoelectric accelerometer sensor as described in claim 1, characterized in that, It includes multiple composite piezoelectric units, with the positive charge ends of each composite piezoelectric unit stacked adjacently or the negative charge ends stacked adjacently to form a series structure; The positive charge terminals of each composite piezoelectric unit are connected in series through a first electrode plate, and the negative charge terminals of each composite piezoelectric unit are connected in series through a second electrode plate. The wire is connected to the first electrode plate and the second electrode plate respectively to draw out the electrical signals of the multiple composite piezoelectric units.

4. The piezoelectric accelerometer sensor as described in claim 1, characterized in that, A compensating pad is sandwiched between the insulating pad between the mass block and the composite piezoelectric unit and the mass block. The compensation pad is used to compensate for changes in preload caused by changes in ambient temperature.

5. The piezoelectric accelerometer sensor as described in claim 1, characterized in that, The inner surface of the outer shell is coated with a boron-containing polyethylene coating to absorb thermal neutrons from the external environment.

6. The piezoelectric accelerometer sensor as described in claim 1, characterized in that, The interior of the outer shell is filled with inert gas.

7. The piezoelectric accelerometer sensor as described in claim 1, characterized in that, The connection between the positive temperature coefficient piezoelectric ceramic, the negative temperature coefficient piezoelectric ceramic, and each electrode sheet in the composite piezoelectric unit is achieved by sintering with gold paste or platinum paste.

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