A method for determining the working power limit of a resonant piezoelectric transducer using an overheat warning mechanism

Abstract

The present invention provides a method for determining the working power limit of a resonant piezoelectric transducer by using an overheating warning mechanism, including measuring the resonant frequency of the piezoelectric transducer by an impedance analyzer, monitoring the input power in real time by building a piezoelectric transducer power monitoring system, and using the deviation and relative change rate of the temperature at the center and edge of the piezoelectric ceramic, a functional element of the piezoelectric transducer, to achieve a warning of the working power limit. The present invention can use temperature to give a piezoelectric transducer an overheating warning, and then determine the maximum working power and working time of the piezoelectric transducer, and has the advantages of low equipment requirements, simple methods, and a wide range of applications.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrasonic sensors, and in particular to a method for determining the working power limit of a resonant piezoelectric transducer by utilizing an overheating early warning mechanism. Background Art

[0002] Piezoelectric ceramics can realize the exchange of mechanical energy and electrical energy, and are widely used in ultrasonic medical treatment, ultrasonic detection, ultrasonic processing and other fields. When used as a transmitting transducer, the driving frequency is usually the resonant frequency of the piezoelectric transducer, so this transducer is also called a resonant transducer. In order to improve the output signal of the transmitting transducer, whether it is the vibration rate or the sound source level, an effective way is to increase the input power by increasing the input current and / or input voltage. However, when the input power exceeds a certain working limit, due to the inherent mechanical loss, dielectric loss and piezoelectric loss of piezoelectric ceramics, the resonant piezoelectric transducer will convert a large amount of input energy into heat, and the heat accumulation in the working environment of the piezoelectric transducer will further cause the ambient temperature to rise, which will cause the performance of the voltage transducer to drop rapidly, and in severe cases, even directly damage the transducer. Summary of the invention

[0003] In view of the defect that when the existing resonant transducer increases the output signal by increasing the input power, it is easy to cause serious heating or even damage to the transducer. The present invention provides a method for determining the working power limit of the piezoelectric transducer by using an overheating warning mechanism. Using a temperature sensor to monitor the ambient temperature of the piezoelectric transducer driven by a continuous sinusoidal voltage is conducive to ensuring the safe operation of the resonant piezoelectric transducer and improving the acoustic emission capability of the piezoelectric transducer by increasing the input power.

[0004] The objective of the present invention is achieved through the following technical solutions:

[0005] A method for determining the working power limit of a resonant piezoelectric transducer using an overheating warning mechanism comprises the following steps:

[0006] (1) Two temperature sensors are adhered to the center and boundary areas of the surface of the piezoelectric ceramic element by means of an adhesive, and the adhesive is used to achieve electrical insulation between the temperature sensor and the surface of the piezoelectric ceramic element;

[0007] (2) Remove oil, excess adhesive or other impurities from the surface of the piezoelectric ceramic element to ensure that the surface of the piezoelectric ceramic element is clean and intact;

[0008] (3) Assemble the piezoelectric transducer, measure the impedance (Z)-frequency (f) curve spectrum of the piezoelectric transducer using an impedance analyzer, and record the resonant frequency f of the piezoelectric transducer s ;

[0009] (4) Use the signal source, power amplifier, oscilloscope, current probe and voltage probe to build a piezoelectric transducer power monitoring system, and adjust the driving signal to a continuous sinusoidal signal with a frequency of f s , and record the initial input power P in ;

[0010] (5) Use the temperature monitoring module and temperature sensor to build a temperature monitoring and early warning system and record the initial temperatures T1 and T2;

[0011] (6) Determine the temperature warning limit condition by combining the relative temperature deviation of the two temperature sensors and the relative rate of temperature change over time;

[0012] (7) Set the input power of the piezoelectric transducer to maintain a certain continuous working time t, and record the real-time input power P int And two temperature sensors real-time temperature T 1t and T 2t ; t is the time that the piezoelectric transducer needs to work continuously in the actual use environment;

[0013] (8) Evaluate the relative temperature deviation and relative temperature change rate of the piezoelectric transducer. If both the deviation and the relative change rate meet the temperature warning limit, the piezoelectric transducer has not yet reached the limit input power. Increase the input power of the transducer and repeat steps (7)-(8).

[0014] (9) If the relative temperature deviation or the relative temperature change rate exceeds the temperature warning limit, the piezoelectric transducer drive power supply is immediately turned off and the maximum input power P int Recorded as the limiting input power.

[0015] Preferably, the temperature sensor in step (1) is a contact temperature sensor with a test accuracy of T ac Meet -2℃≤T ac ≤+2℃;

[0016] Preferably, the binder in step (1) is epoxy resin, unsaturated polyester resin, phenolic resin, polyacrylic resin or polyvinyl chloride resin;

[0017] Preferably, in step (1), the thickness h of the adhesive satisfies 0.5 mm ≤ h ≤ 2 mm, and the contact area S between the adhesive and the surface of the piezoelectric ceramic satisfies 4 mm 2 ≤S≤25mm 2 ;

[0018] Preferably, in step (3), the impedance resonance frequency (f s ) for the minimum impedance value (Z min ) corresponds to the frequency;

[0019] Preferably, in step (4), the input power P in By the input voltage amplitude V in , input current amplitude I in and the phase difference between current and voltage Jointly decide to meet:

[0020]

[0021] The input power P in The improvement is achieved by increasing the input voltage V in and / or input current I in to achieve.

[0022] Preferably, the method for determining the temperature warning limit condition in step (6) is:

[0023] ① Calculate the real-time relative deviation ΔT of the two temperature sensors to satisfy:

[0024] ΔT=T 1t -T 2t ≤50℃;

[0025] ② Calculate the relative deviations ΔT1 and ΔT2 between the real-time temperature and the initial temperature of the temperature sensor respectively, satisfying:

[0026]

[0027] ③ Calculate the relative rate of change of temperature of the temperature sensor over time, k1 and k2, respectively, to meet the following requirements:

[0028] Beneficial effects:

[0029] (1) Accurately monitor the surface temperature of the piezoelectric transducer functional element through a contact temperature sensor;

[0030] (2) The heating state of the piezoelectric transducer during operation is monitored by a temperature sensor, which has low requirements on equipment and low production cost;

[0031] (3) By determining the temperature warning limit conditions of the piezoelectric transducer, the piezoelectric transducer can be operated safely under the limit input power within a large range;

[0032] (4) Wide range of applications, suitable for piezoelectric ceramic components of different sizes and materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The impedance Z-frequency f curve of the piezoelectric transducer of the present invention;

[0034] Figure 2It is a framework diagram of the input power monitoring system and the temperature monitoring system of the present invention;

[0035] Figure 3 is a curve showing the change of input power of the piezoelectric transducer of the present invention over time;

[0036] Figure 4 A curve showing the change of the real-time relative deviation ΔT of two temperature sensors for overheating warning using the present invention over time;

[0037] Figure 5 The curves of the relative deviations ΔT1 and ΔT2 between the real-time temperature and the initial temperature of the temperature sensor for overheating warning using the present invention changing with time;

[0038] Figure 6 The following are curves showing the relative change rates k1 and k2 of the temperature of the temperature sensor for overheating warning using the present invention.

[0039] Among them, 1-signal source, 2-power amplifier, 3-voltage probe, 4-current probe, 5-oscilloscope, 6-piezoelectric transducer, 7-temperature sensor 1, 8-temperature sensor 2, 9-temperature monitoring module. DETAILED DESCRIPTION

[0040] Embodiment 1:

[0041] A method for determining the working power limit of a resonant piezoelectric transducer using an overheating warning mechanism, the method comprising the following steps:

[0042] (1) Prepare a piezoelectric ceramic spherical shell with a size of a42.3*b45*h45mm. Use acrylic adhesive to stick two TPK-01 point thermocouple temperature sensors on the center and boundary area of ​​the inner surface of the piezoelectric ceramic element. Test the accuracy T ac Meet -1.06℃≤T ac ≤+1.06℃, control the thickness of the adhesive to about 1mm, and achieve electrical insulation between the temperature sensor and the piezoelectric ceramic surface;

[0043] (2) Clean the oil and excess adhesive on the surface of the piezoelectric ceramic element to ensure that the surface of the piezoelectric ceramic element is clean and complete. The adhesive area is about 10mm 2 ;

[0044] (3) Assemble the piezoelectric transducer and measure the impedance (Z)-frequency (f) curve spectrum of the piezoelectric transducer using an impedance analyzer, such as Figure 1 As shown, the resonant frequency f of the piezoelectric ceramic transducer is recorded s 24.42kHz;

[0045] (4) Use the Tektronix AFG 31000 signal source, Xi'an Antai Electronics ATA-L8 power amplifier, Tektronix MDO 3000 oscilloscope, current probe and voltage probe to build a piezoelectric transducer power monitoring system, such as Figure 2 As shown. Set the driving signal of the signal generator to a continuous sine signal, the frequency to 24.42kHz, and the input voltage to 1V rms , adjust the power amplifier gear, select 170V gear, 10% voltage input, and record the initial input power

[0046] (5) Use the temperature monitoring module and temperature sensor to build a temperature monitoring and early warning system, and record the initial temperatures T1 = 20.4 °C and T2 = 20.1 °C;

[0047] (6) Set the input power of the piezoelectric transducer according to the input power loading plan. Since the resonant transducer is expected to work continuously for ten minutes during use, each input power is maintained for 10 minutes. Figure 3 As shown, and record the real-time input power P int And two temperature sensors real-time temperature T 1t and T 2t ;

[0048] (7) Calculate the relative deviation ΔT of the two temperature sensors over time, as Figure 4 As shown;

[0049] (8) Calculate the relative deviations ΔT1 and ΔT2 between the real-time temperature and the initial temperature of the temperature sensor, respectively, as follows: Figure 5 As shown;

[0050] (9) Calculate the relative change rate k1 and k2 of the temperature sensor temperature over time, respectively, as follows: Figure 6 As shown;

[0051] (10) The temperature relative deviation and relative temperature change rate of the temperature sensor with different input powers were evaluated. It was found that when the input power was 0.56W, 1.91W, 4.24W and 12.07W, the temperature relative deviation gradually increased with the input power and time, but the maximum relative deviation was still less than 50°C, and the relative change rate only had a peak at the moment when the input power changed, but was far less than ≤1°C / s. This shows that the temperature relative deviation and the temperature relative change rate were both less than the temperature warning limit and the limit input power was not reached;

[0052] (11) When the input power is increased to 17.53W, the relative deviations of the three temperatures increase significantly with time. When the time is 2676s, ΔT is 50.6℃, ΔT1 is 62.4℃, ΔT2 is 12.1℃, k1 and k2 are both 0.575. At this time, ΔT exceeds the temperature limit ΔT≤50℃. The input power should be reduced or controlled immediately to ensure the safe operation of the transducer. Continue to maintain the input power at 17.53W. When the time is 2686s, ΔT is 55.3℃, ΔT1 is 67.2℃, ΔT2 is 12.2℃, k1 and k2 are 1.125 At this time, ΔT, k1 and k2 simultaneously exceed the temperature limit conditions ΔT≤50℃ and k≤1℃ / s. At this time, the resonant transducer is still working, but the ceramic temperature rise rate is significantly increased, and the transducer is in a dangerous working state; continue to maintain the input power at 17.53W, when the time is 2692s, ΔT is 62.3℃, ΔT1 jumps from 69℃ to 74.3℃, k1 and k2 are 0.4, at this time ΔT, ΔT1 and ΔT2 simultaneously exceed the temperature limit conditions ΔT≤50℃, ΔT1≤70℃ and ΔT2≤70℃, the piezoelectric ceramics undergo brittle fracture, and the transducer is completely damaged.

[0053] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A method for determining the working power limit of a resonant piezoelectric transducer using an overheating warning mechanism, characterized in that: The following steps are involved: (1) Two temperature sensors are adhered to the center and boundary areas of the surface of the piezoelectric ceramic element by adhesive, and the adhesive is used to achieve electrical insulation between the temperature sensor and the surface of the piezoelectric ceramic; (2) Remove oil, excess adhesive or other impurities from the surface of the piezoelectric ceramic element to ensure that the surface of the piezoelectric ceramic element is clean and intact; (3) Assemble the piezoelectric transducer and measure the impedance of the piezoelectric transducer using an impedance analyzer -frequency Spectrum, recording the resonant frequency of the piezoelectric transducer ; (4) Use the signal source, power amplifier, oscilloscope, current probe and voltage probe to build a piezoelectric transducer power monitoring system, and adjust the driving signal to a continuous sinusoidal signal with a frequency of , and record the initial input power ; (5) Use the temperature monitoring module and temperature sensor to build a temperature monitoring and early warning system and record the initial temperature and ; (6) Determine the temperature warning limit conditions by combining the relative temperature deviation of the two temperature sensors and the relative rate of temperature change over time; (7) Set the input power of the piezoelectric transducer to maintain a certain continuous working time t, and record the real-time input power And two temperature sensors real-time temperature and ; t is the time that the piezoelectric transducer needs to work continuously in the actual use environment; (8) Evaluate the relative temperature deviation and relative temperature change rate of the piezoelectric transducer. If both the deviation and the relative change rate meet the temperature warning limit, the piezoelectric transducer has not yet reached the limit input power. Increase the input power of the transducer and repeat steps (7)-(8). (9) If the relative temperature deviation or the relative temperature change rate exceeds the temperature warning limit, immediately turn off the piezoelectric transducer drive power supply and increase the maximum input power Recorded as the limiting input power.

2. The method according to claim 1, characterized in that The temperature sensor in step (1) is a contact temperature sensor, and the test accuracy is satisfy .

3. The method according to claim 1, characterized in that: In step (1), the binder is epoxy resin, unsaturated polyester resin, phenolic resin, polyacrylic resin or polyvinyl chloride resin.

4. The method according to claim 1, characterized in that: In step (1), the thickness of the adhesive h satisfies , the contact area S between the adhesive and the piezoelectric ceramic surface satisfies .

5. The method according to claim 1, characterized in that: Impedance resonant frequency in step (3) For minimum impedance The corresponding frequency.

6. The method according to claim 1, characterized in that Input power in step (4) By input voltage amplitude , input current amplitude and the phase difference between current and voltage Jointly decide to meet: ； The input power can be improved by increasing the input voltage and / or input current to achieve.

7. The method according to claim 1, characterized in that The method for determining the temperature warning limit condition in step (6) is: ① Calculate the real-time relative deviation of the two temperature sensors ,satisfy: ； ② Calculate the relative deviation between the real-time temperature and the initial temperature of the temperature sensor and ,satisfy: ； ③ Calculate the relative rate of change of temperature of the temperature sensor over time and ,satisfy: 。

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