阅读说明：本技术 一种基于他激式压电元件的排气装置和方法 (Exhaust device and method based on separately excited piezoelectric element ) 是由 王茂坤 齐雯雯 葛益波 于 2020-12-30 设计创作，主要内容包括：本发明属于液压技术领域,公开了一种基于他激式压电元件的排气装置及方法,包括交流激励源、他激式压电元件、采样元件、解调电路、驱动电路和排气阀；他激式压电元件和采样元件串联于交流激励源两个电源引脚之间,采样元件两端的电压信号输入解调电路；他激式压电元件设在装有待检测介质的容器中；解调电路连接并控制驱动电路,驱动电路连接并控制排气阀,排气阀是装有待检测介质的容器的通气阀门；他激式压电元件为气、液介质检测的敏感元件。本发明具有环境适应性强的优点,依据被检测对象的密度、粘度等物理特性,具有适用对象广、检测灵敏、可靠性高的优点。(The invention belongs to the technical field of hydraulic pressure, and discloses an exhaust device and method based on separately excited piezoelectric elements, which comprises an alternating current excitation source, separately excited piezoelectric elements, a sampling element, a demodulation circuit, a drive circuit and an exhaust valve, wherein the alternating current excitation source is connected with the separately excited piezoelectric elements; the separately excited piezoelectric element and the sampling element are connected in series between two power supply pins of the alternating current excitation source, and voltage signals at two ends of the sampling element are input into the demodulation circuit; the separately excited piezoelectric element is arranged in a container filled with a medium to be detected; the demodulation circuit is connected with and controls the driving circuit, the driving circuit is connected with and controls the exhaust valve, and the exhaust valve is a vent valve of a container filled with a medium to be detected; the separately excited piezoelectric element is a sensitive element for detecting gas and liquid media. The invention has the advantages of strong environmental adaptability, wide applicable objects, sensitive detection and high reliability according to the physical characteristics of the detected objects such as density, viscosity and the like.)

1. An exhaust device based on a separately excited piezoelectric element is characterized by comprising an alternating current excitation source (1), a separately excited piezoelectric element (2), a sampling element (3), a demodulation circuit (4), a driving circuit (5) and an exhaust valve (6); the separately excited piezoelectric element (2) and the sampling element (3) are connected in series between two power supply pins of the alternating current excitation source (1), and voltage signals at two ends of the sampling element (3) are input into the demodulation circuit (4); the separately excited piezoelectric element (2) is arranged in a container filled with a medium to be detected; the demodulation circuit (4) is connected with and controls the driving circuit (5), the driving circuit (5) is connected with and controls the exhaust valve (6), and the exhaust valve (6) is a vent valve of a container filled with a medium to be detected; the separately excited piezoelectric element (2) is a sensitive element for detecting gas and liquid media.

2. An exhaust device based on separately excited piezoelectric elements according to claim 1, wherein the fundamental frequency of the excitation voltage generated by the alternating current excitation source (1) is close to the minimum impedance frequency or the maximum impedance frequency of the separately excited piezoelectric elements (2) in the gas phase or the liquid phase.

3. A separately excited piezoelectric element-based exhaust device according to claim 1, wherein the separately excited piezoelectric element (2) has a sheet structure.

4. A separately excited piezoelectric element-based exhaust apparatus as claimed in claim 3, wherein the separately excited piezoelectric element (2) is a combination of a piezoelectric ceramic plate and a thin elastic element.

5. A separately excited piezoelectric element-based exhaust device according to claim 1, wherein the separately excited piezoelectric element (2) is mounted inside the exhaust valve (6).

6. A method for exhausting based on a separately excited piezoelectric element, which is characterized in that the exhausting device based on the separately excited piezoelectric element as claimed in claim 1 is used, and comprises the following steps:

firstly, an alternating current excitation source (1) generates an excitation voltage with a fundamental frequency close to the minimum impedance frequency of a separately excited piezoelectric element (2) in a gas phase;

secondly, placing the separately excited piezoelectric element (2) in a detected medium;

thirdly, the sampling voltage at the two ends of the sampling element (3) is sent to a demodulation circuit (4), and the demodulation circuit (4) identifies the current medium around the separately excited piezoelectric element (2) according to the amplitude and the frequency characteristic parameter of the sampling voltage; the specific identification method is as follows: the alternating current excitation source (1) generates an excitation voltage with a fundamental frequency close to the minimum impedance frequency of the separately excited piezoelectric element (2) in the gas phase, and the impedance of the separately excited piezoelectric element (2) in the gas phase is minimum; when the separately excited piezoelectric element (2) is placed in a gas phase, the amplitude of sampling voltage at two ends of the sampling element (3) is maximum; when the separately excited piezoelectric element (2) is placed in liquid, the amplitude of sampling voltage at two ends of the sampling element (3) is reduced; taking a certain value in the middle of voltage or frequency characteristic values of the separately excited piezoelectric element (2) in gas and liquid respectively, or a certain value in the middle of characteristic values obtained by conditioning voltage amplitude or frequency as a judgment threshold value k, comparing the characteristic value obtained by detection or conditioning with the value k, and judging whether the medium is liquid or gas according to the comparison result;

fourthly, if the detected medium is gas, generating an exhaust enabling signal, and turning to the fifth step, otherwise, turning to the first step;

fifthly, sending an exhaust enable signal to a driving circuit (5), and enabling the driving circuit (5) to drive an exhaust valve (6);

and sixthly, opening an exhaust valve (6) to exhaust gas in the closed container, and switching to the first step.

7. A method for exhausting based on a separately excited piezoelectric element, which is characterized in that the exhausting device based on the separately excited piezoelectric element as claimed in claim 1 is used, and comprises the following steps:

firstly, an alternating current excitation source (1) generates an excitation voltage with a fundamental frequency close to the minimum impedance frequency of a separately excited piezoelectric element (2) in a liquid phase;

secondly, placing the separately excited piezoelectric element (2) in a medium to be detected;

thirdly, the sampling voltage at the two ends of the sampling element (3) is sent to a demodulation circuit (4), and the demodulation circuit (4) identifies the current medium around the separately excited piezoelectric element (2) according to the amplitude and the frequency characteristic parameter of the sampling voltage;

the specific identification method is as follows: the alternating current excitation source (1) generates an excitation voltage with a fundamental frequency close to the minimum impedance frequency of the separately excited piezoelectric element (2) in the liquid phase, and the impedance of the separately excited piezoelectric element (2) in the liquid phase is minimum; when the separately excited piezoelectric element (2) is placed in a liquid phase, the amplitude of sampling voltage at two ends of the sampling element (3) is maximum; when the separately excited piezoelectric element (2) is placed in a gas phase, the amplitude of sampling voltage at two ends of the sampling element (3) is reduced; taking a certain value in the middle of voltage or frequency characteristic values of the separately excited piezoelectric element (2) in gas and liquid respectively, or a certain value in the middle of characteristic values obtained by conditioning voltage amplitude or frequency as a judgment threshold value k, comparing the characteristic value obtained by detection or conditioning with the value k, and judging whether the medium is liquid or gas according to the comparison result;

fourthly, if the detected medium is gas, generating an exhaust enabling signal, and turning to the fifth step, otherwise, turning to the first step;

fifthly, sending an exhaust enable signal to a driving circuit (5), and enabling the driving circuit (5) to drive an exhaust valve (6);

and sixthly, opening an exhaust valve (6) to exhaust gas in the closed container, and switching to the first step.

8. An exhaust method based on a separately excited piezoelectric element, which is characterized in that the exhaust device based on the separately excited piezoelectric element according to claim 1 is used, and the method comprises the following specific steps:

firstly, an alternating current excitation source (1) generates an excitation voltage with a fundamental frequency close to the maximum impedance frequency of a separately excited piezoelectric element (2) in a gas phase;

secondly, placing the separately excited piezoelectric element (2) in a medium to be detected;

thirdly, the sampling voltage at the two ends of the sampling element (3) is sent to a demodulation circuit (4), and the demodulation circuit (4) identifies the current medium around the separately excited piezoelectric element (2) according to the amplitude and the frequency characteristic parameter of the sampling voltage;

the specific identification method is as follows: the alternating current excitation source (1) generates an excitation voltage with a fundamental frequency close to the maximum impedance frequency of the separately excited piezoelectric element (2) in the gas phase, and the impedance of the separately excited piezoelectric element (2) in the gas phase is maximum at the moment; when the separately excited piezoelectric element (2) is placed in a gas phase, the amplitude of sampling voltage at two ends of the sampling element (3) is minimum; when the separately excited piezoelectric element (2) is placed in a liquid phase, the amplitude of sampling voltage at two ends of the sampling element (3) is increased; taking a certain value in the middle of voltage or frequency characteristic values of the separately excited piezoelectric element (2) in gas and liquid respectively, or a certain value in the middle of characteristic values obtained by conditioning voltage amplitude or frequency as a judgment threshold value k, comparing the characteristic value obtained by detection or conditioning with the value k, and judging whether the medium is liquid or gas according to the comparison result;

fourthly, if the detected medium is gas, generating an exhaust enabling signal, and turning to the fifth step, otherwise, turning to the first step;

fifthly, sending an exhaust enable signal to a driving circuit (5), and enabling the driving circuit (5) to drive an exhaust valve (6);

and sixthly, opening an exhaust valve (6) to exhaust gas in the closed container, and switching to the first step.

9. A method for exhausting based on a separately excited piezoelectric element, which is characterized in that the exhausting device based on the separately excited piezoelectric element as claimed in claim 1 is used, and comprises the following steps:

firstly, an alternating current excitation source (1) generates an excitation voltage with a fundamental frequency close to the maximum impedance frequency of a separately excited piezoelectric element (2) in a liquid phase;

secondly, placing the separately excited piezoelectric element (2) in a medium to be detected;

thirdly, the sampling voltage at the two ends of the sampling element (3) is sent to a demodulation circuit (4), and the demodulation circuit (4) identifies the current medium around the separately excited piezoelectric element (2) according to the amplitude and the frequency characteristic parameter of the sampling voltage;

the specific identification method is as follows: the alternating current excitation source (1) generates an excitation voltage with a fundamental frequency close to the maximum impedance frequency of the separately excited piezoelectric element (2) in the liquid phase, and the impedance of the separately excited piezoelectric element (2) in the liquid phase is maximum at the moment; when the separately excited piezoelectric element (2) is placed in a liquid phase, the amplitude of sampling voltage at two ends of the sampling element (3) is minimum; when the separately excited piezoelectric element (2) is placed in a gas phase, the amplitude of sampling voltage at two ends of the sampling element (3) is increased; taking a certain value in the middle of voltage or frequency characteristic values of the separately excited piezoelectric element (2) in gas and liquid respectively, or a certain value in the middle of characteristic values obtained by conditioning voltage amplitude or frequency as a judgment threshold value k, comparing the characteristic value obtained by detection or conditioning with the value k, and judging whether the medium is liquid or gas according to the comparison result;

fourthly, if the detected medium is gas, generating an exhaust enabling signal, and turning to the fifth step, otherwise, turning to the first step;

fifthly, sending an exhaust enable signal to a driving circuit (5), and enabling the driving circuit (5) to drive an exhaust valve (6);

and sixthly, opening an exhaust valve (6) to exhaust gas in the closed container, and switching to the first step.

Technical Field

The invention belongs to the technical field of hydraulic pressure, relates to an automatic exhaust device and method, and particularly relates to an exhaust device and method based on separately excited piezoelectric elements.

Background

The hydraulic system utilizes hydraulic oil for energy transfer, and requires that the hydraulic oil has good rigidity and continuity. If air is mixed in the hydraulic system, the rigidity and the continuity of hydraulic oil can be obviously reduced, so that the hydraulic system generates vibration impact, the abrasion of hydraulic parts is aggravated, the service life of the system is shortened, and the reliability of the system is reduced.

The exhaust valve is an important part of the hydraulic system, is arranged at the highest point of the closed hydraulic system and is used for exhausting gas generated by the hydraulic system, and the service life and the working reliability of the hydraulic system are ensured. The exhaust valve is developed through three stages of a manual exhaust valve, a mechanical automatic exhaust valve and an electric control automatic exhaust valve.

The manual exhaust valve can not be automatically opened for exhaust, needs an operator to manually open and realize automatic closing, and therefore can be called as a semi-automatic exhaust valve. The manual exhaust valve depends on the experience of the operator and cannot perform effective exhaust.

The mechanical automatic exhaust valve utilizes the difference of the kinematic viscosity of liquid and gas to generate different pressure drops when flowing through the damping pipe, thereby controlling the opening and closing of the exhaust valve core. Because the temperature change range of the airplane hydraulic system is large, generally (-55-135) DEG C, the kinematic viscosity of the hydraulic oil is obviously changed along with the temperature. If the temperature of the hydraulic oil is too high, the kinematic viscosity of the hydraulic oil is close to that of air, and the mechanical automatic exhaust valve is easy to lose effectiveness.

The electric control type automatic exhaust valve consists of an electromagnetic valve and a liquid level detection system, detects whether the liquid level reaches the exhaust liquid level by using detection elements such as photoelectricity or sound wave and the like, sends an exhaust enabling signal to a controller, and the controller makes a decision whether to exhaust and drives the exhaust electromagnetic valve to exhaust. The related technology is patented by foreign companies such as parker, Eton and the like, and the product price is high

Disclosure of Invention

The purpose of the invention is as follows: the exhaust device and the exhaust method based on the separately excited piezoelectric element are high in sensitivity, high in reliability and strong in applicability, and can be suitable for occasions where closed containers exist and exhaust is needed, such as a hydraulic system.

The technical scheme of the invention is as follows:

an exhaust device based on a separately excited piezoelectric element comprises an alternating current excitation source, the separately excited piezoelectric element, a sampling element, a demodulation circuit, a driving circuit and an exhaust valve; the separately excited piezoelectric element and the sampling element are connected in series between two power supply pins of the alternating current excitation source, and voltage signals at two ends of the sampling element are input into the demodulation circuit; the separately excited piezoelectric element is arranged in a container filled with a medium to be detected; the demodulation circuit is connected with and controls the driving circuit, the driving circuit is connected with and controls the exhaust valve, and the exhaust valve is a vent valve of a container filled with a medium to be detected; the separately excited piezoelectric element is a sensitive element for detecting gas and liquid media.

Further, the fundamental frequency of the excitation voltage generated by the alternating-current excitation source is close to the minimum impedance frequency or the maximum impedance frequency of the separately excited piezoelectric element in the gas phase or the liquid phase.

Further, the separately excited piezoelectric element has a thin-plate structure.

Furthermore, the separately excited piezoelectric element is a combination of a piezoelectric ceramic piece and a thin elastic element.

Further, the separately excited piezoelectric element is mounted inside the exhaust valve.

An exhaust method based on separately excited piezoelectric elements, which uses the exhaust device based on separately excited piezoelectric elements, comprises the following steps:

firstly, an alternating current excitation source generates excitation voltage with fundamental frequency close to the minimum impedance frequency of a separately excited piezoelectric element in a gas phase;

secondly, placing the separately excited piezoelectric element in a detected medium;

thirdly, the sampling voltage at two ends of the sampling element is sent to a demodulation circuit, and the demodulation circuit identifies the current medium around the separately excited piezoelectric element according to the amplitude and the frequency characteristic parameter of the sampling voltage; the specific identification method is as follows: the alternating current excitation source generates an excitation voltage with a fundamental frequency close to the minimum impedance frequency of the separately excited piezoelectric element in the gas phase, and the impedance of the separately excited piezoelectric element in the gas phase is minimum; when the separately excited piezoelectric element is placed in a gas phase, the amplitude of sampling voltage at two ends of the sampling element is maximum; when the separately excited piezoelectric element is placed in liquid, the amplitude of sampling voltage at two ends of the sampling element is reduced; taking a certain value in the middle of voltage or frequency characteristic values of the separately excited piezoelectric element in gas and liquid respectively, or a certain value in the middle of characteristic values obtained by conditioning voltage amplitude or frequency as a judgment threshold value k, comparing the characteristic value obtained by detection or conditioning with the value k, and judging whether the medium is liquid or gas according to a comparison result;

fourthly, if the detected medium is gas, generating an exhaust enabling signal, and turning to the fifth step, otherwise, turning to the first step;

fifthly, sending the exhaust enabling signal to a driving circuit, and enabling the driving circuit to drive an exhaust valve;

and sixthly, opening the exhaust valve, exhausting the gas in the closed container, and turning to the first step.

A second exhaust method based on a separately excited piezoelectric element, using the exhaust apparatus based on a separately excited piezoelectric element, includes the following steps:

firstly, an alternating current excitation source generates an excitation voltage with a fundamental frequency close to the minimum impedance frequency of a separately excited piezoelectric element in a liquid phase;

secondly, placing the separately excited piezoelectric element in a medium to be detected;

thirdly, the sampling voltage at two ends of the sampling element is sent to a demodulation circuit, and the demodulation circuit identifies the current medium around the separately excited piezoelectric element according to the amplitude and the frequency characteristic parameter of the sampling voltage;

the specific identification method is as follows: the alternating current excitation source generates an excitation voltage with a fundamental frequency close to the minimum impedance frequency of the separately excited piezoelectric element in the liquid phase, and the impedance of the separately excited piezoelectric element in the liquid phase is minimum; when the separately excited piezoelectric element is placed in a liquid phase, the amplitude of sampling voltage at two ends of the sampling element is maximum; when the separately excited piezoelectric element is placed in a gas phase, the amplitude of sampling voltage at two ends of the sampling element is reduced; taking a certain value in the middle of voltage or frequency characteristic values of the separately excited piezoelectric element in gas and liquid respectively, or a certain value in the middle of characteristic values obtained by conditioning voltage amplitude or frequency as a judgment threshold value k, comparing the characteristic value obtained by detection or conditioning with the value k, and judging whether the medium is liquid or gas according to a comparison result;

fourthly, if the detected medium is gas, generating an exhaust enabling signal, and turning to the fifth step, otherwise, turning to the first step;

fifthly, sending the exhaust enabling signal to a driving circuit, and enabling the driving circuit to drive an exhaust valve;

and sixthly, opening the exhaust valve, exhausting the gas in the closed container, and turning to the first step.

The third exhaust method based on the separately excited piezoelectric element uses the exhaust device based on the separately excited piezoelectric element as described above:

firstly, an alternating current excitation source generates excitation voltage with fundamental frequency close to the maximum impedance frequency of a separately excited piezoelectric element in a gas phase;

secondly, placing the separately excited piezoelectric element in a medium to be detected;

thirdly, the sampling voltages at the two ends of the sampling element are sent to a demodulation circuit, and the demodulation circuit identifies the current medium around the separately excited piezoelectric element according to the amplitude and the frequency characteristic parameters of the sampling voltages;

the specific identification method is as follows: the alternating current excitation source generates an excitation voltage with a fundamental frequency close to the maximum impedance frequency of the separately excited piezoelectric element in the gas phase, and the impedance of the separately excited piezoelectric element in the gas phase is maximum; when the separately excited piezoelectric element is placed in a gas phase, the sampling voltage amplitude values at two ends of the sampling element are minimum; when the separately excited piezoelectric element is placed in a liquid phase, the amplitude of sampling voltage at two ends of the sampling element is increased; taking a certain value in the middle of voltage or frequency characteristic values of the separately excited piezoelectric element in gas and liquid respectively, or a certain value in the middle of characteristic values obtained by conditioning voltage amplitude or frequency as a judgment threshold value k, comparing the characteristic value obtained by detection or conditioning with the value k, and judging whether the medium is liquid or gas according to a comparison result;

fourthly, if the detected medium is gas, generating an exhaust enabling signal, and turning to the fifth step, otherwise, turning to the first step;

fifthly, sending the exhaust enabling signal to a driving circuit, and enabling the driving circuit to drive an exhaust valve;

and sixthly, opening the exhaust valve, exhausting the gas in the closed container, and turning to the first step.

A fourth exhaust method based on separately excited piezoelectric elements, which uses the exhaust device based on separately excited piezoelectric elements, includes the following steps:

firstly, an alternating current excitation source generates an excitation voltage with a fundamental frequency close to the maximum impedance frequency of a separately excited piezoelectric element in a liquid phase;

secondly, placing the separately excited piezoelectric element in a medium to be detected;

thirdly, the sampling voltage at two ends of the sampling element is sent to a demodulation circuit, and the demodulation circuit identifies the current medium around the separately excited piezoelectric element according to the amplitude and the frequency characteristic parameter of the sampling voltage;

the specific identification method is as follows: the alternating current excitation source generates an excitation voltage with a fundamental frequency close to the maximum impedance frequency of the separately excited piezoelectric element in the liquid phase, and the impedance of the separately excited piezoelectric element in the liquid phase is maximum; when the separately excited piezoelectric element is placed in a liquid phase, the sampling voltage amplitude values at two ends of the sampling element are minimum; when the separately excited piezoelectric element is placed in a gas phase, the amplitude of sampling voltage at two ends of the sampling element is increased; taking a certain value in the middle of voltage or frequency characteristic values of the separately excited piezoelectric element in gas and liquid respectively, or a certain value in the middle of characteristic values obtained by conditioning voltage amplitude or frequency as a judgment threshold value k, comparing the characteristic value obtained by detection or conditioning with the value k, and judging whether the medium is liquid or gas according to a comparison result;

fourthly, if the detected medium is gas, generating an exhaust enabling signal, and turning to the fifth step, otherwise, turning to the first step;

fifthly, sending the exhaust enabling signal to a driving circuit, and enabling the driving circuit to drive an exhaust valve;

and sixthly, opening the exhaust valve, exhausting the gas in the closed container, and turning to the first step.

The invention has the advantages that:

the gas-liquid detection sensor adopts the separately excited piezoelectric element as a sensitive element for gas-liquid detection, is structurally formed by bonding a piezoelectric ceramic material and an elastic metal material, and has the advantage of strong environmental adaptability; according to the physical characteristics of the detected object such as density, viscosity and the like, the method has the advantages of wide applicable object, sensitive detection and high reliability.

Drawings

FIG. 1 is a schematic diagram of the venting method of the present invention based on a separately excited piezoelectric element;

the device comprises an alternating current excitation source 1, a separately excited piezoelectric element 2, a sampling element 3, a demodulation circuit 4, a driving circuit 5 and an exhaust valve 6.

Detailed Description

This section is an example of the present invention and is provided to explain and illustrate the technical solutions of the present invention.

The exhaust method of the hydraulic system based on the independent excitation type piezoelectric element is proposed according to the obvious difference of the physical characteristics such as density, viscosity and the like existing in gas and hydraulic pressure. The hydraulic system exhaust method based on the self-excitation independent-excitation piezoelectric element does not depend on the characteristics of electricity, light and the like of a detection object, and has the advantages of high sensitivity, high reliability, strong applicability and the like.

An exhaust device based on separately excited piezoelectric elements comprises an alternating current excitation source 1, separately excited piezoelectric elements 2, a sampling element 3, a demodulation circuit 4, a driving circuit 5 and an exhaust valve 6; the separately excited piezoelectric element 2 and the sampling element 3 are connected in series between two power supply pins of the alternating current excitation source 1, and voltage signals at two ends of the sampling element 3 are input into the demodulation circuit 4; if the detected medium is gas, generating an exhaust signal; the exhaust signal enable drive circuit 5; the driving circuit 5 controls the opening and closing of the exhaust valve 6; the gas in the closed container is discharged after the gas outlet valve 6 is opened; the separately excited piezoelectric element 2 is a sensitive element for detecting gas and liquid media.

The fundamental frequency of the excitation voltage generated by the alternating current excitation source 1 is close to the minimum impedance frequency or the maximum impedance frequency of the separately excited piezoelectric element 2 in a gas phase or a liquid phase;

the separately excited piezoelectric element 2 is of a thin sheet structure;

the separately excited piezoelectric element 2 is installed inside the exhaust valve 6;

embodiment mode 1:

an exhaust method based on separately excited piezoelectric elements uses the exhaust device based on separately excited piezoelectric elements:

firstly, an alternating current excitation source 1 generates an excitation voltage with a fundamental frequency close to the minimum impedance frequency of a separately excited piezoelectric element 2 in a gas phase;

secondly, placing the separately excited piezoelectric element 2 in a detected medium;

and thirdly, the sampling voltage at the two ends of the sampling element 3 is sent to the demodulation circuit 4, and the demodulation circuit 4 identifies the current medium around the separately excited piezoelectric element 2 according to the amplitude and the frequency characteristic parameter of the sampling voltage. The specific identification method is as follows: the alternating current excitation source 1 generates an excitation voltage with a fundamental frequency close to the minimum impedance frequency of the separately excited piezoelectric element 2 in the gas phase, and the impedance of the separately excited piezoelectric element 2 in the gas phase is minimum; when the separately excited piezoelectric element 2 is placed in a gas phase, the amplitude of the sampling voltage at the two ends of the sampling element 3 is the largest; when the separately excited piezoelectric element 2 is placed in liquid, the amplitude of sampling voltage at two ends of the sampling element 3 is reduced; taking a certain value in the middle of voltage or frequency characteristic values of the separately excited piezoelectric element 2 in gas and liquid respectively, or a certain value in the middle of characteristic values obtained by conditioning voltage amplitude or frequency as a judgment threshold value k, and judging that the medium is liquid when the detected or conditioned characteristic value is larger than (or smaller than, different depending on a conditioning circuit) the k value; otherwise, judging that the medium is gas;

fourthly, if the detected medium is gas, generating an exhaust enabling signal, and turning to the fifth step, otherwise, turning to the first step;

fifthly, sending an exhaust enable signal to the drive circuit 5, and enabling the drive circuit 5 to drive the exhaust valve 6;

and sixthly, opening an exhaust valve 6, exhausting gas in the closed container, and transferring to the first step.

Embodiment mode 2:

an exhaust method based on separately excited piezoelectric elements uses the exhaust device based on separately excited piezoelectric elements:

firstly, an alternating current excitation source 1 generates an excitation voltage with a fundamental frequency close to the minimum impedance frequency of a separately excited piezoelectric element 2 in a liquid phase;

secondly, placing the separately excited piezoelectric element 2 in a medium to be detected;

and thirdly, the sampling voltage at the two ends of the sampling element 3 is sent to the demodulation circuit 4, and the demodulation circuit 4 identifies the current medium around the separately excited piezoelectric element 2 according to the amplitude and the frequency characteristic parameter of the sampling voltage. The specific identification method is as follows: the alternating current excitation source 1 generates an excitation voltage with a fundamental frequency close to the minimum impedance frequency of the separately excited piezoelectric element 2 in the liquid phase, and the impedance of the separately excited piezoelectric element 2 in the liquid phase is minimum; when the separately excited piezoelectric element 2 is placed in a liquid phase, the amplitude of the sampling voltage at two ends of the sampling element 3 is the largest; when the separately excited piezoelectric element 2 is placed in a gas phase, the amplitude of the sampling voltage at the two ends of the sampling element 3 is reduced; taking a certain value in the middle of voltage or frequency characteristic values of the separately excited piezoelectric element 2 in gas and liquid respectively, or a certain value in the middle of characteristic values obtained by conditioning voltage amplitude or frequency as a judgment threshold value k, and judging that the medium is gas when the detected or conditioned characteristic value is larger than (or smaller than, different depending on a conditioning circuit) the k value; otherwise, judging that the medium is liquid;

fourthly, if the detected medium is gas, generating an exhaust enabling signal, and turning to the fifth step, otherwise, turning to the first step;

fifthly, sending an exhaust enable signal to the drive circuit 5, and enabling the drive circuit 5 to drive the exhaust valve 6;

and sixthly, opening an exhaust valve 6, exhausting gas in the closed container, and transferring to the first step.

Embodiment mode 3:

an exhaust method based on separately excited piezoelectric elements uses the exhaust device based on separately excited piezoelectric elements:

firstly, an alternating current excitation source 1 generates an excitation voltage with a fundamental frequency close to the maximum impedance frequency of a separately excited piezoelectric element 2 in a gas phase;

secondly, placing the separately excited piezoelectric element 2 in a medium to be detected;

and thirdly, the sampling voltage at the two ends of the sampling element 3 is sent to the demodulation circuit 4, and the demodulation circuit 4 identifies the current medium around the separately excited piezoelectric element 2 according to the amplitude and the frequency characteristic parameter of the sampling voltage. The specific identification method is as follows: the alternating current excitation source 1 generates an excitation voltage with a fundamental frequency close to the maximum impedance frequency of the separately excited piezoelectric element 2 in the gas phase, and at the time, the impedance of the separately excited piezoelectric element 2 in the gas phase is maximum; when the separately excited piezoelectric element 2 is placed in a gas phase, the amplitude of sampling voltage at two ends of the sampling element 3 is minimum; when the separately excited piezoelectric element 2 is placed in a liquid phase, the amplitude of the sampling voltage at the two ends of the sampling element 3 is increased; taking a certain value in the middle of voltage or frequency characteristic values of the separately excited piezoelectric element 2 in gas and liquid respectively, or a certain value in the middle of characteristic values obtained by conditioning voltage amplitude or frequency as a judgment threshold value k, and judging that the medium is gas when the detected or conditioned characteristic value is larger than (or smaller than, different depending on a conditioning circuit) the k value; otherwise, judging that the medium is liquid;

fourthly, if the detected medium is gas, generating an exhaust enabling signal, and turning to the fifth step, otherwise, turning to the first step;

fifthly, sending an exhaust enable signal to the drive circuit 5, and enabling the drive circuit 5 to drive the exhaust valve 6;

and sixthly, opening an exhaust valve 6, exhausting gas in the closed container, and transferring to the first step.

Embodiment 4:

an exhaust method based on separately excited piezoelectric elements uses the exhaust device based on separately excited piezoelectric elements:

firstly, an alternating current excitation source 1 generates an excitation voltage with a fundamental frequency close to the maximum impedance frequency of a separately excited piezoelectric element 2 in a liquid phase;

secondly, placing the separately excited piezoelectric element 2 in a medium to be detected;

and thirdly, the sampling voltage at the two ends of the sampling element 3 is sent to the demodulation circuit 4, and the demodulation circuit 4 identifies the current medium around the separately excited piezoelectric element 2 according to the amplitude and the frequency characteristic parameter of the sampling voltage. The specific identification method is as follows: the alternating current excitation source 1 generates an excitation voltage with a fundamental frequency close to the maximum impedance frequency of the separately excited piezoelectric element 2 in the liquid phase, and the impedance of the separately excited piezoelectric element 2 in the liquid phase is maximum at the time; when the separately excited piezoelectric element 2 is placed in a liquid phase, the sampling voltage amplitudes at the two ends of the sampling element 3 are minimum; when the separately excited piezoelectric element 2 is placed in a gas phase, the amplitude of the sampling voltage at the two ends of the sampling element 3 is increased; taking a certain value in the middle of voltage or frequency characteristic values of the separately excited piezoelectric element 2 in gas and liquid respectively, or a certain value in the middle of characteristic values obtained by conditioning voltage amplitude or frequency as a judgment threshold value k, and judging that the medium is gas when the detected or conditioned characteristic value is larger than (or smaller than, different depending on a conditioning circuit) the k value; otherwise, judging that the medium is liquid;

fourthly, if the detected medium is gas, generating an exhaust enabling signal, and turning to the fifth step, otherwise, turning to the first step;

fifthly, sending an exhaust enable signal to the drive circuit 5, and enabling the drive circuit 5 to drive the exhaust valve 6;

and sixthly, opening an exhaust valve 6, exhausting gas in the closed container, and transferring to the first step.