Detection of structural variations in articles using acoustic resonance method

Abstract

To determine whether fluid is leaking through a valve seat when a valve is in a closed condition.SOLUTION: A gate valve 10 illustrates: a body 12; a stem 14 driven by a handwheel 16 and a through bonnet 18; a gate 20; and a bearing flexible element 22 for sealing a seat part 24. To noninvasively detect small leaks, a broad-band acoustic transmitting transducer 30 and an identical broad-band acoustic receiving transducer 32 are attached. The broad-band acoustic transmitting transducer generates vibrations in the valve 10 when excited by a voltage signal. The identical broad-band acoustic receiving transducer receives the vibrations induced in the valve 10 and converts such signals into voltages.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 015,283, filed April 24, 2020, entitled "LEAK DETECTION IN VALVES VIA ULTRASONIC RESONANCE," the entire disclosure of which is expressly incorporated herein by reference for all that it discloses and teaches. [Background technology]

[0002] Machinery or mechanical structures having internal or external components that are placed away from a set point and that later need to be replaced are common, as are situations where deviations or variations from known articles occur due to manufacturing or counterfeiting. As an example of the former situation, valves controlling volatile gases such as natural gas or other flammable media, or corrosive or reactive fluids, can have a significant impact on safety when a leak occurs.

[0003] Although the focus of valve leakage is generally to reduce the loss of expensive products or to mitigate environmental pollution, when considering leakage in industrial processes, the product is often neither expensive nor dangerous; water is one example. As a practical matter, while small amounts of valve leakage are tolerable in most control applications, for shut-off valves, even the smallest amount of unwanted process medium leakage can cause serious damage. Flow meters are often used to monitor valve seat leakage, but are not very reliable and cannot detect small leaks due to improper seating of the valve.

[0004] In fact, some of the largest industrial disasters in history are believed to have occurred due to faulty water valves. The 1984 Bhopal gas tragedy in Bhopal, India, killed thousands of people. The disaster occurred when a lack of regular maintenance caused one ton of water to leak into a tank containing 40 tons of toxic methyl isocyanate. A highly exothermic reaction pressurized the tank through the production of carbon dioxide, releasing unreacted methyl isocyanate into the plant and throughout the surrounding town. Another well-known disaster was the BP Deepwater Horizon oil spill in 2010, which is believed to have been the result of the failure of two valves that served to stop the flow of oil and gas.

[0005] In addition to safety concerns, valve leaks can cause energy waste and other operational losses. For example, such leaks can cause a drop in system pressure resulting in air-powered tools not functioning efficiently, thereby adversely affecting production. If the fluid is used to deliver energy in power plants, the energy can be dissipated into the atmosphere through leaks, wasting significant energy each year. Summary of the Invention

[0006] In accordance with the purposes of the present invention, as embodied and broadly described herein, an embodiment of an apparatus for determining whether a fluid is leaking through a valve seat when a valve is in a closed condition comprises, in this regard, a valve including a valve seat, a disk or plug for forming a fluid seal with said valve seat, a stem for driving said disk or plug against said valve seat, and a valve body having an outer surface, and a valve body having a valve seat and a stem for driving said disk or plug against said valve seat, said valve body having an outer surface, and a valve body having a valve seat ... and a valve body having a valve seat and a valve body and a valve body having a valve seat and a valve body and a valve body and a valve body and a valve body and a valve body and a valve body and a valve body and a valve body and a valve body and a valve body and a valve body and a valve body and a valve body and a valve body and a valve body and a valve body and a valve body and a valve body and a valve body and a valve body and a valve body and a valve body and a an acoustic transmit transducer disposed in vibrational contact with the exterior surface of the valve for generating vibrations in the valve body when excited by a selected voltage signal; an acoustic receiver disposed in vibrational contact with the exterior surface of the valve for receiving vibrations induced in the valve body and converting the received vibrations into a voltage; a frequency sweep generator in electrical communication with the acoustic transmit transducer for generating a selected excitation voltage signal having a frequency within a selected frequency range; a narrow bandpass tracking filter having a center frequency that tracks the frequency within the selected frequency range generated by the frequency sweep generator and having a selected frequency bandwidth, the narrow bandpass tracking filter for receiving a voltage from the acoustic receiver and filtering the voltage; and a microcontroller for controlling the frequency sweep generator and the narrow bandpass tracking filter, for storing the filtered voltage from the narrow bandpass tracking filter, for generating at least two acoustic resonance spectra of the valve in a closed state and for comparing the at least two generated acoustic resonance spectra to determine if there is a difference therebetween.

[0007] In another aspect of the invention, and in accordance with the purposes of the invention as embodied and broadly described herein, an embodiment of a method for determining whether a fluid is leaking through a valve seat of a valve when said valve is in a closed condition comprises in said valve comprising a valve seat, a disk or plug for forming a fluid seal with said valve seat, a stem for driving said disk or plug against said valve seat, and a valve body having an outer surface, generating vibrations having a selected frequency within a selected frequency range from an acoustic transmitting transducer disposed in vibrating contact with said outer surface of the valve and driven by a frequency sweep generator; receiving induced resonant vibrations in the valve body and converting the received vibrations into a voltage; receiving the voltage and filtering the voltage using a narrow bandpass tracking filter having a center frequency that tracks a selected excitation frequency within the selected frequency range; storing the filtered voltage, whereby an acoustic resonance spectrum of the valve is generated and stored; comparing the generated acoustic resonance spectrum of the valve to at least one other acoustic resonance spectrum obtained with the valve in a closed state; and determining whether there is a difference between the generated acoustic resonance spectrum and the at least one other acoustic resonance spectrum.

[0008] In yet another aspect of the invention, and in accordance with the purposes of the invention as embodied and broadly described herein, an embodiment of a method for determining whether a container that is similar or identical in appearance to another container is similar or identical thereto and contains a similar fluid thereto, includes, in this regard, providing a method for determining whether a container is similar or identical in appearance to another container, the method comprising: the method includes the steps of: generating vibrations having a selected frequency within a selected frequency range from an acoustic transmitting transducer disposed in vibration communication with the exterior surface of the container and driven by a frequency sweep generator; receiving resonant vibrations induced in the container using an acoustic receiving unit disposed in vibration communication with the exterior surface of the container and converting the received vibrations into a voltage; receiving the voltage and filtering the voltage using a narrow bandpass tracking filter having a center frequency that tracks a selected excitation frequency within the selected frequency range; storing the filtered voltage, thereby generating an acoustic resonance spectrum of the container; comparing the generated acoustic resonance spectrum of the container with at least one other acoustic resonance spectrum obtained for the other container; and determining whether there is a difference between the generated acoustic resonance spectrum and the at least one other acoustic resonance spectrum.

[0009] In yet another aspect of the invention, and in accordance with the objects of the invention as embodied and broadly described herein, an embodiment of a method for determining the tightness of a sealing flange for accessing a fluid in a vessel, the method comprising: a cover flange; and a flange attached to a pipe secured by a bolt and nut or a clamp, the flange comprising: generating vibrations having a selected frequency within a selected frequency range in the sealing flange, the nut and bolt or the clamp, the pipe, and the vessel using an acoustic transmitting transducer arranged in vibrational communication with an outer surface of the pipe or the vessel and driven by an acoustic frequency sweep generator; receiving induced and coupled resonant vibrations in the sealing flange, the nut and bolt or the clamp, the pipe, and the vessel using an acoustic receiving unit arranged in vibrational contact with the outer surface of the pipe or the vessel, and measuring the received vibrations. to a voltage; receiving the voltage and filtering the voltage using a narrow bandpass tracking filter having a center frequency that tracks a selected excitation frequency within the selected frequency range; storing the filtered voltage, thereby generating an acoustic resonance spectrum of the combination of the sealing flange, the nut and bolt or the clamp, the pipe, and the container; comparing the generated acoustic resonance spectrum comprising the frequency range of the combination of the sealing flange, the nut and bolt or the clamp, the pipe, and the container with at least one other acoustic resonance spectrum obtained for the combination of the sealing flange, the nut and bolt or the clamp, the pipe, and the container; and determining if there is a difference between the generated acoustic resonance spectrum and the at least one other acoustic resonance spectrum.

[0010] Benefits and advantages of the present invention include, but are not limited to, providing an apparatus and method using acoustic resonance spectroscopy that can be applied to any mechanical device or structure that has an internal or external component that is placed away from a set point and needs to be returned to its original position, such as a valve that is opened to allow fluid to pass and then closed, for non-invasively providing a measurement of deviation from the original position, and for sorting or grouping together multiple objects that appear identical from the outside but may be slightly different on the outside or inside, such as sealed containers filled with different fluids or materials. [Brief description of the drawings]

[0011] The accompanying drawings, which are incorporated in and form a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0012] [Figure 1] Figure 1A is a schematic cross-sectional view of a closed but incompletely seated shut-off valve and an embodiment of an apparatus used to explain an embodiment of the method of the present invention, illustrating a broadband ultrasonic transmit transducer for generating vibrations in the valve when excited by a voltage signal, and an identical broadband ultrasonic receive transducer for receiving the induced vibrations in the valve and converting such signal to a voltage. Figure 1B is a schematic cross-sectional view of the properly closed and sealed shut-off valve illustrated in Figure 1A. [Figure 2A] FIG. 2A is a graphical representation of a sample resonance spectrum and a reference resonance spectrum of a properly seated valve, with the solid vertical line indicating the center of the resonance characteristic. [Figure 2B] FIG. 2B is a graphical illustration of a resonance spectrum (vertical dashed line) that randomly shifts from the resonance location of FIG. 2A, which is the measured resonance spectrum of a poorly seated valve. [Figure 3A]FIG. 3A is a graph showing the repeatability of the resonance spectrum and that when ten data sets taken by removing and placing the transducer on the gate valve are overlaid to obtain a reference template, the resonance peak position remains the same while the amplitude can change. [Figure 3B] FIG. 3B is a graph showing an example resonance spectrum of a fully closed 2-inch gate valve ((a) solid line) (a small section of a larger frequency range to emphasize the difference) and an example resonance spectrum when the valve is not fully seated, causing a small leak ((b) dashed line). [Figure 4] FIG. 4 shows the resonant frequency spectrum obtained from FIG. 3B(a) of a properly seated valve, converted into a bar code form. [Figure 5A] FIG. 5A shows the resonant frequency spectrum of a cylindrical steel container at ambient pressure, converted into the form of a bar code, with the locations of the peaks indicated by vertical lines (reference spectrum). [Figure 5B] FIG. 5B is the resonance spectrum obtained for the vessel in FIG. 5A when the pressure inside the vessel is increased, showing that the frequency spectrum is shifted towards higher frequencies. [Figure 5C] FIG. 5C is a graph showing a pattern matching of the spectra from FIGS. 5A and 5B as obtained by mathematically shifting the reference spectrum in frequency to match the spectrum at higher pressure, with the peaks corresponding to the shift in frequency observed due to the elevated pressure. [Figure 6] FIG. 6 shows the shift in frequency of the entire spectrum as depicted in FIG. 5C as a function of the internal pressure of the cylindrical vessel, and illustrates how pressure linearly shifts the entire spectrum for the range of pressures shown. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Briefly, an embodiment of the device of the present invention, a broadband transmit transducer, and a broadband receive transducer are placed in acoustic contact with the outer surface of an article or object that is to be investigated for structural changes from a selected state or from a selected reference article. The transducers can be placed close to each other but not in contact, or placed further apart. The placement is not important, and for permanent attachment, an epoxy or other adhesive can be used. A frequency sweep generator is controlled by a microcontroller and sends a frequency-varying voltage signal to the transmit transducer through a power amplifier. The power amplifier also provides electrical impedance matching for efficient energy transfer to the transducer. The direction of the frequency sweep is not important, since both generate the same spectrum. The transducer vibrates at the frequency generated by the frequency sweep generator, and the vibrations are coupled into the body of the article. If this excitation vibration signal matches any of the natural vibration modes of the article, a large amplitude response is detected by the receive transducer. The output of the receiving transducer may be amplified and passed through a narrow bandpass tracking filter with a selectable frequency bandwidth. After filtering, the signal is digitized by an A / D converter controlled by a microcontroller. The microcontroller extracts the magnitude of the received signal and records this magnitude at each of the frequencies applied to the source transducer. At the end of the frequency sweep, an acoustic resonance spectrum of the article is generated.

[0014] The embodiments of the present invention are applicable to any mechanical device or structure to provide a measurement of deviation from an original position, having an internal or external component that needs to be placed away from a set point and then returned to the original position, such as a valve that is opened to let fluid through and then closed. It can also be used to determine the tightness of a flange. If a flange or other lid is replaced and some of the bolts are not tightened to the original torque, the resonance spectrum changes and can be detected. A similar situation occurs when clamps such as tri-clover clamps are used to seal flanges, which are common in breweries, food industries, and pharmaceutical industries. Another example is medical screws that are attached to bone. Sometimes these screws come loose, but an x-ray cannot show this. When the screw is firmly attached to the bone, there is a damping of the resonance compared to when the screw is loose, and the resonance pattern may change. An electromagnetic acoustic transducer (EMAT) can be used that can excite a metallic screw. The same transducer can be used to monitor the resonance through the change in its electrical impedance.

[0015] Another embodiment of the present invention can be used to classify or group together objects that appear identical from the outside but may have differences on the inside, such as sealed containers filled with different fluids or materials. Once a reference template spectrum is obtained for each type of container, the type of material in the container being investigated can be identified. Thus, non-invasive identification of the fluid in the sealed container can be achieved. Additionally, embodiments of the present invention can be used to determine the tolerances and uniformity of manufactured or machined items, such as the difference of counterfeit vaccine vials from those produced by approved manufacturers.

[0016] As noted above, embodiments of the present invention include apparatus and methods for the non-invasive detection of leaks in valves. If complete closure of the valve is compromised for any reason, leakage across the valve seat will not be visible on the outside of the valve. However, there can be serious problems with a valve in this state, as unacceptable amounts of process media will continue to flow through the valve. Among other problems, such flow can cause internal damage and shorten the life of the valve.

[0017] A complex object is not a single vibrating mass like a sphere or a cube. Rather, it is multiple volumes with different lengths, widths, etc., each contributing to their individual resonance. The effect of any stress or external condition will be different on each of these regions. Thus, the valve can be thought of as the sum of all of these different regions of metal.

[0018] Any solid object has many natural vibration modes that vibrate with large amplitudes when excited at their vibration frequencies. These vibration modes, when viewed over a range of frequencies, constitute a resonance spectrum. This spectrum depends on the elastic properties of the object's material and its geometric shape. In cases where the object is composed of multiple components, each component contributes to this spectrum. The smaller the components, the higher the resonant frequency. Thus, an object such as a valve generates a complex acoustic resonance spectrum. Any change in the components is reflected in the resonance spectrum. Not all resonant vibration modes are affected in the same way, some modes show large changes due to changes in the internal configuration, and some show little change. Thus, the resonance spectrum can serve as a leak detection principle when a valve is not properly seated.

[0019] All valves through which fluids pass emit a wide range of vibration frequencies (noise), which can often be detected using acoustic transducers. The physical source of leakage noise is the changing pressure field associated with turbulence in the fluid, resulting from flow instabilities where inertial effects dominate viscous resistance. For flow in cylindrical channels, Reynolds numbers between 1000 and 10,000 give rise to turbulence in the fluid and provide a lower limit for leak detection under ideal conditions. There are many other mechanisms that contribute to the vibration signal associated with leakage across a valve, including turbulent mixing, shock-related noise, cavitation in the liquid, and mechanical sources within the valve. These latter sources of noise can be caused by valve seat peening damage, deposits accumulated on the valve seat, or scoring of the valve plug.

[0020] There are commercially available devices that allow the quantification of internal leaks at high pressures in valves with a single fluid, based on acoustic detection of flow-induced vibrations or sounds. The measurement is passive and is achieved with a sensor attached to the valve. To identify and quantify the leaking valve, the valve must be in its closed state and there must be a differential pressure of at least 1 bar across the valve. The leak rate is then determined after certain parameters are entered into a prediction equation. The measurement takes about 2 minutes per valve, but can be hindered by nearby pressure differences in other fluids.

[0021] In practice, there are many considerations that affect the ability to detect leaks, such as: - The leak path for small leaks is usually complex, resulting in much more turbulence and therefore more noise from the actual leak than would otherwise be predicted. Product loss can occur not from a single leak but from multiple leaks distributed around the valve seat. If these are below the critical point of turbulence, no noise will be generated. • If all leaks contain noise, multiple signals will give different results than just one leak path. - The level of noise at the source is not what the sensor actually detects; the signal travels through the valve body to where the sensor is mounted on the outside. Background noise from nearby turbulence or from normal plant noise and vibrations can make measurement location important.

[0022] Generally, there is a lot of ambient vibration from machines and other equipment in which the control valve is used in the industry. Therefore, any detection system must be immune to such ambient vibration. Passive measurements and resonance analysis have been used to detect faults in machines attached to control valves, where the detected vibrations are analyzed using spectra. Typically, rotating parts give rise to distinct resonance characteristics, which the present technique allows for detection. For example, a loose part will rattle when rotated or subjected to strong vibrations.

[0023] To generate a reference spectrum for the valve, multiple spectra of a properly seated valve are obtained by opening and closing the valve each time before a spectrum is recorded. The average of each frequency is recorded and the reference spectrum is replaced by the average position of each peak. The exact amplitude of each resonant peak contributing to the reference spectrum may differ slightly depending on the position of the receiving transducer, but the position of the resonance remains the same, except for negligible changes due to manufacturing tolerances. Any deviation from this reference spectrum beyond a selected amount in the frequency spectrum of the valve is then attributed to the valve not being completely closed. As presented below, a peak position correlation algorithm was developed to correlate the resonant frequencies to determine the closeness of the measured spectrum to the reference spectrum, i.e., the total number of peaks in common within a given spread of frequencies or frequency window for both the reference and measured resonant spectra. The commonly used methodology for cross-correlation of the entire spectrum with the reference spectrum is sensitive to peak amplitudes that may vary with the position of the transducer on the valve, as described.

[0024] In the following description, gate valves are primarily discussed, but other valves, such as ball valves, work with this device as well, and it is not limited to gate valves. In a gate valve, a rectangular gate is inserted perpendicularly into the flowing fluid path, typically by a threaded stem connected to an actuator (hand wheel or motor). The gate then seals against a valve seat with a gland. Gate valves are primarily used for on / off (fully closed or fully open) non-throttling service, and are commonly used in refineries and petrochemical plants where pressures remain relatively low but temperatures can be very high. Gate valves are used less frequently in upstream oil and gas production facilities due to the high operating pressures, long opening / closing times, and harsh environmental conditions when operating in marine atmospheres.

[0025] Abrasive processing methods, cavitation, or flashing can cause progressive erosion of the valve, which results in leakage through the valve seat and disc or plug over the life of the valve. Process fluid continues to leak through the closed valve.

[0026] As mentioned, in practice, small amounts of leakage at the valve seat are acceptable in most control applications. In contrast, for shut-off valves, unwanted leakage of even the smallest amounts of process medium can cause serious damage. Uncontrolled flow of toxic and highly reactive or highly flammable media is an example of an unwanted flow. In such cases, it is important that signs of plug wear are detected at an early stage, and plant operators must be alerted when unacceptable amounts of media flow through a closed valve.

[0027] Hereinafter, the term "ultrasonic" is meant to include both the "sonic" and "ultrasonic" regions of the acoustic spectrum. Additionally, valve leakage refers to flow through a valve placed in an "off" condition or state, i.e., flow through the valve seat as opposed to through the valve stem. As noted above, the significance of such valve leakage depends on what the valve controls. The fluid can be a gas, a liquid, or a combination thereof.

[0028] Reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying figures. In the figures, similar structures are identified using the same reference numerals. It will be understood that the figures are presented for the purpose of describing certain embodiments of the invention and are not intended to limit the invention thereto. Now, in FIG. 1A, a schematic cross-sectional view of a closed but incompletely seated shut-off valve, a type of gate valve 10, is shown, showing the body 12, the stem 14 actuated by the hand wheel 16 and through bonnet 18, the gate 20, and the bearing flexible element 22 for sealing the valve seat 24. In metered or other types of shut-off valves, a disk or plug is used to close the valve seat 24. Also shown is a fluid 26, leak 28, through the valve body 12. In contrast, FIG. 1B is a schematic cross-sectional view of the shut-off valve shown in FIG. 1A, properly closed and sealed. Small leaks are difficult to detect non-invasively.

[0029] Since the resonant vibrations are distributed throughout the valve, a wideband acoustic transmitting transducer 30 that generates vibrations in the valve 10 when excited by a voltage signal, and an identical wideband acoustic receiving transducer 32 for receiving the vibrations induced in the valve 10 and converting such signals into voltages, are mounted (in acoustic or vibrational communication) at any location on the outer surface 34 of the valve body 12 to perform the measurements described herein. The transducers may be placed side-by-side as long as they do not touch each other. For permanent mounting, an adhesive such as epoxy resin may be used. If the valve 10 contains magnetic material, a simple magnetic coupling is sufficient for quick measurements. The transmitting transducer 30 and the receiving transducer 32 are interchangeable if piezoelectric transducers are used. It is not required that the transducers be identical, and different transducers (e.g., magnetostrictive, capacitive, electromagnetic acoustic-EMAT transducers, for example) can be used. Commercially available off-the-shelf 1 MHz center frequency broadband piezoelectric transducers from Olympus NDT were used for both the transmitting (source) and receiving sections, one of each. Typical frequency scans were between about 2 kHz and about 150 kHz.

[0030] A frequency sweep generator 36 controlled by a microcontroller 38 (e.g., Arduino, Raspberry Pi, single board computer, etc.) applies a voltage signal that varies linearly from low to high frequency through a power amplifier 40 to the transmitting transducer 30. The amplifier 40 also provides electrical impedance matching for efficient energy transfer to the transducer 30. The applied voltage signal is non-linear as well, and the direction of the frequency sweep can be reversed if desired, since both sweep directions generate the same spectrum. The frequency may be stepped through a selected frequency range in small frequency steps, the size of the step being determined by the number of desired frequency values ​​in the spectrum, and the transducer 30 oscillates at each of the frequency steps. For example, each frequency can be applied for a short time (~1 ms) and then moved to the next value during the sweep, such that a frequency scan between 1-10 kHz would have 1000 frequency steps. A number of steps greater than 2000 has been found to provide adequate frequency resolution over the full range of any selected frequency sweep, although smaller numbers may also be used. The resulting vibrations generated by the transducer 30 are coupled into the body of the valve (or object). When this excitation vibration signal matches any of the natural vibration modes of the object (e.g., valve), a large amplitude response is detected by the receiving transducer 32.

[0031] The signal received by the transducer 32 is first buffered, if necessary, at the output of the receiving transducer using a buffer amplifier 42 so that the small signal voltage from the receiving transducer 32 can be directed to a signal amplifier 44 without significant distortion or loading. The amplifier 42 can be an integral part of the receiving transducer 32. After amplification, the output of the signal amplifier 44 passes through a narrow bandpass tracking filter 46 having a center frequency at the excitation frequency generated by the frequency sweep generator 36 and a selectable frequency band. The filter 46 thus follows each excitation frequency, thereby reducing electrical noise picked up from ambient vibrations. The tracking filter 46 is synchronized with the sweep generator by a digital signal processor (DPS) / microcontroller 38 and can be implemented in several different ways, such as, for example, heterodyne or homodyne techniques or a vector network analyzer. Following filtering, the signal is digitized by an A / D (analog-to-digital) converter 48, which is also controlled by the microcontroller 38. A 12-bit A / D converter running at 1 MHz would be sufficient for this purpose, although the described embodiment of the device is not limited to these values. The digitized data is stored in the memory of the microcontroller 38 before further processing.

[0032] The microcontroller 38 extracts the magnitude of the received signal and records this magnitude at each of the frequencies applied to the transmitting transducer 30. The microcontroller 38 can also determine the phase shift at each frequency through the DPS. The phase information can be used to determine the exact location of the resonance peak, which is useful in some situations when the amplitude of the resonance peak is small. "Phase" refers to the phase difference between the transmitted and received signals and can be set to a value of zero at the resonance. A simple zero-crossing algorithm can then pinpoint the location of the peak resonance frequency. At the end of the frequency sweep, typically in less than 10 seconds (<10s), a complete resonance spectrum with both amplitude and phase spectra is generated. Although the amplitude spectrum is sufficient in most situations, it is useful to utilize both amplitude and phase information for measurement robustness.

[0033] The measurement time can be reduced depending on the amount of ambient noise. The greater the ambient noise, the smaller the bandwidth for the tracking filter and the slower sweep times are required. To obtain a sharper resonant peak, longer sweep times are also recommended. Thus, if the ambient noise is not too high, a sweep measurement can be completed in less than one second. As described, by limiting the noise level to a small value and averaging the recorded noise, the bandwidth of the tracking filter provides immunity to the ambient noise, thereby providing a signal-to-noise ratio that can be as high as 92 dB.

[0034] Inexpensive, commercially available microcontrollers have sufficient memory to store reference template waveforms for comparison and necessary analysis. A computer capable of interfacing with the above electronics can be used. The analysis can be sped up by using a DSP. After analysis of the valve, the results can be displayed on a screen 50 and / or used to activate an alarm 52. The signal output can be used to provide feedback for operating the valve using a motorized valve drive device (not shown in FIGS. 1A and 1B) instead of the hand wheel 16. For example, if the device shown in FIGS. 1A and 1B detects improper seating, a control signal can be generated to readjust the valve, if possible, until proper seating is observed.

[0035] As discussed in more detail below, the pressure in the fluid 26 may be measured by a pressure sensor 54 .

[0036] As described, embodiments of the invention can be used to determine the tightness of adjacent flanges. If a flange or other lid is placed where some of the nuts and bolts are not tightened to their original torque, or if a clamp used on a sealing flange, such as a tri-clover clamp, which is common in the brewery, food and pharmaceutical industries, is not properly closed, the acoustic resonance spectrum of the system can be changed and detected. In the situation where a tri-clover clamp is used on a sealing flange closing an access port to a fermentation vessel, an acoustic transducer is placed in acoustic communication with the outer surface of the pipe attached to the flange on which the cover flange is placed, or the outer surface of the fermentation vessel to which said access pipe is attached, in a manner similar to that described above for valves. Here, the vibration system includes the adjacent flanges, the access pipe, the vessel, and the clamp or nut and bolt combination, whichever is used. It should be mentioned that an acoustic transducer can also be placed on the cover flange or on the flange attached to said pipe, but this may interfere with the bolts or clamps used.

[0037] In situations where it is desired to classify or group together objects that appear similar or identical in appearance, such as closed containers filled with different fluids or materials, but may have small external or internal differences, and thus are neither similar nor identical to one another in a group of containers, the acoustic transducer is again placed in acoustic communication with the exterior of the vessels or containers. By "similar or identical in appearance" it is meant that the containers are within the manufacturing specifications, or that they are slightly deviating from the manufacturing specifications or are counterfeit, but appear similar or identical in appearance to containers within the manufacturing specifications. It should be mentioned that the transducers can be placed virtually anywhere on the exterior of the object being investigated. Once a spectrum of the reference template is obtained for each container type, the material in the container being investigated can be identified. Thus, a non-invasive identification of the fluid inside the closed container can be achieved. Additionally, the tolerances and uniformity of manufactured or machined items can be determined, such as the deviation of a counterfeit vaccine vial from one produced by an approved manufacturer, or a vial or syringe filled with counterfeit material. Liquid containers can include vials and syringes.

[0038] It should be mentioned that the liquid loading effect appears as a broadening of the resonance peak as a result of the increase in viscosity and frequency shift due to density change. However, this shift is not uniform across the spectrum, as in the case of pressure changes, which will be explained in more detail below, but differs for the various modes. In such cases, the barcode morphology described above may be modified to include width information as full width at half maximum, thereby changing the thickness of these lines.

[0039] In situations where physical contact with the valve is difficult or impossible, non-contact measurements can be made. As an example, a laser Doppler vibrometer can be used to monitor the vibration of the object under investigation from a distance that can exceed 10 m, while excitation can be achieved using sound projection, where a collimated beam of sound is projected onto the valve, if desired. The remainder of the measurement system remains the same as that shown in FIG. 1A.

[0040] Resonance spectra can also be obtained using impulse excitation and the response can be digitized over a certain period of time. However, the electronics detect noise over the entire frequency sweep range and do not offer much immunity to ambient vibration. To obtain a proper resonance spectrum, it is necessary to acquire enough spectra and allow time for the lower frequency resonances to reach equilibrium and be properly recorded. Vibration spectra can be recorded with impulse excitation, but this technique is not practical in industrial environments where ambient vibrations can be large.

[0041] Regular cross-correlation, commonly used in signal processing, is the similarity of two time series (any data set or plot) as a function of the relative displacement of one series with respect to the other. That is, one can determine how well an unknown curve matches a known curve. Cross-correlation of two digitized waveforms involves cross-multiplying the individual waveform elements and summing these cross-products over a common time interval of the waveforms. The cross-correlation function involves progressively sliding one waveform past the other and, for each shift or lag, adding together these cross-products to obtain the cross-correlation as a function of the lag value. Given two digitized finite-length waveforms, x i and y iGiven (i = 1, 2, . . . , n), the cross-correlation function is given by: TIFF2025027116000002.tif18121 where τ is the delay and m is the maximum known delay value of the function. The function depends on the shape (amplitude) of the wave, i.e. the location of the peak is not as important as the amplitude to find the best match. If the curves are similar, the correlation coefficient is 1, whereas if they are completely dissimilar the correlation coefficient is 0.

[0042] Because the amplitudes corresponding to the resonant characteristics of the valve can change due to, for example, environmental factors, long-term use, and the position of the transducer on the valve, a regular cross-correlation will provide different answers based on how the resonant peak amplitudes change, thereby resulting in unreliable numbers. However, a signature correlation based on peak position will not change as the amplitude of any resonance changes, as described in more detail below, providing a very robust answer.

[0043] FIG. 2A is a graph of a sample resonance spectrum with the vertical solid line indicating the center of the resonance characteristic, while FIG. 2B is a graph of a resonance spectrum (vertical dashed line) randomly shifted from the resonance position of FIG. 2A, where FIG. 2A and FIG. 2B are, respectively, a reference resonance spectrum of a properly seated valve and a measured resonance spectrum of a poorly seated valve.

[0044] FIG. 3A is a graph showing the repeatability of the resonance spectrum, where ten sets of data acquired by removing and placing the transducer on the gate valve are overlaid to obtain a reference template, showing that the amplitude can change while the resonance peak position remains the same, while FIG. 3B shows an example resonance spectrum ((a) solid line) of a 2-inch gate valve fully closed or seated (small portion of a larger frequency range to highlight the difference) and an example resonance spectrum ((b) dashed line) when the valve is not fully seated causing a small leak. The change in the spectrum is large and easily observed. As can be observed from FIG. 3A when the valve is fully seated and closed, the spectrum is repeatable in terms of the position of the resonance peak from measurement to measurement. Deviation in the spectrum from this reference beyond a selected amount is considered to indicate that the valve is not fully closed and therefore the valve is leaking. It is difficult to detect such a leak using a pressure gauge or other means.

[0045] Measurements are made with high pressure air flowing through a valve and provide the same results for any gas. For liquids there may be a slight attenuation (broadening) of some spectral lines and a slight shift in frequency.

[0046] As mentioned, the amplitude of each resonance peak may differ slightly depending on the position of the receiving transducer, but the position of the resonance remains the same because the position of the receiving transducer may be at or near a node of a particular resonance mode such that the detected amplitude is small or the peak disappears completely. Therefore, an algorithm was developed by the inventors of the present application to quantify the deviation of the resonance by using many frequencies associated with the resonance peak for analysis. This has been found to improve the robustness of the detection process over algorithms that use only one or a few peaks. The algorithm determines the closeness of the measured spectrum to the reference spectrum while accounting for the fact that each frequency region behaves differently. That is, the shifts in frequency are not each a fixed amount, nor are the shifts in frequency a fixed amount relative to the entire spectrum, which is another reason why traditional cross-correlation methods are not suitable for this type of resonance peak analysis.

[0047] In its most basic form, as a first step, the measured acoustic resonance spectrum from FIG. 3B(a) for a properly seated valve was converted into a frequency-only spectrum as shown in FIG. 4. This barcode-type presentation does not carry amplitude information, rather, only the frequency is presented. Small peaks are counted as much as larger peaks, resulting in a more robust correlation than an amplitude-based analysis. It is possible to generate a spectrum of frequencies that also contains other information such as resonance Q (in terms of peak-width-at-half-maximum) and peak amplitude. Additional information can be coded as line widths and different colors based on amplitude. In order to generate a useful reference template, it is desirable to have a spectrum taken multiple times for that valve by opening and closing a properly seated valve each time before a measurement is made. For some valves, some of the resonant frequencies may show slight changes in peak frequency. Therefore, the average value of each resonant frequency is recorded, and the reference spectrum is replaced with these average positions for all the individual peaks. Furthermore, the change in frequency at each independent peak may be slightly different for multiple measurements. For best discrimination, the entire spectrum is divided into several small frequency bands and the peaks in each band are measured. An average can be taken when the number of peaks in that narrow frequency window (band) exceeds a selected threshold value. Thus, isolated random peaks are not considered. Furthermore, any peaks below a selected amplitude threshold are discarded. Small variations can occur due to large variations in temperature (and pressure) and manufacturing tolerances. The final template is therefore not corrupted by the accidental inclusion of bad data from a given measurement. Individual valves are calibrated to generate their own reference spectra rather than relying on factory calibrations. However, factory calibrations may be acceptable in some circumstances.

[0048] The peak correlation equation is: TIFF2025027116000003.tif18143 where the subscripts t and u refer to "template" and "unknown", respectively, and N t and N u are the number of frequency peaks in the template and unknown data sets, respectively; δf is the frequency window used for correlation, which depends on the tolerances involved; N ave is the average number of resonant peaks in the template and unknown data sets, and sgn is the mathematical sign function, which can take on values ​​of "+" and "-" depending on the sign of the argument inside the brackets.

[0049] The above mathematical cross-correlation process provides the following information: 1. The total number of peaks that are common to both the template and the item under investigation, such as a valve (within a given frequency spread-frequency window). 2. In situations where the item under investigation includes similar containers containing unknown materials, the cross-correlation process can determine which class the unknown item falls into by cross-correlating the unknown set of resonances with all known templates. The template that produces the largest correlation coefficient determines the class for the unknown item. For completely unknown containers (i.e., when there are no reference templates available for that class), the largest cross-correlation coefficient provides information about the best possible match.

[0050] The above correlation provides a theoretical maximum of 100 (100%) for just one number. This number can only be achieved if the transducers have not been moved since the reference spectrum was generated. If either or both transducers are moved, the frequency location will remain the same, but the amplitude may change, and occasionally one or more frequencies will disappear if the transducer happens to be at a nodal location for that particular resonance. Thus, the inventors consider a correlation number greater than 95 to be a perfect match, allowing for some variability. If the correlation falls below the threshold of 95, the valve can be considered to be leaking. In practice, this number is arbitrary, and there is only a statistical judgment from other experiments to use it. The threshold can be set to different values ​​for different applications where relatively large changes are expected. For example, if similar objects with internal differences are grouped together, and a transmit and receive transducer is placed on each object before measurements are made, the measured spectra are expected to have more variation than if the transducers were fixed on just one object, such as a valve. In such circumstances, the threshold may be less than 95.

[0051] Each industry has its own requirements for acceptable valve leakage. The embodiments of the present invention do not quantify valve leakage, but rather identify whether the valve is fully seated. The deviation from fully seated is what is required by the industry. A selected correlation number, for example, better than 95%, can be considered a fully seated condition, and anything greater can be considered an undesirable leakage. Different sizes and configurations of valves can have different standard deviations in repeatability, essentially represented by δf in the above equation. Once the template is generated, several measurements are taken and the standard deviation and average are determined. The average is used in the average template, and δf is the deviation. 1.5 times the standard deviation, etc., can be used.

[0052] For gate valves, the quality of seating when the valve is in the closed position is what matters. Therefore, it does not matter if the leak is slight or large. The smallest leaks need to be detected, and embodiments of the present invention provide a leak detector rather than a leak meter whose readings must be precisely calibrated.

[0053] In many situations, the pressure of the fluid inside a valve or other object may change, thereby affecting the resonant spectrum of the object as measured from the outside. The effect of pressure is similar to applying tension to a vibrating string, where the change in tension shifts the resonant frequency linearly. For a three-dimensional object, all resonant frequencies behave in the same way, shifting frequency simultaneously. This is shown in Figures 5 and 6 herein. Figure 5A is the reference spectrum without pressure (ambient conditions), and Figure 5B is the spectrum obtained when the pressure inside the object (a hollow cylindrical pressure vessel made of steel) is increased. The shift in the spectrum is apparently uniform, and the amount of shift is determined by the configuration of the object (size, shape, wall thickness, material, etc.). The pressure dependence can be predicted mathematically, but it is easier to calibrate for a particular object if necessary. Figure 5C shows the results obtained through pattern matching of the frequency-shifted spectrum with the reference spectrum, obtained by shifting the reference spectrum until the best match with the frequency-shifted spectrum occurs. It should be pointed out that the pattern matching is achieved using a barcode type spectrum where the data is represented by ones and zeros and no amplitude information is used. There are several mathematical approaches available to do this, but FIG. 5C was obtained by shifting the frequency in small steps until a maximum signal was obtained and multiplying the two spectra. The resulting peak position is therefore a measure of the shift in the spectrum. This is the shift of all the resonant peaks in the same direction due to pressure. The pressure can be positive or negative (vacuum) compared to the reference pressure, and in the context of determining the effect of negative pressure, the shift in frequency is in the opposite direction to the positive pressure case. Starting from an ambient pressure of 760 Torr, pressures of approximately 4 Torr were measured.

[0054] FIG. 6 shows experimental data for the large steel cylinder used in FIG. 5, showing the linear shift in frequency as a pressure change of several psi is obtained through the process described in FIG. 5C. This allows a non-invasive approach to pressure measurement in closed vessels, or other vessels or objects. If a calibration has been performed previously, and the same type of object, the calibration from a single object can be used if small errors are acceptable.

[0055] When investigating a leaking valve, if the pressure is known to change significantly and it is expected that there will be a shift in the overall spectrum from the reference, then the shifted spectrum should be used to detect the leak or determine valve seating. By combining such approaches, the method becomes a versatile procedure.

[0056] The foregoing description of the invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or to limit the invention to the precise form disclosed; obviously, many modifications and variations are possible in light of the above teachings. The above embodiments have been chosen and described in order to best explain the principles of the invention and its practical application thereby enabling those skilled in the art to best utilize the invention in various embodiments and with various modifications as suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.

Claims

1. 1. An apparatus for determining whether a fluid is leaking through a valve seat when a valve is in a closed position, comprising: a valve comprising the valve seat, a disk or plug for forming a fluid seal with the valve seat, a stem for driving the disk or plug against the valve seat, and a valve body having an outer surface; an acoustic transmitting transducer disposed in vibrating contact with the exterior surface of the valve, the acoustic transmitting transducer for producing vibrations in the valve body when excited by a selected voltage signal; an acoustic receiver disposed in vibrational contact with the exterior surface of the valve for receiving vibrations induced in the valve body and converting the received vibrations into a voltage; a frequency sweep generator in electrical communication with the acoustic transmit transducer for generating a selected excitation voltage signal having a frequency within a selected frequency range; a narrow band pass tracking filter having a center frequency that tracks the frequency within the selected frequency range generated by the frequency sweep generator and having a selected frequency bandwidth, the narrow band pass tracking filter for receiving a voltage from the acoustic receiver and filtering the voltage; and a microcontroller for controlling the frequency sweep generator and the narrow band pass tracking filter, for storing the filtered voltage from the narrow band pass tracking filter, for generating at least two acoustic resonance spectra of the valve in a closed state, and for comparing the at least two generated acoustic resonance spectra to determine if there are differences therebetween.

2. The apparatus of claim 1 , further comprising an amplifier for receiving the voltage from the ultrasonic receiving transducer and amplifying the voltage.

3. The apparatus of claim 1 further comprising a pressure sensor for determining a pressure of a fluid in the region of the valve seat.

4. The apparatus of claim 1 , wherein the acoustic transmitting transducer and the acoustic receiving portion are not in physical contact with each other.

5. The apparatus of claim 1 , wherein the frequency sweep from the frequency sweep generator is in either direction or both directions.

6. The apparatus of claim 1 , wherein the acoustic transmitting transducer comprises a piezoelectric transducer and the acoustic receiving portion is selected from a piezoelectric transducer and a laser Doppler vibrometer.

7. 1. A method for determining whether a fluid is leaking through a valve seat when the valve is in a closed condition, comprising: generating vibrations having a selected frequency within a selected frequency range in the valve, the valve comprising a valve seat, a disk or plug for forming a fluid seal with the valve seat, a stem for driving the disk or plug against the valve seat, and a valve body having an outer surface, using an acoustic transmit transducer disposed in vibrating contact with the outer surface of the valve and driven by a frequency sweep generator; receiving resonant vibrations induced in the valve body using an acoustic receiver disposed in vibratory contact with the exterior surface of the valve and converting the received vibrations into a voltage; filtering the voltage using a narrow bandpass tracking filter receiving the voltage and having a center frequency that tracks a selected excitation frequency within the selected frequency range; storing the filtered voltage, thereby generating an acoustic resonance spectrum of the valve; and comparing the generated acoustic resonance spectrum of the valve with at least one other acoustic resonance spectrum obtained with the valve in a closed state; determining whether there is a difference between the generated acoustic resonance spectrum and at least one of the other acoustic resonance spectra; A method comprising:

8. The method of claim 7 , wherein the voltage from the acoustic receiver is amplified.

9. The method of claim 7 , wherein the acoustic transmitting transducer and the acoustic receiving portion are not in physical contact with each other.

10. The method of claim 7 , wherein the acoustic transmit transducer is swept in frequency in either or both directions by the frequency sweep generator.

11. The method of claim 7 , wherein the acoustic transmitting transducer comprises a piezoelectric transducer and the acoustic receiving portion is selected from a piezoelectric transducer and a laser Doppler vibrometer.

12. 8. The method of claim 7, wherein the step of comparing the generated acoustic resonance spectrum of the valve with another acoustic resonance spectrum obtained with the valve in a closed state comprises peak position based signature correlation.

13. The method of claim 12 , wherein the peak location based signature correlation is performed using the following formula: where the subscripts t and u refer to “template” and “unknown”, respectively, and N t and N u are the number of frequency peaks in the template and unknown data sets, respectively; δf is the frequency window used for correlation, which depends on the tolerances involved; N ave is the average number of resonant peaks in the template and unknown data sets, and sgn is the mathematical sign function.

14. The method of claim 7 further comprising determining a pressure of a fluid in the region of the valve seat.

15. 15. The method of claim 14, further comprising the step of correcting the generated acoustic resonance spectrum of the valve and at least one other acoustic resonance spectrum obtained with the valve closed for a pressure of a fluid within the valve.

16. 1. A method for determining whether a container that is similar or identical in appearance to another container is similar or identical to the other container and contains a similar fluid as the other container, comprising: generating vibrations in the vessel having a selected frequency within a selected frequency range from an acoustic transmit transducer disposed in vibrational communication with an exterior surface of the vessel and driven by a frequency sweep generator; receiving resonant vibrations induced in the vessel using an acoustic receiver disposed in vibration communication with the exterior surface of the vessel and converting the received vibrations into a voltage; filtering the voltage using a narrow bandpass tracking filter receiving the voltage and having a center frequency that tracks a selected excitation frequency within the selected frequency range; storing the filtered voltage, thereby generating an acoustic resonance spectrum of the vessel; and comparing the generated acoustic resonance spectrum of the container with at least one other acoustic resonance spectrum obtained for the other container; determining whether there is a difference between the generated acoustic resonance spectrum and at least one of the other acoustic resonance spectra; A method comprising:

17. The method of claim 16 , wherein the voltage from the acoustic receiving transducer is amplified.

18. The method of claim 16 , wherein the acoustic transmitting transducer and the acoustic receiving portion are not in physical contact with each other.

19. The method of claim 16 , wherein the acoustic transmit transducer is swept in frequency in either or both directions by the frequency sweep generator.

20. The method of claim 16 , wherein the acoustic receiver is selected from an acoustic piezoelectric transducer and a laser Doppler vibrometer.

21. 17. The method of claim 16, wherein the step of comparing the generated acoustic resonance spectrum of the container with at least one other acoustic resonance spectrum obtained for the other container comprises peak position based signature correlation.

22. 17. The method of claim 16, wherein the container is selected from a vaccine vial and a syringe.

23. 1. A method for determining the tightness of a sealing flange for accessing a fluid in a vessel, the method comprising: a cover flange; and a flange attached to a pipe secured by bolts and nuts or a clamp, the method comprising the steps of: generating vibrations having a selected frequency within a selected frequency range in the sealing flange, the nut and bolt or the clamp, the pipe, and the vessel using acoustic transmitting transducers disposed in vibrational communication with an outer surface of the pipe or the vessel and driven by an acoustic frequency sweep generator; receiving induced and coupled resonant vibrations in the sealing flange, the nuts and bolts or the clamp, the pipe, and the vessel using an acoustic receiver arranged in vibrating contact with the exterior surface of the pipe or the vessel and converting the received vibrations into voltage; receiving the voltage and filtering the voltage with a narrow bandpass tracking filter having a center frequency that tracks a selected excitation frequency within the selected frequency range; storing the filtered voltage, thereby generating an acoustic resonance spectrum of the combination of the sealing flange, the nut and bolt or the clamp, the pipe, and the vessel; comparing the generated acoustic resonance spectrum including the frequency range of the combination of the sealing flange, the nut and bolt or the clamp, the pipe, and the container with at least one other acoustic resonance spectrum obtained for the combination of the sealing flange, the nut and bolt or the clamp, the pipe, and the container; determining whether there is a difference between the generated acoustic resonance spectrum and at least one of the other acoustic resonance spectra; A method comprising:

24. 24. The method of claim 23, wherein the voltage from the acoustic receiver is amplified.

25. 24. The method of claim 23, wherein the acoustic transmitting transducer and the acoustic receiving portion are not in physical contact with each other.

26. 24. The method of claim 23, wherein the acoustic transmit transducer is swept in frequency in either or both directions by the frequency sweep generator.

27. 24. The method of claim 23, wherein the acoustic transmitting transducer comprises a piezoelectric transducer and the acoustic receiving portion is selected from a piezoelectric transducer and a laser Doppler vibrometer.

28. 24. The method of claim 23, wherein the step of comparing the generated acoustic resonance spectrum of the combination of the sealing flange, the nut and bolt or the clamp, the pipe, and the container with other acoustic resonance spectra obtained for the combination of the sealing flange, the nut and bolt or the clamp, the pipe, and the container comprises a signature correlation based on peak position.

29. 30. The method of claim 28, wherein the peak location based signature correlation is performed using the following formula: where the subscripts t and u refer to “template” and “unknown”, respectively, and N t and N u are the number of frequency peaks in the template and unknown data sets, respectively; δf is the frequency window used for correlation, which depends on the tolerances involved; N ave is the average number of resonant peaks in the template and unknown data sets, and sgn is the mathematical sign function.

30. 24. The method of claim 23, further comprising determining a pressure of fluid in the pipe or vessel.

31. 31. The method of claim 30, further comprising the step of correcting the generated acoustic resonance spectrum for the combination of the sealing flange, the nut and bolt or the clamp, the pipe, and the vessel, and at least one other acoustic resonance spectrum obtained for the combination of the sealing flange, the nut and bolt or the clamp, the pipe, and the vessel, for pressure of fluid in the pipe and the vessel.

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