JP2009103459A - Ultrasonic plate thickness measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic plate thickness measuring device, capable of readily measuring and with high accuracy container plate thickness, using a simple constitution that uses ultrasonic waves. <P>SOLUTION: In this ultrasonic plate thickness measuring device 1, ultrasonic waves are transmitted from an ultrasonic transmission part 2 to a system to be measured, while the frequency is changed into a plurality of set values, and the attenuation level of a reverberation vibration waveform by an ultrasonic reception part 2 is measured at each frequency. Then, a frequency in which the attenuation level is minimized in the measurement range is specified as a plate thickness reflection frequency, based on the assembly of the attenuation level measurement results of the reverberation vibration waveform at each frequency; and the plate thickness, corresponding to the specified plate thickness reflection frequency, is calculated as a wall part plate thickness of the container 190 at a measurement executing position, by referring to the plate thickness/frequency relation stored, beforehand. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an ultrasonic plate thickness measuring apparatus.

JP 2004-333314 A

  Ultrasonic liquid in which an ultrasonic transmitter and receiver are arranged on the wall of a container such as an LP gas cylinder, and the presence or absence of the liquid level is determined based on the signal level of echo reflected from the liquid level inside the container or the opposite wall. An area meter is known (Patent Document 1).

  However, in the conventional ultrasonic liquid level gauge, only information related to the liquid level position can be obtained from the echo information, and there is a problem that information related to the container structure, particularly the container plate thickness, cannot be measured.

  The subject of this invention is providing the ultrasonic plate thickness measuring apparatus which can measure a container plate | board thickness easily and with high precision by simple structure using an ultrasonic wave.

Means for Solving the Problems and Effects of the Invention

In order to solve the above problems, the ultrasonic plate thickness measuring apparatus of the present invention is
A container containing a liquid is used as a system to be measured and is attached to a measurement execution position determined on the outer surface of the wall of the container, and after inputting an ultrasonic beam for measurement to the system to be measured for a predetermined time, An ultrasonic transmitter for blocking the input of the ultrasonic beam for measurement;
Reverberation detection means for detecting a reverberation vibration waveform used after being blocked from the input of the measurement ultrasonic beam;
A frequency setting section for setting the ultrasonic frequency to be changeable;
An attenuation level measuring means for transmitting an ultrasonic beam for measurement to the system under measurement by the ultrasonic transmission unit while changing the frequency to a plurality of set values, and measuring the attenuation level of the reverberation vibration waveform by the ultrasonic reception unit at each frequency; ,
Based on a set of attenuation level measurement results of the reverberation vibration waveform at each frequency, a plate thickness reflecting frequency specifying means for specifying a frequency at which the attenuation level is minimized within the measurement range as a plate thickness reflecting frequency;
Plate thickness / frequency relationship storage means for storing the relationship between the plate thickness reflection frequency and the plate thickness of the container;
Referring to the stored plate thickness / frequency relationship, wall thickness calculation means for calculating the plate thickness corresponding to the specified plate thickness reflection frequency as the wall thickness of the container at the measurement execution position;
And a wall thickness output means for outputting the calculation result of the wall thickness.

  According to the configuration of the ultrasonic plate thickness measuring apparatus of the present invention, the ultrasonic wave is transmitted to the measurement target system by the ultrasonic wave transmission unit while changing the frequency to a plurality of set values, and the reverberation by the ultrasonic wave reception unit at each frequency. While measuring the attenuation level of the vibration waveform, based on the set of attenuation level measurement results of the reverberation vibration waveform at each frequency, the frequency at which the attenuation level is minimized within the measurement range is specified as the plate thickness reflection frequency, With reference to the plate thickness / frequency relationship stored in advance, the plate thickness corresponding to the specified plate thickness reflection frequency is calculated as the wall thickness of the container at the measurement execution position. That is, with a simple configuration using ultrasonic waves, the container plate thickness can be easily and highly accurately measured (non-destructively).

  The reverberation detection means detects the reverberation vibration waveform at a position where it is known in advance that there will be no liquid on the container, so that the attenuation reverberation vibration level change near the plate thickness natural frequency is steep. Thus, the measurement accuracy can be increased.

  Moreover, the ultrasonic plate thickness measuring apparatus of the present invention can be provided with an envelope detection means for detecting an envelope of a reverberation vibration waveform. In this case, the attenuation level measuring means measures the attenuation level using the envelope detection waveform of the reverberation vibration waveform. By performing the amplitude identification using the envelope detection waveform of the reverberation vibration, for example, accurate amplitude evaluation can be performed even if the sampling point of the amplitude is deviated from the peak point of the vibration waveform.

  The attenuation level measuring means sweeps the frequency within a predetermined frequency band, and sets the frequency at which the attenuation level is minimized within the sweep band to the natural frequency of the longitudinal natural vibration in the thickness direction of the wall portion. And this can be specified as the plate thickness reflection frequency. When the frequency of the ultrasonic beam for measurement coincides with the natural frequency in the thickness direction of the wall (plate thickness natural frequency), the amplitude of the reverberation vibration also maximizes, and this increases the accuracy by measuring the plate thickness. be able to.

The plate thickness / frequency relationship storage means can store the natural frequencies at various plate thicknesses of the longitudinal natural wave as a plate thickness / natural frequency sequence for a plurality of adjacent orders of the longitudinal natural vibration. The wall portion of the container is, for example, a metal plate material in a gas cylinder or the like. When an ultrasonic wave is input in the thickness direction, the input ultrasonic wave propagates in the thickness direction of the wall portion in the form of longitudinal wave vibration. . At this time, when the frequency setting value of the input ultrasonic wave matches the natural frequency fm of the wall portion at the measurement temperature, the amplitude of the reverberation vibration shows a peak (maximum point) (that is, the attenuation level is minimal). It becomes an attenuation waveform with a long tail). The natural frequency fm is a frequency at which the ultrasonic wave is transmitted through the plate material most efficiently, where λ is the longitudinal wave wave that passes through the plate material, and t is the thickness of the plate.
t = m · λ / 2 (1)
Or
λ = 2t / m (1) ′
If the sound velocity of the longitudinal wave is C and the natural frequency is fm,
fm = C / λ (2)
So from (1) '(2)
fm = m · C / 2t (3)
Here, m is an integer indicating the order of the natural vibration. The natural frequencies correspond to the vibration orders m = 1 (fundamental vibration), 2 (secondary vibration),..., N (Nth vibration), respectively, f1 = 1 · C / 2t, f2 = 2 · C / 2t. ,..., FN = N · C / 2t and appear periodically. Therefore, the maximum point of the reception amplitude also appears periodically corresponding to these natural frequencies. If the plate thickness t changes, the natural frequency of each order also changes in a hyperbolic shape according to the equation (3). If this is drawn on the t (plate thickness) -f (frequency) plane for each value of order m, the result is as shown in FIG. The plate thickness / natural frequency sequence is a curve obtained by substituting the sound velocity C and the order m in accordance with the wall member quality into the equation (3). If the frequency of the ultrasonic beam for measurement is swept at each plate thickness, the frequency dependence of the reverberation vibration amplitude will draw a local maximum periodically at the frequency that intersects the curve position indicating the natural frequency of each order. become.

  In this case, the attenuation level measuring means can set the sweep bandwidth of the frequency of the ultrasonic beam for measurement so that a plurality of extreme points at which the attenuation level is minimized appear in the band (see FIG. 6). The wall thickness calculation means specifies the frequency corresponding to a plurality of extreme points in the band as the extreme frequency group, and the thickness value that the extreme frequency group conforms to the thickness / natural frequency sequence collectively. The wall thickness value can be calculated by searching for. That is, it is determined whether or not the maximum point (damping level minimum point) of the reverberation vibration amplitude that appears due to the natural vibration of the plate conforms to the plate thickness / natural frequency sequence (formula (3)) over a plurality of orders. Thus, spurious components that do not originate from the natural vibration of the plate can be excluded from the plate thickness measurement, and the accuracy of the plate thickness measurement can be further increased.

  However, since the sweep bandwidth that covers the maximum point (damping level minimum point) of the reverberation vibration amplitude over a plurality of orders is considerably wide as shown in FIG. 6, it may be configured as follows. That is, the attenuation level measuring means sweeps in such a manner that the band is a rough search band and the frequency is intermittently changed in the rough search band at the first frequency interval. Shall be measured. Further, the wall thickness calculation means specifies a plurality of poles based on the sweep result by the first frequency interval, and the thickness of the pole frequency group collectively matching the thickness / natural frequency sequence. The value shall be specified as the rough plate thickness value. The attenuation level measuring means selects any one of a plurality of poles as a landmark pole, sets a fine search band narrower than the rough search band in a form including the landmark pole, Is measured while the frequency is intermittently changed at a second frequency interval smaller than the first frequency interval, and the attenuation level at each frequency is measured. The wall thickness calculation means specifies a precise pole corresponding to the mark pole based on the sweep result of the second frequency interval, and gives a precision pole on the plate thickness / natural frequency sequence corresponding to the mark pole A plate thickness value corresponding to the frequency is calculated as a precise plate thickness value. In this way, by adopting the first frequency interval in the entire sweep band, the number of reverberation vibration measurement points can be greatly reduced, and in the vicinity of the pole point for reading the plate thickness, the first frequency interval is smaller than the first frequency interval. By adopting the second frequency interval, it is possible to greatly improve the accuracy of pole identification.

  In this case, the attenuation level measuring means can divide the frequency band into a plurality of sub-bands and perform a sweep for each of the sub-bands. The reverberation detecting means includes a pass frequency band corresponding to a band pass filter having a pass frequency band corresponding to the sub band for each sub band and a band pass filter for passing a reverberation vibration waveform when switching the sub band to be swept. And a filter switching means for sequentially switching to the one, and detecting a reverberation vibration waveform by the measurement ultrasonic beam after passing through a band-pass filter of a pass frequency band to which the frequency of the measurement ultrasonic beam belongs, can do. Thereby, the influence of spurious and noise derived from multiple reflection interference, overtone vibration, unwanted resonance coupling between members, and the like can be removed by the bandpass filter, and the S / N ratio of the reverberation signal to be detected can be increased.

  The attenuation level measurement means obtains the amplitude of the reverberation vibration waveform when a predetermined time has elapsed after blocking the input of the measurement ultrasonic beam as information reflecting the attenuation level, and gives the maximum value of the amplitude. The frequency can be found as the natural frequency of the longitudinal natural vibration in the thickness direction of the wall, and can be configured to be specified as the thickness reflection frequency. According to this method, the elapsed time after the excitation is cut off is fixed, and the amplitude of the reverberation vibration waveform is uniformly measured after the time has elapsed, so that the change behavior of the attenuation level performed while sweeping the frequency can be easily grasped. As a result, the operation algorithm for finding the thickness reflection frequency can be simplified. Similarly, the attenuation level measuring means integrates the envelope detection waveform in a predetermined integration period, acquires the integrated value as information reflecting the attenuation level, and gives the maximum value of the integrated value. Can be found as the natural frequency of the longitudinal natural vibration in the plate thickness direction of the wall, and this can be specified as the plate thickness reflection frequency. By acquiring the information reflecting the attenuation level as an integral value, it becomes less susceptible to noise and the like than when using the instantaneous value of the waveform amplitude, and the measurement accuracy can be improved.

  On the other hand, the attenuation level measuring means has attenuation time measuring means for measuring the attenuation time until the attenuation level of the damped reverberation vibration reaches a predetermined reference level, and the attenuation time is information that reflects the attenuation level. In addition, the frequency that gives the maximum value of the decay time can be found as the natural frequency of the longitudinal natural vibration in the thickness direction of the wall, and can be specified as the thickness reflection frequency. In this method, it is necessary to monitor temporal changes in the damped reverberation vibration, and the number of sampling times increases. However, sudden change in parameter values due to noise or the like can be easily identified as an error, so that the determination accuracy can be improved. There are advantages.

  An embodiment of a liquid plate thickness measuring apparatus according to the present invention will be described with reference to the drawings. FIG. 1 shows an example of a container to be measured, and is configured as an LPG or LNG metal tank 190. The metal tank 190 is made of steel, and has a structure in which a bottom surface portion 202 and a top surface portion 203 are welded and joined to the top and bottom of a cylindrical container body 200 (container body). The upper surface portion 203 is formed as an integral lid member in which the upper end portion of the side wall portion is connected to the periphery of the uppermost surface portion of the container. Moreover, the container main-body part 200 makes the remainder part of a side wall part. A gas extraction part 203V in which a pressure control valve is incorporated is formed in the upper center of the upper surface part 203. The liquid L made of LPG or LNG is accommodated in the metal tank 190 to constitute a system to be measured.

  The liquid plate thickness measuring apparatus 1 is configured to measure the plate thickness of the wall portion in the metal tank 190 from outside the tank at a desired measurement execution position. Specifically, the liquid plate thickness measuring apparatus 1 can be pressed against an outer surface of the container main body 200 of the container 190 at an arbitrary position in the liquid depth direction (that is, attached to an arbitrary measurement position desired by the user). It has an ultrasonic transducer 2 (possible). The ultrasonic transducer 2 has a function of an ultrasonic transmission unit that transmits ultrasonic waves to the system to be measured and an ultrasonic reception unit that receives reflected waves based on the input ultrasonic waves (that is, the ultrasonic transducer 2). , Function as an ultrasonic transmission / reception unit).

  FIG. 2 is a block diagram conceptually showing an electric circuit configuration of the liquid plate thickness measuring apparatus 1. The liquid plate thickness measuring apparatus 1 has a housing 3 made of a resin or the like that can be held by a user's hand, and an ultrasonic transducer 2 is fitted on the front end surface thereof. The front end surface of the ultrasonic transducer 2 serving as the ultrasonic wave emitting surface is located in an opening formed at the front end of the housing 3 and the acoustic impedance matching layer 2P is attached so as to be in close contact with the surface. The acoustic impedance matching layer 2P has an acoustic impedance intermediate between the ultrasonic transducer 2 (piezoelectric ceramic) and the container body 200 (steel) (preferably the geometric average value of both), and is pressed against the container body 200. It is made of a flexible elastic material (for example, a silicone resin) that can be deformed following the contact with the outer surface of the material.

  The ultrasonic transducer 2 transmits an ultrasonic beam by applying a driving voltage from the driving circuit 101, and outputs an electric signal (reception signal) to the signal processing circuit 103 by receiving a reflected wave. Specifically, the piezoelectric ceramic diaphragm 21 polarized in the plate thickness direction, and the electrode pair 2e formed to face each other with the piezoelectric ceramic diaphragm 21 sandwiched between the main surfaces of the piezoelectric ceramic diaphragm 21. , 2e. The electrode pairs 2e and 2e serve as drive electrodes to which a drive voltage for ultrasonically vibrating the piezoelectric ceramic diaphragm 21 is applied when transmitting an ultrasonic beam, and vibrations of the piezoelectric ceramic diaphragm 21 are received when a reflected wave is received. It becomes an output electrode which outputs the electrical signal accompanying. The connection between the electrode pair 2e, 2e, the drive circuit 101, and the signal processing circuit 103 is switched by a changeover switch 101s.

  The drive circuit 101 has a D / A converter 101c that converts a digital frequency instruction value from the microcomputer 100 into an analog frequency instruction voltage, and a VCO (Voltage Controlled) that receives the analog frequency instruction voltage and oscillates at a corresponding frequency. Oscillator) 101b, and a main circuit (amplifier) 101a that amplifies the output of the VCO 101b and outputs the amplified signal to the piezoelectric ceramic diaphragm 21 as a drive signal. The signal processing circuit 103 also includes an amplifier 103 a that amplifies the vibration waveform of the piezoelectric ceramic diaphragm 21, an envelope detection unit 103 b that detects the amplified damped vibration waveform, and digitally converts the detection output to the microcomputer 100. An A / D converter 103c for input.

  Returning to FIG. 2, the drive circuit 101, the changeover switch 101 s, the frequency setting unit 102, and the signal processing circuit 103 are connected to the microcomputer 100 that controls these operation sequences. The microcomputer 100 is also connected with an input unit 105 and a display unit 104. The input unit 105 includes a push button switch, a keyboard, and the like, and is used for a start trigger operation for thickness measurement. The display unit 104 outputs a plate thickness measurement result by numbers and the like, and is configured by, for example, a 7-segment LED or a liquid crystal display.

  A power supply voltage is supplied from the replaceable dry battery B through the stabilized power supply circuit 102 to each circuit block (the microcomputer 100, the drive circuit 101, and the signal processing circuit 103) of the liquid plate thickness measuring apparatus 1.

Hereinafter, the operation of the liquid detection device 1 will be described with reference to the flowchart of FIG. As shown in FIG. 1, first, the surface of the acoustic impedance matching layer 2P on the ultrasonic transducer 2 (hereinafter referred to as a detection surface) is placed at a desired measurement position with respect to the outer surface of the container body 200 of the container 190. 2 and a measurement start input is performed from the input unit 105 in FIG. 2 (for example, a detection button 105a included in the input unit 105 is pressed: FIG. 3, S0). Then, the microcomputer 100 starts the measurement driving program and starts the measurement process. First, in S1, as an initial setting of the ultrasonic transducer 2, a burst pulse drive application time, a frequency sweep bandwidth, and the like are set. Then, set the drive frequency in the band starting value _{f min} of sweep, to start operating VCO101b in Figure 2 at the frequency. In S2, the changeover switch 101S switches to a drive connection state in which the ultrasonic transducer 2 is connected to the drive circuit 104, and the drive circuit 104 generates a burst pulse of the drive AC voltage one or more times at the set frequency. Apply to the ultrasonic transducer 2. Thereby, the ultrasonic beam SW is output from the ultrasonic transducer 2 toward the container main body 200 at the measurement position.

  The burst pulse application of the driving AC voltage is forcibly cut off when the application pulse period tn set to, for example, about 10 to 50 μs is completed. 2 is switched to a signal detection connection state in which the ultrasonic transducer 2 is connected to the signal processing circuit 103, and the ultrasonic transducer 2 detects the reverberation vibration from the container 190 after the excitation is cut off. . Actually, the period required for the switching operation of the changeover switch 101S is taken into consideration, and the detection of the reverberation vibration is started after a certain delay time Δt has elapsed after the excitation is cut off.

  FIG. 4A and FIG. 4B show an example of the detection waveform of the reverberation vibration. In the non-existing portion (liquid-free portion), the inside of the container 190 container main body 200 becomes a void, and the inner surface of the wall portion is the boundary. The acoustic impedance difference becomes very large. If the excitation frequency of the ultrasonic beam for measurement input to the container main body 200 matches the natural frequency determined by the material and thickness of the wall of the container main body 200, almost all of the ultrasonic beam on the inner surface of the wall is obtained. Reflection returns to the inside of the metal container main body 200 and continues to vibrate, so that it is difficult for attenuation to occur. As a result, as shown in FIG. 4A, the reverberation tail is very long. However, since the liquid L is present inside the container main body 200 in the liquid existing portion (the liquid present portion), the above-described acoustic impedance difference is reduced, and the inside of the liquid having a large internal friction is transmitted through the container main body 200. Since the ratio of sound waves leaking into the channel increases, vibration damping becomes significant as shown in FIG. 4B. Therefore, when the frequency of the ultrasonic beam for measurement is swept in a certain band, the frequency change of the amplitude of the damped vibration appears more prominently in the non-existing part of liquid (no liquid part), and the plate thickness natural vibration The change of the damped reverberation vibration level (the amplitude of the damped vibration or the degree of tailing) in the vicinity of the number becomes steep, and the measurement accuracy can be improved. Therefore, when measuring the plate thickness, it is desirable to select the liquid-free portion and determine the measurement execution position in order to improve the measurement accuracy. As the liquid-free portion, for example, the upper portion of the container main body portion 200 may be adopted, or an arbitrary position of the container main body portion 200 can be adopted as the liquid-free portion by adopting a container that is known to be empty from the beginning.

  Specifically, as shown in FIG. 4A, for each frequency in the sweep, the amplitude of the damped reverberation vibration when the predetermined time ts has elapsed after the input of the measurement ultrasonic beam SW is cut off is used as attenuation level information. To get to. In the signal processing circuit of FIG. 2, as shown in FIG. 5, the damped oscillation waveform is amplified by the amplifier 103a (step 1), half-wave rectified by the detection circuit 103b (step 2), and the half-wave rectified waveform is enveloped. Line detection is performed (step 3). And the level after the time ts progress of the waveform by which the envelope detection was carried out is acquired as an amplitude value.

  The above measurement is repeatedly performed while sweeping the frequency of the ultrasonic beam for measurement within a predetermined frequency band, and the frequency at which the amplitude of the damped oscillation waveform is maximized within the sweep band (that is, the attenuation level). Is found as the natural frequency of the natural vibration of the longitudinal wave in the plate thickness direction of the wall, and this is specified as the plate thickness reflection frequency. Specifically, for a plurality of adjacent orders of longitudinal natural vibration, the natural frequency at various plate thicknesses of longitudinal natural vibration is a plate thickness / natural frequency sequence, and the memory (ROM) in the microcomputer 100 in FIG. Etc.).

Here, the wall of the container is an iron plate (metal plate material), and as described above, its natural frequency fm is λ for the wave of the longitudinal wave transmitted through the iron plate, t for the thickness of the plate, and C for the sound velocity of the longitudinal wave. , Where the natural frequency is fm (m is the order)
fm = m · C / 2t (3)
It is. If the equation (3) is drawn on the t (plate thickness) -f (frequency) plane for each value of m, the plate thickness / natural frequency sequence is represented by the equation (3) as the wall member quality as shown in FIG. The curve is obtained by substituting the corresponding sound speed C and order m. The plate thickness / natural frequency sequence data may be stored as discrete data of (t, fm) that satisfies equation (3), or equation (3) itself is stored as a function. Also good.

  At this stage, the plate thickness t is not yet specified, but the plate thickness t itself is not changed, so that the frequency of the ultrasonic beam for measurement is set (at a position corresponding to an unknown plate thickness t on FIG. 6). When swept, the frequency dependence of the reverberation vibration amplitude periodically draws a local maximum at a frequency that intersects with the curve position indicating the natural frequency of each order. Then, the frequency sweep bandwidth of the measurement ultrasonic beam is set such that a plurality (specifically, 2 to 4) of extreme points at which the attenuation level is minimized appear in the band.

  The frequency band is set to be divided into a plurality of (here, three) sub-bands as shown in FIG. 6, and a sweep is performed for each sub-band (FIG. 3: S3). For each subband, bandpass filters F-1 (passband: 1100 to 1350 kHz), F-2 (passband: 900 to 1100 kHz), F-3 having a pass frequency band corresponding to the subband. (Pass band: 650 to 900 kHz) is provided. Then, the bandpass filter that passes the reverberation vibration waveform is sequentially switched to the corresponding pass frequency band in accordance with the switching of the subband for performing the sweep. The reverberation vibration waveform by the measurement ultrasonic beam is passed through a band-pass filter in the pass frequency band to which the frequency of the measurement ultrasonic beam belongs, and is then used for specifying the amplitude (attenuation level) (FIG. 3: S4). , S5, S6). In this embodiment, each band-pass filter is configured as a software filtering program executed by the microcomputer 100 with respect to the digital envelope detection waveform captured on the microcomputer 100, but the analog envelope detection waveform is a signal. It is also possible to configure as a passive filter circuit or an active filter circuit that allows direct passage.

  Within the above band, as shown in FIG. 7, the frequencies f1, f2, and f3 at which the amplitude is maximum are specified as the pole frequency group on the amplitude data of the damped vibration obtained by frequency sweeping. Then, on the plate thickness / natural frequency sequence of FIG. 6 stored in the memory, the plate thickness values to which these pole frequency groups f1, f2, and f3 are matched together are searched, and this is used as the wall plate thickness value. calculate. In FIG. 6, the entire plate thickness range that can be measured (here, 2.4 to 15.9 mm) is divided into a plurality of sections (here, five sections A, B, C, D, and E). When matching the thickness / natural frequency train of the pole frequency groups f1, f2, and f3, the number of natural frequencies giving the poles and the appearance interval differ from section to section, which section is the pole frequency group f1. , F2, and f3 are determined in advance. For example, in FIG. 6, since each plate thickness / natural frequency sequence is a hyperbolic function as described above, the rate of change becomes steeper toward the lower plate thickness side, and the appearance interval in the frequency direction of the adjacent plate thickness / natural frequency sequence is Become wider. Therefore, the appearance interval becomes maximum in the section A on the lowest thickness side, and decreases in the order of sections B, C, D, and E.

  Therefore, in which section of A, B, C, D, and E the frequency interval of the specified pole frequency groups f1, f2, and f3 is closest to the appearance interval in the frequency direction of the plate thickness / natural frequency sequence It can be said that it is effective in determining the section in advance. Even if the frequency intervals of the pole frequency groups f1, f2, and f3 do not coincide with the appearance intervals of any section, or even if only the intervals match in a certain section, the appearance frequency position of the plate thickness / natural frequency sequence If the validity of the theoretical collation cannot be obtained, such as in the case of non-coincidence, the amplitude / frequency profile of the damped vibration obtained by frequency sweeping is likely to contain unnecessary spurious as shown in FIG. In S8 of FIG. 3, the specified pole frequency groups f1, f2, and f3 are determined to be inappropriate, and the process returns to S2 and the measurement is performed again.

  Note that the sweep bandwidth that covers the maximum point (damping level minimum point) of the reverberation vibration amplitude over a plurality of orders is a fairly wide band of about 600 kHz in FIG. Therefore, this band is set as a rough search band, and the frequency is intermittently changed within the rough search band at a first frequency interval (for example, 2 to 10 kHz). The attenuation level is measured (FIG. 3: S2 to S8). Then, a plurality of pole points f1, f2, and f3 are specified as described above based on the sweep result by the first frequency interval, and the plate thickness in which these pole frequency groups are collectively adapted to the plate thickness / natural frequency sequence. The value is specified as the rough plate thickness value t ′. Next, one of a plurality of poles is selected as a landmark pole. Then, a fine search band narrower than the rough search band is set so as to include the landmark pole, and the fine search band is set to a second frequency interval (for example, 50 to 1000 Hz) smaller than the first frequency interval. ) Measure the attenuation level at each frequency while sweeping in the form of intermittent changes.

  For example, when the section D is specified, as an example, among the three pole points f1, f2, and f3, the center one f2 can be used as the mark pole point. The rough plate thickness value t ′ at this time is about 11.5 mm, and the fine search band including the mark pole point f2 can be set as 1010 to 1050 kHz. Also, the fine search band may be set at equal intervals (for example, ± 20 kHz) around the frequency f2 specified in the rough search band.

  Then, based on the sweep result by the second frequency interval, it is specified as a precision pole corresponding to the mark pole, and the board thickness corresponding to the frequency that gives the precision pole on the plate thickness / natural frequency sequence corresponding to the mark pole The value is calculated as a precision plate thickness value t. By adopting the first frequency interval for the entire sweep band, the number of reverberation vibration measurements can be greatly reduced, and a second frequency interval smaller than the first frequency interval is near the pole for reading the plate thickness. By adopting it, it is possible to greatly improve the pinpoint identification accuracy.

  As shown in Step 4 of FIG. 5, the envelope detection waveform is integrated using the time ts as the integration period, and the integration value is used as information reflecting the attenuation level, and the maximum of the integration value is used. The frequency that gives the value may be found as the natural frequency of the longitudinal natural vibration in the thickness direction of the wall and specified as the thickness reflection frequency. Further, as shown in FIG. 9, the decay time td until the decay level of the damped reverberation vibration reaches a predetermined reference level Vth is measured, and the decay time td is acquired as information reflecting the decay level. At the same time, the frequency that gives the maximum value of the decay time may be found as the natural frequency of the longitudinal natural vibration in the plate thickness direction of the wall, and this may be specified as the plate thickness reflection frequency.

The schematic diagram which shows the usage example of the ultrasonic plate thickness measuring apparatus of this invention. The block diagram which shows the electrical structural example of the ultrasonic plate thickness measuring apparatus of FIG. The flowchart which shows the flow of the measurement program which the microcomputer of FIG. 2 performs. The figure which shows an example of the damped vibration waveform in the non-existing part of a liquid. The figure which shows an example of the damped vibration waveform in the presence part of a liquid. The figure explaining the processing concept of a damped vibration waveform. The figure which shows the specific example of plate | board thickness / natural frequency sequence. The figure which shows an example of the amplitude data of the damped vibration obtained by frequency sweeping. The figure explaining the influence of the unnecessary spurious in the amplitude data of a damped vibration. The figure explaining another example of the processing concept of a damped vibration waveform.

Explanation of symbols

1 Liquid thickness measuring device 2 Ultrasonic transducer (ultrasonic transmitter, ultrasonic receiver)
SW Ultrasonic beam L Liquid 2 Ultrasonic transducer (Ultrasonic transmitter, reverberation detection means)
SW Ultrasonic beam L Liquid 100 Microcomputer (Attenuation level measuring means, plate thickness reflection frequency specifying means, plate thickness / frequency relation storage means, wall thickness calculation means)
101b VCO (frequency setting unit)
102 frequency setting unit 103 signal processing circuit 103b envelope detection unit (envelope detection means)
104 Display (wall thickness output means)
190 containers

Claims (10)

A container containing a liquid is used as a system to be measured, which is attached to a measurement execution position determined on the outer surface of the wall of the container, and the measurement ultrasonic beam is input to the system to be measured for a predetermined time. Then, an ultrasonic transmission unit that blocks input of the ultrasonic beam for measurement,
Reverberation detection means for detecting a reverberation vibration waveform after being cut off from the input of the ultrasonic beam for measurement;
A frequency setting unit for setting the frequency of the ultrasonic wave to be changeable;
While changing the frequency to a plurality of set values, the ultrasonic transmission unit transmits the ultrasonic beam for measurement to the measurement target system, and measures the attenuation level of the reverberation vibration waveform by the ultrasonic reception unit at each frequency. An attenuation level measuring means,
Based on a set of attenuation level measurement results of the reverberation vibration waveform at each of the frequencies, a plate thickness reflection frequency specifying unit that specifies a frequency at which the attenuation level is minimized within the measurement range as a plate thickness reflection frequency;
Plate thickness / frequency relationship storage means for storing the relationship between the plate thickness reflection frequency and the plate thickness of the container;
Wall thickness calculation means for calculating the thickness corresponding to the specified thickness reflection frequency as the wall thickness of the container at the measurement execution position with reference to the stored thickness / frequency relationship; ,
Wall thickness output means for outputting the calculation result of the wall thickness;
An ultrasonic plate thickness measuring apparatus comprising:   2. The ultrasonic plate thickness measuring apparatus according to claim 1, wherein the reverberation detecting means detects the reverberation vibration waveform at a position where it is known in advance that liquid is present on the container. Envelope detection means for detecting the reverberation vibration waveform as an envelope,
The ultrasonic plate thickness measuring apparatus according to claim 1, wherein the attenuation level measuring unit measures the attenuation level using an envelope detection waveform of the reverberation vibration waveform.   The attenuation level measuring means sweeps the frequency within a predetermined frequency band, and sets the frequency at which the attenuation level is minimized within the sweep band to the characteristic of the longitudinal wave in the plate thickness direction of the wall portion. The ultrasonic plate thickness measuring apparatus according to any one of claims 1 to 3, wherein the ultrasonic plate thickness is identified as a natural frequency of vibration and specified as the plate thickness reflection frequency. The plate thickness / frequency relation storage means stores the natural frequency at various plate thicknesses of the longitudinal natural vibration as a plate thickness / natural frequency sequence for each of a plurality of adjacent orders of the longitudinal natural vibration. And
The attenuation level measurement means sets the sweep bandwidth of the frequency so that a plurality of extreme points at which the attenuation level is minimized appear in the band,
The wall thickness calculating means specifies frequencies corresponding to the plurality of extreme points in the band as extreme frequency groups, and the extreme frequency groups are collectively adapted to the thickness / natural frequency sequence. The ultrasonic plate thickness measuring device according to claim 4, wherein the plate thickness value is calculated by searching for the plate thickness value to be performed. The attenuation level measurement means uses the band as a rough search band and sweeps the frequency intermittently within the rough search band at a first frequency interval, Measure the attenuation level,
The wall thickness calculation means specifies a plurality of the poles based on a sweep result of the first frequency interval, and the pole frequency group is collectively matched to the thickness / natural frequency sequence. Specify the thickness value as the rough plate thickness value,
The attenuation level measuring means selects any one of the plurality of poles as a landmark pole, sets a fine search band narrower than the rough search band in a form including the landmark pole, and Measure the attenuation level at each frequency while sweeping the band intermittently in a second frequency interval smaller than the first frequency interval,
The wall thickness calculation means specifies a precise pole corresponding to the mark pole based on the sweep result by the second frequency interval, and the thickness / natural frequency sequence corresponding to the mark pole 6. The ultrasonic plate thickness measuring apparatus according to claim 5, wherein a plate thickness value corresponding to a frequency giving a precise pole is calculated as a precise plate thickness value. The attenuation level measuring means divides the frequency band into a plurality of subbands and performs the sweep for each of the subbands.
The reverberation detecting means includes: a bandpass filter having a pass frequency band corresponding to the subband for each subband; and a bandpass filter that passes the reverberation vibration waveform when the subband is switched. The ultrasonic plate thickness measuring apparatus according to any one of claims 4 to 6, further comprising filter switching means for sequentially switching to a corresponding pass frequency band.   The attenuation level measurement means acquires the amplitude of the reverberation vibration waveform when a predetermined time has elapsed after blocking the input of the measurement ultrasonic beam as information reflecting the attenuation level, and The super frequency according to any one of claims 4 to 7, wherein a frequency that gives a maximum value is found as a natural frequency of longitudinal natural vibration in the thickness direction of the wall portion, and is specified as the thickness reflection frequency. Sonic plate thickness measuring device.   The attenuation level measuring means includes attenuation time measuring means for measuring an attenuation time until the attenuation level of the damped reverberation vibration reaches a predetermined reference level, and the attenuation time reflects the attenuation level. 5. The frequency obtained as information and giving the maximum value of the decay time is found as the natural frequency of the longitudinal natural vibration in the thickness direction of the wall, and is specified as the thickness reflection frequency. 8. The ultrasonic plate thickness measuring apparatus according to any one of 7 above. While having the requirements of claim 3,
The attenuation level measuring means integrates the envelope detection waveform in a predetermined integration period, acquires the integration value as information reflecting the attenuation level, and provides a frequency that gives the maximum value of the integration value. The ultrasonic plate thickness measuring apparatus according to any one of claims 4 to 7, wherein the ultrasonic wave thickness is identified as a natural frequency of longitudinal natural vibration in the plate thickness direction of the wall portion and specified as the plate thickness reflecting frequency. .

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