JP2009002707A - Ultrasonic liquid sensing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic liquid sensing apparatus having a simple structure, and capable of determining the existing state of a liquid in a container from outside the container in a shorter period of time with excellent workability. <P>SOLUTION: The liquid sensing apparatus 1 has a frequency setting section 102 for changing the frequency of a measuring ultrasonic beam and performing its setting, outputs the measuring ultrasonic beam to measure reverberant vibration, while variously changing the frequency at a frequency setting position on the container known previously as a position of no liquid, to decide a measuring frequency to be used for reverberation detection of the measuring ultrasonic beam, prior to the detection relating to the determination of the existence of the liquid, and finds a frequency at which the lifetime of the reverberant vibration becomes the longest, to decide it as the measuring frequency. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an ultrasonic liquid detection device.

JP 2004-53504 A JP 2002-90210 A JP-A-7-181072

  Conventionally, an ultrasonic transmission unit and a reception unit are arranged so that the ultrasonic transmission surface or reception surface is exposed on the inner surface of the tank, and the time until the ultrasonic beam is reflected at the liquid surface position and returned is measured. There is known a liquid level gauge which can know the height of the liquid level (Patent Documents 1 and 2). However, this type of liquid level gauge must have an ultrasonic transmitter and a receiver exposed inside the container, which complicates the structure and is difficult to apply to containers that do not have a liquid level gauge. . On the other hand, as a method of detecting the liquid level from the outside of the target container in a non-contact manner, the ultrasonic wave transmitted through the container wall is transmitted to the opposite wall (the wall of the opposite steel plate material and the boundary with the medium). ), A reflected wave that passes through the container wall again and returns to the transducer is detected, and the presence or absence of liquid is determined (for example, Patent Document 3).

  However, the transmission-type liquid level detection method has a propagation delay time from when an ultrasonic wave is transmitted until the reflected wave returns, and the propagation distance of the ultrasonic pulse along the reflection path is long, resulting in a loss of signal. There are major drawbacks. After all, the loss of signal means that mechanical vibration noise and reverberation noise that propagates to the container immediately after driving, deterioration of the transducer characteristics due to temperature and aging (especially deterioration of damper characteristics), transducer and container This means that it is easily affected by the mechanical coupling state, etc., and it is inevitable that the sensitivity is easily lowered. In particular, there is a problem that the signal level of the sound wave transmitted through the container wall and the influence of noise due to the attachment state are particularly susceptible to the deterioration of the S / N when detecting the reception signal for determining the presence or absence of liquid.

  Eventually, in the above transmission type, complicated signal processing and control such as filtering are required to prevent a decrease in the S / N ratio, and it is difficult to avoid the complexity of the circuit and software and the increase in cost. Further, it takes a long time to determine the detection frequency and to set and adjust the circuit gain or the comparator level, and the speed of liquid level determination is likely to be impaired.

  An object of the present invention is to provide a liquid detection device that has a simple configuration and can determine the liquid presence state in a container from the outside of the container in a shorter time with good workability.

Means for Solving the Problems and Effects of the Invention

In order to solve the above problems, the ultrasonic liquid detection device of the present invention is:
A container containing liquid is used as a system to be measured, and is detachably attached to a measurement execution position defined on the outer surface of the wall of the container, and a measurement ultrasonic beam is input to the system to be measured for a predetermined time excitation input. After that, an ultrasonic output unit 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;
Liquid presence / absence determining means for determining the presence / absence of liquid at a measurement execution position in the container based on a difference in attenuation characteristics of the damped reverberation vibration,
A liquid presence / absence determination result output means for outputting the determination result;
A frequency setting unit that variably sets the frequency of the ultrasonic beam for measurement;
Prior to detection of reverberation for determining the presence or absence of liquid, in order to determine the measurement frequency used for the detection of the measurement ultrasonic beam, at a frequency setting position that is known in advance to be liquid-free on the container. Measuring frequency determination means for measuring a reverberation vibration by outputting a measurement ultrasonic beam while changing the frequency variously, finding a frequency that maximizes the duration of the reverberation vibration, and determining it as a measurement frequency; It is provided with.

  According to the ultrasonic liquid detection apparatus of the present invention, the acoustic excitation means attached to the outside of the wall portion of the container is used to acoustically excite the container containing the liquid as a system to be measured and the acoustic excitation is cut off. Based on the reverberation information from the measurement system, the presence state of the liquid at the measurement execution position in the container is detected. That is, instead of detecting the reflected information of the excitation sound wave propagating into the liquid as in the past, the reverberation information from the measured system immediately after driving is detected in the form of a free vibration waveform, so that the sound wave propagates through the medium. There is no delay time and detection time is fast. Further, in the conventional transmission type detection method, reverberation immediately after driving acts on the reflected wave as detection information as noise, and particularly in the case of a small container size or a liquid with a high sound speed, the S / N due to reverberation noise. It was difficult to avoid a decrease in the ratio. However, in the present invention, the reverberation information is used as a signal (signal) instead of noise, and when the reverberation information is detected, the input wave for acoustic excitation is cut off. In principle, this cannot be a noise factor. Accordingly, extremely stable and highly sensitive liquid detection is possible, and the reliability is greatly improved.

  Here, in the principle of the liquid detection device described above, if the frequency of acoustic excitation with respect to the container wall part is greatly separated from the natural frequency (including overtone vibration) of the container wall part, it is a non-existing part of the liquid. However, since the reverberation vibration is remarkably attenuated, it is difficult to make a difference in the attenuation characteristics between the liquid existing portion and the determination accuracy of the presence / absence of the liquid is lowered. Therefore, the frequency of the ultrasonic beam for measurement is set to a value corresponding to the natural frequency (for example, a neighboring value belonging to a predetermined width within ± 10% centered on the natural frequency: preferably a matched value). It is desirable that

  Here, if the containers to be measured are always the same, once the above frequency is set to the optimum value, measurement at the same frequency will be performed thereafter, except for fine adjustment associated with deterioration of the ultrasonic transducer over time. Can be continued. However, in order to be able to cope with the measurement in any container with different material and thickness of the container wall with one detection device, the frequency of the ultrasonic beam for measurement is configured to be variable, and the container to be measured is Each time it is changed, it is necessary to use it while adjusting the frequency optimally for each individual container. Specifically, since the natural frequency shows different values depending on the material and thickness of the container wall, it is desirable to set the frequency of the ultrasonic beam for measurement to an optimum value according to the material and thickness. I can say that.

  According to the present invention, the frequency setting unit for variably setting the frequency of the measurement ultrasonic beam is provided, and the measurement frequency used for the detection of the measurement ultrasonic beam is determined prior to the reverberation detection related to the liquid presence / absence determination. In order to achieve this, a measurement ultrasonic beam is output by variously changing the frequency at a frequency setting position that is known to be liquid-free on the container, and reverberation vibration is measured. The frequency that maximizes the duration is found and determined as the measurement frequency. That is, the measurement execution position, which is known to be free of liquid on the container, is selected to measure the damped reverberation vibration at various frequencies, and the attenuation level is set after the measurement ultrasonic beam input is cut off. By selecting the frequency so that the decay time (reverberation time) until reaching a predetermined reference level is maximized, the conditions for maximizing the reverberation time in the absence of liquid, regardless of the container specifications It can be easily determined and the presence or absence of liquid can be reliably determined.

  If the container to be measured is a metal tank (especially made of steel or other material with a relatively low internal acoustic loss), the reverberation is difficult to attenuate in an empty state, and it contains liquid. Therefore, there is an advantage that the liquid detection accuracy is high. In this case, the ultrasonic output unit is preferably attached to the metal wall portion of the metal tank and configured to output a measurement ultrasonic beam in the thickness direction of the metal wall portion.

  The above metal tanks are liquid liquefied gas (liquefied gas for fuel such as liquefied petroleum gas (LPG) and liquefied natural gas (LNG), liquefied carbon dioxide gas, liquefied ammonia gas, cylinders such as liquid nitrogen, tanks, containers, etc.) If the ultrasonic wave is used as an excitation measurement probe, the ripple effect is high. That is, in the case of liquefied gas, the density is low, and the acoustic impedance difference between the tank wall and the inside of the tank is not so large between the state with liquid and the state without liquid. In this case, when an audible band sound source is used as an excitation measurement probe, it is difficult to produce a difference in reverberation behavior and it is difficult to obtain accurate knowledge about the liquid presence state. However, if an ultrasonic beam is used, a large difference occurs in reverberation behavior according to the liquid presence state, and accurate liquid detection becomes possible.

  When a container having a structure in which the upper surface is closed is used as the container, the frequency setting position may be determined on the uppermost surface part of the container where the liquid is surely absent. In accordance with this, the upper part of the container side wall can also be effectively used as the frequency setting position.

Next, the measurement frequency determination means outputs the measurement ultrasonic beam while measuring the reverberation vibration while changing the frequency in the initial measurement at the frequency setting position, thereby measuring the duration of the reverberation vibration. and initial maximum frequency f _0max is the frequency that maximizes the initial frequency measuring means, they initial maximum frequency f _0max and initial minimization similarly measure both the initial minimum frequency f _0min as a frequency to minimize An initial frequency storage means for storing a measurement result with the frequency f _{0 min} can be provided.

Since the top surface of the metal container is surely free of liquid, it is certainly convenient for frequency determination measurement. However, for example, an LPG container may be curved in a convex shape, and the container thickness is also uneven. In many cases, there is a concern that an error is likely to occur in the measurement frequency (particularly, the transmission efficiency of longitudinal sound waves due to the acoustic coupling state between the ultrasonic output unit and the container, and the S / N ratio decrease due to the influence of vibration noise). Therefore, in the above configuration, the duration of the reverberation vibration is maximized by measuring the reverberation vibration by outputting the measurement ultrasonic beam while changing the frequency in the initial measurement at the frequency setting position. and initial maximum frequency f _0max is the frequency, keep both measuring the storage of the same initial minimum frequency f _0min a frequency to minimize. Then, on the side wall of the container, a measurement ultrasonic beam is outputted while variously changing the frequency to measure the reverberation vibration, thereby maximizing the frequency f that is the frequency at which the duration of the reverberation vibration is maximized. A process for measuring both _max and a minimized frequency f _min which is also a frequency to be minimized is performed as a frequency determination measurement, while the process of changing the position of the ultrasonic output unit in the liquid depth direction is performed. measurement results of the minimum frequency f _min at a frequency determined for measuring finds liquid depth direction position as a mismatch with respect to the initial minimum frequency f _0min. When the measurement result of the minimum frequency f _min at this position is consistent with the initial maximum frequency f _0max, if configured to set the the minimization frequency f _min as the measurement frequency, if the frequency set position Even if there is an error in the measured value of the initial maximum frequency f _{0max at} , it can be corrected to an appropriate measuring frequency value by the subsequent frequency determination measurement, and stable measurement can be performed over a long period of time. Reliability can also be improved.

  For example, the metal tank has an integral lid member whose upper end portion of the side wall portion is connected to the periphery of the uppermost surface portion, and the lid member is attached to the upper edge portion of the container main body portion that forms the remaining portion of the side wall portion. If the frequency determination measurement by the fixed frequency determination means is performed at a portion located below the entire circumference welded portion of the side wall portion, an error due to the welded portion is received. There are difficult advantages.

The measurement for determining the frequency is preferably performed at a position where it is known in advance that the liquid is present on the container. Specifically, the measurement for determining the frequency may be performed at the lower end of the side wall. it can. If the time elapses from the initial measurement, the amount of liquid (LPG etc.) inside the container also increases, and the liquid level often decreases. However, if it is the lower end part of a side wall part, it can specify as a place where a liquid exists reliably. Then, at the midpoint until the liquid is replenished (filled) with the container, the maximum frequency f _max that is the frequency at which the duration of the reverberation vibration is maximized at the lower end position of the side wall part removed from the welded part. And the minimum frequency f _min that is also the frequency to be minimized, and if it can be confirmed that the measurement result of the minimum frequency f _min matches the initial maximum frequency f _0max , the minimum frequency f _min Can be adjusted more reliably as a measurement frequency. The same measurement is performed on the side wall of the container at the position where the liquid is not present above the lower end, and the maximum frequency f _max ′ (minimized frequency f _min at the lower end is It is possible to further improve the setting accuracy of the measurement frequency by confirming that it substantially coincides with the initial maximum frequency _f0max .

  Next, the measurement frequency determining means can be configured to have amplitude sampling means for sampling the amplitude of the reverberation vibration at predetermined time intervals. In this case, since the reverberation vibration becomes a damped vibration, the measurement frequency can be determined on the condition that the sampled amplitude monotonously decreases with time.

  The amplitude sampling means can perform accurate amplitude evaluation even if the sampling point is deviated from the peak point of the vibration waveform by sampling the amplitude using the envelope detection waveform of the reverberation vibration. In this case, the amplitude sampling means is configured to divide the detection waveform of the reverberation vibration into a plurality of sections each including a plurality of amplitude peak points, and calculate the average value of the amplitude of each section as the amplitude sampling value. For example, the influence of abnormal sampling values due to noise or the like can be reduced.

  On the other hand, the measurement frequency determining means can also be configured to have an integral calculating means for calculating the integral value of the envelope detection waveform of the reverberation vibration. In this way, the frequency at which the integral value is maximized can be easily determined as the measurement frequency.

  Next, the acoustic excitation means, the reverberation detection means, and the liquid presence state information output means are configured so as to be integrally transportable through the housing and detachable from the container, so that any position on the side wall surface of the container can be obtained. It becomes possible to measure whether or not there is a liquid by attaching it to For example, measurement is performed while sequentially changing the mounting positions of the acoustic excitation means and the reverberation detection means to the container wall in the container depth direction, and the detection state changes from a liquid present state (or no liquid state) to a liquid free state (or liquid present) The position of the liquid level can be known by reading the position that changes to the state. Moreover, it can be used as a simple level sensor to know whether or not the liquid level has reached the level by attaching it to a desired position on the container wall.

  And an ultrasonic output part can be comprised so that attachment or detachment is possible between mutually different containers. In this case, the measurement frequency storage means for storing the measurement frequency value determined for each container in association with the container specifying information, and the container selection means for selecting the container on which the ultrasonic output unit is mounted are selected. The frequency corresponding to the container is read from the measurement frequency storage means, and the measurement frequency selection setting means for setting as the measurement frequency is provided. Even if the frequency is not determined, it is possible to easily and quickly set the optimum measurement frequency for each container by reading the corresponding frequency from the measurement frequency storage means, thereby speeding up the liquid level measurement. Can do.

  In the present invention, since the reverberation after the excitation by the ultrasonic beam is cut off is detected, the excitation period and the reverberation detection period are sequentially performed in time series. Therefore, the ultrasonic output unit can be used as a reverberation detection means as an ultrasonic transducer that can output a measurement ultrasonic beam to the measurement target system and can also receive reverberation ultrasonic waves from the measurement target system. Can be configured. In this way, a single ultrasonic transducer can be used as both the ultrasonic transmission unit and the reverberation detection unit, which contributes to downsizing and cost reduction of the apparatus.

  In the ultrasonic liquid detection device of the present invention, the acoustic impedance matching layer can be arranged in close contact with the ultrasonic transmission / reception surface of the ultrasonic transducer. Then, the acoustic impedance matching layer can be exposed on the surface of the casing, and the exposed surface can be detachably attached and held at the measurement execution position of the container. By providing such an impedance matching layer, reflection of the ultrasonic beam for measurement at the contact surface with the container wall can be reduced, and the sensitivity of liquid detection can be increased.

  In this case, the operator can hold the case by hand while holding the detection surface against the measurement execution position, and in this state, the ultrasonic transducer can be driven to perform measurement related to the presence or absence of liquid. it can. This configuration can be said to be a hand-held liquid level gauge, and presses the detection surface at a desired position on the side wall surface against a container installed at an arbitrary place while holding the housing by hand. Thus, the presence or absence of liquid at that position can be easily detected. In this case, the internal liquid level position can be easily known by detecting the presence or absence of liquid while gradually changing the pressing position of the detection surface from the upper side (or from the lower side) while holding the housing by hand. . For example, the user carries the ultrasonic liquid detection device of this configuration, and visits each home or business place where the liquefied gas cylinder for fuel (LPG, LNG, etc.) is installed, and easily locates the liquid level of each gas cylinder. You can check and go around.

  In this case, if a detachable fixing part is provided that detachably fixes the housing to the side wall surface of the container with the detection surface pressed against the measurement execution position, the desired measurement can be performed without holding the housing by hand. The detection surface can be temporarily fixed at the working position to facilitate the detection of the liquid level, and it can be used as a simple level sensor by setting the fixed position as the detection target liquid level. It becomes.

  The detachable fixing part can be constituted by, for example, a suction cup type fixing part. The suction cup-type fixing part is convenient when the detection surface is to be fixed over a relatively long period of time because it is relatively difficult to cause a positional shift once it is fixed. In this case, if the detection surface is provided so as to be exposed at the bottom of the concave suction surface of the suction cup type fixing portion, only one suction cup type fixing portion is required, and the detection surface has an excellent adhesion holding effect.

  On the other hand, the detachable fixing part can also be constituted by a magnet type fixing part. The configuration using the magnet-type fixing part makes it relatively easy to attach and detach the detection surface. The detection surface position can be changed on the same container, or the attachment and detachment can be repeated frequently for use among multiple containers. Useful if you want to. The method of providing the magnet-type fixing portion is not particularly limited, but if it is constituted by an annular magnet surrounding the detection surface, the fixing stability of the detection surface can be improved. Further, when the detection surface is formed on the front end surface of the vertically long casing, the magnet-type fixing portion can be compactly placed around the front end surface of the casing.

  The ultrasonic output unit can be configured to block the input of the measurement ultrasonic beam after inputting the measurement ultrasonic beam to the system under measurement for a predetermined time. The reverberation detecting means may detect a damped reverberation vibration after the measurement ultrasonic beam input is cut off. And it has a liquid presence / absence determination means for determining the presence / absence of the liquid at the measurement execution position in the container based on the difference in the attenuation characteristic of the damped reverberation vibration detected, and the above-mentioned liquid presence state information output means has the determination result Can be configured to output. In the non-existing portion of the liquid, the inner side of the container wall becomes a void, and the acoustic impedance difference with the inner surface of the wall as a boundary becomes very large. As a result, when the container wall portion is acoustically excited from the outside, the container wall portion is acoustically separated from the inner space because the sound waves reflected and returned into the wall portion are the main, and the wall made of solid Since the vibration continues in a form governed by the natural vibration of the part, the vibration is hardly attenuated. This tendency is particularly remarkable when the container side is made of a metal having low internal friction. However, since the liquid is present inside the container wall in the presence of the liquid, the above-described acoustic impedance difference is reduced, and the ratio of sound waves leaking into the liquid having a large internal friction through the wall inner surface is increased to vibrate. The attenuation is significant. Therefore, it is possible to easily determine the presence or absence of liquid at the measurement execution position in the container based on the difference in the attenuation characteristics of the detected damped reverberation vibration.

  If there is a significant difference in the damping characteristics of the damped reverberation between the presence of the liquid and the non-existence of the liquid, it is easy to determine the presence or absence of liquid by quantifying the difference. Can be executed. There are various methods for quantifying the damping behavior of the vibration waveform, and any of them may be used.

  For example, the liquid presence / absence determining means is based on the detection information of the damped reverberation vibration, and the attenuation level reflecting the attenuation level of the damped reverberation vibration when a predetermined time elapses after the input of the measurement ultrasonic beam is cut off. Information can be acquired, and it can be configured to determine that there is liquid when the attenuation level reflected in the attenuation level information is less than a predetermined threshold and that there is no liquid when the attenuation level similarly exceeds the threshold. According to this method, a parameter that can reflect the attenuation level of the damped reverberation vibration is arbitrarily determined, the elapsed time after the excitation is cut off is fixed, and the parameter value is uniformly measured, thereby reducing the number of parameter samplings. Thus, it is possible to easily determine whether or not the liquid is present. As the parameter value, a peak amplitude value of the damped vibration waveform may be employed, or a time integral value of the damped vibration waveform displacement after the excitation is cut off may be employed.

  On the other hand, the liquid presence / absence determining means monitors the attenuation level of the damped reverberation vibration based on detection information of the damped reverberation vibration, and after the input of the measurement ultrasonic beam is cut off, the attenuation level is determined in advance as a reference level. It has a decay time measuring means for measuring the decay time until it reaches, and is configured to determine that there is no liquid when the decay time exceeds a predetermined threshold and that there is liquid when the fall time is also less than the threshold. May be. In this method, it is necessary to monitor the time change of the parameter value similar to the above, and the number of parameter sampling increases, but sudden change of the parameter value due to noise or the like can be easily identified as an error, so the determination accuracy is improved. There are benefits that can be enhanced.

  In said structure, the envelope detection means which detects an envelope of a reverberation vibration waveform can be provided. The liquid presence / absence determining means can be configured to determine the presence / absence of liquid at the measurement execution position in the container based on the difference in the attenuation characteristics of the damped reverberation vibration reflected in the envelope detection waveform. By detecting an envelope of the reverberation vibration waveform, the attenuation behavior of the amplitude can be grasped more easily and accurately, and the presence / absence determination of the liquid can be more accurately performed. In this case, the liquid presence / absence determining means acquires the attenuation level of the damped reverberation reflected in the envelope detection waveform when a predetermined time elapses after the input of the measurement ultrasonic beam is cut off, and the attenuation When the level is less than a predetermined threshold value, the liquid is present, and when the level is also exceeded, it is determined that the liquid is absent. The liquid presence / absence determining means monitors the attenuation level of the attenuated reverberation vibration reflected in the envelope detection waveform, and after the input of the measurement ultrasonic beam is interrupted, the attenuation level reaches a predetermined reference level. A decay time measuring means for measuring the decay time until it is determined, and it is configured to determine that there is no liquid when the decay time exceeds a predetermined threshold, and that there is liquid when the decay time is also less than the threshold. Good. In any case, by using the envelope detection waveform, it is possible to greatly simplify the algorithm for specifying the attenuation level of the damped reverberation vibration and the configuration of the arithmetic processing circuit (or software).

  The envelope detection means includes a waveform amplification section that amplifies the reverberation vibration waveform from the reverberation detection means, a half-wave rectification section that half-rectifies the amplified reverberation vibration waveform, and an envelope of the half-wave rectified reverberation vibration waveform. A detection circuit having a line detection unit can be used. By half-wave rectifying the waveform amplification output, the peak point on one side of the original damped oscillation waveform can be selectively extracted, and by detecting the envelope, this is a monotonically decreasing type (polarity) for easy attenuation determination If inverted, a monotonically increasing waveform attenuation curve can be obtained.

  In addition, the detection circuit can be configured to have a bias DC component removal unit that removes a bias DC component from the amplified output waveform from the waveform amplification unit, and the half-wave rectification unit has an amplified input waveform after removing the bias DC component. Can be configured as a half-wave rectifier. The bias direct current component includes both a concept that is intentionally added on the side of the waveform amplification unit in order to improve amplification characteristics and a concept that is inevitably superimposed due to the effects of stationary noise and drift. In any case, by removing the bias direct current component, it is possible to determine the amplitude center of the amplified output waveform, and it is possible to reduce the error of the clipping amplitude during half-wave rectification.

  It is also possible to incorporate a waveform tuning unit that tunes the amplified output of the waveform amplification unit to the excitation frequency of the measurement ultrasonic beam. Thereby, a necessary reverberation waveform corresponding to the excitation frequency of the ultrasonic beam for measurement can be extracted, and the influence of errors due to noise vibration and harmonics can be reduced.

  Attenuation that reflects the attenuation characteristics of branch-damped reverberation vibration based on the comparison between the amplified output that integrates the amplified output branched from the waveform amplifier and the integrated output and the envelope detection output from the detection circuit An integral comparison calculation unit that outputs a reflected signal can be provided. The liquid presence / absence determining means determines the presence / absence of liquid based on the attenuation reflection signal. With this configuration, if there is a waveform drift derived from temperature characteristics or stationary noise in the amplified output, the drift component can be canceled by performing a comparison operation (including the difference as a concept) with the integrated operation waveform. The effect can be easily reduced. If the integral comparison calculation unit is configured to output a binary comparison result between the integral output and the envelope detection output as the attenuation reflection signal, the calculation for determining the presence or absence of the liquid can be performed more easily.

  In the ultrasonic liquid detection device of the present invention, a waveform integration means for integrating the reverberation vibration waveform can also be provided. In this case, the liquid presence / absence determining means can be configured to determine the presence / absence of liquid at the measurement execution position in the container based on the difference in the attenuation characteristic of the damped reverberation vibration reflected in the integrated waveform. By determining the presence / absence of liquid using the integrated value of the reverberation vibration waveform, it is possible to keep the determination error low even when the waveform is disturbed by sudden noise or the like. This configuration can also be used in combination with the above-described envelope detection means. In this case, the waveform integration means can be configured to integrate the waveform after the envelope detection. Envelope detection of the reverberation vibration waveform makes it possible to grasp the attenuation behavior of the amplitude more easily and accurately, and is less susceptible to the effects of waveform disturbance due to noise, etc. Can be done.

  An embodiment of a liquid detection device 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 an upper surface portion 203 are joined to each other by an all-around welded portion 201 above and below a cylindrical container body portion 200 (container body portion). 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 200 forms the remaining part of the side wall. Although the wall thickness of the container main body 200 is substantially uniform, the thickness is locally increased at the position of the weld 201 due to the formation of a weld bead. The bottom surface portion 202 and the top surface portion 203 are formed by pressing a steel plate having the same material and thickness as the container main body portion 200 into a cup shape, and the outer peripheral edge portion is smooth toward the welded portion 201 with the container main body portion 200. It is made into the curved surface form which leads to. In addition, a gas extraction portion 203V in which a pressure control valve is incorporated is formed in the upper center of the upper surface portion 203. The liquid L made of LPG or LNG is accommodated in the metal tank 190 to constitute a system to be measured.

  And the liquid detection apparatus 1 is comprised so that the presence state of the liquid L in said metal tank 190, specifically, the position of the liquid level LV can be measured from the tank exterior. Specifically, the liquid detection device 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, can be attached at an arbitrary measurement position desired by the user). A) An ultrasonic transducer 2 is provided. The ultrasonic transducer 2 includes acoustic excitation means for acoustically exciting the system to be measured (the metal tank 190 containing the liquid L) through the side wall surface 200 of the container 190, and acoustic excitation to the system to be measured by the acoustic excitation means. It also serves as reverberation detection means for detecting reverberation information from the system under measurement when the input is shut off. Specifically, the ultrasonic transducer 2 is an ultrasonic output unit that outputs a measurement ultrasonic beam SW having a predetermined frequency in the thickness direction of the metal container main body 200 as an excitation measurement probe for exciting the measurement target system. This function has both the function and the function of a reverberation ultrasonic wave reception unit that receives the reverberation ultrasonic wave from the measurement target system when the output of the measurement ultrasonic beam SW is cut off.

  FIG. 2 is a conceptual diagram showing a configuration example of the liquid detection device 1 together with its electrical configuration. The liquid detection device 1 has a casing 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 drive voltage from the drive circuit 101, and an ultrasonic wave that outputs an electric signal (received signal) to the signal processing circuit 103 by receiving reverberant ultrasonic waves. Combined with reception function. 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 1e and 1e serve as driving electrodes to which a driving voltage for ultrasonically vibrating the piezoelectric ceramic diaphragm 21 is applied when transmitting an ultrasonic beam, and the piezoelectric ceramic diaphragm 21 is receiving a reverberant ultrasonic wave. It becomes an output electrode which outputs an electric signal accompanying vibration. The connection between the electrode pair 1e, 1e and the driving circuit 101 and the signal processing circuit 103 is switched by a changeover switch 101s.

  The drive circuit 101 is an oscillation circuit (here, a VCO (Voltage Controlled Oscillator)) 101b having a variable output frequency, and amplifies the output of the oscillation circuit 101b and outputs it as a drive signal to the piezoelectric ceramic diaphragm 21. The output frequency of the oscillation circuit 101b is changed according to the frequency instruction voltage input from the frequency setting unit 102.

  FIG. 30 shows a configuration example of the drive circuit 101, and a frequency instruction voltage value given as digital information by the microcomputer 100 is inputted from the D / A output port to the instruction voltage input terminal SCK of the VCO 10b as an analog instruction voltage. . The VCO 101b outputs a basic signal (A) including a square wave pulse signal having a frequency that uniquely corresponds to the indicated voltage from the output terminal OU. On the other hand, the microcomputer 100 outputs a driving time pulse signal (B) that defines the driving duration of the burst wave, and inputs it to the main circuit 101a together with the basic signal (A). In the main circuit 101a, the two outputs (A, B) are input to the modulation control gate IC 51, and a burst drive signal obtained by modulating the drive time pulse signal with the basic signal is generated. The burst drive signal is composed of a buffer circuit (a plurality of buffer ICs connected in parallel (here, replaced by AND gates) to secure a sink current): a pull-down resistor R51 is inserted on the output side The signal C is input to the control terminal of the drive transistor Tr51 (here, the gate terminal of the power MOSFET) via the IC52 and IC53.

  Next, the main circuit 101a has a drive coil L51 having one end connected to a drive power supply (VB) and the other end grounded via a pull-down resistor R52. A drive line of the ultrasonic transducer 2 is branched from a connection point between the drive coil L51 and the pull-down resistor R52, and an adjustment resistor R53 and parallel bidirectional diode pairs D51 and D52 are arranged on the line. A bootstrap circuit 51 for impedance conversion is provided. The drive transistor Tr51 is provided on a drive control line that branches separately from the connection point. When the burst drive signal (C) is at L level, the drive transistor Tr51 is cut off and electromagnetic energy is accumulated in the drive coil L51. When the burst drive signal (C) changes to H level, the drive transistor Tr51 becomes conductive, and the electromagnetic energy accumulated in the drive coil L51 is released as an induced current and is sent to the ultrasonic transducer 2 via the drive line. Supplied.

  FIG. 3 shows an example of the configuration of the signal processing circuit 103. The amplifier 103a that amplifies the damped vibration waveform from the piezoelectric ceramic diaphragm 21, the detection circuit 103b that detects the amplified damped vibration waveform as an envelope, and the detection output thereof. An integrating circuit 103c that integrates, and a determination circuit 103d that compares the output from the integrating circuit with a threshold value Vth and outputs a determination signal regarding the presence or absence of liquid. Although various configurations are possible for the detection circuit 103b, in the present embodiment, an unnecessary bias direct current component on the input side (for example, when the amplifier 103 is unipolar amplification is artificially superimposed on the amplifier input signal). A bias-cut capacitor C1 that removes a bias current for amplification), a rectifier diode D1 that half-wave rectifies the AC input waveform after the bias cut, and an envelope detection by removing the ripple after the half-wave rectification And a ripple removing unit having a waveform. The ripple removing unit is a simple low-pass filter circuit composed of a resistor R1 and a capacitor C2. The ripple waveform obtained by enveloping the peak point of the half-wave rectified waveform while sufficiently removing the ripple is not damaged. A constant is set.

  The integrating circuit 103c is composed of the resistor R2 and the capacitor C3. The capacitance of the capacitor C3 increases with the input of the attenuation waveform up to the specified timing tm, so that the output voltage rises to the extent that does not hinder the determination. It is set to be larger than the above ripple removing portion. The determination circuit compares this integrated output voltage with the threshold voltage Vth (provided as a resistance divided voltage of the power supply voltage Vcc by the resistance half bridge (R3, R4)), and outputs the comparison result in binary. The comparator IC1 is used. As shown in FIG. 4, the presence or absence of liquid can be discriminated by the output level of the comparator IC1. In this embodiment, when the integrated output voltage is greater than the threshold voltage Vth, the output of the comparator IC1 is at the H level indicating no liquid, and vice versa.

  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 and a keyboard, and is used for a liquid detection start trigger operation and a frequency setting process. Further, the display unit 104 visually outputs the detection determination result of the presence / absence of liquid, and is configured as an LED lighting unit, for example. Further, the sonar 106 acoustically outputs a detection result of presence / absence of liquid.

  As shown in FIG. 18, the present embodiment includes a first LED 104 a (for example, red) that lights when there is no liquid and a second LED 104 b (for example, green) that lights when there is liquid. It is also possible to identify this by the lighting state of one LED (for example, with liquid = continuous lighting, without liquid = flashing). Further, in order to enable measurement mode display (for example, liquid detection mode and frequency setting processing mode) and operation guidance information output, the display unit is displayed on a display panel 104d such as a liquid crystal display as shown in FIG. It is also possible to configure.

  Further, the output of the sonar 106s is controlled so that the sound output forms are different between when there is no liquid and when there is liquid. For example, with liquid = sonar sound output, without liquid = sonar sound non-output (or reverse), with liquid = sonar sound continuous output, without liquid = sonar sound intermittent output (or reverse), power OFF = sonar A configuration in which sound is not output is also possible.

  In the configuration of FIG. 2, the contents of the liquid level determination signal Vout from the signal processing circuit 103 (no liquid = H level, liquid = L level (the logic on the circuit may be reversed may be reversed)) Based on the result, the microcomputer 100 controls the operation of the display unit 104 or the sonar 106. However, it is also possible to directly control the operation of the display unit 104 or sonar 106 using the liquid level determination signal Vout. FIG. 23 shows a circuit example in that case. In the circuit 250, the binary liquid level determination signal Vout is distributed and input to the comparator IC 801 for the first LED 104a and the comparator IC 802 for the second LED 104b, with one of the levels inverted by the inverter IC 803, Comparison is made with threshold voltages formed by voltage division from the signal power supply voltage Vcc by the resistance half bridges R803 and R804, respectively.

  The first LED 104a and the second LED 104b are connected to the drive voltage + VB (the battery is used as a power source together with other signal voltages in order to configure the device to be portable) via the current adjustment resistors R801 and R802, respectively. Depending on the level of the determination signal Vout, one of the first LED 104a and the second LED 104b is lit by the current drawn by the corresponding comparator IC801 or comparator IC802. Further, in this embodiment, the sonar 106 is sounded in response to “there is liquid”, and the sonar 106 is branched and input from the corresponding signal distribution path of the liquid level determination signal Vout to the sonar 106 side. ing. Here, the drive transistor Tr108 is turned on by this drive signal, and the sonar 106 operates.

  Hereinafter, the operation of the liquid detection device 1 will be described. As shown in FIG. 1, first, a measurement execution position PR in which it is known in advance that the surface of the acoustic impedance matching layer 2P on the ultrasonic transducer 2 (hereinafter referred to as a detection surface) is free of liquid on the container 190. The frequency is set by pressing against (here, set on the upper surface of the container top surface portion 203). The details of the operation at the time of setting will be described later since it is closely related to the liquid presence / absence detection processing.

  When the frequency setting is completed, the detection surface is pressed to a desired measurement execution position against the outer surface of the container main body 200 of the container 190, and measurement start input is performed from the input unit 105 in FIG. Here, the detection button 105a (FIG. 18) included in the input unit 105 is pressed). Then, the microcomputer 100 starts the measurement driving program and starts the measurement process. FIG. 5 is a flowchart showing the flow of the processing (this processing is repeatedly executed until the detection stop button 105b (also used as a power switch button) 105b included in the input unit 105 is pressed, for example. First, in S <b> 1, the changeover switch 101 </ b> S is switched to a drive connection state in which the ultrasonic transducer 2 is connected to the drive circuit 104, and the drive circuit 104 applies a drive AC voltage to the ultrasonic transducer 2 at a set frequency. Thereby, the ultrasonic beam for measurement SW is output from the ultrasonic transducer 2 toward the container main body 200 at the measurement execution position, and this is acoustically excited.

  As shown in FIG. 7A, the drive AC voltage is applied with a pulsed burst drive input waveform, and is forcibly cut off when the applied pulse period tn set to about 10 to 50 μs is completed. At the same time, the changeover switch 101S switches 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. 6 shows an example of the detection waveform of the reverberation vibration. In the non-existing part (liquid-free part) of the liquid L, the inside of the container 190 container body part 200 becomes a gap, and the acoustic impedance with the wall part inner surface as a boundary. The difference becomes very large. The ultrasonic beam for measurement input to the container main body 200 is almost totally reflected by the inner surface of the wall and returns to the metal container main body 200, and the natural vibration determined by the material and thickness of the container main body 200. Vibrations are less likely to occur because the vibrations continue to be controlled by As a result, as shown in the upper part of FIG. 6, the reverberation tail is very long. However, since the liquid L is present inside the container main body 200 in the liquid L existing portion (liquid present portion), the above-described acoustic impedance difference is reduced, and the liquid having a large internal friction is transmitted through the container main body 200. Since the ratio of sound waves leaking into L increases, vibration damping becomes significant.

  Therefore, by extracting from the reverberation vibration waveform a numerical parameter convenient for identifying the difference in the waveform generated as shown in FIG. 6 between the liquid presence portion and the liquid absence portion, and comparing the parameter value with a threshold value, Determination regarding the presence or absence of the liquid L can be performed easily. For example, as shown in FIGS. 7A and 7B, a parameter reflecting the attenuation level of the damped reverberation when a predetermined time ts has elapsed after the input of the measurement ultrasonic beam SW is cut off is used as the attenuation level information. As shown in FIG. 7A, it can be determined that there is no liquid when the attenuation level reflected in the parameter exceeds a predetermined threshold, and there is liquid when the attenuation level is less than the threshold as shown in FIG. 7B.

  In the signal processing circuit of FIG. 2, as shown in FIG. 8, 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 envelope detection waveform is integrated by the integration circuit 103c over the period ts of FIGS. 7A and 7B (step 4). Then, as shown in FIG. 9, the timing at which the period ts ends (the timing at which Δt has elapsed after the interruption may be measured as a time starting point, or the timing at the start of burst driving may be the time starting point. 7A, the output Vout (liquid level determination signal) of the comparator IC1 that compares the integrated output voltage with the threshold voltage Vth is read (time measurement may be performed for tm corresponding to tn + Δt + ts) (FIG. 5: S3). ). Since the waveform attenuation is fast in the portion with the liquid, the increase in the integrated output becomes dull. Conversely, in the portion without the liquid, the waveform attenuation is slow, so the integral output increases quickly. Therefore, when the integrated output at the above time is sampled, as shown in FIG. 4, if the liquid level determination signal is at the H level, there is no liquid output (FIG. 5: S4 → S5). Yes output (FIG. 5: S4 → S6).

  The display unit 104 receives the liquid level determination signal and enters a corresponding display state. For example, as shown in FIG. 1, the first LED 104 a (for example, red) indicating no liquid is lit if it is at the H level (the sonar 106 is not operating), and the second LED 104 b (that is indicating liquid is present if it is the L level). For example, green) lights up (the sonar 106 operates). Thereby, it can be determined whether or not the liquid is present at the position where the detection surface of the apparatus 1 is pressed (that is, the measurement execution position). Therefore, when the above measurement is sequentially performed while holding the housing 3 by hand and changing the measurement execution position from the upper side to the lower side on the container main body 200, the display unit 104 starts from the display state indicating no liquid. The position when the display state changes to “present” can be specified as the liquid level position. Conversely, when the above measurement is sequentially performed while changing the measurement execution position from the lower side to the upper side, the position when the display unit 104 changes from the display state indicating the presence of liquid to the display state indicating the absence of liquid is set to the liquid level. It can be specified as a surface position.

  As shown in FIG. 9, a decay time td until the integrated output (attenuation level of the damped reverberation vibration) reaches a predetermined reference level VR is measured by the microcomputer 100, and the decay time td is determined in advance. If the threshold value is exceeded, the liquid may be present, and if the threshold value is also less than the threshold value, it may be determined that the liquid is absent.

  In addition, in said structure, the detachable fixing | fixed part which fixes the housing | casing 3 to the side wall surface 200w of a container in the state which pressed the detection surface to the measurement implementation position can be provided. If the housing 3 is temporarily fixed at a certain position, the measurement execution position for determining the presence or absence of the liquid is fixed, and it can be easily determined from the detection result whether the liquid level has reached that position. it can. That is, the liquid detection device 1 can be utilized as a simple level sensor in a form in which the fixed position is set as a detection target liquid level.

  The detachable fixing part can be constituted by a suction cup type fixing part 7 as shown in FIG. 20, for example. The suction cup type fixing portion 7 is made of a rubber material (for example, butadiene rubber) that is harder than the constituent material (for example, silicone rubber) of the acoustic impedance layer 2p that constitutes the detection surface in order to secure the fixing support force for the housing 3. It is good to keep. In the configuration of FIG. 20, the detection surface is disposed so as to be exposed at the bottom of the concave suction surface of the suction cup type fixing portion 7. When mounting, hold | maintain the housing | casing 3 by hand and press the concave suction surface side of the suction cup type fixing | fixed part 7 to the container main-body part 200 with the acoustic impedance layer 2p. Thereby, the suction cup type fixing part 7 is elastically deformed while discharging air in the concave suction surface, and the acoustic impedance layer 2p is pressed against the container main body part 200 so as to be crushed in the thickness direction. Elastically deforms. When the pressing force is released, the suction cup type fixing portion 7 is adsorbed and held by the suction cup action while partially elastically returning together with the acoustic impedance layer 2p. A suction cup removing projection 7h is integrally formed on the outer edge portion of the suction cup type fixing portion 7 opposite to the concave suction surface so as to turn up the outer peripheral edge of the suction cup and leak the inside.

  On the other hand, as shown in FIG. 21, the detachable fixing part can also be constituted by a magnet type fixing part 8. In FIG. 21, the magnet type fixing portion 8 is configured by an annular magnet surrounding the detection surface. Here, the housing 3 is vertically long, and a magnet-type fixing portion 8 is provided along the periphery of the detection surface formed on the front end surface thereof. As shown in FIG. 22, the magnet-type fixing portion 8 is formed by covering an annular permanent magnet 8 with a protective layer 8y, and is integrated by a known method such as press-fitting, bonding, or insert molding around the tip of the housing 3. Has been. In the present embodiment, the fixing surface of the magnet type fixing portion 8 has a curved shape corresponding to the outer peripheral surface of the cylindrical container body 200 in order to improve the adhesion stability during fixing. ing.

Next, the frequency setting process described above, as shown in FIG. 1, a position immediately above the weld 201 at the position P _R to the side wall portion of the top surface portion of the frequency setting position (container be a liquid without is know beforehand pressing the sensing surface P _U, etc.) to operate the liquid detection device 1 at the frequency setting processing mode. In FIG. 3, the liquid detection device 1 outputs the drive AC voltage in burst while sweeping the frequency stepwise from the low frequency side or the high frequency side, and the integrated output value when the time ts elapses after the cutoff. And monitoring directly via the A / D converter IC2. Then, the frequency at which the integrated output value becomes maximum (that is, the frequency at which the tail of the attenuation becomes the maximum as shown in FIG. 7A) is read and set as the measurement frequency.

  By using the integral value of the envelope detection waveform, it is possible to keep the determination error low even when the waveform is disturbed due to sudden noise or the like. However, if the influence of noise is not so great, the integrated value is not used, and the level of the envelope detection waveform at the specified determination timing (tm to ts) is directly sampled as shown in FIG. May be compared with the threshold value Vth (in this case, the integration circuit 103c is omitted in FIG. 3 and the output of the detection circuit 103b is directly input to the determination circuit 103d). Further, the microcomputer 100 measures the time (td to td ′) until the level of the envelope detection waveform reaches the reference value VR, and when the time exceeds a predetermined threshold, there is no liquid, and is similarly below the threshold. In such a case, it is possible to perform processing so as to determine that there is liquid.

In addition, as a frequency setting process which does not use an integration process, the following methods can be illustrated. First, as shown in FIG. 37, (to no P _R P _U) Frequency set position in the initial measurement in, by performing the measurement of reverberation oscillation outputs a measuring ultrasonic beam while changing the frequency in various, the duration of the reverberation oscillations to measure both the initial minimum frequency f _0min that the frequency of the initial maximum frequency f _0max, also minimizing the frequency that maximizes (initial frequency measuring means) their initial maximum frequency f _0max a measurement result of the initial minimum frequency _{f 0min} is stored in RAM100mb provided in the microcomputer 100 in FIG. 2 (initial frequency memory means).

Next, as shown in FIG. 37, the duration of the reverberation vibration is maximized by outputting the measurement ultrasonic beam and measuring the reverberation vibration while changing the frequency on the side wall of the container. The process of measuring both the maximum frequency f _max that is the frequency and the minimum frequency f _min that is also the frequency to be minimized is sequentially performed while changing the position of the ultrasonic output unit in the liquid depth direction (P _S → P _L ) Frequency determination measurement). Then, the measurement result is a liquid depth direction position at which mismatch with respect to the initial minimum frequency f _0min minimum frequency f _min at the frequency determined for measuring (here, the position P _L) finding. As shown in FIG. 37, when the measurement result of the minimized frequency f _min at the position P _L substantially coincides with the initial maximized frequency f _0max (for example, an error within 10% is allowable, the minimized frequency f _min is set as the measurement frequency, so that even if an error occurs in the measurement value of the initial maximum frequency f _0max at the frequency setting position P _U , it is more suitable for the frequency determination measurement to be performed subsequently. The frequency value for measurement can be corrected, and stable measurement can be performed over a long period of time, and the reliability can be improved.

As indicated by the broken line in FIG. 37, the measuring determination frequency position to be a presence liquid at the container are know in advance, that may be carried out at the lower end P _B of the side wall portion. If the time elapses from the initial measurement, the amount of liquid (LPG etc.) inside the container also increases, and the liquid level often decreases. However, the lower end portion P _B of the side wall portion can be specified as a place where the liquid is surely present. Then, in the middle stage until the liquid is replenished (filled) with the container, the maximization frequency which is the frequency at which the duration of the reverberation vibration is maximized at the lower end position P _B of the side wall part removed from the welded part. If both f _max and a minimized frequency f _min that is also a frequency to be minimized are measured and it can be confirmed that the measurement result of the minimized frequency f _min matches the initial maximized frequency f _0max , the minimized frequency f _min can be set as the measurement frequency. The same measurement is performed on the side wall of the container at the position where the liquid is not present above the lower end, and the maximum frequency f _max ′ (minimized frequency f at the lower end position P _B at this time) is measured. substantially coincides with _min) is by checking fit that substantially coincides with the initial maximum frequency f _0max, it is possible to further improve the setting accuracy of the measurement frequency. In this case, either the maximization frequency f _max ′ or the minimization frequency f _min may be set as the measurement frequency, or an average value of both may be set as the measurement frequency.

  Next, as shown in FIG. 39, it is possible to sample the amplitude of the reverberation vibration at a predetermined time interval and determine the measurement frequency using the sampling result. As shown in FIG. 40, this sampling is performed using the envelope detection waveform of the reverberation vibration after half-wave rectification (the waveform processing related to half-wave rectification and envelope detection is a program process on the microcomputer 100). Or may be performed by a waveform processing front-end circuit inserted in the preceding stage of the A / D converter 112).

Specifically, since the reverberation vibration becomes a damped vibration, the measurement frequency is determined on the condition that the sampled amplitude monotonously decreases with time. The circuit configuration in this case is preferably the one shown in FIG. 24 capable of digital sampling of the waveform. In FIG. 39, the sampling interval Δt is set to 5 to 10 μs (for example, about one sound wave), and the detection voltage corresponding to each sampling time: tn (t1 t2 t3... Tn): V (n) ( V (1) V (2) V (3)... V (n)) is V (1) ≧ V (2) ≧ V (3). is required. The voltage V is V = V ₀ exp (−Bt)
If we satisfy the relationship of
lnV = lnV ₀ -Bt
It becomes. Therefore, the slope B when the V sampling results are plotted semilogarithmically with respect to time t at various frequencies is calculated by, for example, the least square method, and the frequency at which the value B is minimized is used as the measurement frequency. It is also possible to decide.

  When the reverberation vibration has an ideal damped vibration waveform, the detection voltage V (n) behaves monotonously regardless of the set value of the sampling time. However, this is limited to the case where the resonance characteristics of the ultrasonic transducer have a single resonance point. Actually, the ultrasonic transducer often takes a behavior in which two or more resonances are combined, and the detected voltage V (n) (after envelope detection) is often attenuated to, for example, a pulsation form. In this case, if the sampling time is set too short, the detection voltage V (n) does not necessarily decrease monotonously, which may be an obstacle to finding an appropriate measurement frequency. Therefore, as shown in FIG. 41, if the detection waveform of reverberation vibration is divided into a plurality of sections each including a plurality of amplitude peak points, and the average value of the amplitudes of each section is calculated as an amplitude sampling value, the section Even if the detection voltage V (n) pulsates. The average value for each section monotonously decreases, and the measurement frequency setting accuracy can be increased. In FIG. 41, as time increases, t1⇒t2⇒t3 ........ ⇒V (1) ⇒V (2) ⇒V (3) ⇒ corresponding to the number of n samples of tn. In the magnitude relationship of n voltages of V (n), [V (1) to V (S1)], [V] within the section divided by 1/5 of the number of samples: n V (S1) to V (S2)], [V (S2) to V (S3)], [V (S3) to V (S4)], and [V (S4) to V (n)]. The measurement frequencies are determined on the condition that Va> Vb> Vc> Vd> Ve, where Va, Vb, Vc, Vd, and Ve are averages within the interval. The influence of the pulsation of the detection voltage V (n) as described above can be removed by passing the waveform after the envelope detection through a low-pass filter having a cutoff frequency suitable for the pulsation removal.

  As shown in FIG. 2, the value of the measurement frequency f (f1, f2, f3,...) Determined for each container is associated with the container specifying information (container 1, container 2,. It can memorize | store in the frequency memory | storage part 100m 'for a measurement comprised with the property memory. For example, when the configuration of FIG. 19 is adopted, an ultrasonic output unit is mounted while referring to the display contents of the display unit 104 at the input unit 105 including buttons 105a and 105b (or a mode selection button may be provided separately). (For example, the buttons 105a and 105b are used as cursor movement buttons and the container registration numbers displayed in a list on the display unit 104 are selected by the cursor). The determined measurement frequency is stored in the measurement frequency storage unit 100m 'in the form of using the container registration number as the container specifying information.

  When the measurement mode is selected, a list of registered container numbers is displayed on the initial screen on the display unit 104, and a container number to be used is selected by input from the input unit 105. Then, the frequency corresponding to the container of the selected number is read from the regular frequency storage unit 100m 'and set as the measurement frequency.

  Next, FIG. 11 shows an example of a signal processing circuit 103 which is a further development of FIG. The amplifier 103a constituting the waveform amplifying unit includes an amplifying transistor Tr101 to which the damped vibration waveform from the ultrasonic transducer 2 is input as a base. Gain determining resistors R101 and R103 are inserted in the collector and emitter thereof. On the emitter side, a waveform tuning unit for tuning the amplified output on the collector side to the excitation frequency of the measurement ultrasonic beam is incorporated. In this embodiment, the waveform tuning unit is provided in such a manner that an RC series circuit (capacitor C101 and resistor R102) that lowers the impedance near the excitation frequency is inserted in parallel with the emitter.

  Next, the detection circuit 103e is configured as follows. First, the amplified output from the amplifier 103a is input to the base of the detection transistor Tr202 that also serves as a half-wave rectifier. The detection output is taken out on the emitter side of the detection transistor Tr202, and a DC cut capacitor (bias DC component removal unit) C202 for removing a bias DC component from the amplified output waveform from the waveform amplification unit is inserted on the output system path. Has been. On the grounded emitter path, a ripple removing unit that removes the waveform to obtain an envelope detection waveform is inserted in the form of an RC low-pass filter including a resistor R206 and a capacitor C203 connected in parallel. .

  The amplified output from the amplifier 103a is branched and input to the base of the integrating transistor Tr201 that also serves as a half-wave rectifier. The integration transistor Tr201 constitutes an emitter follower circuit by pull-down resistors R203 and R204, and constitutes an integration unit together with a resistor R201 and a capacitor C201 for determining an integration time constant, and the integration operation output is taken out from the emitter side. .

  The envelope detection waveform output described above and the integral calculation output of the amplified output are input to the comparator IC 201 that forms an integral comparison calculation unit. The comparator IC 201 outputs a binary comparison result between the integration output and the envelope detection output. The reverberation vibration waveform is determined by the DC cut capacitor C202 with respect to the ground level as a reference, and the integral calculation output determined by the voltage dividing ratio of R203 and R204 with respect to the envelope detection output voltage formed based on this. Is superimposed as a bias voltage via the adjustment resistor R206, so that the envelope detection output can be shifted to an arbitrary base voltage level (in this embodiment, the resistance voltage R204 is a variable resistor for setting the base voltage level). That is, it is possible to variably set the relative cutout threshold value of the integrated output with respect to the envelope detection output.

  The binary output of the comparator IC201 is output to the lower integration circuit 103f. On the output side of the comparator IC201, a pull-up resistor R209 inserted between the signal power supply line Vcc and an output control comparator IC202 are connected. Has been. The output control comparator IC202 compares the mask signal from the mask signal generation circuit 103g with a reference voltage (generated by dividing the signal power supply Vcc by the resistance half bridges R207 and R208). When the condition that the magnitude relationship between the mask signal voltage level and the reference voltage is validated on the output mask side is satisfied, the output of the output control comparator IC202 becomes L (ground) level, and the output of the comparator IC201 of the detection circuit 103e. Is bypassed to the ground side in the form of being pulled to the output control comparator IC 202 side. As a result, the output of the comparator IC201 to the integrating circuit 103f is cut off. On the other hand, when the condition that the magnitude relationship between the mask signal voltage level and the reference voltage is validated to the output allowable side is satisfied, the output of the output control comparator IC 202 becomes the H (ground) level. As a result, the output of the comparator IC201 of the detection circuit 103e is pulled up, and the binary output (attenuation reflection signal) is output to the integration circuit 103f side.

  The mask signal is for taking out the output of the detection circuit 103e only for the above-mentioned predetermined period ts after the drive of the ultrasonic transducer 2 is cut off, and masking the signals of other periods so that they are not considered in the liquid presence / absence determination. In this embodiment, the mask signal can be input as a binary level signal to the comparator IC 202. In this case, for example, the mask signal may be output from the port of the microcomputer 100 in FIG. However, in the present embodiment, the mask signal generation circuit 103g is configured by an external circuit for the microcomputer 100 in order to save the port of the microcomputer 100.

  Specifically, the mask signal generating circuit 103g is configured to generate a mask signal by diverting a drive / shutoff command signal that commands the drive / shutoff of the ultrasonic transducer 2. That is, a level edge that defines the drive cutoff timing of the ultrasonic transducer 2 is input to a monostable circuit (not shown) (not shown) by the prescribed drive / shutoff signal, and a pulse from the monostable circuit is input to the resistance half bridge R401. , R402 are input to the base of the mask signal generation transistor Tr401 forming a collector follower circuit (in this case, a pulse is generated immediately after being cut off, but the pulse is generated with a delay by the delay time Δt described above. Can also be configured).

  The collector side of the mask signal generating transistor Tr401 is connected to the signal power source Vcc via a pull-up resistor 403, and a signal level holding capacitor C401 is inserted between the emitter and the grounded emitter. The mask signal generation transistor Tr401 is turned on only during the pulse input period from the monostable circuit, but its collector output as a mask signal has a predetermined period longer than the pulse length determined by the discharge time constant of the capacitor C401 (the time ts described above). The mask signal level is kept below the threshold value, that is, the condition for non-masking is satisfied.

  The integrating circuit 103f is configured as follows. The output of the comparator IC201 of the detection circuit 103e is input to the base of the integration control transistor Tr301 constituting the emitter follower circuit. An integration unit including a capacitor C301 and a resistor R302 is connected to the emitter of the integration control transistor Tr301. R302 connected in parallel with the capacitor C301 is a discharging resistor that discharges the capacitor C301 with a predetermined time constant when the integral output is cut off. The integration control transistor Tr301 is turned on when the output of the comparator IC201 is at H level, and is cut off when the output is also at L level. As a result, the integrating unit integrates the emitter-side output voltage of the integration control transistor Tr301 only when the output of the comparator IC201 is at the H level. This integrated output is input to a liquid presence / absence determination comparator IC 301 that constitutes a determination circuit, and is compared with a threshold voltage (provided as a resistance divided voltage of the power supply voltage Vcc by the resistance half bridge (R303, R304)). The comparison result is output in binary from the comparator IC 301 as a liquid presence / absence determination signal.

  The operation of the signal processing circuit 103 in FIG. 11 will be described with reference to FIGS. As shown in FIG. 12, the ultrasonic transducer is forcibly burst driven for a certain period by the drive / shutoff command signal from the microcomputer 100, and then the drive is shut off. Then, after the interruption, the output of the mask signal (FIG. 11: C) from the mask signal generation circuit 103g is in the L level, that is, in the non-mask state for a certain period ts.

  The envelope detection output indicated by A in FIG. 12 is compared with the integral calculation output indicated by B by the comparator IC201. As shown in the upper part of FIG. 13, the envelope detection output A is attenuated only slowly in the absence of liquid and is rapidly attenuated conversely in the presence of liquid. On the other hand, the integration time constant of the integration unit described above is such that the difference in the time increase rate of the voltage between the liquid-free state and the liquid-containing state of the integral calculation output B is sufficiently larger than the difference in the attenuation rate of the envelope detection output A. It is set to be smaller. As a result, as shown in the middle part of FIG. 13, the time until the magnitude relationship between the envelope detection output input to the comparator IC201 and the integral calculation output is inverted (that is, the time until the output of the comparator IC201 is inverted). Produces a large difference between the absence of liquid and the presence of liquid.

  Of course, it is possible to determine the presence or absence of liquid by directly measuring the above time. However, in the circuit of FIG. 11, the binary output (attenuation reflection) of the comparator IC201 is shown in the lower part of FIG. A value obtained by integrating the signal) for the period ts (FIG. 11E) is used for liquid presence / absence determination. That is, in the integration circuit 103f, the integration value E is compared with the threshold value Vth by the comparator IC301. The output of the comparator IC301 is used as a liquid presence / absence determination output in the same manner as the circuit of FIG.

  Note that the envelope detection circuit, the half-wave rectification circuit, or the integration circuit used in each circuit of FIGS. 3 and 11 is not limited to the one disclosed above. 14 and 15 show an example of an envelope detection circuit using a detection transformer TF501, and a damped oscillation waveform signal that has been DC-cut by a capacitor C501 is passed through a detection transformer TF501 to form a transistor Tr501 (FIG. 14). ) To half-wave rectified by the diode D501 (FIG. 15), and envelope detection is performed by the parallel RC section (R501, C502) inserted in the lower stage. The detection transformer TF501 forms an impedance conversion unit for an input signal, and a secondary coil is combined with a capacitor C502 to form a tuning unit. In the circuit shown in FIG. 16, the damped oscillation waveform signal is input to the operational amplifier IC 601 for impedance conversion, and the diode D601 inserted between the output and the negative period path forms a half-wave rectifier. Further, as shown in FIG. 17, the integrating circuit can be configured as an active integrating circuit in which a capacitor C701 and a resistor R701 for determining an integration time constant are combined with a negative feedback portion of an operational amplifier IC701.

  Next, when the damped vibration waveform can be directly digitally sampled, the presence or absence of liquid can be determined using the attenuation peak value of the acquired waveform as a parameter. FIG. 24 is a circuit diagram in that case, and the attenuation waveform signal from the ultrasonic transducer 2 is captured as a digital waveform by the microcomputer 100 via the amplifier 111 and the A / D converter 112. The flow of processing by the microcomputer 100 is as shown in FIG. First, in the same manner as in FIG. 5, the ultrasonic transducer 2 is burst-driven and then shut off (S51), and digital data of an attenuation waveform is captured (S52).

  As shown in FIG. 25, in the captured digital waveform data, for example, data points where the waveform displacement shows a maximum value (or a minimum value) are extracted as peak values P1, P2,..., Pk (S53). Since the peak values P1, P2,..., Pk of the damped vibration waveform are discrete parameters, the representative value of the peak value that falls within a certain time width tw at the aforementioned determination timing tm (for example, the largest value or the peak value that falls into tw) (Average value) is extracted as the determination peak value Pm (S54), and is compared with the threshold value Vth (S55). If the determination peak value Pm is larger than the threshold value Vth, it is determined that there is no liquid output (S56), and if it is smaller than the threshold value Vth, it is determined that there is liquid output (S57).

  Further, instead of sampling the digital waveform data, a method of detecting the waveform peak value with the peak hold circuit 112 as shown in FIG. 27 is also possible. The flow of processing in this case is shown in FIG. First, the ultrasonic transducer 2 is driven after burst driving (S101), and waits until the determination timing tm arrives (S102). When the determination timing tm arrives, a waveform is input in a certain window period tw, and the maximum waveform value in that period is held as the determination peak value PH (S103: see FIG. 28). If the determination peak value PH is larger than the threshold value Vth, it is determined that there is no liquid output (S104 → S105), and if it is smaller than the threshold value Vth, it is determined that there is liquid output (S104 → S106).

  When the density of the liquid to be detected is relatively large, an audible sound wave output unit (for example, a small speaker) that outputs an audible sound wave signal can be used as an excitation measurement probe instead of the ultrasonic transducer. . Moreover, you may provide the striking mechanism which acoustically excites this by striking the outer surface of the wall part of a container instead of the audible sound wave output part.

  Next, as shown in FIG. 31, the liquid detection device 1 specifically includes a liquid corresponding to a specific liquid level to be detected in the container with respect to the outer surface of the container main body 200 of the container 190. It can be fixedly attached to the detection position and configured as a container with a liquid detection function. In FIG. 31, the liquid detection device 1 includes two liquid detection positions (hereinafter, upper limit liquid level positions) corresponding to the upper limit liquid level position and the lower limit liquid level position defined in the container 190 in the depth direction of the container 190. 1A is attached to the ultrasonic liquid detection device on the side, and 1B is assigned to the ultrasonic liquid detection device on the lower limit liquid surface position side for identification. The acoustic impedance matching layer 2P is fixed to the surface of the container 190 through an appropriate adhesive layer thinner than the acoustic impedance matching layer 2P.

  In FIG. 31, each liquid detection device 1 individually has the electrical configuration shown in FIG. 2, FIG. 24, or FIG. 27, and a liquid level determination signal Vout (no liquid = H level, liquid level) from its signal processing circuit 103. Existence = L level (the logic may be reversed if the logic on the circuit is inverted may be reversed) by the microcomputer 100 of each ultrasonic liquid detection device, and the microcomputer 100 determines that the LED lighting unit 104 is based on the result. The lighting control is performed. However, as shown in FIG. 33, it is also possible to share the detection control unit between the liquid detection devices 21A and 21B. In this case, the liquid level determination signals Vout from the liquid detection devices 21A and 21B are collected in the microcomputer 100 that forms the common control unit, and the operation control of the LED lighting units corresponding to the individual ultrasonic liquid detection devices is also performed collectively. It is. In this case, the LED lighting part can be provided separately from the liquid detection device. This configuration can be detected, for example, when a display unit is provided on a container such as a fuel tank of a vehicle (such as an automobile), or when the detection result is not visible, or because the display unit is provided on the tank because the tank is large. This is effective when it is difficult to visually recognize the result.

  In the configuration of FIG. 33, the transducers of the respective liquid detection devices 21A and 21B are sequentially switched and connected to the drive circuit 101 and the signal processing circuit 103 by the changeover switch 101s that receives a command from the microcomputer 100, and respectively detects the presence or absence of liquid. At the same time, the detection results at each transducer position are stored in the memory of the microcomputer 100. By providing the two ultrasonic liquid detection devices 21A and 21B, as shown in FIG. 32, when the liquid level is lower than the lower limit liquid level position side liquid detection device 1B (0 to 1), the upper limit liquid level position side Three liquids, when the liquid detection device 1A is between the lower limit liquid level position side liquid detection device 1B (1-2) and above the upper limit liquid level position side liquid detection device 1A (2). The surface state can be identified. Therefore, the microcomputer 100 determines which section the liquid level is in the above based on the detection result. For example, when the liquid level is (2), the first LED 104a is lit and the liquid level is Is controlled so that the second LED 104b is lit when (1-2), and the third LED 104b is lit when the liquid level is (0-1).

  Further, it is possible to further provide one or more intermediate liquid detection devices 1c between the upper limit liquid level position side liquid detection device 1A and the lower limit liquid level position side liquid detection device 1B. As shown in 33, the liquid surface position can be displayed in a further subdivided form by the plurality of LEDs 104k according to the detection state of the intermediate liquid detection device 1c. In this case, the total number of liquid detection devices is N, and the inside of the container is divided into N + 1 sections in the depth direction, and the liquid level in which section depends on which of the LEDs 104k corresponding to each section is lit. Can be notified. In addition, you may control so that not only LED104k corresponding to the area where a liquid level exists but all LED104k located below it may light.

  FIG. 34 shows binary liquid level determination signals Vout (A) and Vout (B) from the respective liquid detection devices 1A and 1B (both are H when there is no liquid and L when there is liquid: The example of the circuit which performs lighting control of LED without using a microcomputer based on the explanation is shown. That is, one of the first LED 104a, the second LED 104b, and the third LED 104b is controlled to be turned on based on the input levels of Vout (A) and Vout (B) by the logic according to the truth table in the figure. Yes. Specifically, Vout (A) and Vout (B) are distributed and input to the logical product gate IC 804 and the logical sum gate IC 805, respectively. The output of the AND gate IC 804 is input to the comparator IC 801 for the first LED 104a. Further, the output of the OR gate IC 805 is distributed and input to the comparator IC 802 for the second LED 104b and the comparator IC 803 for the third LED 104c in a state where one of them is inverted by the inverter IC 806. Each of the comparators IC801 to IC803 compares each input voltage with a threshold voltage that is divided from the signal power supply voltage Vcc by the resistor half bridges R803 and R804. Then, on the output side of each of the comparators IC801 to IC803, the LEDs 104a to 104c are connected to the drive voltage + VB via current adjustment resistors R805 to R807, respectively. When the input voltage is active (L), the outputs of the comparators IC801 to IC803 are also active (L), and the corresponding ones of the LEDs 104a to 104c are lit by the current drawn to the comparator side.

  According to the above circuit, when both Vout (A) and Vout (B) are active (that is, at the liquid level (2)), the output of the IC 804 is active, and the first LED 104a is turned on via the IC 801. . When Vout (A) is inactive and Vout (B) is active (that is, when the liquid level is (1 to 2)), the output of IC 805 is active (IC 804 is inactive), and the first is transmitted through IC 802. The second LED 104b lights up. When both Vout (A) and Vout (B) are active (that is, when the liquid level is (1 to 2)), both IC804 and IC805 are inactive, but the distributed output to IC803 side of IC805 Is actively inverted by the IC 806, so that the third LED 104b is turned on via the IC 803. In this way, the corresponding LED (indicator) is alternatively lit according to which of the above sections the liquid level belongs to.

  Next, as shown in FIG. 35, the liquid detection device can be attached to a portion (inclined wall portion) 200j of the container main body 200 of the container 190 that is inclined with respect to the vertical direction. FIG. 35 shows an example in which the present invention is applied to a vehicle fuel tank using an internal combustion engine as a power source, particularly an automobile fuel tank. The upper limit liquid level position side liquid detection device 1A and the lower limit liquid level position side liquid detection are illustrated. Of the apparatus 1B, the latter is attached to the inclined wall portion 200j (in order to avoid interference with other structures on the chassis side where the vehicle fuel tank is densely arranged, the lower portion of the tank is sectioned by the inclined wall portion 200j. Often reduced). This brings the following advantages compared with the conventional reflective ultrasonic liquid level gauge. In other words, the reflection-type ultrasonic liquid level meter detects liquid by detecting the presence or absence of reflected waves on the opposite side wall surface of the ultrasonic beam transmitted through the wall, which is peculiar to the presence of liquid. If the device is mounted on a wall that is inclined with respect to the vertical direction, even if a reflected wave on the opposite side wall surface is generated, the reflected wave repeatedly reflects on the liquid surface, etc. Will also change, making detection very difficult. However, since the reverberation information unrelated to the reflected wave is detected according to the method of the present invention, the presence or absence of liquid can be detected without any problem even when the mounting wall surface 200j of the liquid detection device 1B is inclined.

  As shown in FIG. 36, the liquid detection device 1 can be attached to the bottom wall portion 200B of the container 190, and in this case, the presence or absence of liquid can be detected from the reverberation information. The bottom wall portion 200B may be either parallel to the liquid surface or inclined as shown in the figure.

The schematic diagram which shows the usage example of the ultrasonic liquid detection apparatus of this invention. The schematic diagram which shows the 1st example of the ultrasonic liquid detection apparatus of FIG. 1 with the electrical structure. FIG. 3 is a circuit diagram illustrating an example of a signal processing circuit in FIG. 2. The timing chart which shows the relationship between the output of the comparator of FIG. 3, and the determination result of liquid presence / absence of liquid. The flowchart which shows the control flow of the microcomputer in the structure of FIG. The figure which shows the example of a waveform measurement of a decaying reverberation vibration. The figure which shows the damping behavior of the reverberation vibration in a no-liquid part. The figure which similarly shows the damping behavior of the reverberation vibration in a part with a liquid. Explanatory drawing which shows the operation | movement of the circuit of FIG. 3 with the typical waveform of each part. FIG. 4 is a schematic diagram showing a relationship between an output of the integration circuit of FIG. 3 and a determination threshold value of presence / absence of liquid. The schematic diagram which shows the relationship between a detection output and the determination threshold value with / without liquid when the integration circuit is omitted in FIG. FIG. 3 is a circuit diagram showing a development example of the signal processing circuit of FIG. 2. FIG. 12 is an operation explanatory diagram of the circuit of FIG. 11. Explanatory drawing following FIG. The circuit diagram which shows the 1st modification of a detection circuit. The circuit diagram which shows the 2nd modification of a detection circuit. The circuit diagram which shows the modification of a half wave rectifier circuit. The circuit diagram which shows the modification of an integration circuit. The front view which shows the 1st example of the external appearance of the liquid detection apparatus which concerns on this invention. The front view which shows a 2nd example similarly. Explanatory drawing which shows the example which comprised the detachable fixing | fixed part by the suction cup type fixing | fixed part with the usage method. The perspective view which shows the example which comprised the detachable fixing | fixed part with the magnet type fixing | fixed part. Explanatory drawing which shows the usage method of the magnet type fixing | fixed part of FIG. The circuit diagram which shows an example of the drive circuit of a display part and a sonar. The schematic diagram which shows the 2nd example of the ultrasonic liquid detection apparatus of FIG. 1 with the electrical structure. The schematic diagram explaining the content of the waveform process in the structure of FIG. The flowchart which shows the control flow of the microcomputer in the structure of FIG. The schematic diagram which shows the 3rd example of the ultrasonic liquid detection apparatus of FIG. 1 with the electrical structure. The figure explaining the content of the peak hold process in the structure of FIG. The flowchart which shows the control flow of the microcomputer in the structure of FIG. The circuit diagram which shows an example of a drive circuit. The schematic diagram which shows the 1st example comprised as a container with a liquid detection function. The schematic diagram which shows the arrangement | positioning form of the liquid detection apparatus in the container with a liquid detection function with the modification. The block diagram which shows the example of a structure which controls commonly the drive of a several ultrasonic transducer by one microcomputer. The circuit diagram which shows the modification of an LED lighting control circuit. The schematic diagram which shows the 2nd example comprised as a container with a liquid detection function. The schematic diagram which similarly shows a 3rd example. Explanatory drawing which shows the modification of the determination procedure of the frequency for a measurement. FIG. 38 is a diagram illustrating the principle of the procedure in FIG. Explanatory drawing which shows the 1st example of the waveform sampling for determining the frequency for a measurement. Explanatory drawing which shows the content of the waveform pre-processing which concerns on the waveform sampling of FIG. Explanatory drawing which shows the 2nd example of the waveform sampling for determining the frequency for a measurement.

Explanation of symbols

1 Liquid detector 2 Ultrasonic transducer (acoustic excitation means, reverberation detection means)
Ultrasonic beam for SW measurement L Liquid 7 Suction cup type fixing part 8 Magnet type fixing part 100 Microcomputer (liquid presence / absence judging means, measuring frequency determining means)
100 m initial frequency storage unit 100 m ′ measurement frequency storage unit 102 frequency setting unit 103 signal processing circuit (liquid presence / absence determination means)
103e Detection circuit 104 Display unit (Liquid presence state information output means)
190 Container 200 Metal side wall

Claims (35)

A container containing a liquid is used as a system to be measured, and is detachably attached to a measurement execution position defined on the outer surface of the wall of the container, and the measurement ultrasonic beam is preliminarily set in the system to be measured. An ultrasonic output unit that cuts off the input of the ultrasonic beam for measurement after the excitation input;
Reverberation detection means for detecting a reverberation vibration waveform after being cut off from the input of the ultrasonic beam for measurement;
A liquid presence / absence determining means for determining the presence / absence of the liquid at the measurement execution position in the container based on a difference in attenuation characteristics of the damped reverberation vibration;
A liquid presence / absence determination result output means for outputting the determination result;
A frequency setting unit for variably setting the frequency of the ultrasonic beam for measurement;
Prior to reverberation detection related to liquid presence / absence determination, in order to determine a measurement frequency used for the detection of the measurement ultrasonic beam, a frequency setting position is known in advance that no liquid is present on the container. Measuring the reverberation vibration by outputting the ultrasonic beam for measurement while changing the frequency in various ways, and finding the frequency that maximizes the duration of the reverberation vibration and determining it as the measurement frequency Frequency determining means;
An ultrasonic liquid detection device comprising:   The said container is a metal tank, and the said ultrasonic output part is attached to the metal wall part of this metal tank, and outputs the said ultrasonic beam for a measurement in the thickness direction of the said metal wall part. Ultrasonic liquid detection device.   The ultrasonic liquid detection device according to claim 2, wherein the container has a structure in which an upper surface is closed, and the frequency setting position is determined on an uppermost surface portion of the container. The measurement frequency determining means includes
This is the frequency at which the duration of reverberation vibration is maximized by measuring the reverberation vibration by outputting the measurement ultrasonic beam while variously changing the frequency in the initial measurement at the frequency setting position. and initial maximum frequency f _0max, the initial frequency measuring means for measuring both the initial minimum frequency f _0min a frequency also minimizes,
And a initial frequency storage means for storing the measurement results with those initial maximum frequency f _0max and initial minimum frequency f _0min,
On the side wall of the container, the frequency is maximized by maximizing the duration of reverberation vibration by measuring the reverberation vibration by outputting the measurement ultrasonic beam while changing the frequency variously. The process of measuring both the frequency f _max and the minimized frequency f _min that is also the frequency to be minimized is performed by changing the position of the ultrasonic output unit in the liquid depth direction as the measurement for determining the frequency. In the frequency determination measurement, a position in the liquid depth direction where the measurement result of the minimized frequency f _min does not match the initial minimized frequency f _{0 min} is found, and the minimized frequency f is determined at the position. _{3. The minimum} frequency f _min is set as the measurement frequency when the measurement result of _min matches the initial maximum frequency f _0max. 4. The ultrasonic liquid detection device according to 3. The metal tank has 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, and the lid member is arranged at the upper edge portion of the container body portion that forms the remaining portion of the side wall portion. It has a structure joined by welds,
The ultrasonic liquid detection device according to claim 4, wherein the measurement for frequency determination by the measurement frequency determination unit is performed at a portion located below the all-around welded portion of the side wall portion.   6. The ultrasonic liquid detection device according to claim 4, wherein the frequency determination measurement is performed at a position where it is known in advance that liquid is present on the container.   The ultrasonic liquid detection device according to claim 6, wherein the measurement for determining the frequency is performed at a lower end portion of the side wall portion.   The measurement frequency determining means includes amplitude sampling means for sampling the amplitude of the reverberation vibration at a predetermined time interval, and the measurement frequency is determined on condition that the sampled amplitude monotonously decreases with time. The ultrasonic liquid detection device according to claim 1, which is to be determined.   The ultrasonic liquid detection device according to claim 8, wherein the amplitude sampling means performs sampling of the amplitude using an envelope detection waveform of the reverberation vibration.   The amplitude sampling unit divides the detection waveform of the reverberation vibration into a plurality of sections each including a plurality of amplitude peak points, and calculates an average value of amplitudes in each section as the sampling value of the amplitude. Item 10. The ultrasonic liquid detection device according to Item 9.   The measurement frequency determination means includes integration calculation means for calculating an integral value of an envelope detection waveform of the reverberation vibration, and determines a frequency at which the integral value is maximized as the measurement frequency. The ultrasonic liquid detection apparatus of any one of Claim 3. The ultrasonic output unit is configured to be detachable between different containers,
Measuring frequency storage means for storing the value of the measuring frequency determined for each container in association with the container specifying information;
Container selecting means for selecting the container on which the ultrasonic output unit is mounted;
A measurement frequency selection setting unit that reads out the frequency corresponding to the selected container from the measurement frequency storage unit and sets the frequency as the measurement frequency;
The ultrasonic liquid detection device according to claim 1, comprising:   The ultrasonic liquid detection device according to claim 1, wherein the container is a metal tank and contains liquefied gas as the liquid.   The ultrasonic output unit is an ultrasonic transducer capable of outputting a measurement ultrasonic beam to the measurement target system and capable of receiving reverberation ultrasonic waves from the measurement target system. The ultrasonic liquid detection device according to any one of claims 1 to 13, wherein the ultrasonic liquid detection device is used in combination.   An acoustic impedance matching layer is disposed in close contact with the ultrasonic transmission / reception surface of the ultrasonic transducer, the acoustic impedance matching layer is exposed on the surface of the housing, and the exposed surface serves as a detection surface for the measurement of the container. The ultrasonic liquid detection device according to claim 14, wherein the ultrasonic liquid detection device is detachably attached and held at the implementation position.   The measurement according to the presence or absence of liquid is performed by exciting and driving the ultrasonic transducer in this state while holding the detection surface against the measurement execution position while an operator holds the casing by hand. 15. The ultrasonic liquid detection device according to 15.   The ultrasonic liquid detection device according to claim 15, further comprising: a detachable fixing portion that detachably fixes the casing to the side wall surface of the container in a state where the detection surface is pressed against the measurement execution position.   The ultrasonic liquid detection device according to claim 17, wherein the detachable fixing part is constituted by a suction cup type fixing part.   The ultrasonic liquid detection device according to claim 18, wherein the detection surface is provided so as to be exposed at a bottom of the concave suction surface of the suction cup type fixing portion.   The ultrasonic liquid detection device according to claim 17, wherein the detachable fixing portion is configured by a magnet-type fixing portion.   21. The ultrasonic liquid detection device according to claim 20, wherein the magnet-type fixing part is configured by an annular magnet surrounding the detection surface. The ultrasonic output unit is configured to block the input of the measurement ultrasonic beam after the excitation input of the measurement ultrasonic beam to the measurement target system for a predetermined time,
The reverberation detecting means detects damped reverberation vibration after the input of the measurement ultrasonic beam is interrupted,
A liquid presence / absence determination unit that determines the presence / absence of the liquid at the measurement execution position in the container based on a difference in the attenuation characteristics of the damped reverberation vibration detected; The ultrasonic liquid detection device according to any one of claims 1 to 21, which outputs a result.   The liquid presence / absence determining means is based on the detection information of the damped reverberation vibration, and reflects the attenuation level of the damped reverberation vibration when a predetermined time elapses after the input of the measurement ultrasonic beam is cut off. 23. The ultrasonic wave according to claim 22, wherein level information is acquired and liquid is determined to be present when the attenuation level reflected in the attenuation level information is less than a predetermined threshold value, and no liquid is detected when the attenuation level is also greater than the threshold value. Liquid detection device.   The liquid presence / absence determining means monitors the attenuation level of the damped reverberation vibration based on the detection information of the damped reverberation vibration and refers to a predetermined attenuation level after blocking the input of the ultrasonic beam for measurement. It has an attenuation time measuring means for measuring the attenuation time until reaching the level, and determines that there is no liquid when the attenuation time exceeds a predetermined threshold, and also when there is less than the threshold. The ultrasonic liquid detection device according to claim 22. Envelope detection means for detecting the reverberation vibration waveform as an envelope,
23. The liquid presence / absence determination means is configured to determine the presence / absence of the liquid at the measurement execution position in the container based on a difference in attenuation characteristics of the damped reverberation vibration reflected in the envelope detection waveform. The ultrasonic liquid detection device according to any one of claims 24 to 24.   The liquid presence / absence determining means acquires an attenuation level of the damped reverberation reflected in the envelope detection waveform when a predetermined time elapses after the input of the measurement ultrasonic beam is cut off, and the attenuation 26. The ultrasonic liquid detection device according to claim 25, wherein the liquid is detected when the level is less than a predetermined threshold, and no liquid is determined when the level is also exceeded.   The liquid presence / absence determining means monitors the attenuation level of the damped reverberation vibration reflected in the envelope detection waveform, and reduces the attenuation level to a predetermined reference level after blocking the input of the ultrasonic beam for measurement. An attenuation time measuring means for measuring an attenuation time until it reaches, and determining that there is no liquid when the attenuation time exceeds a predetermined threshold, and that there is liquid when the attenuation time is also less than the threshold. 26. The ultrasonic liquid detection device according to 26.   The envelope detection means includes a waveform amplification section for amplifying the reverberation vibration waveform from the reverberation detection means, a half-wave rectification section for half-wave rectifying the amplified reverberation vibration waveform, and the half-wave rectified reverberation vibration The ultrasonic liquid detection device according to any one of claims 25 to 27, wherein the ultrasonic wave detection device is configured by a detection circuit having a waveform and an envelope detection unit.   The detection circuit includes a bias DC component removal unit that removes a bias DC component from the amplified output waveform from the waveform amplification unit, and the half-wave rectification unit performs a half-amplification on the amplified input waveform after removing the bias DC component. 29. The ultrasonic liquid detection device according to claim 28, wherein the ultrasonic liquid detection device performs wave rectification.   30. The ultrasonic liquid detection device according to claim 29, further comprising a waveform tuning unit that tunes the amplified output of the waveform amplification unit to the excitation frequency of the ultrasonic beam for measurement.   Based on the comparison between the amplified output obtained by integrating the amplified output branched from the waveform amplifier and the envelope output from the integrated output and the detection circuit, the attenuation characteristics of the branched damped reverberation vibration are reflected. 31. The apparatus according to claim 28, further comprising an integration comparison operation unit that outputs an attenuation reflection signal, wherein the liquid presence / absence determination means determines the presence / absence of the liquid based on the attenuation reflection signal. The ultrasonic liquid detection device according to 1.   32. The ultrasonic liquid detection device according to claim 31, wherein the integral comparison calculation unit outputs a binary comparison result between the integral output and the envelope detection output as the attenuation reflection signal. Having waveform integration means for integrating the reverberation vibration waveform;
23. The liquid presence / absence determining means is configured to determine the presence / absence of the liquid at the measurement execution position in the container based on a difference in attenuation characteristics of the damped reverberation vibration reflected in the integrated waveform. Item 33. The ultrasonic liquid detection device according to any one of Item 32.   34. The ultrasonic liquid detection device according to claim 33, further comprising envelope detection means for detecting an envelope of the reverberation vibration waveform, wherein the waveform integration means integrates the waveform after the envelope detection.   The reverberation information is detected at different measurement execution positions in the liquid depth direction in the container, and the liquid level position in the container is reflected based on the detection result of the reverberation information at each measurement execution position. The ultrasonic liquid detection apparatus according to any one of claims 1 to 34, wherein the surface position reflection information can be output.

Images