JP2008203206A - Liquid detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid detector of a simple structure for determining a liquid existence state in a container from the exterior of the container in a shorter time with satisfactory work efficiency. <P>SOLUTION: This liquid detector 1 is used by being mounted on the container 190 at a measurement execution position set on an outer surface of its side wall part 200 with the container 190 containing a liquid L taken as a measured system, and includes an ultrasonic transducer 2 for thereinto inputting an ultrasonic beam for measurement via a side wall surface of the container 190. The ultrasonic transducer 2 functions also as a reverberation detection means for detecting reverberation information from the measured system when stopping the ultrasonic beam being input into the measured system. Even where a waveform is disturbed by accidental noises, etc., it is possible to hold down a determination error by using the integral value of a damping reverberation vibration waveform to determine whether or not a liquid exists. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a 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 liquid detection device of the present invention is:
A container containing a liquid is used as a system to be measured, and is used by being attached to a measurement execution position determined on the outer surface of the wall of the container, and after inputting an ultrasonic beam for measurement to the system to be measured for a predetermined time, An ultrasonic output unit for blocking the input of the ultrasonic beam for measurement;
A reverberation detection means for detecting a damped reverberation vibration waveform after being cut off from the input of the measurement ultrasonic beam;
Waveform integration means for integrating the damped reverberation vibration waveform;
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 reflected in the integrated waveform;
Liquid presence / absence determination result output means for outputting the determination result.

  According to the liquid detection apparatus of the present invention, the ultrasonic wave for measurement is excited by the ultrasonic beam for measurement from the ultrasonic output unit attached to the outside of the wall of the container, with the container containing the liquid as the system to be measured. Based on the damped reverberation vibration waveform from the system to be measured after the input is cut off, the presence state of the liquid at the measurement 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. In addition, since the ultrasonic beam has high directivity and loss due to waveform diffusion is small, liquid detection with higher sensitivity is possible.

  Specifically, in the non-existing portion of the liquid, the inside of the container wall portion becomes a void, and the acoustic impedance difference with the wall portion inner surface 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. By determining the presence or absence of liquid using the integrated value of the damped reverberation vibration waveform, it is possible to keep the determination error low even when the waveform is disturbed due to sudden noise or the like.

  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.

  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 acquires the attenuation level of the damped reverberation vibration reflected in the integrated waveform when a predetermined time has elapsed after the input of the measurement ultrasonic beam is cut off, and the attenuation level is determined in advance. It can be configured that it is determined that there is liquid when it is less than a predetermined threshold and that there is no liquid when the threshold is also exceeded. According to this method, it is possible to easily determine whether or not there is a small amount of liquid by fixing the elapsed time after the excitation is cut off and uniformly measuring the level of the integrated waveform.

  On the other hand, the liquid presence / absence determining means acquires the attenuation level of the damped reverberation vibration reflected in the integrated waveform when a predetermined time elapses after the input of the measurement ultrasonic beam is interrupted, and the attenuation level is determined in advance. It may be configured to determine that there is liquid when it is less than a predetermined threshold and that there is no liquid when the threshold is also exceeded. In this method, it is necessary to monitor the time change of the integrated waveform, and the number of samplings increases. However, since the change due to noise or the like superimposed after execution of integration can be easily identified as an error, it is possible to improve the determination accuracy. There is.

  Next, the liquid detection device of the present invention can be provided with an envelope detection means for detecting an envelope of a damped reverberation vibration waveform. The waveform integration means described above can be configured to integrate the waveform after the envelope detection. Envelope detection of a damped reverberation waveform makes it easier and more accurate to understand the attenuation behavior of the amplitude, and makes it less susceptible to waveform disturbances due to noise, etc. Can be done.

  The envelope detection means includes a waveform amplification section that amplifies the damped reverberation vibration waveform from the reverberation detection means, a half-wave rectification section that rectifies the amplified damped reverberation vibration waveform by half-wave, and the half-wave rectified damped reverberation vibration. The waveform can be constituted by a detection circuit having an envelope detection unit. 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, it is more convenient and monotonous for use in attenuation determination A waveform attenuation curve of a type (monotonically increasing type when polarity is inverted) 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.

  In addition, an amplification output integration unit that integrates an amplification output that is branched and input from the waveform amplification unit, and a comparison between the integration output of the amplification output integration unit and the envelope detection output from the detection circuit, And an integral comparison operation unit that outputs an attenuation reflection signal that reflects the attenuation characteristics of the signal. The waveform integrating means is configured to integrate the attenuation reflected 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 present invention, the above-mentioned metal tank is liquid as a liquefied gas (a liquefied gas for fuel such as liquefied petroleum gas (LPG) or liquefied natural gas (LNG), a cylinder or tank of liquefied carbon dioxide gas, liquefied ammonia gas, liquid nitrogen, etc. In the case of accommodating containers, etc.), the ripple effect of adopting ultrasonic waves as an excitation measurement probe 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.

  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 principle of the liquid detection device of the present invention, if the frequency of the acoustic excitation with respect to the container wall is greatly separated from the natural frequency (including overtone vibration) of the container wall, reverberation occurs even in the absence of liquid. Since the damping of the vibration becomes remarkable, it becomes difficult to make a difference in the damping characteristic between the liquid existing portion and the accuracy of determining 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 Since the natural frequency shows different values depending on the material and thickness of the container wall, it can be said that it is desirable to set the frequency of the ultrasonic beam for measurement to an optimum value according to the material and thickness.

  In any case, in order to optimize the frequency of the ultrasonic beam for measurement, the measurement execution position, which is known in advance to be free of liquid on the container, is selected, and attenuation reverberation vibration is measured at various frequencies. The frequency may be selected so that the attenuation time (reverberation time) until the attenuation level reaches a predetermined reference level after the input of the measurement ultrasonic beam is cut off is maximized. For example, by setting the measurement position at the top of the container side wall or the top surface of the container (top surface) where there is no liquid, the conditions for maximizing the reverberation time in the absence of liquid can be easily determined. The presence or absence of can be determined more reliably.

  If the container to be measured is always the same, once the above frequency is set to the optimum value, measurement at the same frequency can be continued thereafter, except for fine adjustment associated with deterioration of the ultrasonic transducer over time. That's fine. 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. That is, it is desirable that the frequency of the ultrasonic beam for measurement can be variably set according to the container to be measured.

  If reverberation information is detected at different measurement execution positions in the liquid depth direction in the container by the liquid detection device of the present invention, the liquid in the container is based on the detection results of the reverberation information at the individual measurement execution positions. Liquid surface position reflection information reflecting the surface position can be output. In this case, 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 is changed from the liquid state (or no liquid state) to the liquid state (or liquid). The position of the liquid level can be known by reading the position that changes to the presence state. For example, a plurality of sets of acoustic excitation means and reverberation detection means are attached to the container side wall at a predetermined interval in the container depth direction, and the liquid level depends on which position of the reverberation detection means is in a liquid presence state. It is also possible to know the position.

  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 the bottom surface portion 202 and the top surface portion 203 are joined to the top and bottom of the cylindrical side wall portion 200 by welding portions 201, respectively. Although the wall thickness of the side wall part 200 is substantially uniform, the thickness is locally increased at the position of the weld part 201 due to the formation of the weld bead. The bottom surface portion 202 and the top surface portion 203 are formed by press-molding a steel plate having the same material and thickness as the side wall portion 200 in a cup shape, and both of the outer peripheral edge portions are smoothly connected toward the welded portion 201 with the side wall portion 200. It is a curved surface form. In addition, a gas extraction portion 203V in which a pressure control valve is incorporated is formed at the upper center of the top 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 side wall 200 of the container 190 at an arbitrary position in the liquid depth direction (that is, can be attached at an arbitrary measurement execution position desired by the user). ) It has an ultrasonic transducer 2. 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 functions as an ultrasonic output unit that outputs a measurement ultrasonic beam SW having a predetermined frequency in the thickness direction of the metal side wall 200 as an excitation measurement probe for exciting the system under measurement. And a function of a reverberant ultrasonic wave receiving unit that receives a reverberant ultrasonic wave from the system to be measured when the output of the ultrasonic beam SW for measurement 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 side wall 200 (steel) (preferably the geometric average value of both) and is pressed against the container side wall 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 1e formed so as to face each other with the piezoelectric ceramic diaphragm 21 sandwiched between the main surfaces of the piezoelectric ceramic diaphragm 21. , 1e. 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 drive 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. 18 shows a configuration example of the drive circuit 101. A frequency instruction voltage value given as digital information by the microcomputer 100 is input from the D / A output port to the instruction voltage input terminal SCK of the VCO 10b as an analog instruction voltage. . The VCO 10b outputs a basic signal (A) composed of a square wave pulse signal having a frequency uniquely corresponding 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. In addition, the display unit 104 outputs a detection result of the presence / absence of liquid, and is configured as an LED lighting unit, for example. As shown in FIG. 1, the present embodiment includes a first LED 104a (for example, red) that lights when there is no liquid and a second LED 104b (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 output of operation guidance information, the display unit 104 can be configured by a display panel such as a liquid crystal display. is there.

  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 against a desired measurement execution position against the outer surface of the side wall 200 of the container 190, and a measurement start input is performed from the input unit 105 in FIG. 2 (for example, included in the input unit 105). Press the “Measure” button). Then, the microcomputer 100 starts the measurement driving program and starts the measurement process. FIG. 5 is a flowchart showing the processing flow. 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 side wall portion 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 a detection waveform of the reverberation vibration. In the non-existing portion (liquid-free portion) of the liquid L, the inner side of the side wall portion 200 of the container 190 becomes a void, and the acoustic impedance difference with the inner surface of the wall portion as a boundary. Becomes very large. The measurement ultrasonic beam input to the side wall portion 200 is almost totally reflected on the inner surface of the wall portion, returns to the metal side wall portion 200, and is controlled by the natural vibration determined by the material and thickness of the side wall portion 200. Because vibration continues in the shape of a dam, it is difficult for vibration to attenuate. 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 side wall portion 200 in the portion where the liquid L is present (liquid present portion), the above-described acoustic impedance difference is reduced, and the inside of the liquid L having a large internal friction is transmitted through the side wall portion 200. Since the ratio of sound waves leaking into the chamber increases, vibration damping becomes significant.

  Therefore, by extracting from the damped reverberation vibration waveform a numerical parameter convenient for discriminating the difference in waveform generated as shown in FIG. 6 between the portion with liquid and the portion without liquid, and comparing the parameter value with a threshold value. The determination relating to the presence or absence of the liquid L can be easily executed. 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 (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 104a (for example, red) indicating that there is no liquid is lit when it is at H level, and the second LED 104b (for example, green) that indicates that there is liquid is lit when it is at L level. . 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, at the measurement execution position. Therefore, when the above measurement is sequentially performed while changing the measurement execution position from the upper side to the lower side on the side wall part 200, the position when the display unit 104 changes from the display state indicating no liquid to the display state indicating the presence of liquid. 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, the microcomputer 100 measures a decay time td until the integrated output (attenuation level of the damped reverberation vibration) reaches a predetermined reference level VR, and the decay time td is determined in advance. It is also possible to perform processing so as to determine that there is liquid when a predetermined threshold value is exceeded and that there is no liquid when the threshold value is also less than the threshold value.

  As for the frequency setting process described above, as shown in FIG. 1, the liquid detection device is pressed in the frequency setting process mode by pressing the detection surface against a measurement execution position PR that is known to be free of liquid, such as the container top surface portion 203. 1 is activated. 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 original damped vibration waveform is disturbed by sudden noise or the like. However, if the influence of the disturbance of the damped vibration waveform is not so great, the half-wave rectified damped vibration waveform may be integrated without performing envelope detection. As shown in FIG. 10, the signal processing circuit 103 in this case may be configured to omit the envelope detection unit of the detection circuit 103b and leave only the half-wave rectification unit 103b '.

  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 amplification output integration unit together with a resistor R201 and a capacitor C201 for determining an integration time constant, and an integration operation output from the emitter side. It is taken out.

  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. Note that the amplitude center voltage of the damped reverberation vibration waveform is determined by the DC cut capacitor C202 with reference to the ground level, and the integral calculation determined by the voltage dividing ratio of R203 and R204 with respect to the envelope detection output voltage formed based on this. The envelope detection output can be shifted to an arbitrary base voltage level by superimposing the divided voltage of the output as a bias voltage via the adjustment resistor R206 (in this embodiment, in this embodiment). The resistor 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 amplifying output integrating unit comprising 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 amplification output integration unit described above 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. 11 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 amplification output integration unit described above is that the difference in the time increase rate of the voltage between the liquid absence state and the liquid presence state of the integral calculation output B is based on the difference in the attenuation rate of the envelope detection output A. Is set to be sufficiently small. 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.

The schematic diagram which shows the usage example of the liquid detection apparatus of this invention. The schematic diagram which shows the 1st example of the 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 circuit diagram which shows the structure which abbreviate | omitted the envelope detection part 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 circuit diagram which shows an example of a drive circuit.

Explanation of symbols

1 Liquid detector 2 Ultrasonic transducer (acoustic excitation means, reverberation detection means)
Ultrasonic beam for SW measurement L Liquid 100 Microcomputer (Liquid presence / absence judging means)
103 Signal processing circuit (liquid presence / absence judging means)
103e Detection circuit 104 Display unit (Liquid presence state information output means)
190 Container 200 Metal side wall

Claims (15)

A container containing a liquid is used as a system to be measured, which is attached to a measurement execution position determined on the outer surface of the wall of the container, and the measurement ultrasonic beam is input to the system to be measured for a predetermined time. Then, an ultrasonic output unit for blocking the input of the ultrasonic beam for measurement,
Reverberation detection means for detecting a damped reverberation vibration waveform after the input of the ultrasonic beam for measurement is used by being attached to the measurement execution position;
Waveform integrating means for integrating the attenuated reverberation vibration waveform;
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 reflected in the integrated waveform;
A liquid presence / absence determination result output means for outputting the determination result;
A liquid detection device comprising:   The liquid presence / absence determining means obtains an attenuation level of the damped reverberation reflected in the integrated waveform when a predetermined time elapses after the input of the measurement ultrasonic beam is cut off, and the attenuation level is The liquid detection apparatus according to claim 1, wherein the liquid is detected when the liquid is less than a predetermined threshold, and the liquid is not detected when the liquid exceeds the threshold.   The liquid presence / absence determining means monitors the attenuation level of the damped reverberation vibration reflected in the integrated waveform, and after the input of the measurement ultrasonic beam is cut off, the attenuation level reaches a predetermined reference level. 2. An attenuation time measuring means for measuring an attenuation time until the liquid is detected, and it is determined that there is no liquid when the attenuation time exceeds a predetermined threshold value, and that there is liquid when the attenuation time is less than the threshold value. Liquid detection device. Envelope detection means for detecting the attenuated reverberation vibration waveform with an envelope,
4. The liquid detection device according to claim 1, wherein the waveform integration unit integrates the waveform after the envelope detection. 5.   The envelope detection means includes a waveform amplification section that amplifies the attenuated reverberation vibration waveform from the reverberation detection means, a half wave rectification section that half-wave rectifies the amplified attenuation reverberation vibration waveform, and the half-wave rectification The liquid detection device according to claim 4, wherein the damped reverberation vibration waveform is configured by a detection circuit having 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. The liquid detection device according to claim 5, wherein the liquid rectification is performed.   The liquid detection device according to claim 6, 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 integrating unit that integrates the amplified output branched from the waveform amplifying unit and the integrated output of the amplified output integrating unit and the envelope detection output from the detection circuit, the branched attenuated reverberation 8. An integration comparison operation unit that outputs an attenuation reflection signal reflecting a vibration attenuation characteristic, and the waveform integration unit performs an integral operation on the attenuation reflection signal. The liquid detection device according to 1.   The liquid detection device according to claim 8, wherein the integration comparison calculation unit outputs a binary comparison result between the integration output and the envelope detection output as the attenuation reflection signal.   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. The liquid detection device according to claim 9.   The liquid detection device according to claim 10, wherein the metal tank contains a liquefied gas as the liquid.   The ultrasonic output unit is capable of outputting a measurement ultrasonic beam to the measurement target system, and is also an ultrasonic transducer capable of receiving reverberation ultrasonic waves from the measurement target system. The liquid detection device according to claim 1, which is also used as a means.   When measurement of the attenuated reverberation vibration is performed by selecting a measurement execution position that is known in advance to be liquid-free on the container, the attenuation level is determined in advance after the measurement ultrasonic beam input is cut off. The liquid detection device according to any one of claims 1 to 12, wherein a frequency of the ultrasonic beam for measurement is set so that an attenuation time until the reference level is reached is maximized.   The liquid detection device according to claim 13, wherein a frequency of the measurement ultrasonic beam can be variably set according to a container to be measured.   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 liquid detection device according to claim 1, wherein the surface position reflection information can be output.

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