JP2004257983A - Ultrasonic level meter and liquid level detection method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make measurable a liquid level even in the case that the location of the liquid level is low without reduction in S/N ratio by changing over the band of a filter in an ultrasonic level meter having an ultrasonic sensor mounted to a bottom plate of a container for transmitting and receiving ultrasonic waves to and from the liquid level in the container. <P>SOLUTION: A control part 10 is connected to the ultrasonic sensor 20, has a variable type BPF 12 and a reverberation margin detection means 18, measures both the time between the activation of the sensor 20 and the reception of reflected echoes from the liquid level and the time from the activation of the sensor 20 until reflected reverberation of the ultrasonic waves at the bottom plate of the container immediately after the activation is reduced to a prescribed level, detects a measured time difference as a reverberation margin, and, while changing over the frequency band of the variable type BPF 12 according to frequency components of the reflected reverberation at the bottom plate of the container in the case that the reverberation margin is of a prescribed value or smaller, adjusts the frequency band in such a way that the detected reverberation margin may take the prescribed value or greater so as to be able to specify the reflected echoes from the liquid level. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ultrasonic level meter and a liquid level detecting method using the level meter, and more specifically, an ultrasonic level for detecting the liquid level of contents such as liquefied gas contained in a container from outside the container. The present invention relates to a liquid level meter and a liquid level detecting method using the level meter.
[0002]
[Prior art]
An ultrasonic level meter that uses a transmission / reception ultrasonic sensor measures the time it takes to transmit an ultrasonic wave from the ultrasonic sensor and receive its reflected wave, and calculates the distance to the target based on that time. Since the distance to the object can be accurately and easily measured, it is used for various purposes. Since the passing frequency band varies depending on the thickness of a container or a storage tank (hereinafter, referred to as a container), several types of ultrasonic sensors having different applicable frequency ranges are prepared, and the thickness of the container is measured. Although an ultrasonic sensor suitable for the range was selected, it was difficult to obtain a mass production effect and to reduce the cost because of the variety of products. Therefore, it is considered possible to avoid diversification by using an ultrasonic sensor having a wide adaptive frequency range to expand the range of the applicable container thickness.
[0003]
However, S / N degradation occurs as a side effect of the wide band of the ultrasonic sensor, and stable liquid level measurement cannot be performed. Depending on the plate thickness, especially when the plate thickness increases, the S / N ratio decreases in a direction in which the reverberation wave level becomes more dominant than the reflected echo level with respect to the selection of the optimum frequency, and simple gain control alone is not sufficient. S / N cannot be secured.
[0004]
Conventionally, as an object detection method using an ultrasonic sensor, when detecting an object with a probe attached to the outer part of the container, it is used for any thickness and material of the container There has been provided an ultrasonic sensor capable of providing a possible versatile ultrasonic sensor. This involves inputting data of the emission waveform and reflection waveform from the probe, detecting the resonance frequency between the piezoelectric element of the probe and the container based on the difference in the attenuation characteristics of the waveform, and detecting at this time. The resonance frequency is registered as an operation frequency. (For example, see Patent Document 1)
[0005]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2000-213979
[0006]
[Problems to be solved by the invention]
The present invention has been made in view of the above-described circumstances. Even when an ultrasonic sensor having a wide frequency band that can be applied to a wide range of plate thicknesses is used, the band of the band-pass filter can be switched to change the S-band. / N is not reduced, stable liquid level detection is possible, and in addition to the band switching of the band-pass filter, the amplification factor of the signal increases with time starting from the drive timing of the ultrasonic sensor. By changing the oscillation time of the pulse signal input to the ultrasonic sensor, the dead band time (distance) that cannot be detected due to reverberation can be adjusted, so that stable reverberation characteristics and sensitivity characteristics can always be realized. The purpose of this is to make it applicable to a wide range of plate thicknesses and to enable liquid level measurement from low to high liquid level positions. There is provided a liquid level detection method using the wave level meter and ultrasonic level meter.
[0007]
[Means for Solving the Problems]
An invention according to claim 1, wherein the ultrasonic sensor is attached to the bottom outer wall surface of the container, transmits an ultrasonic wave toward a liquid surface of the liquid contained in the container, and receives a reflected wave from the liquid surface. An ultrasonic level meter connected to a control unit that controls the liquid level detection operation based on time information from a time point at which an ultrasonic wave is transmitted by the ultrasonic sensor to a time point at which the reflected wave is received, The control unit inputs a signal corresponding to a reflected wave with respect to the ultrasonic wave transmitted by the ultrasonic sensor, and switches a frequency band according to a transmission frequency component transmitted through the bottom plate of the container to thereby control a frequency component of the input signal. A band variable filter capable of selectively extracting the transmission frequency component from the signal; an amplifying unit for amplifying a signal extracted by the band variable filter at a predetermined amplification factor; Echo timing detecting means for detecting a reflected echo signal from the liquid surface from among the signals amplified based on the width factor and detecting an echo timing, and detecting the position of the liquid surface based on the detected echo timing Liquid level detecting means.
[0008]
According to a second aspect of the present invention, in the first aspect, the ultrasonic sensor transmits an ultrasonic wave based on a pulse signal input from the control unit.
[0009]
According to a third aspect of the present invention, in the first or second aspect of the present invention, the control unit transmits the ultrasonic wave from the start of driving the ultrasonic sensor to the reception of a reflected echo from the liquid surface by inputting a pulse signal. Along with measuring the time, measure the driving reverberation time until the reverberation of the ultrasonic wave detected immediately after the driving of the ultrasonic sensor from the start of driving decreases to a predetermined level, and the measured ultrasonic propagation time and the driving reverberation A reverberation margin detecting means for detecting a difference from time as a reverberation margin is provided.
[0010]
According to a fourth aspect of the present invention, in the method of any one of the first to third aspects, when detecting the position of the liquid surface, the reverberation margin detecting means sets a predetermined amplification factor when the ultrasonic sensor is driven. The reverberation margin is detected based on the detected reverberation margin, and when the detected reverberation margin is equal to or less than a predetermined value, the control unit switches the frequency band of the band variable filter according to a frequency component of reverberation at the container bottom plate. The frequency band is adjusted so that the reverberation margin obtained is equal to or larger than the predetermined value and the reflected echo signal from the liquid surface can be specified.
[0011]
According to a fifth aspect of the present invention, in any one of the first to fourth aspects of the present invention, the amplifying means converts an amplification factor of the signal extracted by the band variable filter into a time starting from when the ultrasonic sensor is driven. The amplification factor can be set according to the position of the liquid surface by changing the amplification factor so as to increase accordingly.
[0012]
According to a sixth aspect of the present invention, in the first aspect of the present invention, the control unit changes the oscillation time of the pulse signal by changing the number of pulses or the pulse width of the pulse signal. An ultrasonic sensor driving means for inputting a pulse signal to the ultrasonic sensor according to the oscillation time, wherein the ultrasonic sensor has a driving frequency corresponding to the pulse signal input from the ultrasonic sensor driving means. Ultrasonic waves can be transmitted while changing the driving time.
[0013]
In the invention according to claim 7, in the invention according to any one of claims 3 to 6, when detecting the position of the liquid surface, the reverberation margin detecting means sets a predetermined amplification factor when the ultrasonic sensor is driven. A reverberation margin is detected based on the detected reverberation margin, and when the detected reverberation margin is equal to or smaller than a predetermined value, the amplifying unit reduces the amplification factor at the time of driving the ultrasonic sensor, and determines the reduced amplification factor according to time. And the ultrasonic sensor driving means changes the oscillation time of the pulse signal input to the ultrasonic sensor, and furthermore, the band changes according to the frequency component of the reverberation at the container bottom plate. While switching the frequency band of the variable filter, the amplification factor and the emission rate are set so that the detected reverberation margin is equal to or larger than the predetermined value and the reflected echo signal from the liquid surface can be specified. Time is obtained by and adjusting each any one or more of the frequency bands.
[0014]
The invention according to claim 8 is the invention according to any one of claims 1 to 7, wherein when detecting the liquid level position inside the container, the ultrasonic sensor driving unit changes the oscillation frequency while changing the oscillation frequency. The ultrasonic sensor transmits ultrasonic waves a plurality of times, and the control unit analyzes the state of reverberation at the container bottom plate for each transmitted ultrasonic wave, thereby transmitting the ultrasonic waves on the bottom outer wall surface of the container. A pulse signal for transmitting an ultrasonic wave in a driving frequency band including the detected resonance frequency can be input to the ultrasonic sensor.
[0015]
According to a ninth aspect of the present invention, in the invention according to the eighth aspect, the control unit switches a frequency band of the band variable filter to obtain a frequency including the resonance frequency from a frequency component of a signal input from the ultrasonic sensor. It is characterized in that components can be extracted.
[0016]
An invention according to claim 10, wherein the ultrasonic sensor is attached to the bottom outer wall surface of the container, transmits ultrasonic waves toward the liquid surface of the liquid contained in the container, and receives reflected waves from the liquid surface. An ultrasonic level meter connected with a control unit for controlling the liquid level detection operation based on time information from the time when the ultrasonic sensor transmits the ultrasonic wave to the time when the reflected wave is received is used. In the liquid level detection method, a signal corresponding to a reflected wave with respect to the ultrasonic wave transmitted by the ultrasonic sensor is input, and the frequency band of the band variable filter is switched according to a transmission frequency component transmitted through the bottom plate of the container. An extraction step of selectively extracting the transmission frequency component from a frequency component of the input signal; an amplification step of amplifying the extracted signal at a predetermined amplification factor; An echo timing detecting step of detecting a reflected echo signal from the liquid surface from inside to detect an echo timing, and a liquid surface detecting step of detecting a position of the liquid surface based on the detected echo timing. It is a characteristic.
[0017]
According to an eleventh aspect, in the tenth aspect, an ultrasonic wave is transmitted from the ultrasonic sensor based on a pulse signal input from the control unit.
[0018]
According to a twelfth aspect of the present invention, in accordance with the tenth or eleventh aspect of the present invention, the ultrasonic wave propagation time from when the ultrasonic sensor starts to be driven to when a reflected echo from the liquid surface is received is measured by inputting a pulse signal. Measuring the driving reverberation time until the reverberation of the ultrasonic wave detected immediately after the driving of the ultrasonic sensor from the start of driving decreases to a predetermined level, and calculates the difference between the measured ultrasonic propagation time and the driving reverberation time. It is characterized in that it is detected as a reverberation margin.
[0019]
According to a thirteenth aspect of the present invention, when detecting the position of the liquid level, a reverberation margin is detected based on a predetermined amplification factor when the ultrasonic sensor is driven, and the detected reverberation margin is detected. Is less than or equal to a predetermined value, while switching the frequency band of the band variable filter according to the frequency component of the reverberation at the container bottom plate, the detected reverberation margin is equal to or more than the predetermined value, and the reflection from the liquid surface The frequency band is adjusted so that an echo signal can be specified.
[0020]
According to a fourteenth aspect of the present invention, in any one of the tenth to thirteenth aspects, the amplification factor of the signal extracted by the band variable filter is increased with time starting from when the ultrasonic sensor is driven. The amplification factor can be set in accordance with the position of the liquid surface by changing the value to.
[0021]
According to a fifteenth aspect of the present invention, in any one of the tenth to fourteenth aspects, the number of pulses or the pulse width of the pulse signal is changed to change the oscillation time of the pulse signal. In response, a pulse signal is input to the ultrasonic sensor, and ultrasonic waves can be transmitted from the ultrasonic sensor while changing a driving time at a driving frequency according to the input pulse signal. is there.
[0022]
According to a sixteenth aspect of the present invention, in the method of any one of the twelfth to fifteenth aspects, when detecting the position of the liquid level, the reverberation margin is detected based on a predetermined amplification factor when the ultrasonic sensor is driven. When the detected reverberation margin is equal to or less than a predetermined value, the amplification factor is reduced at the time of driving the ultrasonic sensor, and the reduced amplification factor is changed so as to increase at a predetermined ratio according to time, While changing the oscillation time of the pulse signal input to the ultrasonic sensor, and further switching the frequency band of the band variable filter according to the frequency component of the reverberation in the container bottom plate, the detected reverberation margin is the predetermined value As described above, and adjusting any one or more of the amplification factor, oscillation time, and frequency band so that a reflected echo signal from the liquid surface can be specified. It is obtained by the butterfly.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a view for explaining a configuration example in which an ultrasonic level meter to which the present invention is applied is installed in a container. In the figure, 10 is a controller (control unit), 20 is an ultrasonic sensor (piezoelectric sensor), Reference numeral 21 denotes an ultrasonic wave transmitted from the ultrasonic sensor 20, reference numeral 17 denotes a display unit of the controller 10, reference numeral 30 denotes a storage tank or a container (hereinafter, represented by a container) for storing a liquid such as liquefied gas or kerosene, and reference numeral 31 denotes a liquid surface. . The ultrasonic level meter includes a controller 10 and an ultrasonic sensor 20. The ultrasonic sensor 20 is installed on an outer bottom surface of the container 30 by a magnet (not shown) or the like, and is connected to the controller 10 by a wire. The communication between the ultrasonic sensor 20 and the controller 10 may be configured to be performed via wireless communication. In this case, it is possible to avoid malfunctions due to damage to wiring or intentional disconnection by a third party. Becomes possible. In this example, the case where the liquid level of the liquid inside the container is detected as a detection target will be described as a representative example.However, the target detectable by the ultrasonic level meter is not limited to the liquid level of the liquid. It is also applicable to object detection.
[0024]
In the above-described configuration, for example, when trying to detect the liquid level 31 of the liquid, the operator operates the controller 10 to transmit the ultrasonic waves 21 from the ultrasonic sensor 20, and mainly detects the liquid level 31 at the liquid level 31. The reflected echo returned by reflection is received, and a liquid surface position, that is, a distance to the liquid surface 31 (hereinafter, referred to as a liquid surface distance) is calculated based on the received reflected echo. The liquid volume in the container 30 can be calculated based on this.
[0025]
When detecting the height of the liquid level 31, the ultrasonic sensor 20 transmits ultrasonic waves upward toward the bottom wall of the container 30. The transmitted ultrasonic wave is reflected by the liquid surface 31 and returns, but the delay time until the ultrasonic sensor 20 receives the reflected wave differs according to the height of the liquid surface 31. The controller 10 holds data for calculating the liquid level distance from the delay time of the received reflected wave, for example, sound speed data or the like corresponding to a temperature or a propagation medium (air or liquid, etc.), and based on this data. Calculate the liquid surface distance.
[0026]
Here, in the case where the bottom wall of the container 30 is, for example, an iron plate, when the ultrasonic sensor 20 is attached to the iron plate, as the thickness of the iron plate increases, the reverberation occurs due to the influence of sound waves reflected at the boundary of the iron plate. The characteristics become remarkable, thereby lowering the minimum detection distance margin, which makes it difficult to perform stable liquid level detection especially on the short distance side. In addition, the approach of the transmission frequency solution of the iron plate due to the increase in the plate thickness, and at the same time, the frequency solution reflected at the boundary of the iron plate also increases and approaches, so that the boundary between the free vibration region due to the reverberation wave of the ultrasonic sensor and the above-mentioned boundary. The echoes reflected at the same time overlap, resulting in apparently large reverberation characteristics. The ultrasonic level meter of the present invention does not lower the S / N by switching the band of the band-pass filter, even when using an ultrasonic sensor having a wide frequency band applicable to a wide range of plate thicknesses. And a band-pass band-pass filter for attenuating reverberation waves on the short distance side where the liquid level is low and obtaining an effect as a band filter in a region required as a received signal.
[0027]
In addition, due to the acoustic coupling between the ultrasonic sensor 20 and the iron plate, the vibration state of the sensor vibration system including the iron plate, that is, the state of free vibration due to reverberation waves changes from the relationship between the sensor resonance frequency band and the transmission frequency spectrum of the iron plate. Resulting in. For this reason, when measuring the liquid level when the liquid level is low, the reflected wave from the liquid level may overlap with free vibration, that is, overlap with the reverberation wave. In such a case, a dead band time (distance) occurs in which the reflected wave cannot be captured and the liquid level distance cannot be measured. The ultrasonic level meter of the present invention can reduce the influence of reverberation waves and maintain the sensitivity required for receiving reflected echoes, enabling liquid level measurement from low to high liquid level positions. Is what you do.
[0028]
FIG. 2 is a diagram showing an example of a circuit configuration of the ultrasonic level meter of the present invention. The controller 10 of the present ultrasonic level meter includes a receiving circuit 11, a variable band-pass filter (hereinafter, referred to as a variable BPF) 12, an amplifying unit 13, a detection circuit 14, an echo timing detecting unit 15, a liquid level detecting unit 16, It has a unit 17, reverberation margin detecting means 18, ultrasonic sensor driving means 19, and a CPU (not shown). The ultrasonic sensor 20 transmits an ultrasonic wave based on a pulse signal input from the controller 10, and the pulse signal is desirably a rectangular wave pulse signal including all frequency components. Even when the thickness and the material change, it is possible to respond. In the present embodiment, the receiving circuit 11 and the variable BPF 12 are illustrated separately, but the variable BPF 12 may be physically included in the receiving circuit 11.
[0029]
Hereinafter, the operation of the controller 10 will be described in detail.
The variable BPF 12 inputs a signal corresponding to a reflected wave with respect to the ultrasonic wave transmitted by the ultrasonic sensor 20, and switches a frequency band according to a transmission frequency component transmitted through the bottom plate of the container 30, thereby changing the frequency of the input signal. The transmission frequency component can be selectively extracted from the frequency component. For example, in a state where the ultrasonic sensor 20 is attached to the bottom iron plate of the container 30, constants for obtaining an attenuation effect due to the transient response of the LC filter shown in FIG. By appropriately switching the filters, reverberation characteristics and reflection sensitivity characteristics are made compatible in all frequency bands according to a predetermined range of plate thickness.
[0030]
FIG. 3 is a diagram illustrating a circuit configuration example of the variable BPF 12 according to a predetermined plate thickness range to which the present invention is applied. The variable BPF 12 includes a switching unit 12a. The variable BPF 12 according to the present embodiment has three types of frequency bands corresponding to a plate thickness of about 4.5 mm to 15 mm: 650 to 850 kHz (filter A), 800 to 1050 kHz (filter B), and 1000 to 1300 kHz (filter C). To be used after being appropriately switched. In this case, by using a photo moss having a capacitance value of 100 P or less when the switching unit 12a is OFF, a wide band characteristic can be realized without impairing the band. Further, by turning on the photo moss at the same time, it is also possible to design to widen the band in a higher order depending on the capacitance value, and it is possible to realize a wider band by a combination.
[0031]
As described above, the variable BPF 12 allocates a constant for obtaining an attenuation effect due to the transient response of the LC filter to three types of frequency bands, and achieves both reverberation characteristics and reflection sensitivity characteristics over the entire frequency band according to the plate thickness. Can be done. Based on the bottom plate thickness of the container 30, the controller 10 controls the variable BPF 12 for a band where the reverberation level becomes maximum in relation to the resonance frequency of the ultrasonic sensor 20 and the plate thickness natural frequency actually transmitted. Switch to have a large damping effect. Further, based on the range of the plate thickness and the absolute value level of reverberation, switching of the variable BPFs 12 is suppressed to the minimum number and combined. In the case of the above-mentioned thickness range (about 4.5 to 15 mm), switching is performed in a minimum of three steps. Thus, high-speed stability can be improved by minimizing the number of switching.
[0032]
The amplification unit 13 amplifies a signal corresponding to the frequency component extracted by the variable BPF 12 at a predetermined amplification factor. The echo timing detecting means 15 specifies the echo signal reflected from the liquid surface 31 based on the amplification factor set in the amplifying means 13 and detects the echo timing. The liquid level detecting means 16 detects the position of the liquid level 31 based on the echo timing detected by the echo timing detecting means 15.
[0033]
The reverberation margin detecting means 18 measures the ultrasonic propagation time from the time when the ultrasonic sensor 20 is driven to the time when the reflected echo from the liquid surface 31 is received by the input of the pulse signal, and the time when the ultrasonic sensor 20 is driven. The reverberation of the ultrasonic wave detected immediately after the driving, that is, the reverberation caused by the reflected wave at the bottom plate of the container 30, or the reverberation caused by self-vibration due to inertia after the driving is stopped, etc. The driving reverberation time until the reduction is measured, and the difference between the measured ultrasonic propagation time and the driving reverberation time is detected as a reverberation margin.
[0034]
The ultrasonic sensor driving unit 19 changes the oscillation time of the pulse signal by changing the number of pulses or the pulse width of the pulse signal, and inputs the pulse signal to the ultrasonic sensor 20 according to the changed oscillation time. Can be. The ultrasonic sensor 20 can transmit ultrasonic waves while changing the driving time at a driving frequency corresponding to the pulse signal input from the ultrasonic sensor driving unit 19. In this case, the ultrasonic sensor driving unit 19 outputs a pulse signal corresponding to each oscillation frequency within a range of the oscillation frequency including the resonance frequency of the container 30 and the ultrasonic sensor 20 from, for example, 50 μs to a maximum of 100 μm every 5 μs. You may make it input into the ultrasonic sensor 20.
[0035]
Here, in order to improve the transmittance of the ultrasonic waves with respect to the plate thickness of the container 30, the driving frequency of the ultrasonic waves transmitted from the ultrasonic sensor 20 is optimized according to the plate thickness and the material of the container 30, that is, resonance. It is necessary to set to drive the ultrasonic sensor 20 at the frequency. Normally, the ultrasonic sensor 20 and the driving frequency are customized according to the container 30, so that the ultrasonic sensor 20 is optimally driven at the resonance frequency. However, when the driving frequency of the ultrasonic sensor 20 is variable, the resonance frequency of the container 30 and the ultrasonic sensor 20 is obtained when the ultrasonic sensor is mounted on the container, and the resonance frequency is determined by the driving frequency of the ultrasonic sensor 20. You may make it set as. In this case, the ultrasonic sensor driving means 19 causes the ultrasonic sensor 20 to transmit ultrasonic waves a plurality of times while changing the oscillation frequency of the pulse signal, and analyzes the state of reverberation of each transmitted ultrasonic wave, thereby A resonance frequency suitable for transmitting ultrasonic waves through the bottom outer wall surface of the bottom 30 is detected, and a pulse signal for transmitting ultrasonic waves in a drive frequency band including the detected resonance frequency is input to the ultrasonic sensor 20. As an example of a technique for analyzing the state of the reverberation, the degree of attenuation of reverberation differs between resonance and non-resonance, and the resonance frequency can be detected by looking at this degree of attenuation.
[0036]
Usually, the resonance frequency is a unique value of the material, and can be obtained from the thickness and material of the container 30. However, the connection between the ultrasonic sensor 20 and the container 30 is generally performed with grease or the like. In this case, the matching layer of the ultrasonic sensor 20 and the container 30 are ideally connected, and thus the ultrasonic sensor 20 and the container 30 are connected. 30 will be the resonance frequency. Therefore, the resonance frequency does not always match the resonance frequency of the container 30. Therefore, if the coupling between the ultrasonic sensor 20 and the container 30 is made of a resin material (silicon sheet), the influence of the coupling between the ultrasonic sensor 20 and the container 30 is small, and the ultrasonic sensor 20 may be driven at the resonance frequency of the container 30. The resonance frequency can be easily obtained.
In addition, when the material of the container 30 is known, the thickness of the container 30 can be calculated by back calculation. For example, as described above, when the liquid level is converted into the remaining amount and displayed. In addition to obtaining the volume of the container 30 from the dimensions of the container 30, the volume of the container 30 can be obtained in consideration of the thickness information. The quantity can be determined.
[0037]
The display unit 17 displays information on the liquid level detected by the liquid level detecting unit 16.
[0038]
Here, when detecting the distance to the liquid surface 31, the reverberation margin detecting means 18 determines the reverberation margin based on a predetermined amplification factor (at the time of previous setting or at the time of initial setting) when the ultrasonic sensor 20 is driven. When the detected reverberation margin is equal to or smaller than the predetermined value, the controller 10 switches the frequency band of the variable BPF 12 according to the frequency component of the reverberation at the bottom plate of the container 30 while maintaining the detected reverberation margin at the predetermined value. As described above, the frequency band is adjusted so that the reflected echo signal from the liquid surface 31 can be specified.
[0039]
According to the present invention, even when a broadband ultrasonic sensor is used, only a transmission frequency component corresponding to the thickness of the container bottom plate can be extracted, so that unnecessary noise can be removed.
Further, by configuring the band variable BPF with a simple circuit including a relatively inexpensive LC filter circuit and a switch element, cost performance can be improved.
Further, since a sufficient S / N can be ensured as compared with the case of using the narrow band sensor, it is possible to reduce power consumption while securing a sufficient S / N when driving the ultrasonic sensor. As a result, a small-capacity battery can be used, and the life can be extended.
[0040]
FIG. 4 is a diagram showing another example of the circuit configuration of the ultrasonic level meter of the present invention. The controller 10 of the ultrasonic level meter according to the present embodiment includes a receiving circuit 11, a variable BPF 12, a time-varying characteristic amplifying unit 13a, a time-varying characteristic correcting unit 13b, a detecting circuit 14, an echo timing detecting unit 15, and a liquid level detecting unit 16. , A display unit 17, a reverberation margin detecting unit 18, an ultrasonic sensor driving unit 19, and a CPU (not shown). The ultrasonic sensor 20 transmits an ultrasonic wave based on a pulse signal input from the controller 10, and the pulse signal is desirably a rectangular wave pulse signal including all frequency components. Even when the thickness and the material change, it is possible to respond. In the present embodiment, the receiving circuit 11 and the variable BPF 12 are illustrated separately, but the variable BPF 12 may be physically included in the receiving circuit 11.
[0041]
The difference between the circuit configuration of the controller 10 in the present embodiment and the circuit configuration of the controller 10 shown in FIG. 1 is that a time-varying characteristic amplifying unit 13a and a time-varying characteristic correcting unit 13b are provided instead of the amplifying unit 13. It is. Therefore, the other units are the same, and the description is omitted here.
The time-varying characteristic amplifying unit 13a and the time-varying characteristic correcting unit 13b input a signal corresponding to a reflected wave of the ultrasonic wave transmitted by the ultrasonic sensor 20, and determine the amplification factor of the input signal when the ultrasonic sensor 20 is driven. By changing the starting point so as to increase with time, the amplification factor is adjusted according to the position of the liquid surface 31 and the adjustment value is set. The ultrasonic level meter according to the present embodiment controls the time-varying characteristic amplifying unit 13a, the time-varying characteristic correcting unit 13b, the ultrasonic sensor driving unit 19, and the variable BPF 12, and controls the reverberation characteristic and the reflection sensitivity stably. It realizes the characteristics and enables the liquid level measurement even when the liquid level is low.
[0042]
Here, when calculating the distance to the liquid surface 31, the reverberation margin detecting means 18 calculates the reverberation margin based on a predetermined amplification factor (at the time of previous setting or at the time of initial setting) when the ultrasonic sensor 20 is driven. If the detected reverberation margin is equal to or smaller than a predetermined value, the time-varying characteristic amplifying unit 13a and the time-varying characteristic correcting unit 13b reduce the amplification factor at the time of driving the ultrasonic sensor 20, and reduce the reduced amplification factor over time. In such a manner as to increase at a predetermined rate. At this time, the ultrasonic sensor driving means 19 changes the oscillation time of the pulse signal input to the ultrasonic sensor 20. Further, the frequency band of the variable BPF 12 is switched according to the frequency component of the reverberation at the bottom plate of the container 30. Conditions for changing the amplification factor and the oscillation time can be arbitrarily set, and the oscillation time may be fixed and the amplification factor may be changed. The controller 10 adjusts one or more of the amplification factor, the oscillation time, and the frequency band so that the detected reverberation margin is equal to or larger than the predetermined value and the reflected echo signal from the liquid surface 31 can be specified. .
[0043]
Hereinafter, the adjustment of the amplification factor and the oscillation time will be specifically described with reference to FIG.
In the time-varying characteristic amplifying means 13a and the time-varying characteristic correcting means 13b shown in FIG. 4, the AMP circuit of the transistor Q1 includes the emitter resistor R10 of the first-stage AMP and the emitter resistor R10 including the coupling C7 in the first-stage base. When the ring C7 is appropriately adjusted to give a time dead zone time (distance) based on the time constant of the first-stage AMP, and when the delay time of the reflected wave is short (for a short distance), the transistor Q2 does not operate completely. AMP gain is changed with respect to time (distance). Thus, the ultrasonic level meter of the present invention can achieve both reverberation characteristics and sensitivity characteristics.
[0044]
In the time-varying characteristic amplifying means 13a, a voltage of 1.0 V is applied as a DC bias voltage of the transistor Q2, and a voltage between the terminal: TEST1 and the ground, that is, the voltage after passing through the variable BPF 12 by the bidirectional diode D1 on the input side. Since the level is clamped to ± (0.6 to 0.7) V, the current flowing into or out of the capacitor C1 changes. At this time, the base bias potential of the transistor Q2 periodically changes in a range of about 0.3 to 1.7 V according to the driving frequency. The time constant of the capacitor C7 differs depending on the magnitude relationship between the impedance of the transistor Q2 and the impedance of the diode D1, and the time constant of the transistor Q2 is long. To a lower potential.
[0045]
Until the sensor is driven by the forced vibration due to the driving of the ultrasonic sensor 20, a low bias is applied to the capacitor C7 in this cycle, the electric charge is charged, and when the forced vibration ends, the same bias is applied in the cycle of the free vibration of the circuit. Even if the potential on the diode D1 side converges to 0 V, the transistor Q2 is low biased for a while due to the input impedance of the transistor Q2 side and the time constant of the capacitor C7 while the change is biased. Converges to 0.0V. During this period, the signal amplification factor with respect to time can be gradually increased with respect to the liquid level due to the bias gradient at which the low bias potential with respect to 1.0 V returns with time.
[0046]
The time-varying characteristic correction means 13b determines the delicate gain gradient by arbitrarily determining the number of resistors and the resistance value of the emitter resistor with respect to the main resistor R10 as resistors R11, R12, R13,. Can be given. Further, instead of switching the capacitor C7, the switch S7 may be used by switching to the capacitor C8 and the resistor R14. In this case, the range of the gain gradient can be further expanded. At this time, the switches S4, S5, S6,... Are switched by a signal from a CPU (not shown).
[0047]
Here, the reflection from the liquid surface 31 is based on the amplification factor and / or the oscillation time of the pulse signal adjusted by the time-varying characteristic amplifying unit 13a and the time-varying characteristic correcting unit 13b and the frequency band switched by the variable BPF 12. After specifying the echo signal and measuring the ultrasonic propagation time according to the specified reflected echo signal, the liquid level detecting means 16 calculates and calculates the distance from the measured ultrasonic transmission time to the liquid level 31. The calculated distance value is displayed on the display unit 17. At this time, the liquid level detecting means 16 can calculate the volume of the liquid stored in the container 30 based on the calculated distance calculation value, and displays the calculated volume of the liquid on the display unit 17 as liquid volume information. You may do so.
[0048]
At the reverberation level and sensitivity level based on the amplification factor, oscillation time, and frequency band adjusted as described above, for example, the operation from transmitting the ultrasonic wave from the ultrasonic sensor 20 to receiving the reflected echo signal is described. The distance calculation value at that time may be output when a predetermined number of times are performed, and when it is confirmed that there is no variation in the measured ultrasonic propagation times and the average value thereof is within the allowable value. . At this time, if the average value does not fall within the allowable value, one or more of the amplification factor, the oscillation time, and the frequency band are repeatedly adjusted to adjust the reverberation level and the sensitivity level again.
[0049]
FIG. 5 is a diagram showing a characteristic curve in the relationship between the frequency band of the ultrasonic sensor 20 and the bottom plate thickness of the container 30. Reference numeral 41 denotes a filter C, 43 denotes a filter B, and 45 denotes a filter A. In this example, the applicable frequency band of the ultrasonic sensor 20 is 880 to 1350 kHz, and three stages of filters are prepared for this frequency band.
These three types of filters are referred to as filter C, filter B, and filter A, respectively. Reference numeral 42 denotes a band in which the filter C (41) and the filter B (43) overlap, and reference numeral 44 denotes a band in which the filter B (43) and the filter A (45) overlap.
[0050]
As described above, it has been difficult heretofore to secure a reflection sensitivity equal to or higher than a required level and control the minimum detection distance to a predetermined level or lower (for example, 100 mm or lower).
This is because the frequency solution increases as the bottom plate thickness of the container 30 increases, and the interval between the solutions decreases. At the same time, the reverberation characteristics become remarkable due to the influence of the ultrasonic waves reflected at the bottom boundary of the container 30, and this influence reduces the minimum detection distance margin, that is, the reverberation margin. As a result, it has been difficult to perform stable liquid level detection when the liquid level is low.
[0051]
Therefore, the three types of filters A, B, and C are appropriately switched. For example, the reverberation margin decreases at a thickness of about 9.0 mm. A frequency band is divided into two parts around the vicinity of the sensor anti-resonance frequency, and a sufficient attenuation characteristic can be obtained by adapting the transmission frequency band transmitting through the bottom of the container 30 and the LC filter in response to the ultrasonic wave. Thus, the mode is switched to either the filter B (43) or the filter C (41). As a result, reverberation waves due to an increase in the bottom plate thickness of the container 30 can be reduced, and stable reflection sensitivity characteristics can be controlled. At this time, since the sensitivity characteristic is emphasized in selecting the filter B (43) or the filter C (41) at the frequency band boundary, the reverberation characteristic is secured without impairing the short-range sensitivity by adjusting the time constant of the first-stage AMP. Adjust to a frequency band that can be used.
[0052]
Basically, the filter is switched to the filter C (41) or the filter A (45) based on the filter B (43). Since the variable BPF 12 can select an optimal filter based on frequency information, By combining the time-varying characteristic amplifying unit 13a and the time-varying characteristic correcting unit 13b based on the information and the current liquid level position information, the optimal adjustment value for an arbitrary liquid level, that is, the optimal frequency band , Can be adjusted to the amplification factor.
[0053]
FIG. 6 is a waveform diagram showing an example of a voltage waveform with respect to time in the ultrasonic level meter of the present invention. In FIG. 6, reference numeral 51 denotes a collector output waveform, and 52 denotes a reflected wave waveform. This example will be described based on the circuit configuration shown in FIG. In the reflected wave waveform 52 based on the collector output waveform 51 shown in FIG. 6A, the result of coping with the increase in the reverberation level due to the increase in the plate thickness by switching the variable BPF 12 is shown. It can be seen that the reverberation level is large. Further, FIG. 6B shows the state of the collector output waveform 51 after changing the gain gradient by changing the emitter resistance in the collector output waveform 51 shown in FIG. 6A and changing the gain gradient. It can be seen that the reverberation of the reflected wave waveform 52 can be reduced in accordance with the change in the gain gradient.
[0054]
FIG. 7 is a waveform diagram showing another example of a voltage waveform with respect to time in the ultrasonic level meter of the present invention. In FIG. 7, reference numeral 53 denotes a reflected wave waveform. This example will be described based on the circuit configuration shown in FIG. From the reflected wave waveform 53 shown in FIG. 7A, in the natural frequency solution on the low frequency side by switching the frequency band of the variable BPF 12, when the wideband ultrasonic sensor 20 is used, the reverberation is affected by the high frequency solution. Will occur. Therefore, as shown in FIG. 7B, the filter of the variable BPF 12 is switched to converge to the center of the band of the ultrasonic sensor 20 (around about 1070 kHz), thereby suppressing the occurrence of reverberation.
[0055]
FIG. 8 is a flowchart illustrating an example of a liquid level detection method using an ultrasonic level meter to which the present invention is applied. In this example, the flow of the filter switching process of the variable BPF 12 will be described based on the circuit configuration shown in FIG. First, the ultrasonic sensor 20 and the controller 10 are installed in the container 30, and initialization is performed in the controller 10 (step S1). Next, a pulse signal is input from the controller 10 to the ultrasonic sensor 20 to drive the ultrasonic sensor 20 (step S2), and the waveform of a reflected wave (reflected echo) with respect to the ultrasonic wave transmitted from the ultrasonic sensor 20 is detected. Then, the echo timing is measured based on the ultrasonic wave propagation time until the detected reflected wave is received (step S4). Next, the reverberation state when the ultrasonic sensor 20 is driven is checked (step S5). If there is no problem with the reverberation state (OK), that is, if the reverberation margin is equal to or more than a predetermined value, the liquid level detection value (liquid level) The distance is output (step S7), and the process shifts to a standby state for the liquid level detection request (step S8).
[0056]
If there is a problem in the reverberation state (NG) in step S5, a filter switching process is performed (step S6), and the result is returned to step S1 and set in the controller 10. Here, in step S6, as the filter switching process, for example, in the case of the filter characteristics shown in FIG. 5, the filter B (43) → the filter A (45), the filter B (43) → the filter C (41) Are switched.
[0057]
FIG. 9 is a flowchart for explaining another example of the liquid level detection method using the ultrasonic level meter to which the present invention is applied. In this example, the flow of the time-varying characteristic correction processing and the filter switching processing will be described based on the circuit configuration shown in FIG. First, the ultrasonic sensor 20 and the controller 10 are installed in the container 30, and initialization is performed in the controller 10 (step S11). Next, a pulse signal is input from the controller 10 to the ultrasonic sensor 20 to drive the ultrasonic sensor 20 (step S12), and the waveform of a reflected wave (reflected echo) with respect to the ultrasonic wave transmitted from the ultrasonic sensor 20 is detected. Then, the echo timing is measured based on the ultrasonic wave propagation time until the detected reflected wave is received (step S13). Next, the reverberation state when the ultrasonic sensor 20 is driven is checked (step S15). If there is no problem in the reverberation state (OK), that is, if the reverberation margin is equal to or more than a predetermined value, the liquid level detection value (liquid level) The distance is output (step S17), and the process shifts to a standby state for a liquid level detection request (step S18).
[0058]
In step S15, when there is a problem in the reverberation state (in the case of NG), time-varying characteristic correction processing and filter switching processing are performed (step S16), and the result returns to step S11 and is set in the controller 10. Here, in step S16, the following processes (1), (2), and (3) are appropriately combined as the time-varying characteristic correction process and the filter switching process.
(1) AMP gain is switched. This is performed, for example, by switching in the order of the switches S4 → S5 → S6 → S7 → (S4) → shown in FIG.
(2) Change the sensor drive time (tn). This is performed by sequentially switching, for example, tn (unit: μs) = 50 → 55 → 60 → 65 → (maximum 100).
(3) In the case of the filter characteristics shown in FIG. 5 described above, two types of switching are performed: filter B (43) → filter A (45), filter B (43) → filter C (41).
[0059]
FIG. 10 is a flowchart for explaining another example of the liquid level detection method using the ultrasonic level meter to which the present invention is applied. FIG. 10A is a processing flow shown in FIG. 9 described above. Is described in detail. FIG. 11 is a diagram illustrating an output waveform and a gain gradient change parameter corresponding to the processing flow illustrated in FIG. In FIG. 10A, first, a sensor drive burst pulse time to be input to the ultrasonic sensor 20 is set (step S21). At this time, the sensor drive frequency variable Vco is operated. Further, the comparator level for peak search is set to the comparator level (1) shown in FIG. 11B, the AMP gain is set to the switch S4 in the circuit configuration shown in FIG. Is set to the filter B (43) shown in FIG. Next, based on the conditions set in step S21, the ultrasonic sensor 20 transmits the ultrasonic wave, performs the analysis processing / statistical processing of the reflected echo with respect to the ultrasonic wave, and performs the peak voltage equal to or higher than the comparator level (1). (Step S22).
[0060]
As a result of the search for the reflected echo in step S22, the reflected echo having a peak voltage equal to or higher than the comparator level (1) is determined as the first reflected echo, that is, the liquid surface distance is determined (step S23). The comparator level is set to the comparator level (2) shown in FIG. 11B (step S24). Next, a reverberation margin, that is, a minimum detection distance is determined based on the comparator level (1) and the comparator level (2). The reverberation margin is a portion circled by a dotted line shown in FIG. Next, it is checked whether or not the reverberation margin is equal to or greater than a predetermined value (step S25). If the reverberation margin is equal to or greater than a predetermined value (OK), the measured liquid level distance determined in step S23 is output (step S29). ).
[0061]
If the reverberation margin is equal to or smaller than a predetermined value (NG) in step S25, in step S26,
(1) AMP gain is switched. This is performed, for example, by switching in the order of the switches S4 → S5 → S6 → S7 → (S4) → shown in FIG.
(2) Change the sensor drive time (tn). This is performed by, for example, switching from tn (unit: μs) = 50 → 55 → 60 → 65 → (maximum 100).
(3) In the case of the filter characteristics shown in FIG. 5 described above, two types of switching are performed: filter B (43) → filter A (45), filter B (43) → filter C (41).
The gain gradient change parameter at this time is shown in FIG. FIG. 11D is a diagram showing a waveform when tn = 55 shown in FIG. 11C and the switch S7 is set as a parameter, and the reverberation margin is larger than the waveform shown in FIG. 11B. It can be seen that the reverberation is reduced. By adjusting the gain, the sensor drive time (tn), and the filter in accordance with the gain gradient change parameter, the optimum value of the gain (AMP gain) is set and the sensor drive time (tn) is set ( Step S27).
[0062]
Based on the measurement conditions set in step S27, the ultrasonic sensor 20 is driven to detect the waveform and detect the echo timing. Then, the sensitivity and reverberation level of the acquired reflected echo are confirmed (step S28), and the sensitivity and reverberation are determined. If there is no problem with the level (in the case of OK), the liquid surface distance measurement value calculated based on the echo timing is output (step S29). If there is a problem in the sensitivity and reverberation level of the reflected echo in step S28 (in the case of NG), the process returns to step S26, and the time-varying characteristic correction processing and the filter switching processing are repeatedly performed.
[0063]
【The invention's effect】
According to the present invention, even when an ultrasonic sensor having a wide frequency band applicable to a wide range of plate thicknesses is used, S / N is not reduced by switching the band of the band-pass filter, and stable liquid level detection is performed. Is possible.
Further, in addition to the band switching of the band-pass filter, the driving timing of the ultrasonic sensor is used as a starting point to change the amplification factor of the signal according to time so as to increase, and the oscillation time of the pulse signal input to the ultrasonic sensor is changed. By changing them, the dead zone time (distance) that cannot be detected due to reverberation can be adjusted, and always stable reverberation characteristics and sensitivity characteristics can be realized.
In addition, it is possible to provide an ultrasonic level meter that can be applied to a wide range of container plate thicknesses and that can measure the liquid level from a low level to a high level.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining a configuration example in which an ultrasonic level meter to which the present invention is applied is installed in a container.
FIG. 2 is a diagram showing a circuit configuration example of an ultrasonic level meter of the present invention.
FIG. 3 is a diagram illustrating a circuit configuration example of a variable BPF according to a predetermined plate thickness range to which the present invention is applied.
FIG. 4 is a diagram showing another example of the circuit configuration of the ultrasonic level meter of the present invention.
FIG. 5 is a diagram showing a characteristic curve in a relationship between a frequency band of an ultrasonic sensor and a bottom plate thickness of a container.
FIG. 6 is a waveform diagram showing an example of a voltage waveform with respect to time in the ultrasonic level meter of the present invention.
FIG. 7 is a waveform diagram showing another example of a voltage waveform with respect to time in the ultrasonic level meter of the present invention.
FIG. 8 is a flowchart illustrating an example of a liquid level detection method using an ultrasonic level meter to which the present invention is applied.
FIG. 9 is a flowchart for explaining another example of the liquid level detection method using the ultrasonic level meter to which the present invention is applied.
FIG. 10 is a flowchart for explaining another example of the liquid level detection method using the ultrasonic level meter to which the present invention is applied.
FIG. 11 is a diagram illustrating an output waveform and a gain gradient change parameter corresponding to the processing flow illustrated in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Controller (control part), 11 ... Reception circuit, 12 ... Variable BPF, 12a ... Switching part, 13 ... Amplification means, 13a ... Time-varying characteristic amplifying means, 13b ... Time-varying characteristic correction means, 14 ... Detection circuit, 15: echo timing detecting means, 16: liquid level detecting means, 17: display unit, 18: reverberation margin detecting means, 19: ultrasonic sensor driving means, 20: ultrasonic sensor (piezoelectric sensor), 21: ultrasonic wave, 30 ... Container, 31 ... Liquid level, 41 ... Filter C, 43 ... Filter B, 45 ... Filter A, 42, 44 ... Overlap band, 51 ... Collector output waveform, 52, 53 ... Reflected wave waveform.

Claims (16)

An ultrasonic sensor attached to the bottom outer wall surface of the container and transmitting an ultrasonic wave toward the liquid surface of the liquid contained in the container and receiving a reflected wave from the liquid surface, and an ultrasonic sensor In the ultrasonic level meter connected with a control unit that controls the detection operation of the liquid level based on time information from the time when the sound wave is transmitted to the time when the reflected wave is received, the control unit includes the ultrasonic wave A signal corresponding to a reflected wave with respect to the ultrasonic wave transmitted by the sensor is input, and the transmission frequency component is selected from the frequency components of the input signal by switching a frequency band according to a transmission frequency component transmitted through the bottom plate of the container. Band variable filter that can be extracted automatically, amplification means for amplifying a signal extracted by the band variable filter at a predetermined amplification rate, and amplification based on the amplification rate of the amplification means Echo timing detection means for detecting an echo timing by specifying a reflected echo signal from the liquid surface from among the detected signals, and liquid level detection means for detecting a position of the liquid surface based on the detected echo timing. An ultrasonic level meter, comprising: 2. The ultrasonic level meter according to claim 1, wherein the ultrasonic sensor transmits an ultrasonic wave based on a pulse signal input from the control unit. 3. 3. The ultrasonic level meter according to claim 1, wherein the control unit determines an ultrasonic propagation time from a drive start time of the ultrasonic sensor to a reception of a reflected echo from the liquid surface by input of a pulse signal. 4. Along with the measurement, the drive reverberation time until the reverberation of the ultrasonic wave detected immediately after the drive from the drive start time of the ultrasonic sensor is reduced to a predetermined level is measured, and the measured ultrasonic propagation time and drive reverberation time are measured. An ultrasonic level meter having reverberation margin detecting means for detecting a difference in the reverberation margin as a reverberation margin. 4. The ultrasonic level meter according to claim 1, wherein, when detecting the position of the liquid surface, the reverberation margin detecting unit is configured to detect a position of the liquid level based on a predetermined amplification factor when the ultrasonic sensor is driven. 5. When the reverberation margin is detected and the detected reverberation margin is equal to or less than a predetermined value, the control unit switches the frequency band of the band variable filter according to the frequency component of the reverberation at the container bottom plate, and performs the reverberation detection. An ultrasonic level meter, wherein the frequency band is adjusted so that a margin is equal to or more than the predetermined value and a reflected echo signal from the liquid surface can be specified. 5. The ultrasonic level meter according to claim 1, wherein the amplifying unit determines an amplification factor of a signal extracted by the band variable filter according to time starting from when the ultrasonic sensor is driven. 6. An ultrasonic level meter, wherein an amplification factor according to the position of the liquid surface can be set by changing the level so as to increase. 6. The ultrasonic level meter according to claim 1, wherein the control unit changes the oscillation time of the pulse signal by changing the number of pulses or the pulse width of the pulse signal. Ultrasonic sensor driving means for inputting a pulse signal to the ultrasonic sensor according to the oscillation time, wherein the ultrasonic sensor has a driving time at a driving frequency corresponding to the pulse signal input from the ultrasonic sensor driving means. An ultrasonic level meter characterized in that an ultrasonic wave can be transmitted while changing the level. The ultrasonic level meter according to any one of claims 3 to 6, wherein, when detecting the position of the liquid surface, the reverberation margin detecting means is configured to perform the operation based on a predetermined amplification factor when the ultrasonic sensor is driven. A reverberation margin is detected, and when the detected reverberation margin is equal to or less than a predetermined value, the amplifying unit reduces the amplification factor at the time of driving the ultrasonic sensor, and sets the reduced amplification factor to a predetermined ratio according to time. And the ultrasonic sensor driving means changes the oscillation time of the pulse signal input to the ultrasonic sensor, and furthermore, the band variable filter according to the reverberation frequency component at the container bottom plate. While switching the frequency band, the detected reverberation margin is equal to or larger than the predetermined value, and the amplification factor and the oscillation are set so that the reflected echo signal from the liquid surface can be specified. During ultrasonic level meter and adjusting each any one or more of the frequency bands. The ultrasonic level meter according to any one of claims 1 to 7, wherein the ultrasonic sensor driving unit changes an oscillation frequency when detecting a liquid level position inside the container. The ultrasonic wave is transmitted a plurality of times, and the control unit analyzes the state of reverberation at the container bottom plate for each transmitted ultrasonic wave, so that the ultrasonic wave is suitable for transmission of ultrasonic waves on the bottom outer wall surface of the container. An ultrasonic level meter, wherein a resonance frequency is detected and a pulse signal for transmitting an ultrasonic wave in a driving frequency band including the detected resonance frequency can be input to the ultrasonic sensor. 9. The ultrasonic level meter according to claim 8, wherein the control unit switches a frequency band of the band variable filter to convert a frequency component including the resonance frequency from a frequency component of a signal input from the ultrasonic sensor. An ultrasonic level meter characterized in that it can be extracted. An ultrasonic sensor attached to the bottom outer wall surface of the container and transmitting an ultrasonic wave toward the liquid surface of the liquid contained in the container and receiving a reflected wave from the liquid surface, and an ultrasonic sensor A liquid level detection method using an ultrasonic level meter connected to a control unit that controls the liquid level detection operation based on time information from the time when the sound wave is transmitted to the time when the reflected wave is received, A signal corresponding to a reflected wave with respect to the ultrasonic wave transmitted by the ultrasonic sensor is input, and a frequency band of the band variable filter is switched according to a transmission frequency component transmitted through the bottom plate of the container. An extraction step of selectively extracting the transmission frequency component; an amplification step of amplifying the extracted signal at a predetermined amplification factor; and, from among the amplified signals, An ultrasonic level meter comprising: an echo timing detecting step of detecting a reflected echo signal to detect an echo timing; and a liquid level detecting step of detecting a position of the liquid level based on the detected echo timing. Liquid level detection method using The liquid level detecting method using the ultrasonic level meter according to claim 10, wherein the ultrasonic sensor transmits ultrasonic waves based on a pulse signal input from the control unit. Liquid level detection method using 12. The liquid level detection method using an ultrasonic level meter according to claim 10 or 11, wherein ultrasonic wave propagation from the start of driving of the ultrasonic sensor by the input of a pulse signal to the reception of a reflected echo from the liquid level is received. Along with measuring the time, measure the driving reverberation time until the reverberation of the ultrasonic wave detected immediately after the driving of the ultrasonic sensor from the start of driving decreases to a predetermined level, and the measured ultrasonic propagation time and the driving reverberation A liquid level detection method using an ultrasonic level meter, wherein a difference from time is detected as a reverberation margin. In the liquid level detection method using an ultrasonic level meter according to claim 12, when detecting the position of the liquid level, detecting a reverberation margin based on a predetermined amplification factor when driving the ultrasonic sensor, If the detected reverberation margin is equal to or less than a predetermined value, the detected reverberation margin is equal to or greater than the predetermined value while switching the frequency band of the band variable filter according to the frequency component of the reverberation at the container bottom plate, and the A liquid level detection method using an ultrasonic level meter, wherein the frequency band is adjusted so that a reflected echo signal from the liquid level can be specified. The liquid level detection method using an ultrasonic level meter according to any one of claims 10 to 13, wherein an amplification factor of a signal extracted by the band variable filter is set to a time starting from when the ultrasonic sensor is driven. A liquid level detection method using an ultrasonic level meter, wherein an amplification factor according to the position of the liquid level can be set by changing the gain so as to increase accordingly. 15. The liquid level detection method using an ultrasonic level meter according to claim 10, wherein the number of pulses or the pulse width of the pulse signal is changed to change the oscillation time of the pulse signal. A pulse signal is input to the ultrasonic sensor in accordance with the oscillating time, and the ultrasonic sensor can transmit ultrasonic waves while changing the driving time at a driving frequency corresponding to the input pulse signal. Characteristic liquid level detection method using ultrasonic level meter. A liquid level detection method using an ultrasonic level meter according to any one of claims 12 to 15, wherein the position of the liquid level is detected based on a predetermined amplification factor when the ultrasonic sensor is driven. A reverberation margin is detected, and if the detected reverberation margin is equal to or less than a predetermined value, the amplification factor is reduced at the time of driving the ultrasonic sensor, and the reduced amplification factor is increased at a predetermined rate according to time. While changing the oscillation time of the pulse signal input to the ultrasonic sensor, and further switching the frequency band of the band variable filter in accordance with the frequency component of the reverberation at the bottom plate of the container. Each of one or more of the amplification factor, oscillation time, and frequency band is set so that a margin is equal to or more than the predetermined value and a reflected echo signal from the liquid surface can be specified. Liquid level detection method using the ultrasonic level meter and adjusting.

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