JP4079823B2 - Liquid level detection method of ultrasonic level meter and ultrasonic level meter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for detecting a liquid level of an ultrasonic level meter and an ultrasonic level meter, and more specifically, a time until an ultrasonic wave is transmitted from the outer wall of the bottom surface of a container and a reflected wave from an internal liquid interface returns. The liquid level detection method of the ultrasonic level meter which detects the liquid level position inside a container based on this.
[0002]
[Prior art]
An ultrasonic level meter that uses an ultrasonic sensor for both transmission and reception measures the time until an ultrasonic wave is transmitted from the ultrasonic sensor and the reflected wave is received, and the distance to the object is calculated based on that time. Therefore, since the distance to the object can be measured accurately and easily, it is used for various purposes.
[0003]
FIG. 7 is a block diagram showing a circuit configuration example of a conventional ultrasonic level meter, in which 50 is a control unit of the ultrasonic level meter, and the control unit 50 includes an amplification factor switching circuit 51, an AMP (amplification circuit). ) 52, ENVDET (detection circuit) 53, A / D converter 54, CPU 55, LCD (display unit) 56, RAM 57, ROM 58, D / A converter 59, VCO (oscillation circuit) 60, gate element 61, DRV (drive circuit) ) 62, and 70 is an ultrasonic sensor (hereinafter referred to as a sensor) of an ultrasonic level meter, and the control unit 50 and the ultrasonic sensor 70 are connected by wire or wirelessly.
[0004]
First, at the time of transmitting ultrasonic waves, the D / A converter 59 converts the data from the CPU 55 into a voltage and inputs it to the VCO 60. The VCO 60 oscillates at an oscillation frequency corresponding to the voltage data from the D / A converter 59 and inputs the oscillation wave to the gate element 61. The gate element 61 outputs the oscillation wave from the VCO 60 to the DRV 62 based on the pulse output from the CPU 55. The DRV 62 converts the output from the gate element 61 into a high potential amplitude and outputs a drive signal for driving the sensor 70. The sensor 70 transmits ultrasonic waves at the oscillation frequency based on the input of the drive signal from the DRV 62.
[0005]
Further, at the time of reception of the ultrasonic wave, the sensor 70 receives the reflected wave that is returned from the ultrasonic wave transmitted as described above and reflected by an object such as the liquid level inside the container, and the received signal is amplified. Input to the switching circuit 51. This amplification factor switching circuit 51 is provided so as to be able to select 0 dB as an amplification factor for frequency adjustment and 17 to 20 dB as an amplification factor for liquid level position measurement. When measuring the liquid level position, 17 is selected. A high gain of ˜20 dB is selected, and a low gain of 0 dB is selected during frequency adjustment. Further, the AMP 52 amplifies the received signal at an amplification factor instructed by the CPU 55, and the ENVDET 53 rectifies and detects the input waveform from the AMP 52 and outputs an envelope waveform. The A / D converter 54 digitally converts the envelope waveform from the ENVDET 53 and inputs it to the CPU 55. The CPU 55 calculates the distance to the object based on time information from the time when the ultrasonic wave is transmitted by the sensor 70 to the time when the reflected wave is received.
[0006]
Here, when the liquid surface position is measured based on the circuit configuration as described above, the primary reflection echo may not be captured due to liquid surface fluctuation or the like. There was a need to measure. Further, when the liquid surface position is close, there is an influence of driving reverberation. Therefore, when the primary reflection echo is close to the driving reverberation, it is difficult to measure the liquid surface position. In addition, when noise or the like is mixed, an error may occur in the liquid level measurement result. Thus, in the conventional ultrasonic level meter, it was not possible to perform stable liquid level measurement against liquid level fluctuations, noise, and when the liquid level position is close.
[0007]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and has an integer ratio relationship even when the primary reflection echo cannot be captured due to liquid level fluctuations or the like in the ultrasonic level meter. An object of the present invention is to provide an ultrasonic level meter liquid level detection method and an ultrasonic level meter capable of determining the echo timing of a primary reflected echo based on the echo timing of another reflected echo. is there.
[0008]
[Means for Solving the Problems]
The invention of claim 1 is an ultrasonic sensor that is attached to the outer wall surface of the bottom 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. Liquid level of an ultrasonic level meter connected to a control unit that controls the detection operation of the liquid level based on time information from the time when the ultrasonic wave is transmitted by the ultrasonic sensor to the time when the reflected wave is received In the detection method, from the ultrasonic sensor More than once Whether the echo detection step for detecting a plurality of echoes based on the reflected waves repeatedly reflected from the liquid surface according to the transmitted ultrasonic wave and the time interval of the echoes until the detection are in an integer ratio relationship with each other Echo that was determined to be an integer ratio relationship And the echo timing of that echo group And a liquid level detecting step of detecting the position of the liquid level based on the determined echo timing of the primary echo based on the determined echo timing of the primary echo. It is characterized by.
[0009]
According to a second aspect of the present invention, in the first aspect of the invention, the first-order echo determination step. Is , It is determined whether or not the time intervals until the echoes are detected are in an integer ratio relationship with respect to the plurality of echoes detected in the echo detection step. Echo timing corresponding to the integer = 1 in the integer ratio relation is calculated based on the echo timing of the echo group in which the obtained acquisition frequency is maximized. And is determined as the primary echo timing.
[0010]
According to a third aspect of the present invention, in the first aspect of the invention, the first-order echo determination step. Is , It is determined whether or not the time intervals until the echoes are detected are in an integer ratio relationship with respect to the plurality of echoes detected in the echo detection step. Echoes are grouped together, the total echo intensity for each echo group is calculated, and the total of the calculated echo intensities corresponds to the integer = 1 of the integer ratio relationship based on the echo timing of the echo group that has the maximum. The echo timing is calculated and determined as the primary echo timing.
[0011]
The invention according to claim 4 is an ultrasonic sensor attached to the outer wall surface of the bottom of the container, for transmitting an ultrasonic wave toward the liquid surface of the liquid contained in the container and receiving a reflected wave from the liquid surface; In the ultrasonic level meter connected to the control unit for controlling the liquid level detection operation based on time information from the time when the ultrasonic wave is transmitted by the ultrasonic sensor to the time when the reflected wave is received, The control unit is configured from the ultrasonic sensor More than once Whether the echo detection means for detecting a plurality of echoes based on the reflected waves repeatedly reflected from the liquid surface according to the transmitted ultrasonic wave and the time intervals of the echoes until the detection are in an integer ratio relationship with each other Echo that was determined to be an integer ratio relationship And the echo timing of that echo group And a liquid level detecting means for detecting the position of the liquid level based on the determined echo timing of the primary echo. It is characterized by.
[0012]
According to a fifth aspect of the present invention, in the invention of the fourth aspect, the primary echo determination means has a time interval until the echo is detected for a plurality of echoes detected by the echo detection means in an integer ratio relationship. As a result, the echoes determined to have an integer ratio relationship are grouped, and the echo acquisition frequency for each echo group is calculated, and the calculated acquisition frequency is maximized. Based on the echo timing of the echo group, the echo timing corresponding to the integer = 1 in the integer ratio relation is calculated and determined as the primary echo timing.
According to a sixth aspect of the present invention, in the fourth aspect of the present invention, the primary echo determination means has an integer ratio relationship between time intervals until the echoes are detected for a plurality of echoes detected by the echo detection means. As a result, the echoes determined to have an integer ratio relationship are grouped, the total echo intensity for each echo group is calculated, and the calculated total echo intensity is the maximum. On the basis of the echo timing of the echo group, the echo timing corresponding to the integer = 1 in the integer ratio relation is calculated and determined as the primary echo timing.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram for explaining a configuration example when an ultrasonic level meter to which the present invention is applied is installed in a container. In the figure, 10 is a control unit (hereinafter referred to as a controller), and 30 is an ultrasonic sensor. (Piezoelectric sensor), 31 is an ultrasonic wave transmitted from the ultrasonic sensor 30, 15 is a display unit of the controller 10, 40 is a storage tank or container (hereinafter referred to as a container) for storing a liquid such as liquefied gas or kerosene, 41 Is the liquid level. The ultrasonic level meter includes a controller 10 and an ultrasonic sensor 30. The ultrasonic sensor 30 is installed on the outer bottom surface of the container 40 with a magnet or the like (not shown) and connected to the controller 10 by wire. In addition, you may comprise so that communication between the ultrasonic sensor 30 and the controller 10 may be performed via radio | wireless, In this case, avoiding the malfunction by wiring damage or the intentional cutting | disconnection by a third party, etc. Is possible. In this example, the case where the liquid level inside the container is detected as a detection target will be described as a representative example. However, the target that can be detected by the ultrasonic level meter is not limited to the liquid level. It can also be applied to the detection of objects.
[0014]
In the configuration as described above, for example, when detecting the liquid level 41 of the liquid, the operator operates the controller 10 to transmit the ultrasonic wave 31 from the ultrasonic sensor 30, and mainly at the liquid level 41. The reflected echo that has been reflected back is received, the liquid surface position, that is, the distance to the liquid surface 41 (hereinafter referred to as the liquid surface distance) is calculated based on the received reflected echo, and the calculated liquid surface distance is further calculated. Based on this, the liquid volume in the container 40 can be calculated.
[0015]
When detecting the height of the liquid surface 41, the ultrasonic sensor 30 transmits the ultrasonic wave 31 upward toward the bottom outer wall of the container 40. The transmitted ultrasonic wave 31 is reflected by the liquid surface 41 and returned, but the delay time until the ultrasonic sensor 30 receives the reflected wave differs depending on the height of the liquid surface 41. 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 according to temperature and propagation medium (air or liquid, etc.), and based on this data. The liquid level distance is calculated.
[0016]
Even if the primary reflection echo cannot be captured due to liquid level fluctuation or the like, the ultrasonic level meter of the present invention is based on the echo timing of other reflection echoes having an integer ratio relationship. For the purpose of determining the echo timing of the reflected echo, it is assumed that the circuit configuration shown in FIG.
[0017]
FIG. 2 is a block diagram showing a circuit configuration example of an ultrasonic level meter according to an embodiment of the present invention. The controller 10 of the ultrasonic level meter includes an AMP (amplifier circuit) 11, an ENVDET (detector circuit) 12, and a CMP. (Comparator) 13a, CPU 14, LCD (display unit) 15, RAM 16, ROM 17, D / A converter 18, VCO (oscillation circuit) 19, gate element 20, DRV (drive circuit) 21 and 30 is an ultrasonic level It is assumed that the controller 10 and the sensor 30 are connected by wire or wireless in a total ultrasonic sensor (hereinafter referred to as a sensor). The ROM 17 stores echo detection means 17a, primary echo determination means 17b, and liquid level detection means 17c as programs, and the CPU 14 performs the above-described primary echo determination processing when performing the primary echo determination processing of the present invention. Read and execute the program. Note that the program may be stored in the RAM 16.
[0018]
In FIG. 1 and FIG. 2, during transmission of ultrasonic waves, the D / A converter 18 converts data from the CPU 14 into a voltage and inputs the voltage to the VCO 19. The VCO 19 oscillates at an oscillation frequency corresponding to the voltage data from the D / A converter 18 and inputs the oscillation wave to the gate element 20. The gate element 20 outputs the oscillation wave from the VCO 19 to the DRV 21 based on the pulse output from the CPU 14. The DRV 21 converts the output from the gate element 20 into a high potential amplitude and outputs a drive signal for driving the sensor 30. The sensor 30 transmits the ultrasonic wave 31 at the oscillation frequency based on the input of the drive signal from the DRV 21.
[0019]
Further, at the time of receiving the ultrasonic wave, the sensor 30 receives the reflected wave returned from the ultrasonic wave 31 transmitted as described above to the liquid surface 41 of the container 40 and inputs the received signal to the AMP 11. . The AMP 11 amplifies the received signal at an amplification factor instructed by the CPU 14, and the ENVDET 12 rectifies and detects the input waveform from the AMP 11 and outputs an envelope waveform.
[0020]
The CMP 13a compares the envelope waveform from the ENVDET 12 with the reference potential, and outputs a logical value 1 to the CPU 14 when the envelope waveform exceeds the reference potential. The CPU 14 calculates the distance to the liquid level 41 based on time information from the time when the ultrasonic wave 31 is transmitted by the sensor 30 to the time when the reflected wave is received.
[0021]
The echo detection means 17 a detects a plurality of echoes based on the reflected waves that are repeatedly reflected from the liquid surface 41 in accordance with the ultrasonic waves transmitted from the sensor 30. The echo detection means 17a has a timer for measuring time from the start of pulse output to the DRV 21 based on an instruction from the CPU 14, reads the timer count value at the rising timing of the comparator of the CMP 13a, and stores it in the RAM 16. . Thereby, this ultrasonic level meter acquires the time interval until the echo is detected as the echo timing.
[0022]
The primary echo determination means 17b determines whether or not the time intervals of echoes until detection by the echo detection means 17a have an integer ratio relationship, and as a result, the echo determined to have an integer ratio relationship Is used to determine the echo timing of the primary echo.
[0023]
Here, the primary echo determination means 17b determines whether or not the time intervals until the echoes are detected with respect to the plurality of echoes detected by the echo detection means 17a are in an integer ratio relationship, and as a result, Echoes determined to have an integer ratio relationship are grouped, the echo acquisition frequency for each echo group is calculated, and the integer ratio relationship is based on the echo timing of the echo group with the calculated acquisition frequency being maximized An echo timing corresponding to an integer of 1 is calculated and determined as a primary echo timing. The embodiment in this case will be described in detail based on the flowchart shown in FIG. 3 described later.
[0024]
The liquid level detection means 17c detects the position of the liquid level 41 based on the echo timing of the primary echo determined by the primary echo determination means 17b.
[0025]
According to the ultrasonic level meter of the present invention, the primary echo timing can be determined from the n-th echo timing (n ≧ 2) even when the primary echo timing cannot be reliably captured. Stable liquid level measurement can be performed even if there is shaking.
In addition, it is possible to stably perform near-surface liquid level measurement that makes it difficult to capture the primary echo timing due to the influence of drive reverberation.
In addition, the liquid level position calculation process does not detect isolated echo timing that is not in an integer ratio relationship, so even if noise is mixed, it is not affected by this, and high-precision liquid level measurement is possible. It can be performed.
[0026]
FIG. 3 is a flowchart for explaining an example of the liquid level detection method of the ultrasonic level meter to which the present invention is applied. FIG. 4 is a diagram showing an example of calculating the frequency distribution in the flowchart shown in FIG. This example will be described based on the apparatus configuration of the ultrasonic level meter shown in FIG.
First, the ultrasonic level meter receives the reflected wave from the liquid surface of the ultrasonic wave transmitted from the sensor 30, and acquires measurement data obtained by measuring the echo timing of the reflected wave by the echo detection means 17a (step S1). In the case of this example, the case where the number of ultrasonic transmissions is 4 times, and there is an echo loss or noise is shown, the measurement data of the dotted line part shown in the second and third times in the figure is an echo loss. Indicates.
[0027]
Next, an example of the primary echo determination means 17b will be described in detail.
First, as a first stage of echo grouping, a frequency distribution is obtained for the four measurement data obtained in step S1 (step S2). In the case of this example, the section interval is set to 10 μs, and each section median (100, 110, 150,..., 460) has a section width of ± 9 μs, for example. As a result, in the case of the section median value of 150 μs, it has a width of 141 μs to 159 μs, and 151, 152, and 150 μs are included in the width based on the first to fourth measurement data, so the frequency is calculated as 3. . The frequency is calculated with the same calculation method for the other median values. The interval between the sections is not limited to 10 μs, and the section width is not limited to ± 9 μs. These can be arbitrarily set by the operator.
[0028]
Here, it is also possible to set the segment intervals so as to change in a geometric series instead of the regular intervals as in the above example. Further, the section width can be set so as to change according to the section median, for example. As a specific example, when 10% of the segment median is defined as the segment width, the segment width is ± 7.5 us when the segment median is 150 us, and the segment width is ± 15 us when the segment median is 300 us.
[0029]
Next, as the second stage of echo grouping, the primary echo determination means 17b obtains a frequency including an integer multiple based on the frequency distribution for each measurement data obtained in step S2 (step S3). ). The frequencies shown in this example are created from the frequency distribution calculation table shown in FIG. In the same manner as described above, for example, when the median value is 150 μs, the calculation is performed including the frequency of the timing at an integer multiple of this timing (150 μs). That is, the frequency 3 at 150 μs is calculated by including the frequency 4 at 300 μs (twice 150 μs) and the frequency 3 at 450 μs (3 times 150 μs). As a result, the total frequency 3 + 4 + 3 = 10 is obtained as the echo acquisition frequency of the echo group having an integer ratio relationship with the echo timing section median 150 μs. With respect to the other segment median values, the frequency sum, that is, the echo acquisition frequency for each echo group is calculated by the same calculation method.
[0030]
Finally, the primary echo determination means 17b searches for an echo group having the maximum acquisition frequency among the echo acquisition frequencies obtained in step S3, and based on the echo timing of the echo group, an integer ratio The echo timing corresponding to the relation integer = 1 is calculated (step S4). In the case of the above example, since the frequency total 10 is the maximum, the echo timing corresponding to the integer = 1 integer number relation is calculated from the echo timing having the integer ratio relation to the maximum frequency division median 150 (± 9) μs. To do. That is, the echo timing corresponding to the integer = 1 in the integer ratio relationship is the echo timing value belonging to the section median value 150 (± 9) μs and the echo timing value belonging to the section median value 300 (± 9) μs that is twice that value. And an average of the value of 1/3 of the echo timing value belonging to the divided median value 450 (± 9) μs, which is three times the value. An example of the calculation is shown below.
t = [(151 + 152 + 150) / 1 + (299 + 301 + 303 + 298) / 2 + (451 + 452 + 449) / 3] /10=15.04 μs
The echo timing corresponding to the integer = 1 of the integer ratio relationship thus obtained is determined as the primary echo timing.
[0031]
In the ultrasonic level meter of the present invention, the liquid level position is calculated and displayed by the liquid level detection means 17c based on the primary echo timing determined by calculation as described above. It should be noted that when calculating the liquid level position, the sound speed correction is applied in consideration of temperature information from a temperature sensor (not shown) or the like. Thus, even when the primary reflected echo cannot be reliably captured, the echo timing of the primary reflected echo is determined based on the echo timing of other reflected echoes having an integer ratio relationship. Therefore, stable liquid level measurement is possible for liquid level fluctuations, noise, and when the liquid level position is close.
[0032]
FIG. 5 is a block diagram showing an example of the circuit configuration of an ultrasonic level meter according to another embodiment of the present invention. The controller 10 of the ultrasonic level meter includes an AMP (amplifier circuit) 11, an ENVDET (detector circuit) 12, An A / D converter 13b, a CPU 14, an LCD (display unit) 15, a RAM 16, a ROM 17, a D / A converter 18, a VCO (oscillation circuit) 19, a gate element 20, a DRV (driving circuit) 21, and 30 is an ultrasonic wave It is assumed that the controller 10 and the sensor 30 are connected to each other by wire or wireless. The ROM 17 stores echo detection means 17a, primary echo determination means 17b, and liquid level detection means 17c as programs, and the CPU 14 performs the above-described primary echo determination processing when performing the primary echo determination processing of the present invention. Read and execute the program. Note that the program may be stored in the RAM 16.
[0033]
A difference from the embodiment shown in FIG. 2 is that an A / D converter 13b is provided instead of the CMP 13a. The A / D converter 13b converts the envelope waveform from the ENVDET 12 into digital time-series data (multi-tone level) ( Waveform data). The echo detection means 17a in the present embodiment first averages waveform data obtained by averaging waveform data acquired by transmitting ultrasonic waves a plurality of times (total value sequence or average value sequence of A / D converter values at each sampling timing). Then, a comparison with a predetermined slice level is performed at each sampling timing, and a binarization process is performed to associate a logical value 1 when the slice level is exceeded and a logical value 0 if the slice level is not exceeded. Next, the echo detector 17a in this embodiment acquires the echo timing by examining the rising timing from the binarized data string signal obtained by the binarization process.
[0034]
Further, the primary echo determination unit 17b of the present embodiment determines whether or not the time intervals until the echoes are detected with respect to the plurality of echoes detected by the echo detection unit 17a are in an integer ratio relationship with each other, As a result, the echoes determined to have an integer ratio relationship are grouped, and the total echo intensity for each echo group is calculated. Based on the echo timing of the echo group in which the calculated total echo intensity is maximized Thus, the echo timing corresponding to integer = 1 in the integer ratio relation is calculated and determined as the primary echo timing. The embodiment in this case will be described in detail based on the flowchart shown in FIG.
[0035]
FIG. 6 is a flowchart for explaining another example of the liquid level detection method of the ultrasonic level meter to which the present invention is applied. This example will be described based on the apparatus configuration of the ultrasonic level meter shown in FIG.
First, the echo detection means 17a receives the reflected wave from the liquid surface of the ultrasonic wave transmitted from the sensor 30, and acquires the waveform data (step S11). In the case of this example, the case where the number of times of ultrasonic transmission is set to 4 and an echo dropout, noise, or the like is included is shown. Next, the echo detection means 17a obtains average waveform data (total value sequence or average value sequence of A / D converter values for each sampling timing) based on the acquired waveform data of four times. Finally, the echo detection means 17a performs binarization processing on the average waveform data, and obtains the echo timing by examining the rising timing from the obtained binary data string signal. In the next step S12, four average waveform data and each echo timing of the detected echo are shown. As a specific example, a state in which five echo timings 101us, 151us, 301us, 392us, and 451us are detected will be described.
[0036]
The primary echo determination means 17b searches the average waveform data and obtains a peak value as the echo intensity of the echo corresponding to each echo timing obtained by the echo detection means 17a. Specifically, the maximum value within a predetermined time after the echo timing is searched for and used as the peak value. In this way, the peak value corresponding to the echo timing of each echo is obtained. As a specific example, in step S12, the peak values of echoes corresponding to the five echo timings 101us, 151us, 301us, 392us, 451us are sequentially described as voltage values 32mV, 131mV, 98mV, 19mV, 55mV.
[0037]
Next, a set of reflected waves (echo group) that is an integral multiple of the rising timing (in this example, each timing value has a width of ± 9 μs) based on the rising timing and the peak value obtained in step S12. And the sum of the peak values of each reflected wave set is obtained (step S13). For example, the data included in the integral multiple (± 9 μs) of the rising timing of 151 μs (crest value 131 mV) is 151 μs (131 mV), 301 μs (98 mV), 451 μs (55 mV), and the sum of the crest values is 131 + 98 + 55 = 284 mV. Become. The width is not limited to ± 9 μs and can be arbitrarily set by the operator.
[0038]
Here, the breakdown of the total peak value at the timing of 151 μs (131 mV) is shown below.
Data falling within the range of 151 × 2 ± 9 μs: 301 μs (98 mV)
Data falling within the range of 151 × 3 ± 9 μs: 451 μs (55 mV)
Data falling within the range of 151 × 4 ± 9 μs: Not present
[0039]
Similarly, the breakdown of the total peak value (32 + 98 + 19 = 149 mV) at the timing of 101 μs (32 mV) is shown below.
Data falling within the range of 101 × 2 ± 9μs: Not present
Data falling within the range of 101 × 3 ± 9 μs: 301 μs (98 mV)
Data falling within the range of 101 × 4 ± 9 μs: 392 μs (19 mV)
[0040]
In the above example, the case of 101, 151 μs is shown as a representative example, but the peak value sum is similarly calculated for other rising timings, 301, 392, 451 μs. The results are shown below.
In the case of 301 μs, only data that falls within the range of 301 ± 9 μs is 98 mV
In the case of 392 μs, only 19 mV of data within the range of 392 ± 9 μs
In the case of 451 μs, only 55 mV is included in the data range of 451 ± 9 μs.
[0041]
The total peak value calculated as described above is shown below.
101 μs (32 mV) integer multiple data: peak value total 149 mV
151 μs (131 mV) integer multiple data: peak value total 284 mV
Data of integral multiple of 301 μs (98 mV): total peak value 98 mV
Data of integer multiple of 392 μs (19 mV): total peak value 19 mV
Integer data of 451 μs (55 mV): Total peak value 55 mV
[0042]
Finally, the primary echo determination means 17b sets the echo timing of the data having the maximum peak value in step S13 as the primary echo timing (step S14). In the case of the above example, since the peak value total 284 mV is the maximum, the timing at the peak level data of 151 μs is set as the primary echo timing.
[0043]
The liquid level detection means 17c calculates and displays the liquid level position based on the primary echo timing determined as described above. It should be noted that when calculating the liquid level position, the sound speed correction is applied in consideration of temperature information from a temperature sensor (not shown) or the like.
[0044]
In the primary echo determination means 17b of this example, the peak value is used as the echo intensity of the echo corresponding to each echo timing. As another example, the echo intensity may be an integral value of the echo wave instead of the peak value. Specifically, the integral value of the echo wave is, for example, a value obtained by summing A / D values within a predetermined time after the echo timing. As another example, the echo intensity may be an echo rising speed. Specifically, the echo rising speed is, for example, an A / D value after a predetermined time from the echo timing.
[0045]
In the primary echo determination means 17b of the present example, as a method for obtaining the peak value, first, average waveform data is obtained, and then, the mean waveform data is searched to obtain the peak value. As another method, for each waveform data, first, echo timings exceeding a predetermined slice level are detected, and the respective echo timings and individual peak values corresponding to the echo timings are obtained. There is a method for obtaining a statistical echo timing and a peak value for each group.
[0046]
The statistical value of the peak value by the above method may be an average or sum of the peak values in the group, or may be a maximum value. Further, the echo timing statistics by this method may be the average or total of the echo timings in the group, or may be the minimum value. It is clear that the average and sum generally have a similar effect. Comparing the case where the echo is reliably obtained compared to the case where the echo is weak, the echo timing becomes small (because the rise is fast), and the peak value becomes large.
[0047]
Using the minimum value in the group as the statistics of the echo timing and using the maximum value in the group as the statistics of the crest value is sufficient when the liquid level fluctuates periodically and the period T1 is sufficient. If there is no long sampling period T2 (period from the first transmission time to the end of waveform data collection by the last transmission) (for example, when T2 is about 1 to 2 times T1), More accurate results may be obtained than using averages and sums as statistics. Because the period of the liquid level fluctuation and the period of the sampling period are not usually in an integer ratio relationship, the average (or total) fluctuation occurs depending on the phase relation between the liquid level fluctuation and the sampling start, and may not be ignored. Because there is.
[0048]
Therefore, for the same reason as described above, the primary echo determination means 17b of this example obtains the peak value based on the average waveform data, but a sufficient sampling period is provided for the cycle of the liquid level fluctuation. If there is not, the more stable primary echo can be determined by obtaining the peak value using the maximum waveform data (maximum value sequence of A / D converter values at each sampling timing) instead of the average waveform data. is there.
[0049]
The ultrasonic level meter of the present invention calculates and displays the liquid level position based on the primary echo timing determined as described above. Thus, even when the primary reflected echo cannot be reliably captured, the echo timing of the primary reflected echo is determined based on the echo timing of other reflected echoes having an integer ratio relationship. Therefore, stable liquid level measurement is possible for liquid level fluctuations, noise, and when the liquid level position is close.
[0050]
【The invention's effect】
According to the present invention, even if the primary reflection echo cannot be captured by the ultrasonic level meter, the echo of the primary reflection echo is based on the echo timing of other reflection echoes having an integer ratio relationship. Since the timing can be determined, stable liquid level position measurement can be performed even if there is liquid level fluctuation or the like.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining a configuration example when an ultrasonic level meter to which the present invention is applied is installed in a container.
FIG. 2 is a block diagram showing a circuit configuration example of an ultrasonic level meter according to an embodiment of the present invention.
FIG. 3 is a flowchart for explaining an example of a liquid level detection method of an ultrasonic level meter to which the present invention is applied.
4 is a diagram showing a calculation example of a frequency distribution in the flowchart shown in FIG. 3. FIG.
FIG. 5 is a block diagram showing a circuit configuration example of an ultrasonic level meter according to another embodiment of the present invention.
FIG. 6 is a flowchart for explaining another example of the liquid level detection method of the ultrasonic level meter to which the present invention is applied.
FIG. 7 is a block diagram showing a circuit configuration example of a conventional ultrasonic level meter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10,50 ... Control part (controller) 11,52 ... AMP, 12,53 ... ENVDET, 13a ... CMP, 13b ... A / D converter, 14,55 ... CPU, 15,56 ... LCD, 16,57 ... RAM , 17, 58 ... ROM, 17a ... Echo detection means, 17b ... Primary echo determination means, 17c ... Liquid level detection means, 18, 59 ... D / A converter, 19, 60 ... VCO, 20, 61 ... gate elements 21, 62 ... DRV, 30, 70 ... sensor, 31 ... ultrasonic wave, 40 ... container, 41 ... liquid level, 51 ... gain switching circuit, 54 ... A / D converter.

Claims (6)

An ultrasonic sensor that is attached to the outer wall surface of the bottom 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; In the liquid level detection method of the ultrasonic level meter connected with the control unit that controls the detection operation of the liquid level based on time information from the time of transmitting the sound wave to the time of receiving the reflected wave,
An echo detection step for detecting a plurality of echoes based on a reflected wave repeatedly reflected from the liquid surface in response to an ultrasonic wave transmitted a plurality of times from the ultrasonic sensor, and an echo time interval until the detection is mutually It is determined whether or not an integer ratio relationship is established, and as a result, echoes determined to be in an integer ratio relationship are grouped, and the echo timing of the primary echo is determined based on the echo timing of the echo group . A liquid level detection method for an ultrasonic level meter, comprising: a primary echo determination step; and a liquid level detection step of detecting the position of the liquid level based on the determined echo timing of the primary echo. 2. The ultrasonic level meter liquid level detection method according to claim 1, wherein the primary echo determination step has a time interval until a plurality of echoes detected in the echo detection step are detected. It is determined whether there is an integer ratio relationship with each other, and as a result, echoes determined to have an integer ratio relationship are grouped, and the echo acquisition frequency for each echo group is calculated. Liquid level detection of an ultrasonic level meter, wherein an echo timing corresponding to integer = 1 in the integer ratio relation is calculated based on the echo timing of the echo group that is maximized and is determined as a primary echo timing Method. 2. The ultrasonic level meter liquid level detection method according to claim 1, wherein the primary echo determination step has a time interval until a plurality of echoes detected in the echo detection step are detected. It is determined whether there is an integer ratio relationship with each other. As a result, echoes determined to have an integer ratio relationship are grouped, and the total echo intensity for each echo group is calculated. An ultrasonic level meter liquid characterized by calculating an echo timing corresponding to an integer = 1 in the integer ratio relation based on an echo timing of an echo group having a maximum sum and determining it as a primary echo timing Surface detection method. An ultrasonic sensor that is attached to the outer wall surface of the bottom 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; In the ultrasonic level meter connected to the 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 an echo detection unit that detects a plurality of echoes based on reflected waves that are repeatedly reflected from the liquid surface in response to an ultrasonic wave transmitted a plurality of times from the ultrasonic sensor, and an echo until the detection. Are determined to be in an integer ratio relationship, and as a result, the echoes determined to be in an integer ratio relationship are grouped, and the echoes of the primary echo are based on the echo timing of the echo group. An ultrasonic level meter, comprising: primary echo determination means for determining timing; and liquid level detection means for detecting the position of the liquid level based on the determined echo timing of the primary echo.   5. The ultrasonic level meter according to claim 4, wherein the time interval until the primary echo determination unit detects the echoes for the plurality of echoes detected by the echo detection unit has an integer ratio relationship. Group, and as a result, the echoes determined to have an integer ratio relationship are grouped, and the echo acquisition frequency for each echo group is calculated. An ultrasonic level meter characterized in that an echo timing corresponding to integer = 1 in the integer ratio relation is calculated based on the echo timing and determined as a primary echo timing.   5. The ultrasonic level meter according to claim 4, wherein the time interval until the primary echo determination unit detects the echoes for the plurality of echoes detected by the echo detection unit has an integer ratio relationship. As a result, the echoes determined to have an integer ratio relationship are grouped, the total echo intensity for each echo group is calculated, and the calculated total echo intensity is maximized An ultrasonic level meter, wherein an echo timing corresponding to an integer = 1 in the integer ratio relation is calculated based on an echo timing of an echo group and determined as a primary echo timing.

Images