JP2010203899A - Ultrasonic liquid level meter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic liquid level meter exactly distinguishing a liquid level reflection echo from a reverberation echo and precisely detecting a liquid level while dropping below a lower-limit measurement value in a power-saving manner even if it is measured while dropping below the lower-limit measurement value. <P>SOLUTION: An ultrasonic sensor 5 transmits an ultrasonic wave from the bottom of a container to the liquid level of a liquid in the container and receives a reflected wave from the liquid level. The ultrasonic liquid level meter detects the liquid level based on a reception timing of the reflected wave in the ultrasonic sensor 5. As a result of detecting the liquid level, however, when the liquid level is below a predetermined liquid level, and/or when the liquid level is above a previously detected liquid level, a drive time of the ultrasonic sensor 5 is extended to perform redetection. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an ultrasonic liquid level gauge that detects a liquid level based on reception timing of an ultrasonic liquid level echo transmitted to a liquid level.

  An ultrasonic liquid level gauge using an ultrasonic sensor for both transmission and reception measures the time taken to transmit an ultrasonic wave from the ultrasonic sensor and receive the reflected wave, and the distance to the object based on that time. Since the distance to an object can be measured accurately and easily, it is used for various purposes.

  As an example of such an ultrasonic level gauge, Patent Documents 1 and 2 disclose that an ultrasonic wave is transmitted toward the liquid level of a liquid attached to the bottom outer wall surface of the container and contained in the container. An ultrasonic sensor that receives a reflected wave from the surface, and 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. A connected ultrasonic level meter is disclosed. In the ultrasonic level meters described in Patent Documents 1 and 2, various measures are taken for both hardware and software in order to ensure measurement stability.

  In the ultrasonic level meter described in Patent Document 1, the ultrasonic sensor transmits an ultrasonic wave based on a pulse signal input from the control unit, and the control unit starts driving the ultrasonic sensor based on the input of the pulse signal. Measurement of the ultrasonic propagation time from when the ultrasonic wave is reflected to the reception of the reflected echo from the liquid level, and the drive reverberation time until the ultrasonic reverberation detected immediately after the start of driving of the ultrasonic sensor is reduced to a predetermined level. The reverberation margin detecting means for detecting the difference between the measured ultrasonic propagation time and the driving reverberation time as a reverberation margin, and a signal corresponding to the reflected wave with respect to the ultrasonic wave transmitted by the ultrasonic sensor are input and input. Amplifying means capable of setting the amplification factor according to the position of the liquid level by changing the amplification factor of the signal so as to increase according to time from the time of driving the ultrasonic sensor; The echo timing detection means for detecting the echo timing by identifying the reflected echo signal from the liquid surface among the signals amplified based on the amplification factor set in the width means, and the position of the liquid surface based on the detected echo timing A reverberation margin detection unit that detects a reverberation margin based on a predetermined amplification factor when the ultrasonic sensor is driven, and detects the reverberation margin. Is less than or equal to a predetermined value, the amplifying means decreases the amplification factor and changes the decreased amplification factor to increase at a predetermined rate according to time, the detected reverberation margin becomes larger than the predetermined value, In addition, the amplification factor is adjusted so that the reflected echo signal from the liquid surface can be specified.

  The control unit of the ultrasonic level meter in Patent Document 2 includes an echo detection unit that detects a plurality of echoes based on reflected waves that are repeatedly reflected from the liquid surface according to the ultrasonic waves transmitted from the ultrasonic sensor a plurality of times. It is determined whether or not the time intervals of echoes until detection are in an integer ratio relationship, and as a result, echoes determined to be in an integer ratio relationship are grouped, and based on the echo timing of the echo group A primary echo determining means for determining the echo timing of the primary echo; and a liquid level detecting means for detecting the position of the liquid level based on the determined echo timing of the primary echo.

  However, an ultrasonic liquid level meter that has been commercialized by utilizing the techniques of Patent Document 1 and Patent Document 2 is erroneous when the remaining amount of liquid in the container has approached the empty state by cutting into the measurement lower limit range. It was confirmed that it would measure.

  This will be described more specifically with reference to FIG. FIG. 11 is a trend graph showing the results of measuring the remaining amount of the LP gas bulk storage over time using the ultrasonic liquid level gauge. In the figure, the remaining points obtained by the ultrasonic liquid level gauge are indicated by black dots. The remaining amount ratio calculated from the quantity measurement value is shown, and the solid line graph shows the actual remaining amount ratio. As a result of measuring the remaining amount value with the ultrasonic liquid level gauge, a remaining amount ratio of 12% was sometimes obtained, but gas was exhausted after several hours. Considering the amount of gas consumed, if the remaining amount ratio was 12%, the gas was supposed to be supplied for about one week.

  As described above, in the conventional ultrasonic liquid level gauge, erroneous measurement is performed in a state in which the remaining amount of liquid in the container has approached the empty state by interrupting the measurement lower limit value. Such an erroneous measurement is whether the reflected wave received by the ultrasonic sensor is a reflected wave from the liquid surface (liquid surface reflection echo) or a reflected wave of noise due to reverberation (noise echo / reverberation echo). However, if the measurement lower limit value is interrupted, it cannot be determined.

  Further, when the remaining amount cuts the measurement lower limit value, that is, when the condition is out of the specification, the remaining amount measurement value needs to be undisplayed (or displayed to indicate that the lower limit value is interrupted). , And not displayed due to erroneous measurement as described above (or display indicating that the lower limit value is interrupted). Further, it is desirable that the detection of the liquid level is executed with power saving.

  The present invention has been made in view of the above circumstances, and its purpose is to accurately distinguish between the liquid surface reflection echo and the reverberation echo even when the liquid level is measured in a state where the measurement lower limit value is interrupted. An object of the present invention is to provide an ultrasonic liquid level gauge that can accurately detect the measurement lower limit value with low power consumption.

  In order to solve the above-described problem, the first technical means of the present invention transmits an ultrasonic wave from the bottom of the container toward the liquid surface of the liquid in the container and receives a reflected wave from the liquid surface. An ultrasonic level gauge that includes an ultrasonic sensor and detects the liquid level based on the reception timing of the reflected wave in the ultrasonic sensor, and as a result of detecting the liquid level, the liquid level is below a predetermined liquid level When it becomes, and / or when it becomes larger than the liquid level detected last time, the detection time is extended by extending the driving time of the ultrasonic sensor.

  According to a second technical means, in the first technical means, the re-detection is performed by detecting a liquid level from the reflected wave according to a High / Low duty ratio of the pulse of the reflected wave after the driving time is extended. This is performed by determining the reflected wave and calculating the liquid level based on the reception timing of the liquid surface reflected wave.

  A third technical means includes an ultrasonic sensor that transmits an ultrasonic wave from the bottom of the container toward the liquid level of the liquid in the container and receives a reflected wave from the liquid level. An ultrasonic liquid level gauge that detects a liquid level based on a reception timing of a reflected wave, and receives the reflected wave by driving the ultrasonic sensor for a predetermined driving time, and receives the pulse of the reflected wave The driving time of the ultrasonic sensor is extended only when the High / Low duty ratio is larger than a predetermined value, and further according to the High / Low duty ratio of the pulse of the reflected wave after the driving time is extended, The liquid level reflected wave is determined from the reflected waves, and the liquid level is detected based on the reception timing of the liquid level reflected wave.

  According to the ultrasonic level gauge of the present invention, even when the liquid level is measured in a state where the measurement lower limit value is interrupted, the liquid level reflection echo and the reverberation echo are accurately distinguished, and the measurement lower limit value is interrupted. This can be detected with high accuracy and power saving. Furthermore, even when the liquid level has fallen below the measurement lower limit value due to such detection having measurement stability, the measurement result is surely hidden (or displayed to indicate that the lower limit value has been interrupted). be able to.

It is the schematic which shows the example which installed the ultrasonic type liquid level gauge in the horizontal type LP gas bulk storage tank. It is the schematic which shows the example which installed the ultrasonic type liquid level gauge in the vertical LP gas bulk storage tank. It is a block diagram which shows the structural example of the ultrasonic type liquid level gauge which concerns on the one actual form of this invention. It is a figure which shows the reflective echo waveform on one condition in the ultrasonic type liquid level gauge of FIG. It is a figure which shows the reflective echo waveform on other conditions in the ultrasonic type liquid level gauge of FIG. It is a figure which shows the reflective echo waveform on other conditions in the ultrasonic type liquid level gauge of FIG. It is a figure which shows the reflective echo waveform on other conditions in the ultrasonic type liquid level gauge of FIG. It is a figure which shows the reflective echo waveform on other conditions in the ultrasonic type liquid level gauge of FIG. It is a figure which shows the reflective echo waveform on other conditions in the ultrasonic-type liquid level meter of FIG. 3, and is a figure which shows a reflective echo waveform when extending the drive time from the conditions of FIG. It is a flowchart for demonstrating the operation example of the ultrasonic type liquid level gauge which concerns on one Embodiment of this invention. It is a trend graph which shows the result of having measured the residual amount value of the LP gas bulk storage tank over time using the conventional ultrasonic level gauge.

  The ultrasonic liquid level gauge (also referred to as an ultrasonic level gauge) according to the present invention is a liquid level gauge that detects the liquid level based on the reception timing of the ultrasonic level echo transmitted to the liquid level. By detecting (measuring) the liquid level (the level of the liquid level), the remaining amount ratio of the liquid in the container can be calculated from the shape of the container and the measured liquid level. Can also be used as a fuel gauge. Since the ultrasonic liquid level gauge can be measured without contact with an object to be measured (liquid), it can be suitably used for measuring the remaining amount of combustible liquid in the pressure tank.

  The ultrasonic liquid level gauge according to the present invention (hereinafter simply referred to as “main liquid level gauge”) has a device for preventing erroneous display of measured values in the vicinity of the sky when detecting such a liquid level. In addition, the stability of the function as a fuel gauge is improved. Hereinafter, an example in which the liquid level gauge is installed in an LP gas bulk storage tank (LPG tank) will be described.

  FIG. 1 and FIG. 2 are schematic views showing an example in which an ultrasonic liquid level gauge is installed in horizontal and vertical LP gas bulk storage tanks, respectively. 1 and 2, the LP gas bulk storage tank 1 is filled with an LP liquid 2. This liquid level gauge is composed of an ultrasonic sensor 5 attached to the lower part of the LP gas bulk storage tank 1 and a control unit 4 connected to the ultrasonic sensor 5 and controlling it to detect (calculate) the liquid level at the liquid interface 3. Composed. The ultrasonic sensor 5 may be installed on the outer wall surface (below the liquid level) of the bottom of the LP gas bulk storage tank 1, and the control unit 4 may be installed at an arbitrary position of the LP gas bulk storage tank 1.

  The ultrasonic sensor 5 emits ultrasonic waves into the liquid (LPG) in the LP gas bulk storage tank 1 by emitting ultrasonic waves upward from below the liquid level and passing through the bottom steel plate of the LP gas bulk storage tank 1. To do. The emitted ultrasonic wave propagates in the liquid, reflects off the liquid surface, propagates in the liquid as a reflected wave, passes through the bottom steel plate of the LP gas bulk storage tank 1 again, and is received by the same ultrasonic sensor 5.

  The control unit 4 measures the propagation delay time of the ultrasonic waves transmitted and received by the ultrasonic sensor 5 in this way, and calculates and displays the liquid level height from the measured values. As described above, the control unit 4 detects the liquid level based on the reception timing of the reflected wave in the ultrasonic sensor 5 (reception timing with respect to the transmission timing).

  A transmission / reception sensor is used as the ultrasonic sensor 5 in consideration of constraints, costs, and the like attached to the container. The ultrasonic sensor 5 can measure a liquid level height in a wide range of 100 mm to 3000 mm by being attached by attaching the ultrasonic sensor 5 to a position where the ultrasonic wave is emitted vertically to the liquid interface inside the container.

  FIG. 3 is a block diagram illustrating a configuration example of an ultrasonic liquid level gauge according to an embodiment of the present invention. The liquid level gauge illustrated in FIG. 3 can be installed in the LP gas bulk storage tank 1 as shown in FIGS. The control unit 4 includes a CPU 6, a sensor driving circuit DRV, an amplifier / comparator circuit including an amplifier AMP and a diode Di, and a temperature amplifier TAMP. The ultrasonic sensor 5 illustrated here includes not only an ultrasonic transmission / reception function but also a temperature sensor that detects a temperature and outputs the temperature to the control unit 4.

  The drive signal output from the T terminal of the CPU 6 built in the control unit 4 drives the ultrasonic sensor 5 via the sensor drive circuit DRV, so that ultrasonic waves are emitted to the LP liquid 2 in the LP gas bulk storage tank 1. The Then, this ultrasonic wave is reflected by the liquid interface 3 and returns to the ultrasonic sensor 5 again. The ultrasonic sensor 5 converts this ultrasonic wave (reflected wave) into an electric signal and outputs it to the control unit 4. The control unit 4 inputs this output and transmits it to the terminal R of the CPU 6 through the amplifier / comparator circuit. To do. The CPU 6 measures the elapsed time from the output of the terminal T to the input of the terminal R, and corrects the ultrasonic propagation sound velocity of the LP liquid 2 with the temperature A / D value output from the temperature sensor and amplified by the temperature amplifier TAMP. The liquid level distance is calculated. Of course, based on the liquid level distance and the area corresponding to the distance in the LP gas bulk storage tank 1, the remaining liquid amount and the ratio of the remaining liquid amount to the filling time (remaining ratio) can also be calculated.

  Here, as illustrated by reference numeral 10 in FIG. 3, the amplifier / comparator circuit has a circuit configuration in which the gain characteristic changes with time and also changes with sensor driving time.

  With reference to FIGS. 4 to 9, it will be described that the gain characteristic changes even in the sensor driving time. 4 to 9 are diagrams showing reflected echo waveforms under different conditions in the ultrasonic liquid level gauge of FIG.

  FIG. 4 shows an echo waveform and a comparator output (input of terminal R of CPU 6) when the actual liquid level is 310 mm and the sensor driving time is 50 μS. Repeated reflection echoes on the liquid surface are also observed, which is good. At this time, the measured display value, which is a display value obtained by measuring the remaining amount ratio, is 36%.

  FIG. 5 shows an echo waveform and a comparator output when the actual liquid level is 310 mm and the sensor driving time is 100 μS. The change of the reflected echo due to the extension of the sensor driving time is hardly seen and is good. At this time, the measurement display value is 36% as in the case of the condition of FIG.

  FIG. 6 shows an echo waveform and a comparator output when the actual liquid level is 105 mm (near the product specification lower limit value) and the sensor driving time is 50 μS. The time axis of the reflected echo at the liquid level is compressed according to the liquid level drop from FIG. Although receiving reverberation echo interference, the measured value corresponding to the actual liquid level is stably displayed by an appropriate liquid level detection algorithm in the comparator and the CPU 6. At this time, the measured display value is 6%.

  FIG. 7 shows an echo waveform and a comparator output when the actual liquid level is 105 mm (near the product specification lower limit value) and the sensor driving time is 100 μS. By extending the sensor driving time with respect to the conditions of FIG. 6, the amplification factor (gain) after driving the sensor is kept low according to the circuit characteristics of the amplifier (AMP gain characteristics indicated by reference numeral 10 in FIG. 3). The effect of reverberant echo has been reduced. Thus, it can be seen that the amplifier having the AMP gain characteristic can reduce the influence of the reverberation echo by extending the sensor driving time. At this time, the measurement display value is 6% as in the case of the condition of FIG.

  FIG. 8 shows an echo waveform and a comparator output when the liquid level is lowered under the conditions of FIG. 6, the actual liquid level is 80 mm (out of product specifications), and the sensor drive time is 50 μS. The liquid level reflection echo and the reverberation echo are mixed according to the liquid level drop, and the soft filtering of the liquid level detection algorithm in the comparator and CPU 6 is submerged, and 34% corresponding to a distance 320 mm which is four times the actual liquid level is erroneously displayed. ing. Even though the actual liquid level is below the minimum detection distance of the product specification, it is erroneously measured that the remaining amount is sufficient, which is a serious drawback as a liquid level gauge. This echo waveform varies depending on the amount of gas generated and the like, and it is difficult to obtain stability only by software improvement of the liquid level detection algorithm.

  Therefore, this liquid level gauge utilizes the fact that the influence of reverberant echo can be reduced by extending the sensor driving time. That is, as a result of detecting the liquid level, this liquid level gauge performs detection again by extending the sensor driving time of the ultrasonic sensor 5 when the liquid level becomes equal to or lower than the predetermined liquid level D0.

  FIG. 9 shows a reflected echo waveform when re-detection is performed under the condition that the sensor driving time is extended from the condition of FIG. More specifically, FIG. 9 shows an echo waveform and a comparator output when the actual liquid level is 80 mm (outside the product specification) and the sensor driving time is 100 μS. The reflected echo from the liquid surface is sufficiently large without any attenuation in the vicinity of the minimum detection distance (measurement lower limit value) in the product specification, and the amplification factor (gain) of the amplifier at a short distance (where the remaining ratio is low) Is lowered to improve the S / N ratio of the reverberation echo and the liquid surface reflection echo, thereby ensuring the liquid surface capture. In this liquid level gauge, in order to lower the amplification factor (gain) of the amplifier at a short distance, an amplifier having an AMP gain characteristic indicated by reference numeral 10 in FIG. 3 is used, and the sensor driving time is lengthened.

  In this way, in this liquid level gauge, by controlling the drive time of the sensor drive pulse to be longer when measuring that the amount of liquid in the container is low, the reverberation echo and the liquid surface reflection echo are reduced. We are trying to stratify. The extent of extension may be determined arbitrarily, and may be set later. Further, as can be seen from the comparison of the measurement results under the conditions of FIG. 4 and FIG. 5 and the comparison of the measurement results under the conditions of FIG. 6 and FIG. In the case where the sensor drive time does not exist, there is no problem because the measured value does not change due to such extension of the sensor driving time.

  In addition, under the conditions shown in FIG. 9, the liquid level value can be measured correctly (that is, it is correctly detected that it is out of the product specification, that is, at least below the product specification lower limit value). The measurement display value to be displayed on the LCD or the like may not be displayed as “----” so that the operator can recognize that there is.

  FIG. 10 shows an operation flow of the ultrasonic liquid level gauge of FIG. 3 including the process of extending the sensor driving time as described above. In the liquid level gauge, first, the ultrasonic sensor 5 is driven for a predetermined driving time to measure the remaining liquid level (step S1). As a result of this measurement, the CPU 6 determines whether or not the measured value is equal to or greater than the previous measured value (step S2). If the measured value is equal to or greater than the previous measured value, the sensor driving time is extended by a predetermined time (step S6) and remeasured (step S6). Redetection) is performed (step S7). The reason why re-detection is extended in the case of YES in step S2 is that, near the measurement lower limit value, a measured value that is equal to or higher than the previous measured value is calculated due to erroneous measurement even though the liquid level has decreased from the previous value. This is because there is a possibility of being. In this way, the determination in step S2 can be adopted as a criterion for determining whether or not the “actual liquid level” may be interrupting the predetermined liquid level D0.

  If NO in step S2, the CPU 6 determines whether or not it is a predetermined liquid level D0 (remaining amount ratio 20% in this example) or less (step S3). Proceed to step S6. After the remeasurement, the sensor drive time is returned to the predetermined drive time in preparation for the next detection (step S1) in consideration of power saving. After step S7, the CPU 6 determines whether or not the measured value is equal to or greater than the expected value (that is, the measurement lower limit value) (step S8), and in the case of NO, performs a measurement display of “----”. (Step S9).

  If YES in step S8 or NO in step S3, the measurement value display is updated (step S4). After step S4 and after step S9, the CPU 6 starts an interval timer (step S5), and returns to step S1 in response to the arrival of the measurement interval. As in step S5, the liquid level gauge measures the liquid level every several hours with a built-in timer of the CPU 6 for the purpose of managing the remaining amount.

  As described with reference to FIG. 10, in the liquid level gauge, as a result of detecting the liquid level, (A) when the liquid level becomes equal to or lower than a predetermined liquid level D0 and / or (B) the liquid level is When it becomes larger than the previously detected liquid level, the sensor driving time of the ultrasonic sensor 5 is extended and redetection is performed.

  That is, in this liquid level gauge, when measuring the area where the measured value adversely affects the remaining amount management (for example, 20% or less), the measurement condition (sensor driving time) is used to ensure the authenticity of the measured value. To change. Instead, in this liquid level gauge, when a value larger than the previous measurement value is measured, the measurement condition (sensor drive time) may be changed to ensure the authenticity of the measurement value. Or you may employ | adopt both as conditions for changing measurement conditions. In any case (when the liquid level measurement result is less than 20% remaining and / or higher than the previous measurement value), consider the hardware circuit characteristics and measurement algorithm to verify that the measurement value is correct. When the remaining amount of liquid is actually present, the measurement is performed correctly, and when it is near the sky, the sensor is driven with a sensor driving time such that a result that the liquid level measurement is uncertain is output.

  As a result, even when the liquid level is measured with the measurement lower limit value interrupted, the liquid level reflection echo and the reverberation echo are accurately distinguished, and the measurement lower limit value is accurately detected with low power consumption. It becomes possible. Moreover, in this liquid level gauge, in order to improve such measurement stability, it is sufficient to add a simple algorithm for changing measurement conditions. In other words, according to this level gauge, it is possible to measure stably without causing erroneous measurement even under conditions outside the product specifications, so it is possible to prevent out-of-gassing accidents, stable operation of the remaining amount monitoring system used in the remote monitoring center, etc. It can be realized only by improving the software. Furthermore, even when the liquid level has fallen below the measurement lower limit value due to such detection having measurement stability, the measurement result is surely hidden (or displayed to indicate that the lower limit value has been interrupted). be able to.

  Supplementing about power saving, according to this liquid level gauge, only a value with a low liquid remaining amount was measured (not only when it was directly detected that the liquid level was lower than D0, but also as shown in (B) above. (Including when it is estimated that there is a possibility of this), the sensor driving time with large battery consumption is extended, so that the increase in power consumption is slight and the battery life is not reduced. Further, when the liquid is filled after the measurement lower limit value is interrupted, when the condition (B) is adopted, only the condition (A) is adopted after re-detection under the condition. In some cases, the liquid level tends to decrease with the use of LPG after re-detection under that condition, so that power consumption can be reduced by driving with the original sensor driving time. For example, when the sensor drive time is set to 100 μs at any remaining amount (in the entire remaining amount range) (conventional method), the sensor drive time is normally set to 50 μs and the actual liquid level is 105 mm (the lower limit value of the product specification) (Neighborhood) When it was reduced to below 100 μs (applying the present invention), the conventional method would shorten the battery life by about 10% compared to the method of the present invention. .

  Further, as another embodiment of the present invention, the liquid level gauge effectively uses the reflected echo pulse width (the reflected echo pulse width increased from before the extension) obtained in the sensor driving time after the extension in the process of FIG. You may make it use for judgment of echo. As a result, further improvement in stability can be expected.

  Such an embodiment will be specifically described. The above-described re-detection (re-measurement in step S7) is performed by the CPU 6 from the actual reflected wave (echo waveform) according to the pulse width of the reflected wave received by driving with the extended sensor driving time. This is performed by determining a reflected wave (a liquid surface reflection echo effective for detection rather than a reverberation echo) and calculating a liquid level based on the reception timing of the liquid surface reflection wave.

  Here, when determining the liquid surface reflected wave according to the pulse width of the reflected wave, utilizing the characteristic that the pulse width of the liquid surface reflected echo reflected on the actual liquid surface increases or decreases in proportion to the sensor driving time, The H (High) / L (Low) duty ratio of the pulse of the reflected wave is analyzed, and the liquid surface reflected wave is determined according to the H / L duty ratio.

  As described above, in this embodiment, the H / L duty ratio of the pulse of the reflected wave (reflected echo) is used as the determination criterion, and the reverberation echo (noise echo) and the liquid surface reflected echo can be divided into layers, Therefore, measurement stability can be further improved. Of course, it is preferable to determine such a liquid surface reflected wave not only at the time of re-detection but also at the first detection (detection before extending the sensor driving time).

  Further, the processing using the H / L duty ratio of the reflected echo pulse of this embodiment as a criterion (hereinafter referred to as second processing) is the case of the above (A) and / or the above described as shown in FIG. Even in the case of (B), it is possible not only to improve the measurement stability but also to maintain a certain level even if it is not used together with the process (hereinafter referred to as the first process) of extending the sensor drive time of the ultrasonic sensor 5 and performing redetection. There is also an effect of power saving.

  More specifically, the liquid level is detected based on the reception timing of the reflected wave in the ultrasonic sensor 5 even in the second process that is not used in combination with the first process. For example, the following process is performed. First, the ultrasonic sensor 5 is driven for a predetermined driving time to receive a reflected wave, the H / L duty ratio of the received reflected wave pulse is analyzed, and when the H / L duty ratio is equal to or less than a predetermined value, Based on the H / L duty ratio, the liquid level reflected wave is determined from the reverberation wave and the reflected wave from the liquid level in the lower limit of the liquid level, and the liquid level is determined based on the reception timing of the determined liquid level reflected wave. Is detected (detected by calculating). On the other hand, when the H / L duty ratio is larger than a predetermined value, the driving time of the ultrasonic sensor 5 is extended, and the H / L duty ratio of the reflected wave pulse received by the extension of the driving time is analyzed. The liquid level reflected wave is determined from the reverberant wave and the reflected wave from the liquid level in the lower limit of the liquid level, and the liquid level is detected (detected by calculating) based on the reception timing of the determined liquid level reflected wave. To do.

  Since the echo waveform in FIG. 6 has a high amplification degree, the comparator output has a high H state and a low L state in the time domain near the sensor drive in a half-saturated state. In the state of FIG. 8 where the liquid level has further decreased, the state of H is further longer. For example, a value between these values may be adopted as the predetermined value. On the other hand, in FIGS. 7 and 9 in which the drive time is extended, since the amplification degree is appropriately suppressed, the echo waveform does not manifest the reverberation echo, and a reflection echo top from the liquid surface is recognized. Thus, the echo from the liquid level can be accurately captured by checking the H / L duty of the pulse of the reflected wave.

  In the second process that is not used in combination with the first process, not only the measurement stability is improved as described above, but also compared with the sensor driving time in an ultrasonic liquid level gauge that has the same measurement lower limit as in the prior art, The total drive time of the drive time and the extended drive time can be shortened. Therefore, in the second process that is not used in combination with the first process, when the same total drive time as the sensor drive time of the conventional ultrasonic liquid level gauge is adopted, the measurement lower limit value can be reduced as compared with the conventional process. It also has a certain effect in terms of power saving.

DESCRIPTION OF SYMBOLS 1 ... LP gas bulk storage tank, 2 ... LP liquid, 3 ... LP liquid interface, 4 ... Control unit, 5 ... Ultrasonic sensor.

Japanese Patent No. 4083037 Japanese Patent No. 4079823

Claims (3)

An ultrasonic sensor for transmitting an ultrasonic wave from the bottom of the container toward a liquid surface of the liquid in the container and receiving a reflected wave from the liquid surface, and receiving timing of the reflected wave in the ultrasonic sensor; And an ultrasonic level gauge that detects the liquid level.
As a result of detecting the liquid level, when the liquid level falls below a predetermined liquid level and / or when the liquid level becomes larger than the previously detected liquid level, the detection time is extended by extending the driving time of the ultrasonic sensor. An ultrasonic liquid level gauge characterized by that.   2. The ultrasonic level gauge according to claim 1, wherein the re-detection is performed by detecting a liquid level from the reflected wave according to a High / Low duty ratio of the pulse of the reflected wave after the extension of the driving time. An ultrasonic liquid level gauge characterized by determining a reflected wave and calculating the liquid level based on the reception timing of the liquid surface reflected wave. An ultrasonic sensor for transmitting an ultrasonic wave from the bottom of the container toward a liquid surface of the liquid in the container and receiving a reflected wave from the liquid surface, and receiving timing of the reflected wave in the ultrasonic sensor; And an ultrasonic level gauge that detects the liquid level.
The ultrasonic sensor is driven for a predetermined driving time to receive the reflected wave, and the driving time of the ultrasonic sensor is extended only when the High / Low duty ratio of the received pulse of the reflected wave is larger than a predetermined value. Further, a liquid level reflected wave is determined from the reflected waves in accordance with a High / Low duty ratio of the pulse of the reflected wave after extending the driving time, and based on the reception timing of the liquid level reflected wave. An ultrasonic liquid level gauge characterized by detecting the liquid level.

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