JP2001108507A - Target type liquid level measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a method for accurately measuring a liquid level by measuring acoustic velocity under a measuring condition and directly or indirectly utilizing the acoustic velocity value, independent of containers or the kinds of contained liquid and the variation of temperature of the liquid. SOLUTION: The target type liquid level measuring method relating to this invention is characterized that a first target T1 and a second target T2 are arranged in liquid 4 contained in a container 2 in a state being shifted in the depth direction of the liquid, a ultrasonic pulse is applied to a bottom wall back surface 16 of the container 2, reflected signals of the ultrasonic pulses from the first target T1, the second target T2, and a liquid surface 14 are received, and the liquid surface height H is measured from the received time information (t1, t2 and t3) on the reflected signals and the position information (Y1 and Y2) on the first target and the second target. Acoustic velocity V in the liquid is derived from the received time information and the position information, and the liquid surface height H is measured by directly utilizing the acoustic velocity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a liquid surface position in a container containing a liquid such as liquefied natural gas or liquefied propane, and more particularly, to an ultrasonic reflecting member (hereinafter referred to as a target) in a liquid. ), And relates to a target-type liquid level measuring method capable of accurately measuring the liquid level using the reflected signal from the target.

[0002]

2. Description of the Related Art As a conventional liquid surface position measuring apparatus, for example, an apparatus as described in Japanese Utility Model Laid-Open No. 2-100039 has been developed. In this apparatus, as shown in FIG. 10, a liquid 4 is accommodated in a container 2, an ultrasonic transmitter / receiver 8 made of a piezoelectric element is arranged on a bottom surface 6 in the container 2, and a back surface of the bottom wall 10 is provided. Is provided by providing an electrode 12.

The measurement of the liquid level using this apparatus is performed as follows. That is, an ultrasonic pulse is transmitted from the ultrasonic wave receiver 8 toward the liquid surface 14, and the ultrasonic pulse reflected by the liquid surface 14 is received by the ultrasonic wave receiver 8.
If the time from transmission to reception is t, the liquid level is H, and the sound velocity in the liquid is V, the liquid level H can be obtained from H = Vt / 2.

Further, another conventional apparatus is disclosed in Japanese Patent Laid-Open No.
There is an apparatus described in Japanese Patent No. 64314. In this device,
As shown in FIG. 11, the ultrasonic wave receiver 8 is disposed in contact with the back surface 16 of the bottom wall 10. It is the same as the case of the method 10 for measuring the liquid level, except that the arrangement on the lower surface 16 is structurally different from FIG.

[0005]

A fundamental disadvantage of these prior art devices is that the velocity of sound V is uncertain. The sound velocity V varies greatly depending on the type of liquid, and even if it is the same type of liquid, it has the property of increasing or decreasing depending on the temperature. Even if the type of liquid changes or its temperature changes, if the liquid level height H is derived using the same sound velocity value, the liquid level level will include a considerable error.

An object of the present invention is to solve the above-described problem in the conventional liquid level measurement using ultrasonic waves, and to measure the sound velocity under measurement conditions, and indirectly or directly measure the sound velocity value. It is a main object of the present invention to realize a liquid level measurement method that can accurately detect the liquid level in a container by directly using the liquid level measurement method.

[0007]

SUMMARY OF THE INVENTION A target type liquid level measuring method according to the present invention has been made to achieve the above-mentioned object, and the invention of claim 1 is directed to a method for measuring a liquid level in a liquid contained in a container. The target and the second target are displaced in the depth direction of the liquid, and an ultrasonic pulse is transmitted to the back surface of the bottom wall of the container, and reflected signals of the ultrasonic pulse by the first target, the second target, and the liquid surface are generated. Receiving, receiving time information of these reflected signals and the first target and the second target.
It is characterized in that the liquid level is measured from target position information.

According to a second aspect of the present invention, a target is disposed at a predetermined height from a bottom in a liquid contained in a container, an ultrasonic pulse is transmitted to the back surface of the bottom wall of the container, and the target and the liquid surface are used. Receiving the reflected signal of the ultrasonic pulse,
The liquid level is measured from the reception time information of these reflected signals and the position information of the target.

According to a third aspect of the present invention, there is provided the target type liquid according to the first or second aspect, wherein a sound velocity in the liquid is derived from the reception time information and the position information, and the liquid level is measured using the sound velocity. This is a surface measurement method.

A fourth aspect of the present invention is the target type liquid level measuring method according to the first, second or third aspect, wherein the target is a round bar arranged horizontally.

According to a fifth aspect of the present invention, the first target and the second target are displaced in the horizontal direction.
It is a target type liquid level measuring method described in the above.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have made intensive studies to determine the speed of sound under various measurement environments,
An ultrasonic reflecting member called a target is immersed and arranged in a liquid, a sound speed is determined from a reflected ultrasonic signal from the target, and a liquid level height is derived from a liquid surface reflected signal using the sound speed. It has arrived. Hereinafter, an embodiment of a target type liquid level measuring method according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view showing a first embodiment of the present invention. In this figure, the same parts as those in FIGS. 10 and 11 are denoted by the same reference numerals. The container 2 contains a liquid 4 such as liquid propane, and the height from the bottom surface 6 of the bottom wall 10 to the liquid surface is H. In the liquid 4, a first target T1 and a second target T2 made of two round bars are arranged.

A first target T1 and a second target T2
Are located at heights Y1 and Y2 from the bottom surface 6, respectively, so that the separation height ΔY between them is Y2-Y1. Further, the targets T1 and T2 are arranged so as to be shifted in the horizontal direction by a separation width ΔX. The separation width ΔX is provided for the reflected ultrasonic waves of the first target T1 and the second target T2 to reach the ultrasonic wave receiver independently, and is designed to be larger than the cross-sectional diameter of the round bar constituting the target. I have.

An ultrasonic wave transmitter / receiver S such as a piezoelectric element is disposed in contact with the back surface 16 of the bottom wall 10, and this element has both the function of transmitting ultrasonic waves and the function of receiving ultrasonic waves in one body. . Of course, an element in which the ultrasonic transmitter and the ultrasonic receiver are integrated may be used, or both may be arranged separately.

An ultrasonic pulse is emitted from the ultrasonic transmitter / receiver S by the pulse circuit P, and the reflected ultrasonic wave is transmitted to the ultrasonic transmitter / receiver S
To receive. The reflected signal is amplified by the amplifier circuit A, detected by the detection control circuit C, and the liquid level H is derived. Various information such as the liquid level, liquid temperature, sound speed, "no reflected wave", and failure are notified to the central control center by the notification circuit I.

FIG. 2 is a time chart of the transmission signal and the reception signal of the ultrasonic transmitter / receiver. (1) is an outgoing signal,
It indicates that the ultrasonic pulse has been transmitted P _S at time t = 0. (2) on the reception signal, time t = a reflected ultrasonic waves by the first target T1 received P _R1 at t1, t = t2 in the second
The reflected ultrasonic wave from the target T2 is received P _R2 and t = t
3 indicates that the reflected ultrasonic wave from the liquid surface 14 was received and _RL .

The thickness of the bottom wall 10 is Δ, the speed of sound in the bottom wall is v,
Assuming that the sound speed in the liquid is V, 2Δ / v + 2y1 / V = t
1,2Δ / v + 2y2 / V = t2 and 2Δ / v + 2H
/ V = t3 holds. From these equations, V = 2 (y2
-Y1) / (t2-t1) and H = y1 + V (t3-
t1) / 2 or H = y2 + V (t3-t2) / 2 is obtained. Therefore, the liquid surface height H can be obtained from the sound velocity V.

Two types of expressions are established for the liquid surface height H. When the expression of the liquid sound velocity V is substituted, both expressions are H.
= {(T3-t1) y2- (t3-t2) y1} / (t
2-t1). In this case, the liquid level H is obtained from the reception time information of the reflected ultrasonic wave and the position information of the target. Therefore, the sound velocity V
May or may not be used, and the liquid surface height H can be obtained by using either expression.

Further, the liquid temperature T can be derived from the liquid sound velocity V. In general, the liquid sound velocity V is expressed as V = (k / ρ) ^1/2 by the bulk modulus k and the density ρ. Since this equation depends on the temperature T, it is written as V = f (T). Conversely, T = f ^-1 (V), that is, T = g (V), and the liquid temperature T
Is obtained from the sound velocity V. Therefore, liquid temperature information can be obtained from the liquid sound velocity.

When the reflected ultrasonic signal cannot be received,
When the liquid runs out, various causes such as a displacement of the target and a failure of the ultrasonic wave emitting / receiving device are considered, and it can be generally indicated as failure (accident). Classification and display of failures are also possible in combination with other devices.

The liquid level height H can be approximated. For the sound velocity V, an exact V = 2 (y2-y1) / (t2
-T1) is used. It is assumed that the thickness Δ of the bottom wall can be ignored when calculating the liquid level height H. That is, when Δ≪H, 2H /
From V = t3, H = Vt3 / 2, and H = (y2-y
1) It becomes t3 / (t2-t1). In this equation, it is sufficient if there is positional information of the interval ΔY between the first target T1 and the second target T2, and the positional information Y1 and Y2 of each target is sufficient.
May not be required.

FIG. 3 is a flowchart for the liquid level measurement of the detection control circuit. At step n1, an ultrasonic pulse is transmitted at time t = 0. First target T1 at t = t1
Is received (n2), the reflected signal of the second target T2 is received at t = t2 (n4), and the liquid level 1 is received at t = t3.
4 is received (n6). If not received, a failure is determined (n3, n5, n7).

The liquid sound velocity V is derived (n8) from the position information (Y1, Y2) and the reception time information (t1, t2), and the liquid temperature T is calculated from this sound velocity V (n9). Sound velocity V, position information (Y1) and reception time information (t1, t)
The liquid level height H (n10) is obtained from 3). In step 10, a formula of H = Y2 + V (t3-t2) / 2 may be used. These various information, that is, the sound velocity V, the temperature T, the liquid level H, and the failure are transmitted to the central control center (n11).
Is done.

FIG. 4 is a diagram showing the state of reflection of ultrasonic waves by the target. The target T1 has a circular cross section. When an ultrasonic wave is reflected, a reflected wave immediately below returns to the ultrasonic wave receiver S, but a reflected wave at a slightly shifted position does not return. In other words, the reflected wave at the height position Y1 of the target T1 is received, and other reflected waves are not received, so that reception time information that accurately reflects the position Y1 can be obtained.

FIG. 5 is a layout view of a target having an elliptical cross section. Since the cross section of the target is elliptical, it does not return to the ultrasonic transmitter / receiver except for the reflection at the lowest point, and more accurate reflection information can be obtained. Further, since the minor axis direction of the ellipse is arranged in the horizontal direction, the separation width ΔX between the targets T1 and T2 can be reduced, and the target device can be made compact.

FIG. 6 is a sectional configuration view of a second embodiment of the present invention. In the present embodiment, only the first target T1 is used and the second target T2 is not used. Only this point is different from the case of the first embodiment. Therefore, the same parts as those of FIG. 1 are denoted by the same reference numerals and the description thereof will be omitted.

FIG. 7 is a time chart of the transmission signal and the reception signal of the ultrasonic transmitter / receiver in FIG. (1) in the outgoing signal, indicating at time t = 0 the ultrasonic pulse is transmitted P _S. (2) is a reception signal. At time t = t1, the reception ultrasonic wave reflected by the first target T1 is received _PR1 , and t = t3.
Indicates that the ultrasonic wave reflected by the liquid surface 14 has been received _PRL .

The thickness of the bottom wall 10 is Δ, the speed of sound in the bottom wall is v,
Assuming that the sound speed in the liquid is V, 2Δ / v + 2y1 / V = t
1 and 2Δ / v + 2H / V = t3 hold. Assuming that the thickness Δ of the bottom wall 10 is sufficiently small in this embodiment, both equations can be approximated as 2y1 / V = t1, 2H / V = t3. From these, the sound velocity V and the liquid level H are V = 2y
1 / t1 and H = y1 · t3 / t1.

With respect to the liquid level height H, 2 through V and H
Although it appears that a multiple approximation is included, only an approximation of V is actually included. That is, from the previous equation, t3−t1 = 2
(H-y1) / V is obtained exactly, and H = y1 + V (t3
−t1) / 2. Substituting V = 2y1 / t1 into this gives H = y1 · t3 / t1.

From the sound velocity V, the liquid temperature T becomes T =
g (V). The liquid surface height H can be obtained from H = y1 + V (t3−t1) / 2 through the sound speed V, or from H = y1 · t3 / t1 without passing through the sound speed. Either one may be used, but in the latter case, the sound velocity V may be indirectly used.

FIG. 8 is a measurement flowchart for the liquid level of the liquid level detection control circuit of FIG. At step n21, an ultrasonic pulse is transmitted at time t = 0. At t = t1, a reflection signal of the first target T1 is received (n22), and t = t3
First, a reflection signal of the liquid surface 14 is received (n24). If not received (n23, n25), it is determined that a failure has occurred.

Position information (Y1) and reception time information (t1)
Is derived (n26), and the liquid temperature T is calculated from this sound velocity V (n27). Then, the liquid level H (n28) is obtained from the sound velocity V, the position information (Y1), and the reception time information (t1, t3). Of course, H = y from only the position information (Y1) and the reception time information (t1, t3).
H may be obtained through 1 · t3 / t1. These various information, that is, the sound velocity V, the liquid temperature T, the liquid level H, and the failure are transmitted to the central control center (n29).

FIG. 9 is a block diagram of a management system for centrally managing the liquid level information of a plurality of containers. In the n containers 2, a first target T1 and a second target T2 are arranged. The liquid level information of each container 2 is sent from the notification circuit I to the central control center CC. The central control center CC manages a plurality of liquid level information and performs various tasks such as liquid replenishment and repair.

The target type liquid level measuring method according to the present invention is not limited to the above embodiment, and various modifications and design changes may be made within the technical scope of the present invention without departing from the technical scope of the present invention. Is included.

[0036]

According to the first aspect of the present invention, since two targets are immersed in the liquid, the liquid level can be accurately and accurately measured from the reflected signals and the positional information. it can.

According to the second aspect of the present invention, since one target is immersed in the liquid, if the thickness of the bottom wall of the container is sufficiently smaller than the target position or the liquid level, In addition, the liquid level can be accurately measured.

According to the third aspect of the present invention, since the speed of sound in the liquid is first derived, the liquid temperature can be measured simultaneously with the liquid level, so that the liquid level can be multilaterally managed.

According to the fourth aspect of the present invention, since the target is a round bar, the reflected ultrasonic wave at a position shifted from the lowermost end of the round bar is reflected at a wide angle and is hardly received by the ultrasonic receiver. The reflected ultrasonic wave at the lowermost position is strongly received, and the liquid level can be measured with high accuracy.

According to the fifth aspect of the present invention, since the first target and the second target are shifted in the horizontal direction, the reflected ultrasonic waves do not interfere with each other and the reflected signals from both targets are received independently. The liquid level can be measured with high accuracy.

[Brief description of the drawings]

FIG. 1 is a sectional configuration diagram of a first embodiment of the present invention.

FIG. 2 is a time chart of a transmission signal and a reception signal of the ultrasonic transmitter / receiver.

FIG. 3 is a measurement flowchart of a detection control circuit.

FIG. 4 is a diagram illustrating a reflection state of an ultrasonic wave by a target.

FIG. 5 is a layout view of a target having an elliptical cross section.

FIG. 6 is a sectional configuration diagram of a second embodiment of the present invention.

FIG. 7 is a time chart of a transmission signal and a reception signal of the ultrasonic transmitter / receiver in FIG. 6;

FIG. 8 is a measurement flowchart of the detection control circuit of FIG. 6;

FIG. 9 is a management configuration diagram for centrally managing liquid level information of a plurality of containers.

FIG. 10 is a sectional view of a first conventional example of a liquid surface position measuring device.

FIG. 11 is a sectional view of a second conventional example of a liquid level measuring device.

[Explanation of symbols]

2 is a container, 4 is a liquid, 6 is a bottom surface, 8 is an ultrasonic transmitter / receiver,
10 is a bottom wall, 12 is an electrode, 14 is a liquid surface, 16 is a back surface, A
Is an amplification circuit, C is a detection control circuit, I is a notification circuit, P is a pulse circuit, and S is an ultrasonic wave receiver.

Claims (5)

[Claims] 1. A method according to claim 1, wherein the first target and the second target are displaced in a depth direction of the liquid in the liquid contained in the container.
Transmitting an ultrasonic pulse to the back surface of the bottom wall of the container;
Receiving reflected signals of ultrasonic pulses from the target, the second target, and the liquid surface, and measuring the liquid surface height from reception time information of these reflected signals and position information of the first target and the second target. Target type liquid level measurement method. 2. A target is disposed at a predetermined height from a bottom surface in a liquid contained in a container, an ultrasonic pulse is transmitted to the back surface of the bottom wall of the container, and the ultrasonic pulse is reflected by the target and the liquid surface. A target type liquid level measurement method, comprising: receiving a signal; and measuring a liquid level from the reception time information of the reflected signal and the position information of the target. 3. The target type liquid level measuring method according to claim 1, wherein a sound velocity in the liquid is derived from the reception time information and the position information, and the liquid level is measured using the sound velocity. 4. The target type liquid level measuring method according to claim 1, wherein the target is a horizontally disposed round bar. 5. The target type liquid level measuring method according to claim 1, wherein the first target and the second target are arranged to be shifted in a horizontal direction.