JP2018025390A - Level measuring device and level measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a level measuring device capable of measuring the position of liquid level in a piping without requiring any mechanical scanning using a detector installed outside of the piping.SOLUTION: A level measuring device disposed outside a container, includes: a first ultrasonic element which is disposed to inject ultrasonic in a plate length direction of a container wall; a level measuring part that calculates the position of liquid level based on a reflection wave within the container wall; and a signal processing part that outputs a liquid level position signal.EFFECT: The level measuring device is capable of measuring the position of liquid level within a piping without carrying out any mechanical scanning using a detector installed outside a piping.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a liquid level measuring device and a liquid level measuring method for measuring a liquid level position of a liquid in a pipe or a container using ultrasonic waves.

  A level meter that detects a liquid surface position using a detector installed outside the container is disclosed in Patent Document 1.

  In the technique disclosed in Patent Document 1, an ultrasonic transducer installed outside the container propagates ultrasonic waves in a direction parallel to the liquid surface and measures the reflected waves. The position of the ultrasonic transducer is determined by utilizing the fact that the reflected wave of the ultrasonic wave differs between the gas and liquid when the position facing the ultrasonic transducer across the container wall (ie, inside the container) is liquid. The position of the liquid level in the container is detected by searching for the position where the reflected wave changes.

JP 2008-256451 A

  In the level meter disclosed in Patent Document 1, it is necessary to mechanically change (scan) the position of the ultrasonic transducer, so that there is a problem that it is difficult to apply to applications in which the liquid surface position is continuously monitored. there were.

  In order to eliminate mechanical scanning, it is possible to install a plurality of level gauges disclosed in Patent Document 1 outside the container to detect the liquid level position. There is a problem that the resolution (accuracy) of the liquid level measurement is limited by the spatial interval. Also, if the number of level meters installed is increased in order to increase the resolution, a large number of ultrasonic transducers are required, which increases the equipment cost, increases the time and effort of installation, and further complicates the maintenance of each level meter. The problem of becoming.

  In view of the above problems, an object of the present invention is to provide a liquid level measuring device capable of measuring the liquid level position of a liquid in a pipe without performing mechanical scanning by a detector installed outside the pipe. .

  The present invention provides a first ultrasonic element that is disposed outside a container and is disposed so that an ultrasonic wave is incident in a plate length direction of a container wall of the container, and a liquid surface from a reflected wave in the container wall. A liquid level measuring unit for calculating a position is provided, and a signal processing unit for outputting a liquid level position signal is provided.

  According to the liquid level measuring device of the present invention, it is possible to measure the liquid level position of the liquid in the pipe without performing mechanical scanning by a detector installed outside the pipe.

It is a figure which shows the structure of the liquid level measuring apparatus of 1st Example by this invention. It is a figure explaining the installation angle of the ultrasonic element in this invention. It is a figure for demonstrating the operation principle of the 1st Example of this invention. It is a figure explaining the 2nd Example by this invention. It is a figure which shows the structure of the 3rd Example by this invention.

  Flow measurement that measures the amount of liquid flowing in piping is indispensable for fluid measurement, plant efficiency improvement, operation management, and so on.

  Flowmeters include ultrasonic flowmeters and electromagnetic flowmeters. Ultrasonic flowmeters have the advantage of being able to measure the flow velocity of liquid in a pipe by installing a sensor outside the pipe. For this reason, ultrasonic flowmeters are particularly suitable for places that do not like pollution, such as pharmaceuticals and food manufacturing, and places that may contaminate sensors such as oil transportation and sewerage. The ultrasonic flowmeter can also meet the demand for adding a flow measurement function to existing piping.

  On the other hand, the ultrasonic flowmeter measures the flow velocity of the liquid. More specifically, since the operation principle of the ultrasonic flowmeter is to measure a change in sound velocity and a change in Doppler frequency due to the flow of the liquid, the ultrasonic flowmeter measures the flow velocity of the liquid.

  The flow rate can be measured by multiplying the liquid flow rate by the cross-sectional area occupied by the liquid in the pipe. A normal ultrasonic flowmeter calculates a flow rate value from a flow velocity measurement value on the assumption that the entire pipe is filled with a liquid.

  The state where the entire pipe is filled with liquid is called “full water”, and the state where there is an unfilled space is called “non-full”.

  As is clear from the above, the liquid level must be measured in order to measure the flow rate in a pipe that is not full.

  Several measuring instruments that measure the liquid level in pipes and containers are known as level meters. A microwave method, a float method, an ultrasonic method, etc. are known, but many methods are configured such that the detector to be measured is in contact with the inside of the pipe or the container. Surface measurement is not possible.

  Therefore, the present invention relates to a liquid level measuring device and a liquid level measuring method for measuring a liquid level position of a liquid in a pipe or a container using ultrasonic waves.

  Hereinafter, the configuration of the liquid level measuring device 20 according to the present embodiment will be described with reference to FIG.

(Measurement target)
First, the configuration of an object to be measured by the liquid level measuring device 20 will be briefly described.

  The container 501 contains a liquid 505 to be measured.

  The container 501 may be a container such as a tank that stores liquid, or may be a pipe through which liquid flows.

  The container 501 includes a vessel wall 502 and an internal space. The interior space contains liquid 505 and gas 504. The liquid 505 and the gas 504 may be a mixture of a plurality of types of substances.

  The material of the container wall 502 of the container 501 does not matter as long as it is a material that propagates ultrasonic waves. Examples of such materials include metals such as iron, stainless steel, and aluminum, and resin materials such as acrylic.

  In this embodiment, an example of a pipe 501 through which water flows is shown. The container 501 in FIG. 1 shows a cross-sectional view of the pipe 501. The material of the pipe in this embodiment is stainless steel.

  The container 501, the container wall 502, and the liquid 505 are objects to be measured by the liquid level measuring device of the present embodiment, and are not included in the liquid level measuring device of the present embodiment.

  The liquid level measuring device 20 of the present embodiment includes an ultrasonic element 21 and a signal processing unit 40.

  The ultrasonic element 21 is installed on the outside of the vessel wall 502 of the container 501, that is, on the vessel wall opposite to the liquid 505 across the vessel wall 502.

  The signal processing unit 40 is electrically connected to the ultrasonic element 21. The signal processing unit 40 includes a transmission / reception circuit 41 and a liquid level measurement unit 42 and outputs a liquid level position signal 44.

(Installation angle of ultrasonic element)
The installation angle of the ultrasonic element 21 will be described with reference to FIG.

  FIG. 2 is an enlarged view of the installation site of the ultrasonic element 21 on the vessel wall 502.

  The direction in which the ultrasonic element 21 emits ultrasonic waves is referred to as an ultrasonic emission axis 312. In this specification, an angle formed by the ultrasonic emission axis 312 and the normal 311 of the instrument wall 502 is defined as an “installation angle” 313 of the ultrasonic element. FIG. 2 (a) shows a case where the surface of the vessel wall 502 is flat, and FIG. 2 (b) shows a case where the surface of the vessel wall 502 is a curved surface having a curvature. In either case, the installation angle A313 is defined with reference to the normal 311 of the wall at the installation position of the ultrasonic element.

  In this embodiment, the ultrasonic element 21 is installed so that the installation angle A313 of the ultrasonic element is a non-zero value. In other words, the ultrasonic element is installed such that the ultrasonic emission axis 312 is inclined with respect to the normal 311 of the vessel wall 502. By installing with a non-zero installation angle A in this way, the ultrasonic wave 321 emitted from the ultrasonic element is incident toward the “plate length direction” of the instrument wall 502.

(Definition of plate length direction and plate thickness direction)
Here, “plate length direction” is a term used in contrast to “plate thickness direction”. In other words, “ultrasonic wave in the plate thickness direction” means “ultrasonic wave that reaches the inside of the container across the wall” as in the prior art, whereas “ultrasonic wave length” “Directional ultrasonic waves” means “ultrasonic waves traveling along the wall of the instrument wall” (along the wall), and the ultrasonic waves travel in the longitudinal direction while reflecting inside the instrument wall plates. To do. For example, when the container 501 is a pipe as shown in FIG. 1, the ultrasonic wave travels in the circumferential direction of the pipe.

  As shown in FIG. 2, in order to install the ultrasonic element 21 at a non-zero installation angle A313, a shoe 31 is installed between the ultrasonic element 21 and the instrument wall 502 as necessary. The shoe 31 is made of, for example, a resin such as polystyrene, and the ultrasonic element 21 can be installed at a desired installation angle A313 by appropriately designing the shape thereof.

  Since the installation angle A313 of the ultrasonic element 21 is an angle formed by the ultrasonic emission axis 312 and the normal 311 of the instrument wall 502, an element that emits ultrasonic waves in an oblique direction is used as the ultrasonic element 21. In some cases, the shoe 31 is not necessarily required.

(Liquid level measurement process)
Next, the process of measuring the liquid level will be described.
(1) When the transmission / reception circuit 41 applies the excitation pulse signal to the ultrasonic element 21, the ultrasonic element converts the electric signal into an ultrasonic wave, and the ultrasonic pulse is incident into the vessel wall 502 of the container 501.
(2) After that, the ultrasonic wave element receives the reflected wave generated at the container wall position in contact with the gas 504-liquid 505 interface position in the container wall 502, converts it into an electric signal, and transmits it to the transmission / reception circuit 41.
(3) The liquid level measuring unit 42 receives the received signal from the transmission / reception circuit 41, calculates the propagation time of the reflected wave, and calculates the liquid level position from the propagation time. And it outputs as a liquid level position signal.

(Measurement principle)
The measurement principle of the liquid level measuring device of this embodiment will be described with reference to FIG.

  Since the ultrasonic element 21 is installed with a non-zero inclination angle with respect to the normal line of the wall 502 of the pipe 501, the ultrasonic pulse transmitted from the ultrasonic element is the length of the plate in the wall 502. Propagate in the direction.

  Of the vessel wall 502, the portion in contact with the first phase (the gas phase 504 in this embodiment) in the container and the portion in contact with the second phase (the liquid phase 505 in this embodiment) in the container , The acoustic impedance of the wall is different. For this reason, reflection of ultrasonic waves occurs at the wall position in contact with the interface between the first phase and the second phase (that is, the liquid level). This is the reflected wave received in step (2).

  In this specification, the vessel wall position in contact with the interface between the first phase and the second phase (that is, the liquid level) is referred to as the vessel wall liquid level position 511. As shown in FIG. 2, the length of the path along the instrument wall 502 from the ultrasonic element installation position to the instrument wall liquid level position 511 is defined as L1.

  Since the reflected wave received in step (2) is a wave that has returned to the ultrasonic element after reciprocating along the path on the wall of length L1, its reflected time, that is, reflected from the transmission time of the ultrasonic pulse. The time difference Δtp until the wave reception time has a relationship of (Equation 1) between the vessel wall liquid level position 511 and the vessel wall length L1 between the ultrasonic element installation positions.

  Here, c is the speed of sound of the ultrasonic wave inside the vessel wall 502. In this way, the wall length L1 between the liquid surface position 511 on the container wall and the ultrasonic element installation position is obtained.

  The liquid surface position can be measured from the container wall length L1 between the liquid surface position 511 on the container wall and the ultrasonic element installation position and the installation position of the ultrasonic element 21.

  In this way, the liquid level position is calculated from the ultrasonic element that is arranged outside the container and is arranged so that the ultrasonic wave is incident in the plate length direction of the container wall of the container, and the reflected wave in the container wall. A liquid level measuring unit that outputs a liquid level position signal so that ultrasonic waves are incident in the plate length direction of the container wall of the container. There is no need to scan manually. Therefore, the ultrasonic element can measure the liquid level in the container without performing mechanical scanning.

  Next, this embodiment will be described with reference to FIG.

In the configuration of the present embodiment, the following steps are added to the above steps (1) to (3).
(4) The ultrasonic element receives the circulating wave in which the incident wave of the ultrasonic pulse makes one return around the container 502, converts it into an electrical signal, and transmits it to the transmission / reception circuit.
(5) The liquid level measuring unit calculates the liquid level position from the propagation time Δtp1 of the reflected wave calculated in step (3) and the propagation time Δtp0 of the circulating wave calculated in step (4). And it outputs as a liquid level position signal.

  In the configuration in which these steps (4) and (5) are added, the liquid surface position is measured as follows.

  The ratio of the propagation time Δtp1 of the reflected wave and the propagation time Δtp0 of the circulating wave is as follows.

  Here, L0 = c × Δtp0 is the length of one round of the container in the circumferential direction. Since L0 is a known length, the vessel wall length L1 between the vessel surface liquid level position 511 and the ultrasonic element installation position can be obtained from the ratio Δtp1 / Δtp0 of the two propagation times. That is, the liquid level position can be measured.

  According to this embodiment, it is not necessary to use the value of the sound velocity c in the vessel wall to measure the liquid surface position, and the liquid surface position can be measured from the ratio of the propagation time of the reflected wave and the propagation time of the circulating wave. . For this reason, even if environmental conditions such as ambient temperature change and the sound velocity in the wall fluctuates, the liquid level position can be measured with high accuracy.

  As described above, according to the present embodiment, there is an effect that liquid level measurement with high accuracy that is not easily affected by a change in temperature or the like can be performed.

  The liquid level measuring apparatus according to this embodiment will be described with reference to FIG.

  The present embodiment is characterized in that a second ultrasonic element 22 is provided in addition to the first ultrasonic element 21.

  The second ultrasonic element 22 is installed so that an ultrasonic pulse is incident on the wall 502 of the container 501. However, it is installed so that the propagation directions of ultrasonic waves in the vessel wall 502 are opposite to each other.

  The ultrasonic element 22 is electrically connected to the transmission / reception circuit 41. The transmission / reception circuit 41 selectively operates the ultrasonic element 21 and the ultrasonic element 22 by using a multiplexer or the like.

  In the present embodiment, by operating the ultrasonic element 21, the liquid level position 511 on the vessel wall can be measured in the same manner as in the first embodiment. Further, by operating the ultrasonic element 22, the liquid surface position 512 on the opposite side of the vessel wall can be measured. The reason why each of the two liquid surface positions 511 and 512 on the vessel wall can be measured in this way is that the two ultrasonic elements 21 and 22 have the ultrasonic wave propagation directions in the vessel wall 502 opposite to each other. It is because it is installed.

  In this embodiment, as shown in FIG. 5, the liquid surface positions 511 and 512 on the container wall at two locations where the liquid and the container wall are in contact with each other can be measured in the cross section of the container. There is an effect that the surface position can be measured.

  Further, the second embodiment can be combined with the present embodiment.

  In the present invention, the proposed embodiment may be implemented alone, or in some cases, a plurality of embodiments may be combined.

  The present invention can be implemented in various other forms without departing from the spirit or main features thereof. It goes without saying that the embodiments described in this specification are merely examples and should not be interpreted in a limited manner.

20 ... Liquid level measuring device,
21 ... Ultrasonic element,
31 ... Shoe,
41 ・ ・ ・ Transceiver circuit,
42: Liquid level measuring unit,
44 ... Liquid level position signal,
312 ... Ultrasonic output axis,
313: Installation angle A,
501 ... container,
502 ・ ・ ・ Vessel wall,
504 ... Gas,
505 ... Liquid,
511 ・ ・ ・ Liquid level on the vessel wall

Claims (6)

A liquid level measuring device for measuring a liquid level position in a container,
A first ultrasonic element that is arranged so that an ultrasonic wave is incident in a plate length direction of the vessel wall of the container;
A liquid level measuring apparatus comprising a liquid level measuring unit that calculates a liquid level position from a reflected wave in the vessel wall. The liquid level measuring device according to claim 1,
The liquid level measuring apparatus according to claim 1, wherein the ultrasonic element is installed with a non-zero installation angle with respect to the normal of the vessel wall. The liquid level measuring device according to claim 1,
The liquid level measuring device is characterized in that the liquid level measuring unit measures a liquid level position using a propagation time of the reflected wave and a propagation time of a circulating wave. The liquid level measuring device according to claim 1 or 3,
A second ultrasonic element, wherein the second ultrasonic element has a propagation direction of an ultrasonic wave incident on the vessel wall in a direction opposite to the ultrasonic wave incident on the first ultrasonic element; There is a liquid level measuring device. A container containing a liquid, an ultrasonic element installed outside the vessel wall of the container, and a liquid level measuring method using the ultrasonic element,
Incident ultrasonic waves toward the plate length direction of the vessel wall of the container;
Receiving a reflected wave generated at a wall position in contact with an interface position within the wall;
Calculating a liquid surface position from the propagation time of the reflected wave;
A liquid level measuring method comprising: A container containing a liquid, an ultrasonic element installed outside the vessel wall of the container, and a liquid level measuring method using the ultrasonic element,
Incident ultrasonic waves toward the plate length direction of the vessel wall of the container;
Receiving a reflected wave generated at a wall position in contact with an interface position within the wall;
Receiving an orbital wave in which the ultrasonic wave incident on the vessel wall returns around the container once;
A liquid level measurement method comprising: calculating a liquid level position from the reflected wave and the propagation time of the round wave.

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