Level meter

Abstract

The invention provides a level meter. In order to reduce reflected waves causing spurious signal waves in a level meter, the level meter includes a sensor substrate, a radio wave shaping member, a dielectric lens, and a radio wave absorbing member. The radio wave shaping member includes: an element housing covering an internal space including a transmitting unit and a receiving unit mounted on a sensor substrate; a waveguide, one end of which is in electromagnetic communication with the element housing; and a horn having a radio wave path that gradually expands from the other end of the waveguide toward the traveling direction of the transmitted radio waves. The dielectric lens is provided at a front end of the horn and deflects radio waves from the transmitter to an object through the radio wave shaping member. The radio wave absorbing member is disposed along an inner wall of the element housing and absorbs radio waves.

Description

Technical Field

[0001] The present invention relates to a level meter for measuring the horizontal height of an object. Background Art

[0002] In containers storing flowable materials such as liquids, powders, and granules, level meters that measure the height of the material interface, i.e., the water level (liquid level, the height of the upper surface of the powder, etc.), can be used (JP 2014-002091A). DE 102015113955 A1 describes a level meter that transmits a radio wave transmission signal into the container during measurement operation and receives an echo signal reflected from the surface of the flowable material after a transit time that depends on the water level. Millimeter waves are typically used as the radio wave transmission signal.

[0003] Level meters that use electromagnetic transmission signals typically include millimeter-wave radars. Millimeter-wave radars primarily use a configuration that transmits and receives radio waves using a patch antenna configured using a pattern formed on a circuit board. To improve radar directivity, the radio wave signal emitted from the patch antenna is typically transmitted after narrowing its spread by passing through a horn antenna and a lens antenna.

[0004] Instead of a patch antenna, a radar IC with an antenna-on-package structure can be used, which is more versatile and less expensive than a patch antenna. Radar ICs typically separate transmit and receive waves, but to configure a level meter, it is necessary to balance the transmit and receive paths used by the radar.

[0005] By including an element housing, a waveguide, a horn, and a lens as elements for this purpose, the transmission path and the reception path are aligned and the directivity is enhanced.

[0006] However, in conventional level meters using radar ICs, signal waves are rarely reflected in the element housing, lenses, and other components. Consequently, when the surface of a fluid material is located close to the level meter, reflected waves representing spurious signals are received, and the resulting spurious signals are superimposed on the detection signal as noise. Consequently, when performing level detection at close range, the margin for detection is reduced.

[0007] Furthermore, for example, when detecting the level of a fluid substance with a lower relative dielectric constant than water, the level of the reflected wave is lower than that of water due to the relative dielectric constant. Therefore, when detecting the level of a substance other than water with a low relative dielectric constant at close range, detection stability is reduced. Summary of the Invention

[0008] Therefore, an object of the present invention is to reduce reflected waves that cause stray signal waves in a level meter.

[0009] In order to solve the above problems, a level meter as an example of an embodiment of the present invention includes:

[0010] A substrate on which the transmitter and receiver are mounted.

[0011] The level meter includes:

[0012] a radio wave shaping member comprising: an element housing covering a space including the transmitter and the receiver mounted on the substrate; a waveguide having one end in electromagnetic communication with the element housing; and a horn having a radio wave path gradually expanding from the other end of the waveguide toward a direction of travel of transmitted radio waves;

[0013] a dielectric lens that is provided at a front end of the horn and deflects radio waves from the transmitter toward an object via the radio wave shaping member; and

[0014] A radio wave absorbing member is provided along an inner wall of the element case and absorbs radio waves.

[0015] In the level meter as another example of the embodiment of the present invention, the radio wave absorbing member is provided along the inner wall of the horn.

[0016] A level meter as another example of an embodiment of the present invention includes:

[0017] a metal housing that houses the substrate, the radio wave shaping member, and the dielectric lens; and

[0018] An attachment member formed of a dielectric for attaching the dielectric lens to the metal housing in contact with the dielectric lens.

[0019] In a level meter as another example of an embodiment of the present invention, the dielectric lens is formed of a lens material including a low dielectric constant material having a relative dielectric constant of 2 to 3 and a high dielectric loss tangent material having a dielectric loss tangent higher than that of the low dielectric constant material.

[0020] In a level meter according to yet another example of an embodiment of the present invention, the high dielectric loss tangent material is polychlorotrifluoroethylene resin.

[0021] In a level meter as still another example of an embodiment of the present invention, the waveguide includes a waveguide tube and coaxially couples a transmission wave from the transmitter and a reception wave to the receiver.

[0022] In a level meter as still another example of an embodiment of the present invention, the dielectric lens has a protruding cross-sectional shape protruding toward the waveguide.

[0023] A level meter as another example of an embodiment of the present invention includes:

[0024] a housing that houses the substrate, the radio wave shaping member, and the dielectric lens, the housing being attachable to a container that stores a substance having fluidity; and

[0025] an adapter attached to the container and capable of attaching the housing,

[0026] Wherein a first distance from a surface of the flowable substance to the substrate when the housing is attached to the adapter is longer than a second distance from the surface of the flowable substance to the substrate when the housing is attached to the container.

[0027] The level meter of the present invention includes a radio wave absorbing member disposed along the inner wall of the element housing, which covers the space containing the transmitter and receiver mounted on the substrate. This absorbs unnecessary reflected waves, in addition to those from objects. Consequently, the level meter can reduce the amount of reflected waves that can cause spurious signals. Consequently, the level meter's detection performance is improved, particularly at distances close to the surface of an object. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a three-dimensional diagram of the level meter;

[0029] Figure 2 It is a longitudinal cross-sectional view of the level meter;

[0030] Figure 3 is a diagram showing a state in which the level meter is attached to a container accommodating an object;

[0031] Figure 4 is a diagram showing the travel path of a transmitted wave;

[0032] Figure 5 is a diagram showing the travel path of the reflected wave;

[0033] Figure 6 is a block diagram showing an example of the relationship between components of a level meter;

[0034] Figure 7 FIG. 1 is a diagram showing an example of the configuration of a radar control unit and a transmission / reception unit;

[0035] Figure 8 is a diagram showing the relationship between the transmitted wave and the reflected wave;

[0036] Figure 9 is a longitudinal sectional view of a main part of a first example of a level meter;

[0037] Figure 10 Graph showing the intensity of the reflected wave that becomes a spurious signal and the intensity of the reflected wave from the target;

[0038] Figure 11 is a graph showing that the detection performance of the interface of the object is improved at a distance close to the level meter;

[0039] Figure 12 is a longitudinal sectional view of a main part of a second example of a level meter;

[0040] Figure 13 It shows the Figure 12 A diagram showing the collimation state of the transmitted wave of the level meter;

[0041] Figure 14 is a diagram showing a state of a transmission wave from a level meter in a case where the dielectric lens does not include a convex portion protruding toward the waveguide;

[0042] Figure 15 is a perspective view showing a state in which the level meter is attached to the adapter; and

[0043] Figure 16 is a cross-sectional view showing a state in which the level meter is attached to the adapter. DETAILED DESCRIPTION

[0044] Next, a level meter 10 as an example of an embodiment of the present invention will be described with reference to the accompanying drawings. Figure 1 The perspective view of FIG shows a level meter 10 according to this embodiment. The level meter 10 is a device that measures the level of an object (e.g., liquid, powder, granules, etc.). The measured level is the height of the interface of the object. Specific examples of the level include the height of the liquid surface within a container.

[0045] The level meter 10 has a longitudinal direction A. Figure 1 As shown, the level meter 10 has a generally cylindrical shape extending in the longitudinal direction A. The level meter 10 includes a housing 15 and a sensor unit 16. The housing 15 and the sensor unit 16 are arranged in the longitudinal direction A. The sensor unit 16 is provided at one end side ( Figure 1 ), and the housing 15 is arranged on the other end side ( Figure 1One end of the longitudinal direction A of the sensor unit 16 is the measuring end 40. Figure 1 As shown, the housing 15 and the sensor unit 16 each include a portion having a cylindrical shape extending in the longitudinal direction A.

[0046] Hereinafter, one end side of the level meter 10 in the longitudinal direction A may be referred to as a lower side, and the other end side in the longitudinal direction A may be referred to as an upper side. The sensor unit 16 measures the level of the object in such a manner that the lower side in the longitudinal direction A faces the object. Figure 1 A measuring axis is provided in the sensor unit 16. The sensor unit 16 measures the horizontal height along the measuring axis. Figure 1 The sensor unit 16 measures the object's level with its measuring end 40 facing the object. When the level meter 10 measures the object's level, the direction of change in the measured object's level (e.g., a liquid such as water) is preferably aligned with the longitudinal direction A. That is, the direction of the measuring axis of the sensor unit 16 is preferably aligned with the longitudinal direction A. For example, when the level meter 10 measures the liquid level (level), the longitudinal direction A is preferably aligned with the direction of change in the liquid level, i.e., the vertical direction (height direction, gravity direction).

[0047] exist Figure 1 In the level meter 10, radio waves as transmission waves are transmitted from the measuring end 40 to the object, and reflected waves reflected by the object are received by the measuring end 40. The level meter 10 calculates the level of the object based on the transmission wave and the reflected wave.

[0048] An attachment screw 18 threaded on a cylindrical surface is provided above the measuring end 40 in the sensor unit 16. An attachment portion 17 having a larger diameter than the attachment screw 18 is provided above the attachment screw 18. Figure 1 The attachment portion 17 in the embodiment has a nut shape. It should be noted that the attachment portion 17 is not limited to a nut shape as long as it is a structure capable of attaching the level meter 10 to the attachment object (such as a tank for storing liquid). For example, the attachment portion 17 may have a cylindrical shape in which an anti-slip protrusion is formed. When the level meter 10 is attached or detached (rotationally attached or detached) while rotating around the longitudinal direction A relative to the attachment object, the anti-slip protrusion of the attachment portion 17 serves as an anti-slip portion. An attachment flange for attaching the level meter 10 to the attachment object may be formed instead of the attachment portion 17 and the attachment screw 18. Even in the case of forming the attachment flange, the attachment portion 17 and the attachment screw 18 may be provided in addition to the attachment flange.

[0049] The housing 15 disposed above the sensor unit 16 is provided with a display portion 20. The display portion 20 is provided on the outer peripheral surface of the housing 15 extending in the longitudinal direction A. Figure 1In the embodiment, a flat portion along the longitudinal direction A is provided in a part of the outer peripheral surface of the housing 15 , and the display section 20 is provided in the flat portion.

[0050] The operation switch 30 is also provided in a portion of the outer surface of the housing 15 where the display section 20 is provided. Figure 1 The operation switch 30 is disposed adjacent to the rectangular active matrix display elongated in the longitudinal direction A and includes a setting key 32 and a direction key 33 arranged in the longitudinal direction A. The direction key 33 includes an up key 34 and a down key 35 arranged in the longitudinal direction A. A user of the level meter 10 can change operating parameters of the level meter 10 by operating the operation switch 30. Specifically, the user can change the display content and the level range settings on the display unit 20 by operating the operation switch 30.

[0051] The connection portion 12 is provided on the upper side of the housing 15 . Figure 1 The connection portion 12 in the embodiment has a cylindrical shape extending along an axis parallel to the longitudinal direction A. The outer peripheral surface of the cylindrical connection portion 12 is a connection screw portion 14 threaded.

[0052] The status light 52 is provided between the connection portion 12 and the display portion 20 so as to surround the lower side (root) of the connection portion 12. Figure 1 In the embodiment, since the connecting portion 12 has a cylindrical shape extending along an axis parallel to the longitudinal direction A, the status light 52 is provided so as to surround the axis parallel to the longitudinal direction A. The lighting state of the status light 52 changes according to the measured horizontal height of the object. The user can roughly understand the state of the object by visually observing the lighting state of the status light 52.

[0053] refer to Figure 2 , the internal structure of the level meter 10 will be described. Figure 2 It shows Figure 1 1 is a sectional view of a section of the level meter 10 , the sectional view being taken along a plane intersecting the display portion 20 (and a plane parallel to the longitudinal direction A).

[0054] In the sensor unit 16, a sensor IC 41 and a sensor board 42 supporting the sensor IC 41 are arranged. The sensor IC 41 performs signal processing for transmitting and receiving radio waves and measuring the level of an object. The signal processed by the sensor IC 41 is sent to the display panel 60 in the housing 15.

[0055] As the sensor IC 41, for example, an MMIC (Monolithic Microwave Integrated Circuit) is used. An MMIC is an IC in which a plurality of semiconductor components that perform transmission of radio waves, reception of radio waves, signal processing based on transmitted and received radio waves, and the like are integrated into a single semiconductor device (one chip). Figure 2 In the sensor IC 41, the antenna is integrated with the MMIC using the antenna in package (AiP) technology or the antenna on package (AoP) technology. Figure 2 , the sensor IC 41 is an antenna-integrated package (antenna-on-package) in which a transmitting unit that transmits radio waves and a receiving unit that receives radio waves are integrated in a single semiconductor device. Since an antenna-integrated MMIC is used as the sensor IC 41, the volume occupied by the configuration for transmitting and receiving radio waves is reduced, and the overall size of the level meter 10 becomes compact. The sensor IC 41 is not limited to a single antenna-integrated MMIC, and may include a plurality of ICs. The sensor IC 41 may include, for example, an MMIC and a microcomputer. Then, the antenna-integrated MMIC may include a radio wave transmitting antenna, a radio wave receiving antenna, and a circuit that performs radio wave transmission / reception control, and the microcomputer may include a circuit that performs signal processing or arithmetic processing based on a received signal received from the antenna-integrated MMIC.

[0056] The sensor IC 41 is mounted on the lower surface of the sensor board 42. The sensor board 42 is an electronic circuit board in which various electronic circuit elements are arranged on a board made of an insulator such as glass or resin. Figure 2 In the embodiment, the sensor plate 42 is arranged in a direction orthogonal to the longitudinal direction A ( Figure 2 (horizontal direction in the image). If the sensor IC 41 is an antenna-integrated MMIC, the sensor IC 41 includes a transmitting unit 43T that transmits radio waves and a receiving unit 43R that receives radio waves. Since the sensor IC 41 includes the transmitting unit 43T and the receiving unit 43R, the sensor unit 16 includes the transmitting unit 43T and the receiving unit 43R. By mounting the sensor IC 41 on the lower surface of the sensor board 42, the transmitting unit 43T and the receiving unit 43R are arranged on the lower surface of the sensor board 42 (on one end side in the longitudinal direction A).

[0057] The measuring end 40 is located below the sensor plate 42 . Figure 2The measuring end 40 includes a waveguide 45, a horn 46, and a dielectric lens 48 as its internal structure. In the case where the sensor IC 41 is an antenna-integrated MMIC, a radio wave serving as a transmission wave is transmitted from the sensor IC 41. The transmission wave transmitted from the sensor IC 41 is guided toward the object through the waveguide 45, the horn 46, and the dielectric lens 48 in sequence. The reflected wave reflected by the object and incident on the measuring end 40 is guided toward the sensor IC 41 through the dielectric lens 48, the horn 46, and the waveguide 45 in sequence. The waveguide 45 makes the transmission wave from the transmitting unit 43T and the reflected wave to the receiving unit 43R, that is, the reception wave, coaxial. In the case where the portion of the attachment screw 18 provided on the lower side of the sensor unit 16 is cylindrical, its cross section is circular. In this case, the circular dielectric lens 48 can be provided on the lower side of the cylindrical portion (one end side in the longitudinal direction A). That is, when the sensor unit 16 has a cylindrical portion on the lower side, the cylindrical portion can serve as both a portion of the level meter 10 attached to an attachment target (e.g., a tank) and an arrangement position of the dielectric lens 48, so the overall size of the level meter 10 becomes compact.

[0058] On the other hand, a rotating mechanism 19 is provided in the housing 15 provided above the sensor unit 16 . Figure 2The rotation mechanism 19 is disposed at the lower end of the housing 15 (one end in the longitudinal direction A), that is, between the housing 15 and the sensor unit 16. The rotation mechanism 19 enables the housing 15 to rotate relative to the sensor unit 16 about a rotation axis 19A. For example, the rotation mechanism 19 comprises a shaft extending along the rotation axis 19A between the housing 15 and the sensor plate 42. This shaft is connected to the housing 15 via bearings disposed about the axis and is configured so that rotation of the housing 15 about the rotation axis 19A is not transmitted to the sensor unit 16. Preferably, the rotation mechanism 19 maintains the desired relative rotation angle between the housing 15 and the sensor plate 42. For example, the rotation mechanism 19 may include components such as a damping element that acts as a rotational resistance and a rotation lock that prevents rotation to maintain a specific rotation angle. In addition to the above configuration, the rotation mechanism 19 may also include an engaging protrusion formed on the sensor unit 16 and a plurality of hooks provided on the housing 15. The engaging protrusion is provided on the outer circumference of the cylindrical portion located above the sensor unit 16 and is formed to be elongated along the circumferential direction. The engaging protrusion of the sensor unit 16 can have a continuous shape so as to make a circle in the circumferential direction. The multiple hooks of the housing 15 are arranged in a ring-shaped manner at intervals corresponding to the engaging protrusions of the sensor unit 16. Each hook engages with the lower surface of the engaging protrusion. When subjected to an external force, each hook rotates while sliding in the circumferential direction. In the case where the rotating mechanism 19 includes the engaging protrusion and the hook, the housing 15 can be provided with an elastomer that generates a pressing force that pushes and expands between the sensor unit 16 and the housing 15. Due to the provision of the elastomer, the sliding resistance between the engaging protrusion and each hook can be adjusted. Figure 2 The rotating mechanism 19 is configured such that the rotation axis 19A is oriented in a direction parallel to the longitudinal direction A ( Figure 2 The display 20 is arranged on a flat surface formed in the housing 15 at a position offset from the rotation axis 19A. That is, the flat surface of the housing 15 is away from the plane including the rotation axis 19A. Due to the provision of the rotation mechanism 19, the user can turn the display 20 in a direction that is easy to see by rotating the housing 15. Specifically, when the level meter 10 is attached to a container (e.g., a tank) containing a measurement target via the attachment screws 18, the user can point the display 20 in a direction that the user can easily see the display 20 without moving the entire level meter 10.

[0059] In the housing 15, a display panel 60 is provided above the rotating mechanism 19. The display panel 60 is an electronic circuit board in which various electronic circuit elements are arranged on a board made of an insulator such as glass or resin. Figure 2 In the embodiment, the display panel 60 is arranged in a direction parallel to the longitudinal direction A ( Figure 2The horizontal height of the object measured by the sensor unit 16 is converted into a signal for displaying the horizontal height on the display unit 20. Figure 2 The display panel 60 is provided on the back side of the display unit 20 ( Figure 2 (inside the housing 15).

[0060] Figure 2 The display unit 20 in the embodiment includes a display device 28 and a transparent display window 29. The display device 28 is, for example, an LCD, in particular an LCD capable of color display. The display window 29 is, for example, a plate made of an optically transparent material such as glass, acrylic, polyarylate, or polycarbonate, and optically transmits the display content of the display device 28 to the outside of the housing 15. The display device 28 points in the direction of the display surface 20A along the longitudinal direction A. In addition, Figure 2 , the display panel 60 is oriented along the display surface 20A.

[0061] Since the display device 28 and the display panel 60 are oriented in the longitudinal direction A, the components of the display unit 20 for operating the display device 28 are arranged inside the level meter 10 along the longitudinal direction A (height direction). Therefore, the area occupied by the components for operating the display unit 20 in the direction perpendicular to the longitudinal direction A (radial direction) is reduced, and the overall size of the level meter 10 becomes compact. Figure 1 and Figure 2 , the diameter size of the cylindrical housing 15 is smaller than the diameter size of the sensor unit 16. Note that the diameter size of the housing 15 is not necessarily smaller than the diameter size of the sensor unit 16, and the diameter sizes of the housing 15 and the sensor unit 16 may be the same, or the diameter size of the sensor unit 16 may be smaller.

[0062] Status light 52, disposed between display unit 20 and connection unit 12 above display unit 20 (on the other end side in longitudinal direction A), includes a plurality of status LEDs 50 serving as a light source and a transmissive window 53 that diffuses light emitted from status LEDs 50 in a direction intersecting longitudinal direction A. A post for supporting connection unit 12 may be disposed between status LEDs 50 and transmissive window 53. Multiple status LEDs 50 are disposed above display panel 60 and display unit 20. The lighting state of status LEDs 50 changes depending on the level of an object measured by sensor unit 16. Transmissive window 53, which includes a light-diffusing member (e.g., a light-diffusing film), is disposed above status LEDs 50. Light emitted from status LEDs 50 is diffused in a direction intersecting longitudinal direction A through transmissive window 53 and guided outside housing 15. Therefore, since the lighting state of status LEDs 50 changes depending on the level of an object, the lighting state of status light 52 also changes. Since the transmission window 53 includes a member that diffuses light, and the status light 52 (specifically, the transmission window 53) is arranged around an axis parallel to the longitudinal direction A, the light emitted from the status LED 50 is diffused uniformly in all directions around the connecting portion 12. Each status LED 50 can emit light in a single color (for example, red, yellow, green, etc.), or can emit light by switching a plurality of colors (for example, red, yellow, green, etc.). When the status LED 50 emits light by switching a plurality of colors, a plurality of light-emitting elements that emit light of different colors can be included in one LED, or a combination of a plurality of LEDs that emit light of different colors can be arranged as the status LED 50. The status LED 50 can emit light by mixing a plurality of colors. When the status LED 50 emits light by switching a plurality of colors, the status LED 50 can emit light in a color that is consistent with the scale 24 ( Figure 1 The status light 52 is illuminated by a color corresponding to the color of a subsection of the scale 24 corresponding to the level range to which the measured level belongs. Each status LED 50 is preferably switchable between a non-illuminating state (light-off state), an illuminating state, and a flashing state. The light source of the status light 52 only needs to be able to control the illuminating state and can be, for example, a light-emitting element using an organic EL.

[0063] The connection portion 12 is provided on the other end side (upper side) of the display portion 20 in the longitudinal direction A and on an extension line of the rotation axis 19A. Figure 1, the connection portion 12 is arranged at the upper end of the housing 15 (the other end in the longitudinal direction A). The connection portion 12 includes an external input terminal 12C and an external output terminal 12D, which serve as connection terminals with external devices. The external input terminal 12C is a terminal for inputting signals, power, or both from the outside to the level meter 10. The external output terminal 12D is a terminal for outputting signals from the level meter 10 to the outside. The external output terminal 12D may include multiple signal lines or multiple output terminals. For example, signals can be output to the outside from different signal lines or different output terminals according to the level range to which the measured level belongs. Since the connection portion 12 is arranged on the extension line of the rotation axis 19A, the position of the connection portion 12 does not change even if the housing 15 is rotated relative to the sensor unit 16 by the rotation mechanism 19. Therefore, even when the housing 15 is rotated by the rotation mechanism 19, the connection with the outside through the connection portion 12 is not hindered. The position where the connection portion 12 is provided is not limited to the upper end of the housing 15. For example, the connection portion 12 can be provided on the surface of the housing 15, at a position close to (near) the display portion 20 in a direction from which the user can visually identify the display portion. In this case, in order to make the display portion 20 visible to the user, it is desirable that there are no obstacles in the direction from which the user can visually identify the display portion 20. Therefore, when the connection portion 12 is provided at a position close to the display portion 20 in a direction from which the user can visually identify the display portion 20, it is easy to ensure space for wiring cables connected to the connection portion 12, and the level meter 10 is easy to install. The connection portion 12 can be provided on the rear surface relative to the display portion 20. In this case, since the connection portion 12 can be provided in an unused inactive space, the size of the level meter 10 can be reduced. The external output terminal 12D may include multiple signal lines or multiple output terminals. For example, signals can be output to the outside from different signal lines or different output terminals according to the level range to which the measured level belongs.

[0064] Will refer to Figure 3 An example of a usage state of the level meter 10 will be described. Figure 3 1 is a diagram showing a state where the level meter 10 is attached to a tank 70 containing an object 72. The object 72 is, for example, liquid such as water, and a level Y of the object 72 is a height from the bottom of the tank 70 to an interface 74 (liquid surface) of the object 72.

[0065] The tank 70 contains water as an object 72 in, for example, a water treatment facility. For example, when the object 72 in the tank 70 is supplied to a liquid treatment process, etc., the level Y of the object 72 in the tank 70 decreases. When the tank 70 is replenished with the object 72, the level Y of the object 72 in the tank 70 increases. For example, a water inlet 75 is provided on the outer wall ( Figure 3The water injection pipe 76 is fluidically connected to the tank 70 via the water injection port 75. The water injection pipe 76 is then connected to a water injection device 78 (including devices such as pumps, valves, etc.) provided outside the tank 70. The water injection device 78 is a device that supplies (injects) the object 72 into the tank 70 from the outside of the tank 70. The water injection device 78 adjusts the amount of water injected into the tank 70 according to the level Y of the object 72 in the tank 70. The water injection device 78 stops water injection according to the level Y of the object 72 in the tank 70. The water injection device 78 controls the supply of the object 72 to the tank 70 according to the level Y of the object 72 in the tank 70, so that the level Y of the object 72 in the tank 70 falls within a predetermined range, which decreases as the object 72 is consumed, for example, by a liquid processing process.

[0066] Figure 3 The level meter 10 is attached to the upper side of the tank 70. An attachment hole 71 is provided above the tank 70. The attachment hole 71 is a screw hole into which the attachment screw 18 of the level meter 10 is screwed, thereby attaching the level meter 10 to the tank 70. For example, a user of the level meter 10 can screw the attachment screw 18 into the attachment hole 71 by rotating the nut-shaped attachment portion 17 while aligning the front end of the attachment screw 18 with the attachment hole 71. The structure for attaching the level meter 10 to the tank 70 is not limited to this. For example, it is also possible to attach the level meter 10 to the tank 70 by screwing a nut onto the attachment screw 18 exposed inside the tank 70 without providing threads on the attachment hole 71. Alternatively, the level meter 10 can be attached to a mounting bracket provided above the tank 70 using the nut and attachment screw 18 while the upper surface of the tank 70 is open. In addition, the method of attaching the level gauge 10 to the tank 70 is not limited to the threaded connection using the attachment screws 18, and threads may not be formed on the outer peripheral surface of the sensor unit 16. For example, a flange may be provided on one or both of the level gauge 10 and the tank 70, and the level gauge 10 may be attached to the tank 70 by fastening the flange to the level gauge 10 or the tank 70 with bolts.

[0067] exist Figure 3 , the longitudinal direction A of the level meter 10 in the state of being attached to the tank 70 is the same as the direction in which the level Y of the object 72 changes.

[0068] The level meter 10 transmits a radio wave as a transmission wave Tx from the measuring end 40 toward the object 72. The transmission wave Tx is then reflected at the interface 74 of the object 72, generating a reflected wave Rx, which is received by the measuring end 40. The level meter 10 calculates the horizontal height Y of the object 72 based on the transmission wave Tx and the reflected wave Rx. For example, when measuring using a time of flight (ToF) method, the level meter 10 calculates the distance YA from the measuring end 40 to the interface 74 based on the difference between the transmission wave Tx and the reflected wave Rx, and calculates the horizontal height Y based on the distance YA. For example, when measuring using a radar method using a frequency modulated continuous wave (FMCW), the level meter 10 calculates the distance YA from the measurement window 40 to the interface 74 based on the frequency of the waveform obtained by mixing the transmission wave Tx and the reflected wave Rx, and calculates the horizontal height Y based on the distance YA.

[0069] A connecting cable 92 is connected to the connection portion 12 of the level meter 10. The connecting cable 92 connects a control device 90 (e.g., a programmable controller) disposed outside the tank 70 to the level meter 10. An analog signal indicating the level Y of the object 72 measured by the level meter 10 is transmitted to the control device 90 via the connecting cable 92. The control device 90 controls the operation of the water injection device 78 based on the measured level Y.

[0070] Figure 4 3 is a diagram showing a travel path of a transmission wave Tx. Figure 5 is a diagram showing the path of the reflected wave Rx. Figure 4 and Figure 5 , the transmission wave Tx is guided to the object 72 through the horn 46 and the dielectric lens 48, and the reflected wave Rx is guided to the receiving unit 43R.

[0071] The sensor unit 16 includes a transmitting unit 43T that transmits a transmission wave Tx and a receiving unit 43R that receives a reflected wave Rx. Specifically, the sensor IC 41 disposed within the sensor unit 16 includes the transmitting unit 43T and the receiving unit 43R. The transmitting unit 43T and the receiving unit 43R are respectively a semiconductor electromagnetic wave generating device and a semiconductor electromagnetic wave receiving device mounted on the chip of the sensor IC 41.

[0072] An enclosing wall 47, a waveguide 45, a horn 46, and a dielectric lens 48 are provided between the transmitting unit 43T and the object 72 in the order of proximity to the transmitting unit 43T. The enclosing wall 47 surrounds the space including the transmitting unit 43T and the receiving unit 43R on the sensor board 42 and is in communication with the waveguide 45. The enclosing wall 47 has conductivity. The waveguide 45 is a hollow tube formed of a conductor. The horn 46 is surrounded by a conical wall surrounding the space in communication with the waveguide 45. The conical wall of the horn 46 has conductivity. These are arranged so that the direction of the directivity of the waveguide 45 and the horn 46 coincides with the direction of the optical axis 40A of the dielectric lens 48. In Figure 4 and Figure 5 In the embodiment, the measuring end 40 is arranged so that the optical axis 40A is parallel to the longitudinal direction A (the length direction of the level meter 10 ). Hereinafter, the direction of the directivity of the waveguide 45 and the horn 46 may also be referred to as the optical axis 40A.

[0073] The transmission wave Tx transmitted from the transmission unit 43T passes through the surrounding wall 47 and the space within the waveguide 45, and enters the dielectric lens 48 via the horn 46. Figure 4 and Figure 5 In the figure, the isophase plane of the radio wave is indicated by the dotted lines in the surrounding wall 47, in the horn 46, and below the measuring end 40. Note that in the waveguide 45, the isophase plane should originally be shown as a straight line, but in order to make it easier to understand the direction of travel of the radio wave, it is shown to the side of the travel direction ( Figure 4 The lower side, Figure 540A). The waveguide 45 converts the transmission wave Tx so that the transmission wave Tx becomes a spherical wave that travels in a spherical shape along the optical axis 40A from the transmitting end of the waveguide 45, regardless of the relative positional relationship between the transmitting unit 43T and the waveguide 45. Therefore, the transmitting end of the waveguide 45 can be regarded as a point-like transmission source. The diameter of the waveguide 45 can be set to a diameter that only allows fundamental mode radio waves to pass through the waveguide 45, so that the transmitting end of the waveguide 45 becomes an ideal point-like transmission source. On the other hand, when the diameter of the waveguide 45 is less than half the wavelength of the radio wave, the radio wave does not pass through the waveguide 45. For example, when the frequency of the radio wave is 50 GHz to 70 GHz, the wavelength is about 4.3 mm to about 6.0 mm, and the half wavelength is about 2.15 mm to about 3.0 mm. In this case, when a diameter greater than 3 mm and less than 4.3 mm is selected as the diameter of the waveguide 45, only fundamental mode radio waves can pass through the waveguide 45. The diameter of the waveguide 45 that satisfies the above conditions is, for example, 4 mm. When the dimension of the waveguide 45 along the optical axis 40A is short, radio waves other than the fundamental mode pass through the waveguide 45 even if the diameter of the waveguide 45 satisfies the above conditions. For example, the dimension of the waveguide 45 along the optical axis 40A can be set to a length equal to or greater than one wavelength of the radio wave. The longer the dimension of the waveguide 45 along the optical axis 40A, the longer the dimension of the level meter 10 in the longitudinal direction A. After passing through the waveguide 45, the transmission wave Tx travels as a spherical wave in the horn 46 and is converted into a plane wave by the dielectric lens 48.

[0074] like Figure 4 As shown, the transmission wave Tx travels in the horn 46 as a spherical wave, and then the transmission wave Tx incident on the dielectric lens 48 is refracted between the horn 46 and the dielectric lens 48, and between the dielectric lens 48 and the surrounding air (atmosphere), and is guided in a direction parallel to the optical axis 40A. Since the optical axis 40A is parallel to the longitudinal direction A, the transmission wave Tx is guided in the direction pointed by one end (lower side) of the longitudinal direction A of the sensor unit 16, that is, the direction of the object 72. The transmission wave Tx travels as a plane wave corresponding to the effective diameter of the dielectric lens 48 and diffracted waves around the plane wave. The transmission wave Tx forms a radio wave beam with high directivity. Therefore, since the area of ​​the detection target surface (the area irradiated by the transmission wave Tx in the interface 74 of the object 72) is narrowed, unnecessary reflections caused by surrounding obstacles, etc. are reduced.

[0075] The transmission wave Tx guided to the object 72 is reflected at the interface 74 of the object 72 and becomes a reflected wave Rx. Figure 5As shown, the reflected wave Rx propagating as a plane wave is received at the measuring end 40. The reflected wave Rx received by the measuring end 40 first enters the dielectric lens 48. The reflected wave Rx incident on the dielectric lens 48 is refracted between the surrounding air and the dielectric lens 48, and between the dielectric lens 48 and the horn 46, and propagates in the horn 46 as a spherical wave close to the optical axis 40A. As a result, the reflected wave Rx is guided to the receiving unit 43R via the waveguide 45 as a radio wave transmitted from a point-like transmission source at the end portion on the surrounding wall 47 side.

[0076] The waveguide 45, horn 46, and dielectric lens 48 arranged within the sensor unit 16 guide the direction of travel of radio waves toward the optical axis 40A through their respective directivities with respect to the radio waves. Therefore, combined, they exhibit strong directivity with respect to the entire radio wave. Therefore, even if the longitudinal dimension (length along the longitudinal direction A) of the sensor unit 16 is small, the transmitted wave Tx and the reflected wave Rx can be appropriately guided by aligning them with the waveguide 45. Furthermore, by appropriately guiding the transmitted wave Tx and the reflected wave Rx, even if the positions of the transmitting unit 43T and the receiving unit 43R differ within the sensor IC 41, the transmitted wave Tx can be transmitted and the reflected wave Rx can be received by the shared measurement end unit 40. Therefore, by using the waveguide 45, horn 46, and dielectric lens 48, the designer of the level meter 10 can reduce the longitudinal dimension of the level meter 10, including the sensor unit 16, and make the level meter 10 as a whole more compact.

[0077] Next, refer to Figure 6 The relationship between the components of the level meter 10 will be described. Figure 6 1 is a block diagram schematically showing an example of the relationship between the components of the level meter 10. Figure 6 As shown, the sensor IC 41 of the sensor unit 16 includes a transmitting / receiving unit 43, a radar control unit 44, a storage unit 63, and a computing unit 64. The transmitting / receiving unit 43 includes a transmitting unit 43T that transmits a transmission wave Tx and a receiving unit 43R that receives a reflected wave Rx. The sensor IC 41 may include multiple ICs. For example, the sensor IC 41 may include an antenna-integrated MMIC and a microcomputer.

[0078] The radar control unit 44 includes a transmission control unit 80 that determines the waveform of the transmission wave Tx, a radar transmission / reception circuit 81 that performs mutual conversion between digital signals and radio waves, and a signal processing unit 89 that performs signal processing based on the transmission wave Tx and the reflected wave Rx. When the sensor IC 41 includes an antenna-integrated MMIC and a microcomputer, the antenna-integrated MMIC may include the portion of the radar control unit 44 excluding the signal processing unit 89 (the transmission control unit 80 and the radar transmission / reception circuit 81) and the transmission / reception circuit 43, and the microcomputer may include the signal processing unit 89, the storage unit 63, and the calculation unit 64.

[0079] The storage unit 63 stores various setting values ​​(data) related to the operation of the level meter 10. The calculation unit 64 performs various calculations related to the operation of the level meter 10 based on the setting values ​​stored in the storage unit 63, the signal processing results of the signal processing unit 89, and the like. The storage unit 63 includes a storage device such as a RAM or a ROM. The calculation unit 64 includes a processor such as a CPU. The storage unit 63 and the calculation unit 64 can be provided on the display panel 60 in the housing 15. Alternatively, the storage unit 63 and the calculation unit 64 can be separately provided in the sensor unit 16 and the housing 15, respectively, and the stored data and the responsible arithmetic processing can be shared by the sensor unit 16 and the housing 15.

[0080] On the other hand, the display panel 60 of the housing 15 includes an input unit 65 and an output unit 66. The input unit 65 is an interface circuit that inputs input provided from outside the level meter 10 as a signal to the level meter 10. Input provided from outside the level meter 10 includes, for example, a user's operation of the operating switch 30, a control signal provided from an external device (e.g., the control device 90) via the external input terminal 12C, and the like. The input unit 65 causes the storage unit 63 to store, for example, flag information indicating that the operating switch 30 has been operated, and data such as a setting value provided via the external input terminal 12C.

[0081] The output unit 66 is an interface circuit that outputs signals generated within the level meter 10 to the outside. The output unit 66 changes, for example, the display content of the display unit 20 and the lighting state of the status lamp 52 based on the calculation results of the calculation unit 64 (such as the value of the level Y). Furthermore, the output unit 66 transmits the calculation results of the calculation unit 64 to an external device via the external output terminal 12D.

[0082] refer to Figure 7 and Figure 8 The measurement of the level Y by the level gauge 10 is described in more detail. Figure 7 4 is a diagram showing a configuration example of the radar transmission / reception circuit 81 and the transmission / reception unit 43 included in the sensor IC 41 . Figure 8 This is a diagram showing the relationship between the transmitted wave Tx and the reflected wave Rx.

[0083] like Figure 7 As shown, the radar transmit / receive circuit 81 includes a ramp wave generator 82 , a power amplifier 83 , a low noise amplifier 84 , a mixer 85 , a low pass filter 86 and an analog-to-digital converter 87 .

[0084] The level meter 10 of this embodiment measures the horizontal height Y using the FMCW radar method. A ramp wave generator 82 is connected to the transmission control unit 80. Upon receiving data indicating the waveform of the transmission wave Tx determined by the transmission control unit 80, the ramp wave generator 82 generates a transmission signal having the waveform of the transmission wave Tx based on the data. Here, a waveform with increasing and decreasing repetition frequency is used as the waveform of the transmission wave Tx.

[0085] Figure 8 It is a graph showing the change of the frequency of the transmission wave Tx (and the reflected wave Rx) with respect to time. Figure 8 , the frequency of the transmission wave Tx increases linearly over time from a minimum value (Min) and returns to the minimum value again when it reaches a maximum value (Max). In this way, the frequency of the transmission wave Tx repeatedly increases and decreases. The frequency increase / decrease pattern is not limited to this, for example, a pattern in which the frequency decreases linearly from a maximum value over time and returns to the maximum value again when it reaches a minimum value can be used. Alternatively, a pattern in which a linear increase / decrease is repeated between a maximum value and a minimum value can be used. The transmission wave Tx used in this embodiment is a radio wave in the 60 GHz frequency band, and the minimum value of the frequency is, for example, 58 GHz and the maximum value is, for example, 69 GHz. The frequency band to be used is not limited to this, and for example, a frequency of 77 GHz to 81 GHz can be used.

[0086] Depend on Figure 7 The transmission signal generated by ramp wave generator 82 is amplified by power amplifier 83 and transmitted to transmission unit 43T. Transmission unit 43T generates a radio wave having a waveform corresponding to the transmission signal and transmits this radio wave as transmission wave Tx to object 72. Transmission wave Tx is reflected by interface 74 of object 72 and becomes reflected wave Rx, which is received by receiving unit 43R as a received signal. Reflected wave Rx is a wave that is out of phase with transmission wave Tx.

[0087] like Figure 8 As shown by the dotted line in FIG, the reflected wave Rx is a wave that is offset from the transmitted wave Tx by a time difference Δt. The time difference Δt is the distance YA ( Figure 3 Since the reflected wave Rx reciprocates between the measuring end 40 and the object 72, there exists a relationship of Δt=2×YA / c, where c is the speed of light.

[0088] A frequency difference ΔF corresponding to the magnitude of the time difference Δt then arises between the transmitted wave Tx and the reflected wave Rx. A certain relationship exists between the frequency difference ΔF and the time difference Δt, depending on the waveform of the transmitted signal Tx. The waveform of the transmitted wave Tx is a waveform whose frequency changes linearly over time. That is, a certain relationship exists between the frequency difference ΔF and the time difference Δt, depending on the frequency change per unit time in the waveform of the transmitted wave Tx. For example, the frequency of the transmitted wave Tx increases linearly from a minimum value (Min) to a maximum value (Max) over time. In this case, the relationship between the frequency difference ΔF and the time difference Δt is uniquely determined by the difference between the maximum and minimum values ​​of the frequency of the transmitted wave Tx, which is the bandwidth of the frequency modulation. This frequency relationship changes over time. Therefore, the level meter 10 can calculate the time difference Δt based on the difference between the transmitted wave Tx and the reflected wave Rx, that is, the frequency difference ΔF. The level meter 10 can then calculate the distance YA (Δt×c / 2) based on the time difference Δt. Furthermore, the level meter 10 can calculate the value of the horizontal height Y based on the distance YA. Specifically, the difference between the depth of the tank 70 (the distance from the bottom of the tank 70 to the measuring end 40) and the distance YA is the value of the horizontal height Y. In addition, since there is a certain relationship between the frequency difference ΔF and the time difference Δt depending on the waveform of the transmission wave Tx, the corresponding relationship between the frequency difference ΔF and the distance YA can be obtained in advance. The corresponding relationship between the frequency difference ΔF and the distance YA can be stored in advance. Figure 6 in the storage unit 63.

[0089] like Figure 7 As shown, the received signal corresponding to the reflected wave Rx received by the receiving unit 43R is input to the mixer 85 via the low-noise amplifier 84. The transmitted signal corresponding to the waveform of the transmitted wave Tx output from the ramp wave generator 82 is also input to the mixer 85. The mixer 85 generates a signal corresponding to the mixed wave Mx obtained by mixing the waveforms of the transmitted wave Tx and the reflected wave Rx. Specifically, the mixer 85 mixes the transmitted signal and the received signal to generate an IF signal (intermediate frequency) corresponding to the mixed wave Mx.

[0090] The IF signal corresponding to the mixed wave Mx has a waveform consisting of a high-frequency component derived from the 60 GHz frequency band of the transmitted wave Tx and the reflected wave Rx, and a low-frequency component corresponding to the frequency difference ΔF between the transmitted wave Tx and the reflected wave Rx. The IF signal corresponding to the mixed wave Mx is input to a low-pass filter 86, where a low-frequency waveform corresponding to the frequency difference ΔF is extracted. The extracted low-frequency waveform is input to an analog-to-digital converter 87. The analog-to-digital converter 87 converts the low-frequency waveform into a digital value and outputs the digital value to a signal processing unit 89.

[0091] The signal processing unit 89 converts the low-frequency waveform output from the analog-to-digital converter 87 into a frequency signal Px by fast Fourier transforming the frequency signal Px or the like. The frequency signal Px is a signal indicating the intensity of the wave of each frequency, and the frequency corresponding to the maximum peak value PS of the frequency signal Px is the frequency difference ΔF between the transmission wave Tx and the reflected wave Rx. The signal processing unit 89 transmits the frequency signal Px to the Figure 6 The calculation unit 64 in.

[0092] The calculation unit 64 calculates the values ​​of the distance YA and the level Y based on the frequency signal Px. When calculating the values ​​of the distance YA and the level Y, the calculation unit 64 refers to the setting values ​​stored in the storage unit 63. For example, the storage unit 63 stores the correspondence between the frequency difference ΔF and the distance YA, the value for calculating the level Y (the depth of the tank 70) from the distance YA, and the like.

[0093] Depending on the measurement environment, peaks other than the maximum peak PS may appear in the frequency signal Px due to elements other than the interface 74 of the object 72 (for example, a device such as a stirrer provided in the tank 70). Even if multiple peaks exist in the frequency signal Px, the calculation unit 64 can specify only the maximum peak PS originating from the object 72 by performing appropriate calculations. For example, data of the frequency signal Px previously obtained in a state where the object 72 is not present (the tank 70 is empty) can be stored in the storage unit 63. The calculation unit 64 can specify the maximum peak PS derived from the object 72 by examining the difference between the frequency signal Px obtained in the state where the object 72 is not present and the frequency signal Px obtained in the state where the object 72 is present.

[0094] After calculating the frequency difference ΔF corresponding to the maximum peak value PS of the frequency signal Px, the calculation unit 64 calculates the values ​​of the distance YA and the level Y based on the frequency difference ΔF and the setting value stored in the storage unit 63. The calculation unit 64 sends the calculated value of the level Y to the output unit 66. The output unit 66 changes the display content of the display unit 20 and the lighting state Y of the status lamp 52 according to the value of the level Y. The value of the level Y is sent to the control device 90 ( Figure 3 ). The output unit 66 can output a binary or multi-valued control signal to the control device 90 through the external output terminal 12D based on the comparison result between the calculated value of the water level Y and the threshold value. Alternatively, instead of the value of the water level Y itself, a signal indicating a specific control to be performed according to the state of the water level Y can be sent to the control device 90. For example, when the water level Y exceeds a specific threshold value or falls below a specific threshold value, a signal indicating that the operation of a pump, valve, etc. should be changed can be sent to the control device 90.

[0095] Figure 9FIG. 4 shows a detailed internal structure of the sensor unit 16 of the level meter 10 according to the first example of the embodiment of the present invention. As shown in the figure, the element housing 49 is composed of a surrounding wall 47. Although the shape of the internal space 51 of the element housing 49 is arbitrary, Figure 9 The illustrated element housing 49 is formed into a rectangular parallelepiped shape in accordance with the shape of the sensor IC 41 housed in the internal space 51. Therefore, the surrounding wall 47, which serves as the inner wall of the element housing 49, has four flat surfaces on the inner surface. The element housing 49 has a bottom wall 31, which serves as an inner wall, at a portion connected to the waveguide 45, which serves as a waveguide.

[0096] The dielectric lens 48 is made of a dielectric such as synthetic resin or glass. The element housing 49, waveguide 45, and horn 46 are made of members having moldability and radio wave reflectivity. Examples of such members include a member obtained by nickel plating an aluminum die-cast member, a member obtained by subjecting an aluminum scraping member to an aluminum oxide film treatment, a member obtained by nickel plating a zinc die-cast member, a stainless steel member, and a member obtained by nickel plating a resin such as ABS or liquid crystal polymer.

[0097] In the housing 54 of the sensor unit 16, a radio wave shaping member 59 is provided, which includes an element housing 49, a waveguide 45 and a speaker 46 covering an internal space 51, wherein the internal space 51 includes a sensor IC 41 mounted on a sensor board 42 and includes a transmitting unit 43T and a receiving unit 43R.

[0098] The radio waves transmitted from the transmitting unit 43T of the sensor IC 41 are reflected by the element housing 49 inside the sensor unit 16 and the surface 48A of the dielectric lens 48 facing the interior of the sensor unit 16. The radio waves reflected by the surface 48A of the dielectric lens 48 are further reflected in the horn 46. The reflected waves become spurious signal waves and exist inside the sensor unit 16. In particular, the intensity of the radio waves reflected by the inner surface of the element housing 49 is very high.

[0099] On the inner surface of the bottom wall 31 and the inner surfaces of the four surrounding walls 47 constituting the element case 49, that is, at positions along the bottom wall 31 and the surrounding walls 47, a radio wave absorbing member 11 that absorbs reflected waves that have become stray signal waves is provided. As the radio wave absorbing member 11, any member can be used as long as it can absorb radio waves transmitted from the transmitting unit 43T of the sensor IC 41 except for the radio waves transmitted from the transmitting unit 43T. Figure 3 The reflected wave is shown as being partially reflected by the object 72 beyond the interface 74 .

[0100] Specifically, radio wave absorbing members using the dielectric loss principle, radio wave absorbing members using the magnetic loss principle, and radio wave absorbing members using the reflection loss principle can be exemplified. Examples of radio wave absorbers used for radio wave absorbing members include magnetic radio wave absorbers, dielectric radio wave absorbers, and conductive radio wave absorbers.

[0101] As shown in the radio wave absorbing member 11, a radio wave absorbing sheet can be used as appropriate. In the radio wave absorbing member 11 in the form of a radio wave absorbing sheet, radio waves incident on the sheet from the front surface of the sheet are attenuated by passing through the sheet in the thickness direction, reflected on the rear surface of the sheet, and then passing from the rear surface side of the sheet toward the front surface side in the thickness direction to be attenuated again. A portion of the radio waves is transmitted through the front surface of the sheet, and the remaining portion is reflected on the front surface and further passes through the sheet in the thickness direction to repeat the attenuation.

[0102] Measures must be taken so that radio waves can be reliably reflected on the rear surface of the sheet. For example, in the case where the element housing 49 is made of a conductor such as aluminum as described above, reflection can be performed without any problems simply by attaching the radio wave absorbing sheet directly to the element housing 49. On the other hand, in the case where the element housing 49 is made of resin, it is necessary to reliably perform reflection by attaching a sheet-like conductor (i.e., shielding material) to the rear surface of the radio wave absorbing sheet. The radio wave absorbing sheet integrated with the sheet-like conductor can be attached to the element housing 49 formed of the conductor together with the sheet-like conductor.

[0103] Examples of the material of the radio wave absorbing member 11 include a material obtained by adding silicon carbide filler to a silicone base material, a material obtained by adding silicon carbide to ceramics and sintering the silicon carbide, a material obtained by adding silicon carbide to silicone grease to form a paste, and a material obtained by adding silicon carbide to a silicone adhesive to form a coating agent.

[0104] Specifically, the radiowave absorbing member 11 ideally has a low relative dielectric constant. Due to the low relative dielectric constant, radio waves attempting to enter the radiowave absorbing member 11 can be effectively prevented from being reflected on the surface of the radiowave absorbing member 11. To this end, in practice, the radiowave absorbing member 11 is preferably made of a low dielectric constant material with a relative dielectric constant of 2 to 3. In addition, the radiowave absorbing member 11 ideally has a high dielectric loss tangent. Due to the high dielectric loss tangent, radio waves that pass through the radiowave absorbing member 11 (i.e., the radiowave absorbing sheet), i.e., reflected waves that have become stray signal waves, can be effectively absorbed and reduced.

[0105] From this perspective, silicone-based materials and ceramics correspond to materials and base materials with low relative dielectric constants, while silicon carbide corresponds to materials with high dielectric loss tangent.

[0106] Examples of materials with a low relative dielectric constant include polypropylene, silicone resin, epoxy resin, polyurethane, chloroprene, and ceramics. Examples of materials with a high dielectric loss tangent include ferrite, silicon carbide, and titanium oxide. As described above, a solution in which a filler composed of a material having a higher dielectric loss tangent than that of the low relative dielectric constant material is mixed with a base material composed of a low relative dielectric constant material can be preferably used.

[0107] The sheet conductor attached to the rear surface of the radio wave absorbing sheet is preferably made of aluminum foil, copper foil, carbon fiber, etc. By being made of aluminum foil, copper foil, carbon fiber, etc., it can flexibly follow the shape of the element case 49 .

[0108] Figure 10 is a graph showing the intensity of the reflected wave that has become the stray signal wave and the intensity of the reflected wave from the interface of the object. Figure 10 , the horizontal axis represents the distance from the level meter 10, and the vertical axis represents the intensity of the signal detected by the level meter 10. Figure 9 In the level meter 10 of the illustrated structure, the solid line represents an example of a detection signal when the sensor unit 16 includes the speaker 46, the waveguide 45, and the element housing 49 but does not include the radio wave absorbing member 11. In the figure, the dotted line represents an example of a detection signal when the sensor unit 16 does not include the speaker 46, the waveguide 45, the element housing 49, and the radio wave absorbing member 11. As shown in the figure, since the sensor unit 16 includes the speaker 46, the waveguide 45, and the element housing 49, the signal strength is higher than the signal strength when these components are not included.

[0109] exist Figure 10 In FIG, the pulse detection signal 21 on the right side represents the detection signal of the surface (ie, the interface of the detection object). Figure 10The portion with high signal intensity near the vertical axis in the graph represents the detection signal 22 generated by detecting a reflected wave from outside the interface of the object (i.e., a reflected wave that has become a stray signal wave). As shown in the figure, the closer the reflected wave that has become a stray signal wave is to the vertical axis (i.e., the level meter 10), the higher the signal intensity of the detection signal 22. Then, the signal intensity of the detection signal 22 of the reflected wave that has become a stray signal wave is higher to a certain extent than the signal intensity of the detection signal 21 of the interface at a distance position close to the level meter 10. In the area where the signal intensity of the detection signal 22 of the reflected wave that has become a stray signal wave is higher than the signal intensity of the detection signal 21 of the interface, the detection signal 21 of the interface is buried in the detection signal 22 of the reflected wave that has become a stray signal and can therefore no longer be detected. That is, when the interface of the object approaches the level meter 10 to a certain extent or more, it is no longer possible to detect the horizontal height of the interface.

[0110] Note that the signal intensity of the interface detection signal 21 increases as the interface approaches the level meter 10. This is because the intensity of the reflected wave from the interface, when received by the level meter 10, increases as the interface approaches the level meter 10. Furthermore, the signal intensity of the interface detection signal 21 decreases as the relative dielectric constant of the detection object decreases. The relative dielectric constant of water is approximately 80, while the relative dielectric constant of cottonseed oil is 3.1. Therefore, in the level meter 10, the intensity of the detection signal 21 of the reflected wave from the interface is lower when detecting the level of cottonseed oil than when detecting the level of water.

[0111] Figure 11 The graph shows the effect of installing the radio wave absorbing member 11 on the Figure 9 The element housing 49 shown improves the detection performance of the level of the interface of the object at a distance close to the level meter 10. Figure 10 , the horizontal axis represents the distance from the level meter 10, and the vertical axis represents the intensity of the signal detected by the level meter 10. In the drawing, the signal intensity indicated by the dotted line is similar to Figure 10 The signal strength indicated by the solid line in Figure 9 The structure of the level meter 10 shown is similar to that of the Figure 11 The dashed line in FIG represents an example of a detection signal in the case where the sensor unit 16 includes the horn 46, the waveguide 45, and the element housing 49 but does not include the radio wave absorbing member 11. In the drawings, the solid line represents an example of a detection signal for a sensor unit having Figure 9 An example of a detection signal of the level meter 10 of the illustrated configuration. That is, an example of a detection signal in a case where the sensor unit 16 includes all of the horn 46, the waveguide 45, the element case 49, and the radio wave absorbing member 11 will be described.

[0112] Will Figure 11 Comparing the detection signal with a solid line (i.e., the detection signal when the radio wave absorbing member 11 is included) with the detection signal with a dashed line (i.e., the detection signal when the radio wave absorbing member 11 is not included), at a position far from the level gauge 10 (i.e., at an interface where an object is present), there is no significant difference between the intensity of the detection signal 23 in the solid line when the radio wave absorbing member 11 is included and the intensity of the detection signal 21 in the dashed line when the radio wave absorbing member 11 is not included. Specifically, the difference between the intensity of the detection signal 23 at the solid line interface when the radio wave absorbing member 11 is included and the intensity of the detection signal 21 at the dashed line interface when the radio wave absorbing member 11 is not included is approximately 10 dB. On the other hand, at a position close to the level gauge 10, the intensity of the detection signal 13 indicated by the solid line, which has become a reflected wave of a stray signal wave when the radio wave absorbing member 11 is included, is significantly lower than the intensity of the detection signal 22 indicated by the dashed line, which has become a reflected wave of a stray signal wave when the radio wave absorbing member 11 is not included. The intensity difference reaches approximately 30 dB.

[0113] Figure 11 Arrow 25A in FIG. 1 represents a change in the peak value of the detection signal 21 at the interface when the interface of the object approaches the level meter 10 in a case where the radio wave absorbing member 11 is not provided. Figure 11 The arrow 25 in FIG. 1 indicates a change in the peak value of the detection signal 21 at the interface when the interface of the object approaches the level meter 10 in the case where the radio wave absorbing member 11 is provided. The arrow 25A and the arrow 25B in FIG. Figure 11 The graph shows an upward and leftward slope in the figure, indicating that the intensity of the detection signal increases as the interface approaches the level meter 10 as described above. In the case where the radio wave absorbing member 11 is not provided, the distance from the level meter 10 corresponding to the point where the detection signal 22 indicated by the dotted line and the arrow 25A intersect represents the detection limit of the level meter 10 near the distance 36 in the case where the radio wave absorbing member 11 is not provided. In the case where the radio wave absorbing member 11 is included, the distance from the level meter 10 corresponding to the point where the solid line detection signal 13 and the arrow 25 intersect represents the detection limit of the level meter 10 near the distance 37 in the case where the radio wave absorbing member 11 is included.

[0114] It is clearly shown that the detection limit of the level meter 10 near the distance 37 when the radio wave absorbing member 11 is included is significantly closer to the level meter 10 than the detection limit of the level meter 10 near the distance 36 when the radio wave absorbing member 11 is not included. That is, when the radio wave absorbing member 11 is provided, the interface of the object can be detected at a distance closer to the level meter 10 than when the radio wave absorbing member 11 is not provided.

[0115] Figure 11 Also shown is a detection signal 26 at the interface of another object having a lower relative dielectric constant than the object generating the detection signal 23 at the interface, in the case where the radio wave absorbing member 11 is provided. For simplicity, it is assumed that the detection signal 26 represents both the detection signal when the radio wave absorbing member 11 is not provided and the detection signal when the radio wave absorbing member 11 is provided. However, since the peak value of the detection signal when the radio wave absorbing member 11 is not provided and the peak value of the detection signal when the radio wave absorbing member 11 is provided differ by about 10 dB as described above, Figure 11 Only the difference, ie the difference between the two peak values, is shown.

[0116] Figure 11 Arrow 27A in FIG. 3 indicates a change in the peak value of the detection signal 26 at the interface when the interface of the object approaches the level meter 10 in the case where the radio wave absorbing member 11 is not provided. In the case where the radio wave absorbing member 11 is not provided, the distance from the level meter 10 corresponding to the point where the detection signal 22 obtained by detecting the reflected wave that has become a stray signal wave and the arrow 27A intersect represents the detection limit of the level meter 10 near the distance 38 in the case where the radio wave absorbing member 11 is not provided. Figure 11 Arrow 27 in FIG. 1 indicates a change in the peak value of the detection signal 26 at the interface when the interface of the object approaches the level meter 10 in the case where the radio wave absorbing member 11 is provided. In the case where the radio wave absorbing member 11 is provided, the distance from the level meter 10 corresponding to the point where the solid-line detection signal 13 generated by detection of the reflected wave that has become a stray signal wave intersects with the arrow 27 represents the detection limit of the level meter 10 near the distance 39 in the case where the radio wave absorbing member 11 is provided.

[0117] The change in the peak value of the detection signal 26 when detecting an interface with another object having the aforementioned low relative permittivity is lower in signal strength than the change in the peak value of the detection signal 23 when detecting an interface with an object having a relatively low relative permittivity. However, even in this case, it is clearly shown that the detection limit of the level meter 10 near distance 39 when the radio wave absorbing member 11 is included is significantly closer to the level meter 10 than the detection limit of the level meter 10 near distance 38 when the radio wave absorbing member 11 is not included. That is, when the radio wave absorbing member 11 is provided, even when detecting an interface with another object having a low relative permittivity, the object's interface can be detected at a distance closer to the level meter 10 than when the radio wave absorbing member 11 is not provided. This improves detection stability at distances close to the level meter 10.

[0118] In particular, Figure 11 In the illustrated example, when detecting an interface with another object having a low relative permittivity at a position close to the level gauge 10 based on the characteristics of the detection signal 13 (indicated by the solid line) as a reflected wave of a stray signal wave in the case where the radio wave absorbing member 11 is included, and the detection signal 22 (indicated by the dotted line) as a reflected wave of a stray signal wave in the case where the radio wave absorbing member 11 is not included, the difference between the detection limit of the level gauge 10 at a distance 39 near the distance 39 when the radio wave absorbing member 11 is included and the detection limit of the level gauge 10 at a distance 38 near the distance 38 when the radio wave absorbing member 11 is not included further increases compared to the case of detecting an interface with an object having a relatively low relative permittivity. That is, when detecting an interface with another object having a relatively low relative permittivity, the detection stability at a distance close to the level gauge 10 (in other words, the detection performance at a short distance) is further improved compared to the case of detecting an interface with an object having a relatively high relative permittivity.

[0119] This is because, Figure 11 As shown, the lower the signal strength is, the farther the detection signals 13 and 22 , which have become reflected waves of stray signal waves at a position close to the level meter 10 , exist at a distance from the level meter 10 .

[0120] Therefore, in the Figure 3 In the case where the tank 70 of the container shown stores oil, granular resin, etc., when the level is detected, the level up to the vicinity of the top plate of the tank 70 can be reliably detected.

[0121] Attachment of the radio wave absorbing member 11 to the horn 46 will be described.

[0122] As described above, the intensity of the reflected wave from the dielectric lens 48 is lower than the intensity of the reflected wave from the element housing 49. Therefore, even in a case where the level meter 10 is small and the reflected wave from the dielectric lens 48 becomes a stray signal wave, the metal inner surface of the horn 46 can be exposed as long as the detection of the reflected wave from the object interface by the sensor IC 41 is not substantially adversely affected.

[0123] However, in the case where the level meter 10 is not small, the reflected wave from the dielectric lens 48 is likely to significantly and adversely affect the detection of the reflected wave from the object interface by the sensor IC 41. Figure 9As shown, the radio wave absorbing member 11 is preferably also attached to the inner periphery of the portion of the horn 46 near the surface 48A of the dielectric lens 48. In the case where the diameter of the dielectric lens 48 is 37 mm, the range where the radio wave absorbing member 11 is preferably installed is, for example, 5 mm to 15 mm away from the dielectric lens 48 in the vertical direction. The sheet-like radio wave absorbing member 11 can be attached to the inner peripheral surface of the horn 46 using, for example, acrylic double-sided tape.

[0124] Furthermore, if the radiowave absorbing member 11 is installed over a wide range, the radiowave absorbing member 11 may absorb a large amount of reflected waves even from the interface of the object, and conversely, the level of the interface may not be accurately detected. From this perspective, it is desirable to consider the installation range of the radiowave absorbing member 11 based on, for example, the magnitude of the S / N ratio.

[0125] Figure 12 The detailed internal structure of the sensor unit 16 of the level meter 10 according to the second example of an embodiment of the present invention is shown. Here, since a low-permittivity member is used instead of a metal member in the structure for attaching the dielectric lens 48 to the metal housing 54 in the sensor unit 16, the generation of reflected waves from the attachment structure is prevented. Furthermore, since the dielectric lens 48 is formed of a specific material, the reflected waves that pass through the dielectric lens 48 are absorbed and reduced.

[0126] The structure for attaching the dielectric lens 48 to the metal housing 54 will be described. Figure 9 In the level meter 10 of the first example shown, an inner flange 55 is integrally formed at the lower end, i.e., the open end, of the metal housing 54 of the sensor unit 16. On the other hand, a pair of outer flanges 56 and 56 are integrally formed on the edge of the dielectric lens 48 along the direction of the optical axis 40A. The dielectric lens 48 is inserted downwardly into the housing 54 through the opening at the upper end thereof, and the lower outer flange 56 strikes the inner flange 55 of the housing 54, thereby positioning and securing the dielectric lens 48 within the housing 54. A packing 57, such as an O-ring, is provided between the outer flanges 56 and 56 for sealing between the dielectric lens 48 and the housing 54. However, in this configuration, since the metal inner flange 55 contacts the outer flange 56 of the dielectric lens 48, there is a concern that reflected waves from the metal inner flange 55 of the housing 54, which could become stray signal waves, may be generated.

[0127] On the other hand, Figure 12 In the level gauge 10 of the second example shown, an attachment member 58 formed of a low dielectric constant member is provided. The attachment member 58 is hooked onto one outer flange 56 of the dielectric lens 48 and onto an appropriate portion in the housing 54, thereby fixing the dielectric lens 48 in a position relative to the housing 54.

[0128] With this construction, since the attachment member 58 formed of a low dielectric constant member is in contact with the outer flange 56 of the dielectric lens 48, the reflected waves of stray signals generated on the contact surface between the outer flange 56 of the dielectric lens 48 and the attachment member 58 can be reduced compared to the reflected waves of stray signal waves generated on the contact surface between the outer flange 56 of the dielectric lens 48 and the metal inner flange 55.

[0129] In order to reduce the generation of reflected waves that become stray signal waves from dielectric lens 48, dielectric lens 48 is preferably formed of a high dielectric loss tangent member. As the high dielectric loss tangent member, polytrifluoroethylene (PCTFE) resin is particularly preferably used. Since dielectric lens 48 is formed of a high dielectric loss tangent member, radio waves passing through dielectric lens 48 are effectively attenuated. In particular, since polytrifluoroethylene (PCTFE) resin is a high dielectric loss tangent member and a low dielectric constant member, it can achieve the effect of reducing reflected waves that become stray signal waves by reducing the reflection of radio waves.

[0130] Since the dielectric lens 48 is formed of a high dielectric loss tangent member, the original transmission wave toward the interface of the object and the original detection reflected wave reflected by the interface of the object and then entering the sensor unit 16 are slightly attenuated. However, compared with the disadvantage of attenuation, the reduction in the generation of the reflected wave that becomes a stray signal wave brings better results in the detection of the sensor unit 16.

[0131] exist Figure 12 In the sensor unit 16 of the level meter 10 according to the second example of the embodiment of the present invention shown, the cross-sectional shape of the dielectric lens 48 is suitable for reducing side lobes. Specifically, the transmission wave incident on the dielectric lens 48 and transmitted through the dielectric lens 48 from the transmission unit 43T of the sensor IC 41 includes a main lobe 61 that travels toward the interface of the object through the central portion of the dielectric lens 48 and a side lobe 62 that diverges to the periphery of the level meter 10 through the peripheral portion of the dielectric lens 48. The side lobe 62 is a noise component with low intensity caused by leakage or diffraction of the transmission wave, but always occurs. When generated, the side lobe 62 becomes a noise component from the dielectric lens 48. Figure 3 The level meter 10 shown is attached to a tank 70 to which a reflected wave of a surrounding structure is generated. That is, a reflected wave that becomes a stray signal wave is generated from an area close to the level meter 10.

[0132] In order to reduce the side lobe 62, the dielectric lens 48 has a protruding cross-sectional shape in which a surface 48A facing the inside of the horn 46 protrudes toward the waveguide 45. Then, in the dielectric lens 48, a surface 48B facing the outside of the level meter 10 is formed to be relatively flat compared to the surface 48A facing the inside of the horn 46. This is different from the case in which the dielectric lens 48 is formed to be relatively flat. Figure 9 In the dielectric lens 48 of the level meter 10 of the first example shown, the surface 48A on the waveguide 45 side has a flat end, and the surface 48B facing the outside of the level meter 10 has a protruding cross-sectional shape.

[0133] Figure 13 Shows when using Figure 12 The dielectric lens 48 shown is the state of the wavefront 67 of the transmission wave Tx. Figure 14 Shows when using Figure 9 The dielectric lens 48 shown is the state of the wavefront 68 of the transmitted wave Tx. Figure 14 In the figure, the side lobe 62 is clearly seen. On the other hand, in Figure 13 No side lobe generation was observed.

[0134] That is to say, according to Figure 12 The dielectric lens 48 shown can reduce the intensity of signals originating from components other than the main lobe 61. As a result, generation of reflected waves from an area near the level meter 10 can be reduced, and reflected waves from an area near the level meter 10 that cause spurious signal waves can be prevented from entering the level meter 10.

[0135] Although not shown, the surfaces 48A and 48B of the dielectric lens 48 are not smooth surfaces but surfaces having fine irregularities, for example, so that generation of reflected waves from an area close to the level meter 10 that causes stray signals in the same manner can be reduced.

[0136] By adopting Figure 12 The structure shown is particularly advantageous because the small level meter 10 is Figure 12 The illustrated configuration can reduce the generation of reflected waves that cause stray signal waves even if the radio wave absorbing member 11 is not attached to the inner periphery of the horn 46 as described above.

[0137] Figure 12 A small level gauge 10 is shown. Figure 12 The small level meter 10 shown is Figure 1 The difference between the non-small level meter 10 and the like shown is that the display part 20 and the rotating mechanism 19 for the display part 20 are not provided. Figure 12 In the small level meter 10 , the display unit is installed at a position away from the level meter 10 in a form separated from the level meter 10 . Figure 12 The small level meter 10 and the cable 69 for transmitting the signal etc. to the display part (not shown) are shown. Figure 12 In the illustrated small level meter 10 , only the status light 52 is installed.

[0138] exist Figure 11In the figure, the position of the vertical axis is the installation position of the level meter 10. Figure 3 In the case where the top plate of the tank 70 is at the position shown, the position of the top plate of the tank 70 is Figure 11 On the other hand, the case where the level meter 10 is moved upward from the top plate of the tank 70 and installed will be described below.

[0139] In this case, the top plate of the tank 70 is located at a distance 91 from the vertical axis (ie, the level gauge 10). At this distance 91, as shown in the figure, the detection signal 13 of the reflected wave causing the stray signal is at a much lower level than the detection signals 23 and 26 at the interface.

[0140] That is, by changing the position of the level meter 10 to a position above the top plate of the tank 70, the close range detection limit can be made closer to the top plate of the tank 70. Figure 3 The top plate of the tank 70 shown. That is, in the tank 70, the level of the interface 74 can be accurately detected up to a position near the top plate without any problems. Therefore, for example, changes in the level of the interface 74 in a small tank 70 can be accurately detected over a wide range.

[0141] Figure 15 and Figure 16 An example of an adapter 93 suitable for moving or installing the level meter 10 to a position above the top plate of the tank 70 is shown. The adapter 93 is formed in a cylindrical shape and has a flange 94 at the lower end for attaching the adapter 93 to the top plate of the tank 70. An inner screw 95 for fixing the level meter 10 to the adapter 93 is formed in an upper end of the adapter 93 in a penetrating state by screwing the connecting screw portion 14 of the level meter 10.

[0142] By providing the adapter 93, the sensor board 42 in which the sensor IC 41 including the receiving unit 43T is mounted in the level meter 10 is moved from the top plate of the tank 70, that is, from Figure 11 The vertical axis of the solid line drawn in Figure 11 The amount of movement corresponds to the height 96 of the adapter 93.

[0143] exist Figures 9 to 16 In each of the examples shown, technical features of other examples may be cited for each example as much as possible.

Claims

1. A level meter, comprising: a substrate on which the transmitter and the receiver are mounted; A radio wave shaping member comprising: an element housing covering a space including the transmitter and the receiver mounted on the substrate; a waveguide having one end in electromagnetic communication with the element housing; and a horn having a radio wave path gradually expanding from the other end of the waveguide toward a traveling direction of transmitted radio waves; a dielectric lens which is provided at a front end of the horn and which deflects radio waves from the transmitter to an object via the radio wave shaping member; and A radio wave absorbing member is provided along an inner wall of the element case and absorbs radio waves.

2. The level meter according to claim 1, wherein: The radio wave absorbing member is provided along an inner wall of the horn.

3. The level meter according to claim 1, comprising: a metal housing accommodating the substrate, the radio wave shaping member, and the dielectric lens; as well as An attachment member formed of a dielectric for attaching the dielectric lens to the metal housing in contact with the dielectric lens.

4. The level meter according to claim 1, wherein: The dielectric lens is formed of a lens material including a low dielectric constant material having a relative dielectric constant of 2 to 3 and a high dielectric loss tangent material having a dielectric loss tangent higher than that of the low dielectric constant material.

5. The level meter according to claim 4, wherein: The high dielectric loss tangent material is polychlorotrifluoroethylene resin.

6. The level meter according to claim 1, wherein: The waveguide includes a waveguide tube, and coaxially couples a transmission wave from the transmitter and a reception wave to the receiver.

7. The level meter according to claim 1, wherein: The dielectric lens has a protruding cross-sectional shape protruding toward the waveguide.

8. The level meter according to claim 1, comprising: a housing that accommodates the substrate, the radio wave shaping member, and the dielectric lens, the housing being attachable to a container that stores a substance having fluidity; as well as an adapter attached to the container and capable of attaching the housing, Wherein, when the housing is attached to the adapter, a first distance from the surface of the flowable substance to the substrate is longer than a second distance from the surface of the flowable substance to the substrate when the housing is attached to the container.

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