JP2582046B2 - Level meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a level meter which is mounted on a storage container for various kinds of fluids and granules to detect the storage amounts of the fluids and granules.

[0002]

2. Description of the Related Art In general, a container for storing various fluids and granular materials is provided with a level meter for detecting the storage amounts of the various fluids and granular materials. For example, a liquid will be described. A container for storing a liquid is provided with a liquid level gauge for detecting a storage amount of the liquid. A typical example of this liquid level gauge is a float type liquid level gauge that floats on a liquid level and detects the liquid level from the position of the float and the buoyancy received by the float. However, in the float method, since the liquid and the float come into contact with each other, the measured value is easily affected by a change in the temperature of the liquid, a fluctuation in the pressure inside the container, a viscosity of the liquid, or a shake of the container. If the stored liquid is a dangerous substance such as petroleum or LPG, static electricity will be generated as the float moves up and down, igniting inside the container,
There is a risk of fire or explosion.

Therefore, a so-called non-contact type liquid level gauge in which the liquid does not come into contact with the measuring means is widely used. As the non-contact type liquid level meter, for example, a capacitance type level measuring device is widely used. The principle of detection of this capacitance-type level measuring device is that a measuring electrode and a ground electrode are arranged in a container so as to face each other with a small gap therebetween. Since the capacitance of the liquid changes, the liquid level is detected by detecting the amount of change.

As a non-contact type liquid level gauge, as shown in FIG. 6, radiation, ultrasonic waves, laser light, microwaves, or the like is applied to a detection window 2 provided opposite to a side wall of a container 1. A liquid level gauge configured by externally attaching a transmitter 3 and a receiver 4 for generating a measurement medium is also used. The liquid level is detected by utilizing the property that the measurement medium is absorbed by the liquid. That is, when the liquid surface reaches the position of the detection window 2, the measuring medium emitted from the transmitter 3 is absorbed by the liquid and the propagation to the receiver 4 is interrupted. The liquid level can be detected by outputting a shutoff signal when the detection is interrupted. In particular, when the measurement medium is a microwave, the microwave has a property of transmitting a substance other than a liquid, such as plastics, ceramics, and paper, so that the liquid level can be detected even if the detection window 2 is contaminated. It has the advantage of being able to.

[0005]

However, since the capacitance-type level measuring device as described above relies on the principle of detecting a change in capacitance between electrodes, the dielectric constant of the object to be detected is particularly high. Is low, the change in capacitance corresponding to the presence or absence of the object to be detected does not appear remarkably, and detection may not be possible. In addition, there is a disadvantage that the influence of the deposits on the electrode surface on the measured value is so large that it cannot be ignored. Also,
In the capacitance level measuring device, since the amplifier and the electrode are connected, a spark discharge occurs when a high voltage is applied between the electrodes due to some kind of failure on the amplifier side or the occurrence of surge voltage. I do. In particular, when the object to be detected is a combustible, there is a risk of fire or explosion, which poses a safety problem.
Further, it is necessary to wire and connect an electric wire to the electrode, which has been troublesome in installation work and maintenance work. In addition, it is necessary to adjust the measurement sensitivity for each object to be detected, and the capacitance slightly changes according to the length of the electric wire and the installation conditions. Therefore, fine adjustment of the amplifier at each installation site is indispensable.

On the other hand, as described above, the transmitter 3 and the receiver 4
In a liquid level gauge configured by disposing the sensors facing each other, when the container is large, the distance between the transmitter 3 and the receiver 4 is increased, and as a result, the output of the transmitter 3 needs to be increased. , The area of the transmitting / receiving section including the detection window 2 must be increased. Further, when the container has a multilayer structure, it is practically impossible to mount the side wall. Further, there is a drawback that microwaves are generally absorbed to a higher degree as the dielectric constant of the object to be detected is higher, and cannot be reliably detected for various oils having a lower dielectric constant. In addition, when the detection target is a granular material, the granular material cannot be detected for the same reason because the dielectric constant is significantly lower than that in the case where the forming substance is a solid.

As described above, there are various problems in the float type level meter, the capacitance type level measuring device, and the liquid level meter constituted by disposing the transmitter 3 and the receiver 4 in opposition. Therefore, an object of the present invention is to solve the above-mentioned problem, that is, regardless of the magnitude of the dielectric constant of the detected object, and even when the detected object is a granular material, the storage level of the detected object is reduced. Not only can it be reliably detected, but it does not require a high-output transmitter, and at the same time, the area of the transmitting and receiving part can be small,
It is another object of the present invention to provide a level meter with excellent safety.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a microwave transmitter, a microwave receiver, and a guide member for guiding microwaves emitted from the microwave transmitter to the microwave receiver. A level meter attached to the storage container by projecting the guide member into the storage container, wherein the guide member is a transmitter-side waveguide connected to the microwave transmitter, This is achieved by a level meter, wherein the microwave receiver is connected to a receiver-side waveguide connected by a guide body made of a solid dielectric. A part of the guide body of the level meter may be configured to have a smaller cross-sectional area than other parts. The guide body of the level meter may have an acute-angled curved portion.
The guide body of the level meter is formed so that both ends thereof are inclined downward, and the tube member has a diameter that is continuous with the end of the guide body and is equal to or less than the microwave leakage diameter. A through hole may be provided. The dielectric forming the guide of the level meter is preferably a low dielectric.

A similar object is to provide a microwave transmitter, a microwave receiver, and a guide member for guiding a microwave emitted from the microwave transmitter to the microwave receiver. A level meter mounted on the storage container by projecting the member into the storage container, wherein the guide member is
One end is connected to the microwave transmitter, and the other end is connected to the microwave receiver, the transmitter-side guide section including a waveguide having a reflecting member made of a dielectric material attached to the other end. And a receiver-side guide section formed of a waveguide having an opening formed at the other end facing the reflection member.
The receiver-side guide may be provided with a shielding member made of a microwave impermeable material immediately below the opening.

A similar object is to provide a microwave transmitter,
A microwave receiver and a guide member for guiding microwaves emitted from the microwave transmitter to the microwave receiver, and the guide member is mounted on the storage container by projecting the guide member into the storage container. A level meter, wherein the guide member is formed of a substantially U-shaped waveguide connecting the microwave transmitter and the microwave receiver, and a part of the curved portion is in air. This is also achieved by a level meter, which is formed to have a diameter equal to or less than the diameter of a tube through which microwaves can propagate, and is provided with a through hole for introducing and discharging an object to be detected into and from the inside of the guide member.

[0011]

The level meter according to the present invention detects the storage level of the object to be detected by detecting a change in the propagation amount (intensity) of the microwave propagating in the guide member.
The propagation state of the microwave changes depending on the material forming the guide member and the shape of the guide member. In the present invention,
By using a dielectric member for the guide member, the fact that the propagation amount of microwaves in the guide member changes due to the difference between the dielectric constant of air and the dielectric constant of the object to be detected is used. In addition, the diameter of the waveguide of the guide member is set to be equal to or smaller than the diameter at which the microwave can propagate in the air, and the propagation state of the microwave is different when the object to be detected is present in the waveguide and when it is not present. Is used. Therefore, the storage level can be detected irrespective of the dielectric constant of the object to be detected, and the invention can be applied to the detection of the storage level of not only liquids but also powders. Moreover, the storage level can be reliably detected without the need for fine adjustment of the sensitivity as in the case of the capacitance type level device at the time of detection.

Further, by forming the cross-sectional area of a part of the guide body smaller than that of the other part, or by forming the guide body with an acute angle, the detection object having a low dielectric constant close to that of air. The signal-to-noise ratio at the time of performing level detection is improved. Further, both ends of the guide body are formed so as to be inclined downward, and the transmitter-side waveguide and the receiver-side waveguide are connected to the end of the guide body. By forming a through hole having a diameter equal to or less than the microwave leakage diameter, water droplets generated by dew condensation inside the pipe member can be discharged to the outside of the guide member, thereby preventing microwave absorption by the water droplets. it can. Moreover, by forming the inclined surface on the guide body, scattering when the microwave enters the guide body can be reduced, and attenuation of the microwave can be suppressed.

Further, in the level meter according to the present invention, the dielectric constant of the microwave reflecting member and the dielectric constant of the object to be detected are reduced by providing the microwave reflecting member made of a dielectric in the transmitter-side guide portion. In the case of approximation, the microwave is transmitted through the microwave reflecting member and is not guided to the microwave introduction opening, and when the dielectric constant of the detection target is large, the microwave is transmitted by the detection target. It is absorbed and no longer guided by the microwave introduction opening. Therefore, the storage level can be detected based on the difference between the dielectric constant of the microwave reflecting member and the dielectric constant of the object to be detected in the same manner as described above, and the storage level of not only the liquid but also the granular material can be detected. Be adaptable. Here, by disposing a shielding member made of a microwave non-transmissive material immediately below the microwave introduction opening, the microwave transmitted through the microwave reflecting member is reflected by the bottom of the storage container and is reflected on the receiver side. It can be prevented from being mixed into the guide portion, and the signal-to-noise ratio in level detection of the detected object can be improved.

Further, by setting the curved portion of the waveguide constituting the guide member to a diameter smaller than a diameter of a tube through which microwaves can propagate in air, the inside of the waveguide is filled with a substance having a dielectric constant larger than that of air. In this case, the microwave can be propagated, and the microwave is guided to the microwave receiver. Therefore, the storage level is detected based on the presence / absence of reception of the microwave receiver. In general, since the dielectric constant of the object to be detected is higher than the dielectric constant of air, it is possible to detect the storage level of a wider range of substances, and particularly to detect the storage level of a low dielectric substance, which has been difficult to detect conventionally. Is also possible. It is also possible to select a detectable substance according to the set value of the propagable pipe diameter.

In addition to the above, in the level meter according to the present invention, the distance between the microwave transmitter and the microwave receiver is short, and the microwave emitted from the microwave transmitter is surely guided by the guide member. To be guided to the microwave receiver,
A microwave transmitter does not require a large output, while a microwave receiver requires a smaller detection area and can be downsized as a whole and consumes less power.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A level meter according to the present invention will be described below in detail with reference to the accompanying drawings. However, the present invention is not limited to only this embodiment.

Embodiment 1 FIG. 1 is a partially cutaway side view showing a first embodiment of a level meter according to the present invention. In the figure, the level meter 100
Enclosure 13 for accommodating microwave transmitter 10, microwave receiver 11 and various circuit elements 12, guide member 14 for guiding microwaves, and connecting enclosure 13 and guide member 14 to storage container 15 And a mounting member 16 for mounting.

The microwave transmitter 10 is a member for generating a microwave, and is, for example, a known microwave oscillator such as a Gunn diode, an impatt diode, a tantalum diode, a trapat diode, a ballit diode, and an LSA diode. Can be used. Further, the output of the microwave transmitter 10 does not require a particularly large output because the propagation of the microwave is only inside the guide member 14.

On the other hand, the microwave receiver 11 is a member for receiving the microwave transmitted from the microwave transmitter 10, and is a known microwave receiver represented by a mixer diode (varistor). Can be used. In addition, the characteristics of the microwave receiver 11 do not need to have a particularly low noise figure.

The circuit element 12 includes, for example, electronic components such as transistors and resistors, switches, various adjustment knobs, terminals,
An indicator light or the like drives and controls the microwave transmitter 10 and the microwave receiver 11. These are mounted on the printed circuit board wiring 17 and housed in the enclosure 13. In addition, it is connected to a power supply and an external device (not shown).

The guide member 14 is provided for the microwave transmitter 10
For guiding the microwaves transmitted from the microwave receiver 11 to the microwave receiver 11, the transmitter-side waveguide 18a connected to the microwave transmitter 10, and the microwave receiver 11
And a receiver-side waveguide 18b connected to a guide body 19 made of a solid dielectric. Each waveguide 1
Reference numerals 8a and 18b denote hollow tubes made of a metal having corrosion resistance such as stainless steel, which are respectively connected to the microwave transmitter 10 and the microwave receiver 11 via the plug member 20 made of a microwave transparent material. Be linked.

If the guide body 19 is made of a material having a low dielectric constant,
The range of the permittivity of the object to be detected is preferably widened.
In addition, it is preferable to be excellent in chemical resistance, heat resistance and the like. In consideration of these requirements, for example, Teflon can be suitably used. The guide body 19 is formed by bending this low dielectric constant material into a substantially U-shape. Then, both ends 19a of the guide body 19 are connected to the transmitter-side waveguide 18a and the receiver-side waveguide 1a.
The guide member 14 is formed by fitting and joining the end of the guide member 8b.

Therefore, the microwave transmitted from the microwave transmitter 10 travels while reflecting on the inner wall surface of the transmitter-side waveguide 18a, as shown by the symbol M in the figure, and then travels along the guide body. After entering the U and passing through the U-shaped curved portion,
The microwave receiver 11 propagates through the receiver-side waveguide 18b and
Arrives at the receiver.

Here, both ends 19a of the guide body 19 are
By being formed to be inclined downward in the figure, scattering when the microwave enters and exits the guide body 19 can be suppressed, and attenuation of the microwave can be prevented. Then, a through-hole 21 is formed in a joint portion of each of the waveguides 18a and 18b with the guide body 19 so as to be continuous with the inclination of both ends 19a of the guide body 19, so that the inside of each of the waveguides 18a and 18b is formed. As a result, it is possible to prevent the water droplets generated by the condensation from being discharged to the outside of the guide member 14, and to prevent the water droplets from staying on the end 19a of the guide body 19 and blocking the propagation of the microwave. The diameter of the through hole 21 needs to be smaller than the microwave leakage diameter. For example, in the case of a commonly used X-band microwave, the microwave leakage diameter is about 1 mm.
Since the diameter is 5 mm, it is desirable to set the diameter to a value smaller than 5 mm. When it is necessary to form the diameter of the through hole 21 to be larger than the microwave leakage diameter, a frame 22 is provided around the through hole 21 to substantially reduce the diameter of the through hole 21. The size can be reduced to prevent microwave leakage.

Next, the principle of detecting the level of the detected object in the storage container 15 by the level meter 100 will be described with reference to FIG. The level meter 100 according to the present embodiment utilizes a characteristic that, when a microwave propagates through a propagation medium made of a dielectric, the amount of propagation (intensity) is reduced by coming into contact with a substance having a different dielectric constant. It is. When the storage level of the detected object stored in the storage container 15 is lower than the guide body 19 (reference L <b> 0), the microwave transmitted from the microwave transmitter 10 causes the guide body 19 to move. The microwave receiver 11 has a certain amount of propagation.
Will be guided to. Here, by forming the guide body 19 with a low dielectric material, the range of the detectable dielectric constant of the detected object is widened. Therefore, the microwave receiver 11 continuously detects a microwave having a certain constant intensity.

However, when the storage level rises and the entire guide body 19 is surrounded by the object to be detected (reference L1), the propagation amount of the microwave propagating through the guide body 19 changes. Here, when the surroundings of the dielectric material forming the guide body 19 are air, the microwave propagating through the transmitter-side waveguide 18a is attenuated in the guide body 19 immediately after entering the guide body 19. However, when it reaches a portion surrounded by a detection object having a higher dielectric constant than air, it diffuses to the detection object side.
Therefore, the propagation amount of the microwave guided to the microwave receiver 11 decreases, and the detection intensity of the microwave receiver 11 decreases. Therefore, the storage level can be detected by configuring a circuit so that a detection signal is output from the microwave receiver 11 when the detection intensity of the microwave receiver 11 changes. Further, since the detection is performed based on the difference in the dielectric constant between the air and the detection target, the detection target can detect not only liquid but also powder and granular material.

Here, by selecting a material having a low dielectric constant as the dielectric material forming the guide body 19, the range of the object to be detected that can be detected can be expanded. Further, by changing the length of the waveguides 18a and 18b of the guide member 14, the storage amount can be arbitrarily set.

By the way, when the guide member 19 is formed of a dielectric rod having a constant diameter as described above, the guide member 19 is surrounded by the detected object when the dielectric constant of the detected object is close to the dielectric constant of air. In this case, the amount of diffusion of the microwave decreases, and accordingly, the amount of change in the reception intensity in the microwave receiver 11 also decreases, and the detection accuracy decreases. Generally, when a microwave propagates through a dielectric, the attenuation increases if the cross-sectional area of the dielectric is small. In view of this, in the present invention, the guide body 19 is configured as shown in FIG. That is, the guide body 23 has its U-shaped curved portion connected to the waveguides 18a, 18b.
The portion to be joined is made to have a large diameter (D1), and the curved central portion is made to have a minimum diameter (D2), so that the diameter gradually becomes smaller.
With this configuration, a considerable amount of microwaves is attenuated in the U-shaped curved portion of the guide body 23, and even in a state in which minute microwaves surrounded by a material having a low dielectric constant are diffused,
The amount of change in the reception intensity in the microwave receiver becomes large, and a substance having a low dielectric constant can be reliably detected.

Further, the same effect as reducing the diameter of the guide member 19 can be realized by the guide member 24 having an acute curved portion as shown in FIG. in this case,
The microwave leaks from the acute angle portion 25 of the guide body 24 to the detection target. Note that the guide body 24 is connected to the acute angle portion 25 thereof.
It can be configured so that the diameter gradually decreases toward.

Embodiment 2 A second embodiment of the level meter according to the present invention will be described with reference to FIG. Illustration and description of the same parts as those in the first embodiment are omitted. FIG. 4 is a cross-sectional view of a main part showing a guide member 30 corresponding to the guide member 14 in the first embodiment. As shown in the figure, a guide member 30 is provided at a lower end portion of a transmitter-side waveguide 31a with a reflection member 32 made of a dielectric material.
And a receiver-side guide section 35 having an opening 34 at the lower end of the receiver-side waveguide 31b.

The reflection member 32 is provided directly below the lower end opening of the transmitter-side waveguide 31a at an angle of 45 ° with respect to the microwave traveling axis M. The opening 34 is formed by a lower extension 36 that extends from the lower end of the receiver-side waveguide 31b and curves toward the reflection member 32. The reflection member 32 and the opening 34 are arranged to face each other at a predetermined interval.

The microwave emitted from the microwave transmitter (not shown) is led out from the lower end of the waveguide 31a on the transmitter side as shown by the symbol M in the figure, and is disposed therebelow. The light is reflected by the reflecting member 32 and guided to the opening 34 of the receiver-side waveguide 31b. Then, it is guided to a microwave receiver (not shown).

The detection of the storage level of the object to be detected is performed by surrounding the reflection member 32 and the opening 34 of the guide member 30 with the object to be detected. Here, if the dielectric constant of the object to be detected is close to the dielectric constant of the dielectric forming the reflection member 32, the region including the reflection member 32 has a substantially uniform dielectric constant. For this reason, the reflecting member 32 loses the function of reflecting the microwave, so that most of the microwave is not reflected, but almost passes through the reflecting member 32 and goes straight down in the drawing. As a result, the microwave guided to the opening 34 disappears, and the microwave receiving intensity in the microwave receiver is drastically reduced. Based on the change in the reception intensity, the storage level of the object to be detected is detected.

On the other hand, when the dielectric constant of the object to be detected is higher than the dielectric constant of the dielectric forming the reflection member 32, the propagation of the microwave to the opening 34 is blocked by the object to be detected. Similarly, the reception intensity at the microwave receiver is drastically reduced. Therefore, the storage level is detected from the change in the reception intensity.

In the configuration of the guide member 30 described above, when microwaves pass through the reflection member 32, the reflection from the bottom and the wall of the storage container may enter the opening 34 and become a noise source. is there. Therefore, a shielding member 37 made of a material that does not transmit microwaves, for example, a metal,
By disposing the microwave below the lower extension 36 of the receiver-side waveguide 31b, the reflected microwave can be cut off.

Embodiment 3 A third embodiment of the level meter according to the present invention will be described with reference to FIG. Illustration and description of the same parts as those in the first embodiment are omitted. FIG. 5 is a cross-sectional view of a main part showing a guide member 40 corresponding to the guide member 14 in the first embodiment. As shown in the figure, the guide member 40 includes a waveguide 41 having a substantially U-shape that connects a microwave transmitter and a microwave receiver (not shown). Here, the waveguide 41 is formed such that the curved portion has a diameter (D3) of the waveguide 41 as a large diameter portion, and the center of the curved portion has a small diameter portion (D4), and gradually becomes smaller in diameter. A plurality of through holes 42 for introducing and discharging the detection body into and from the waveguide 41 are formed.

Usually, when a microwave propagates through a waveguide,
There is a pipe diameter that can propagate in accordance with the frequency of the microwave. It is also known that the diameter of the pipe that can propagate varies depending on the dielectric constant of the filler when the inside of the waveguide is filled. Specifically, the tube diameter is d (mm), the dielectric constant of the filler is ε, and the microwave frequency is f (GH
z), a relational expression of d = 175.70 / f (ε) ^1/2 follows. That is, assuming that the frequency f of the microwave is constant, a material having a higher dielectric constant ε has a smaller propagable diameter d.

Therefore, by making the small diameter portion (D4) of the curved portion of the waveguide 41 constituting the guide member 40 smaller than the diameter of the tube through which the microwave can propagate in the air, the dielectric constant is larger than that of the air. When a substance enters the pipe member 41 through the through hole 42 and the inside of the pipe is filled with the substance, the propagation of the microwave becomes possible, and the microwave is received by the microwave receiver (not shown). Therefore, the storage level is detected based on the presence / absence of reception of the microwave receiver. In general, since the dielectric constant of the object to be detected is higher than the dielectric constant of air, it is possible to detect the storage level of a wider range of substances, and particularly to detect the storage level of a low dielectric substance, which has been difficult to detect conventionally. Is also possible. It is also possible to select a detectable substance according to the set value of the propagable pipe diameter.

[0039]

As described above, according to the level meter of the present invention, the storage level can be detected irrespective of the dielectric constant of the object to be detected, and the storage level of not only liquid but also granular material can be detected. Is also applicable. Moreover, the storage level can be reliably detected without the need for fine adjustment of the sensitivity as in the case of the capacitance type level device at the time of detection. Also,
The distance between the microwave transmitter and the microwave receiver is short,
Moreover, since the microwave emitted from the microwave transmitter is reliably guided to the microwave receiver by the guide member, the microwave transmitter does not require a large output, while the microwave receiver is also required. The area of the detection unit can be small, the size of the entire device can be reduced, and the power consumption can be small. In addition, there is no danger that the microwaves scatter in the air and cause radio interference.

[Brief description of the drawings]

FIG. 1 is a partially cutaway side view showing a first embodiment of a level meter according to the present invention.

FIG. 2 is a cross-sectional view of a main part showing another structure of the guide member of the level meter shown in FIG.

FIG. 3 is a sectional view of a main part showing another structure of the guide member of the level meter shown in FIG. 1;

FIG. 4 is a sectional view of a main part showing a second embodiment of the level meter according to the present invention.

FIG. 5 is a sectional view of a main part showing a third embodiment of the level meter according to the present invention.

FIG. 6 is a partial sectional perspective view showing a conventional non-contact type level meter using microwaves.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Microwave transmitter 11 Microwave receiver 12 Circuit element 13 Enclosure 14 Guide member 15 Storage container 16 Mounting member 17 Printed wiring board 18a, 18b Waveguide 19 Guide body 20 Plug member 21 Through hole 22 Frame 23 Guide Body 24 Guide body 25 Sharp portion 30 Guide member 31a, 31b Waveguide 32 Reflecting member 34 Opening 37 Shielding member 40 Guide member 41 Waveguide 42 Through hole 100 Level meter

Claims (8)

(57) [Claims] A microwave transmitter; a microwave receiver; and a guide member for guiding microwaves emitted from the microwave transmitter to the microwave receiver. A level meter mounted on the storage container by projecting a member into the storage container, wherein the guide member includes a transmitter-side waveguide connected to the microwave transmitter, and the microwave receiver. A level meter comprising: a receiver-side waveguide connected to a wave device; and a guide body made of a dielectric material. 2. The level meter according to claim 1, wherein a part of the guide body is configured to have a smaller sectional area than other parts. 3. The level meter according to claim 1, wherein the guide body has a curved portion with an acute angle. 4. The guide body is formed so that both ends thereof are inclined downward, and the transmitter-side waveguide and the receiver-side waveguide are provided with the guide body. 4. The level meter according to claim 1, wherein a through hole provided with a frame body is formed at an end portion. 5. The level meter according to claim 1, wherein the dielectric forming the guide body is a low dielectric. 6. A guide comprising: a microwave transmitter; a microwave receiver; and a guide member for guiding microwaves emitted from the microwave transmitter to the microwave receiver. A level meter mounted on the storage container by projecting a member into the storage container, wherein the guide member has one end connected to the microwave transmitter and the other end provided with a reflection member made of a dielectric. And a waveguide having one end connected to the microwave receiver and the other end formed with an opening facing the reflection member. And a guide unit on the receiver side. 7. The level meter according to claim 5, wherein a shield member made of a microwave impermeable material is attached to the receiver-side guide portion immediately below the opening. 8. A guide comprising: a microwave transmitter; a microwave receiver; and a guide member for guiding microwaves emitted from the microwave transmitter to the microwave receiver. A level meter mounted on the storage container by projecting a member into the storage container, wherein the guide member has a substantially U-shape connecting the microwave transmitter and the microwave receiver. A part of the curved portion is formed to have a diameter equal to or less than a diameter of a tube through which microwaves in air can be transmitted, and a through hole for introducing and discharging a detection target into and from the guide member is formed. Level meter characterized by being established.