JP3755684B2 - Radio wave level gauge - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radio wave level gauge used for an oil storage tank, a ballast tank, and other various liquid storage tanks in a tanker, for example.
[0002]
[Prior art]
Conventionally, a radio wave level gauge has been proposed that measures the liquid level in a tank using radio waves. Hereinafter, a conventional radio wave level gauge will be briefly described. In FIG. 4, reference numeral 51 denotes a radar antenna that emits a microwave toward the liquid level stored in the tank and receives a reflected wave reflected by the liquid level.
[0003]
Reference numeral 52 denotes a transmission / reception apparatus that emits a microwave from the radar antenna 51 and transmits the emitted microwave and a reflected wave received by the radar antenna 51 to the signal processing unit 53. The transmitter / receiver 52 includes a microwave transmitter / receiver 52a and a transmitter / receiver mixer circuit (including a preamplifier) 52b. The radar antenna 51 and the transmission / reception device 52 constitute a sensor unit 50.
[0004]
Reference numeral 53 denotes a signal processing unit, which includes an audio amplifier 53a, an A / D converter 53b, an FFT (Fast Fourier Transform) circuit 53c, a signal processing circuit (including a display circuit) 53d, and a trapezoidal wave generation circuit 53e. It is configured.
[0005]
Next, a liquid level measurement method performed by the sensor unit 50 and the signal processing unit 53 will be described. In FIG. 5, the solid line indicates the transmission frequency of the microwave emitted from the radar antenna 51. A broken line indicates a reception frequency of a reflected wave received by the radar antenna 51, that is, a reflected wave in which a microwave is reflected on the liquid surface.
[0006]
The transmission frequency is continuously changed from a certain frequency f1 to f2, that is, in the range of the sweep frequency B, from a certain time t1 to t2, that is, with respect to the sweep time T. This is output according to the slope of the trapezoidal wave output from the trapezoidal wave generating circuit 53e. The reception frequency is received by the radar antenna 51 with a certain time delay determined by the distance to the liquid surface. Therefore, the difference Δf between the transmission frequency and the reception frequency at a certain time t is proportional to the distance from the radar antenna 51 to the liquid level in the tank.
[0007]
At this time, as shown in FIG. 6, Δf shows a constant value throughout the sweep time T. In other words, the difference Δf between the transmission frequency and the reception frequency at a certain time t shows a constant value in any cross section from t1 to t2. When the distance from the radar antenna 51 to the liquid level in the tank is short, Δf indicates a low value, and when the distance from the radar antenna 51 to the liquid level in the tank is long, Δf is High value. In either case, Δf is the audio frequency band. By appropriately amplifying this Δf and inputting it to the FFT circuit 53c, it can be converted into a distance from the radar antenna 51 to the liquid level in the tank. FIG. 7 shows the output of the FFT circuit 53c, and the distance from this output to the liquid level can be known.
[0008]
In the signal processing unit 53, first, a beat signal (audio frequency band) between the transmission frequency of the microwave and the reception frequency of the reflected wave transmitted from the sensor unit 50 is appropriately amplified by the audio amplifier 53a. Then, the analog signal is converted into a digital signal by the A / D converter 53b, and frequency analysis, that is, fast Fourier transform is performed by the FFT circuit 53c, and from the radar antenna 51 to the liquid level in the tank. It can be detected as a distance. That is, the liquid level in the tank can be measured.
[0009]
In the radio wave level gauge described above, a protection plate is provided between the radar antenna 51 and the liquid level in the tank in order to protect the radar antenna 51 from the pressure from the tank. The radar antenna 51 is attached at a position that does not adversely affect the electromagnetic field.
[0010]
[Problems to be solved by the invention]
However, the conventional protective plate has a problem that if it is provided at a position that does not adversely affect the electromagnetic field of the radar antenna 51, the entire apparatus becomes large. Therefore, in order to reduce the size of the apparatus, it is considered that the radar antenna 51 is a flat antenna. However, in order to make the radar antenna 51 a flat plate antenna, various technical problems must be solved. That is, in order to reduce the size of the apparatus, it is desirable that the protective plate be as close as possible to the flat plate antenna. However, as the protective plate is brought closer to the flat plate antenna, the protective plate becomes an obstacle to transmission of microwaves. In addition, when oil is stored in the tank, the oil may evaporate and the paraffin may be condensed on the protective plate. With the conventional protective plate, the paraffin condensed on the protective plate must be removed. Therefore, the paraffin condensed on the protective plate becomes an obstacle to the transmission of electromagnetic waves, and there is a problem that accurate measurement cannot be performed. In particular, when the protective plate is attached close to the flat antenna, there is a great obstacle to electromagnetic wave transmission due to the paraffin.
[0011]
The present invention was made in order to solve the problems of the prior art as described above, and allows paraffin to flow from the central part where the electric field strength of the antenna is strong to the peripheral part to transmit as strong radio waves as possible. It is another object of the present invention to provide a radio wave level gauge that can be miniaturized by providing a protective plate at the shortest distance that does not adversely affect the electromagnetic field of the antenna.
[0012]
[Means for Solving the Problems]
According to the first aspect of the present invention, a microwave is emitted toward the liquid surface stored in the tank and a reflected wave from the liquid surface is received, and the microwave emitted from the flat antenna and the flat plate are received. A radio wave level gauge having a transmitting / receiving device for transmitting a reflected wave received by an antenna to a data processing unit and a protective plate for protecting the flat antenna, wherein the protective plate is formed in a cone shape. The protection plate is provided with the conical top of the protection plate facing the lower surface of the flat antenna, and is provided at the shortest distance that does not adversely affect the electromagnetic field of the flat antenna, and the antenna and the transceiver The installation space is filled with an inert gas .
[0015]
According to a second aspect of the invention of claim 1 Symbol placement, thickness of the protective plate, said the with a thickness that can withstand the pressure in the tank, a uniform thickness To do.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of a radio wave level meter according to the present invention will be described with reference to the drawings. In FIG. 1, the code | symbol 1 has shown the tank which stores various liquids. A top plate 10 of the tank 1 constitutes a part of the hull, and a ring-shaped first flange 2 is attached on the top plate 10. An opening is formed in the top plate 10 at a position facing the center hole of the first flange 2.
[0017]
A protection plate 5 is attached on the first flange 2 so as to cover the center hole of the first flange 2. The protection plate 5 is provided to protect a flat plate antenna 6 to be described later from pressure from the tank 1 and the like. The protective plate 5 is made of a dielectric material such as a fluororesin, and for example, Teflon (trade name) can be used as the material.
[0018]
The protective plate 5 is formed in a conical shape, and is mounted on the first flange 2 with the conical top portion of the protective plate 5 facing the lower surface of a flat antenna 6 described later. The distance between the protective plate 5 and the flat plate antenna 6 described later is set to the shortest distance that the protective plate 5 does not adversely affect the electromagnetic field of the flat plate antenna 6. Details of the protection plate 5 will be described later.
[0019]
On the first flange 2, in order to fix the protective plate 5 while covering the periphery of the protective plate 5 and maintaining airtightness, the inner peripheral edge of the protective plate 5 is smaller in diameter than the first flange 2. A ring-shaped second flange 7 covering the portion is fixed by screw portions 7a and 7a. Further, since the O-ring 2a is mounted on the first flange 2 at a position facing the bottom surface of the outer peripheral edge of the protective plate 5, the tank 1 is sealed by the protective plate 5. It has become.
[0020]
Furthermore, on the first flange 2, a terminal box 3 in which a flat antenna 6 and the like to be described later are accommodated is attached. On the upper surface of the terminal box 3, a terminal box cover 4 is fixedly fixed by screw parts 4a, 4a and an O-ring 4b. Therefore, the inside of the terminal box 3 is in a sealed state.
[0021]
Within the terminal box 3, a casing 8 is tightly fixed on the second flange 7 by screws 7 a and 7 a and an O-ring 7 b. Therefore, the inside of the casing 8 is in a sealed state.
[0022]
The flat antenna 6 is horizontally attached to the casing 8 by screws 8a and 8a. The flat antenna 6 emits microwaves toward the liquid level stored in the tank 1 and receives reflected waves from the liquid level. Further, the distance between the protective plate 5 and the flat antenna 6 is set to the shortest distance at which the protective plate 5 does not adversely affect the electromagnetic field of the flat antenna 6 as described above.
[0023]
Reference numeral 9 denotes a transmission / reception device, which is provided on the flat antenna 6 in the casing 8. The transmission / reception device 9 transmits a microwave emitted from the flat antenna 6 and a reflected wave received by the flat antenna 6 to a cargo handling console (data processing unit) 30 described later.
[0024]
Next, the configuration of the transmission / reception device 9 and the cargo handling console 30 will be described. In FIG. 2, the sensor unit 20 includes the flat antenna 6 and the transmission / reception device 9. The transmission / reception device 9 includes a microwave transmitter / receiver 9a and a transmission / reception wave mixer circuit (including a preamplifier) 9b.
[0025]
The cargo handling console 30 includes an audio amplifier 30a, an A / D converter 30b, an FFT circuit 30c, a signal processing circuit (including a display circuit) 30d, and a trapezoidal wave generating circuit 30e. Further, as shown in FIG. 3, the cargo handling console 30 is installed at an appropriate position on the hull 40, for example, a bridge, and inputs and outputs data with the sensor unit 20.
[0026]
Next, a signal processing method for measuring the liquid level in the tank 1 performed by the sensor unit 20 and the cargo handling console 30 will be described. In FIG. 5, the solid line indicates the transmission frequency of the microwaves emitted from the flat antenna 6 toward the liquid surface in the tank 1. The broken line indicates the reception frequency of the reflected wave received by the flat antenna 6, that is, the reflected wave reflected by the liquid surface of the microwave emitted toward the liquid surface in the tank 1.
[0027]
The transmission frequency is continuously changed from a certain frequency f1 to f2, that is, in the range of the sweep frequency B, from a certain time t1 to t2, that is, with respect to the sweep time T. This is output by the trapezoidal wave generating circuit 30e. The reception frequency is received by the flat antenna 6 with a certain time delay. Therefore, the difference Δf between the transmission frequency and the reception frequency at a certain time t is proportional to the distance from the flat antenna 6 to the liquid level in the tank 1.
[0028]
At this time, as shown in FIG. 6, the difference Δf between the transmission frequency and the reception frequency shows a constant value over the entire sweep time T. In other words, the difference Δf between the transmission frequency and the reception frequency at a certain time t shows a constant value in any cross section from t1 to t2.
[0029]
When the distance from the flat antenna 6 to the liquid level in the tank 1 is short, Δf indicates a low value, and when the distance from the flat antenna 6 to the liquid level in the tank 1 is long, Δf is High value. In both cases, Δf is the audio frequency band. This Δf is appropriately amplified and converted into a distance from the flat antenna 6 to the liquid level in the tank 1 by the FFT circuit 30c. FIG. 7 shows the values at this time.
[0030]
In the cargo handling console 30, a beat signal (audio frequency band) between the transmission frequency of the microwave and the reception frequency of the reflected wave transmitted from the sensor unit 20 is appropriately amplified by the audio amplifier 30a. Then, the analog signal is converted into a digital signal by the A / D converter 30b, and frequency analysis, that is, fast Fourier transform is performed by the FFT circuit 30c, from the flat antenna 6 to the liquid level in the tank 1. Can be detected as a distance. That is, the liquid level in the tank can be measured.
[0031]
Here, when oil or the like is stored in the tank 1, the oil or the like may evaporate and the paraffin may be condensed on the protection plate 5. Since the flat antenna 6 has the strongest electric field strength at the center of the flat antenna 6, if paraffin condenses near the top of the cone of the protective plate 5 facing the central portion of the flat antenna 6, the flat antenna 6 However, the protective plate 5 has a conical shape as described above, and the top of the conical shape faces the lower surface of the flat antenna 6. Therefore, the paraffin condensed on the protective plate 5 can flow down to the peripheral portion along the conical surface, and the microwave transmission obstacle caused by the paraffin is suppressed, and high-precision measurement is performed. be able to.
[0032]
Further, since the protective plate 5 is set to the shortest distance that does not adversely affect the electromagnetic field of the flat antenna 6 as described above, the entire apparatus can be reduced in size as compared with the conventional device. The shortest distance that does not adversely affect the electromagnetic field of the flat antenna 6 may be generally ½ of the wavelength of the electromagnetic wave used, but the protective plate 5 used in the present invention has a cone shape. Therefore, it is not possible to apply a generally determined distance. Therefore, the operating gain may be measured while changing the distance between the protective plate 5 and the flat antenna 6 and set to the most suitable distance for the frequency to be used. FIG. 8 and FIG. 9 show data obtained by measuring the operating gain for three types of frequencies while changing the distance between the protective plate 5 made of a derivative and the flat antenna 6. As is apparent from FIGS. 8 and 9, when the distance between the flat antenna 6 and the derivative is continuously changed, the peak of the operating gain appears periodically, and the peak position of the operating gain is shifted by the electromagnetic wave used. Therefore, the distance between the flat antenna and the protective plate made of a dielectric is short for each frequency used, and the distance at which the peak of the operating gain appears may be set.
[0033]
Further, the thickness of the protective plate 5 is such that it can withstand the pressure in the tank 1 and is made uniform so that the flat antenna 6 can be more satisfactorily connected to the tank 1. Can be protected from the pressure of
[0034]
In addition, as shown in FIG. 1, an installation space for the antenna 6 and the transmission / reception device 9, that is, a gas sealing means 11 for sealing an inert gas in the casing 8 is provided in the casing 8. 6 and the transmission / reception device 9 can be filled with an inert gas, and fires due to electrical troubles (such as a short circuit) of the transmission / reception device 9 can be prevented.
[0035]
In the illustrated embodiment, the protective plate 5 has a conical shape, but the intended purpose can be achieved even if it has a pyramid shape. In terms of characteristics and manufacturing cost, the conical shape is more advantageous.
[0036]
【The invention's effect】
According to invention of Claim 1, while emitting a microwave toward the liquid level currently stored in the tank, the flat plate antenna which receives the reflected wave from the said liquid level, and the microwave emitted from the said flat plate antenna and a transceiver for transmitting and receiving the reflected wave to the data processing unit by the plate antenna, an electric wave liquid level gauge with a protective plate for protecting the flat antenna, the protection plate is in a circular cone shape be formed, along with are provided to face the circular conical top portion of the lower surface to the protective plate of the flat antenna, due to the provision of the shortest distance that is inferior affect the electromagnetic field of the flat plate antenna, as compared with the conventional The entire apparatus can be reduced in size. Furthermore, because paraffin condensed on the protective plate by evaporation of stored oil etc. can flow down to the periphery along the cone-shaped inclined surface, it is possible to suppress radio wave transmission disturbance due to paraffin, Highly accurate measurement can be performed.
Since the installation space between the antenna and the transmission / reception device is filled with an inert gas, it is possible to prevent a fire due to an electrical trouble (such as a short circuit) of the transmission / reception device.
[0039]
According to the second aspect of the present invention, in the invention according to the first SL mounting, the thickness of the protective plate, with a thickness that can withstand the pressure in the tank, because you uniform thickness, and more The flat antenna can be well protected from the pressure in the tank.
[Brief description of the drawings]
FIG. 1 is a front sectional view showing an embodiment of a radio wave level gauge according to the present invention.
FIG. 2 is a block diagram showing a configuration of a sensor unit and a data processing unit applicable to the embodiment of the present invention.
FIG. 3 is an overall view showing an arrangement relationship between a sensor unit and a data processing unit applicable to the embodiment of the present invention.
FIG. 4 is a block diagram showing a configuration of a data processing unit of a conventional radio wave level gauge.
FIG. 5 is a graph showing a part of the principle of the measuring method of the liquid level gauge.
FIG. 6 is a graph showing another part of the principle of the measuring method of the liquid level meter.
FIG. 7 is a graph showing still another part of the principle of the measuring method of the liquid level gauge.
FIG. 8 is a graph showing a relationship between a distance between a protective plate made of a dielectric material necessary for carrying out the present invention and a flat antenna and an operation gain.
FIG. 9 is a graph showing the relationship between the distance between the protective plate and the flat antenna and the operating gain, while changing the distance scale.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Tank 5 Guard plate 6 Flat antenna 9 Transmission / reception apparatus 20 Sensor part 30 Data processing part

Claims (2)

A flat plate antenna that emits microwaves toward the liquid level stored in the tank and receives reflected waves from the liquid level;
A transmission / reception device for transmitting the microwave emitted from the flat antenna and the reflected wave received by the flat antenna to the data processing unit;
A radio wave level gauge having a protective plate for protecting the flat antenna,
The protective plate be formed in a circular cone shape, along with are provided to face the circular conical top of the protective plate on the bottom surface of the flat plate antenna, the shortest not be inferior affect the electromagnetic field of the flat plate antenna Provided in the distance ,
A radio wave level gauge characterized in that an installation space between the antenna and the transmission / reception device is filled with an inert gas . The thickness of the protective plate, with a thickness that can withstand the pressure in the tank, electric-wave liquid level gauge according to claim 1, wherein the uniform thickness der Rukoto.

Images