JP2018146574A - Level detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a level detection device that can detect a level change of a fluid or a powder in a tank, as keeping air-tightness of the tank.SOLUTION: In a level detection device having a level sensor detecting a level of a storage object by use of a micro wave provided on an outer wall of tank storing the storage object, in which the level sensor is attached with the level sensor exposed outward the outer wall of the tank, the level detection device is configured to detect presence or absence of the storage object at a measurement position on the basis of a difference between a first signal level of the micro wave reflecting from the storage object in the tank and to be received by the level sensor, and a second signal level of the micro wave reflecting from a reflection plate provided in an inner face of the tank or in the tank, and to be received by the level sensor.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a level detection device, and more particularly to a level detection device using a microwave.

  In various fields such as industrial production, agricultural production, wastewater treatment and water resource management, detection of the surface level of liquids and powders is required. In particular, when liquid or powder is stored in a tank, various level detection devices are used to detect the surface level of the liquid and powder in the tank.

  For example, in Patent Document 1, electrostatic capacity is detected by an electrode mounted in a storage container and protruding into the storage container, and is oscillated at a frequency that is inversely proportional to the electrostatic capacity. A capacitance type level detection device that outputs a detection signal of the level position of a stored item is described.

  In Patent Document 2, a blade that swings around a swing center is swung by a drive unit, and the object to be measured that contacts the blade is detected by detecting that the swing angle of the blade has become a predetermined value or less. There is described a pendulum type level detection device provided with a level detection circuit for detecting the level of the above.

  Patent Document 3 discloses an ultrasonic level sensor that emits ultrasonic waves from a probe fixed to the outer wall of a container to the inner surface of the container and detects the presence or absence of liquid based on a difference in decay time between the emitted wave and the reflected wave. An apparatus is described.

JP 2006-322770 A JP 2006-145265 A JP 2004-28765 A

  In the level detection apparatus conventionally used, in many cases, a part of a measuring instrument is installed in a tank. For example, in Patent Document 1, electrodes are arranged in a tank, and in Patent Document 2, blades are installed in the tank. However, in order to maintain the strength and airtightness of the tank and simplify the installation and maintenance of the apparatus, it is preferable that measurement from outside the tank is possible. Especially for tanks containing corrosive substances such as sulfuric acid, hydrochloric acid, hydrofluoric acid, etc., and corrosive substances such as alkaline solutions, tanks containing toxic substances, and applications that require strict avoidance of contamination in the food industry, pharmaceutical industry, etc. For the tanks used, a level detector that can be measured from outside the tank is desired from the viewpoint of protecting the measuring device, avoiding leakage of the contents, and preventing foreign matter (outside air, dust, germs, etc.) from entering the tank. ing. The ultrasonic level sensor device of Patent Document 3 can determine the presence or absence of liquid from the outside of the tank. However, when an outer wall (such as ceramic) or air that does not easily propagate ultrasonic waves is present, measurement using ultrasonic waves is possible. Is difficult to apply.

  An object of the present invention is to provide a level meter capable of measuring the surface level of fluid and powder such as liquid and slurry in the tank from the outside while maintaining the hermeticity of the tank.

  The level detection device of the present invention is a level detection device in which a level sensor for detecting the level of the stored item using a microwave is provided on the outer wall of a tank for storing the stored item. In this level detection apparatus, the level sensor may be attached so as to be exposed to the outside of the tank. According to this level detection device, the level of fluid (liquid, slurry) or powder inside the tank can be detected by using the microwave while maintaining the hermeticity of the tank. Further, since the level sensor is exposed to the outside of the tank, the level sensor can be easily maintained and inspected.

  The level detection device reflects the first signal level of the microwave reflected from the stored item in the tank and received by the level sensor, and reflects from the inner surface of the tank or the reflector provided on the tank and receives the level sensor. The level detection device may be configured to detect the presence or absence of the stored item at the measurement position based on a difference from the second signal level of the microwave. For example, the level detection device detects the output DC voltage of the microwave received by the level sensor by being reflected from the inner surface of the tank or the reflection plate when the tank is empty or when there is no stored item at the detection position. By comparing the value with the value detected at the time of measurement, the presence or absence of the stored item at the measurement position may be detected.

  The level detection device includes an oscillator in which the level sensor oscillates a microwave, a first antenna that transmits the microwave to the outside of the main body, and a second antenna that receives the reflected microwave. A level detection in which a gap is provided between an antenna surface including the front surfaces of the first and second antennas and an outer surface of the tank, and the size of the gap is set so that the signal level difference is maximized. It may be a device. For example, the level sensor includes a sensor positioning member installed on the outer wall of the tank and a sensor main body installed on the positioning member, and the distance between the antenna surface of the sensor main body and the tank outer wall is determined by the positioning member. It may be adjustable. According to the level detection device having such a configuration, the sensitivity of level detection can be optimized in accordance with the type of stored items. Since the presence or absence of stored items at a predetermined level can be detected by a single sensor, the configuration for detection can be simplified.

  The level detection device may be a level detection device provided with a reflection plate disposed inside the tank so as to face the level sensor and reflecting the microwave. This makes the tank compact because no reflector is present outside the tank. However, it may be a level detection device provided with a reflection plate disposed on the outer wall surface of the tank so as to face the level sensor and reflecting the microwave.

  In the level detection apparatus, a microwave Doppler sensor can be used as the level sensor.

  According to the level detection apparatus of the present invention, it is possible to detect the level of liquid, slurry, powder, etc. while maintaining the sealing property of the tank. Since the level detection apparatus of the present invention uses microwaves for detection, even when air is interposed between the sensor and the stored item, the presence or absence of the stored item can be detected.

It is the schematic which shows the structure of the level detection apparatus concerning one Embodiment of this invention. When the calculation is performed under the conditions shown in Table 1, it corresponds to the sensor displacement of the output DC voltage and the difference (dotted line) when the tank is empty (solid line) and when there is something in the measurement position (dashed line) It is a figure which shows the fluctuation | variation to do. In Example 2, when the water in the acrylic tank is measured through an acrylic plate having a thickness of 20 mm, when the tank is empty (solid line) and when there is a stored item at the measurement position (broken line) It is a figure which shows the fluctuation | variation corresponding to a sensor displacement of an output DC voltage and its difference (dotted line). It is sectional drawing (side view about a sensor main body) which shows the arrangement | positioning state of the sensor of the level detection apparatus concerning one Embodiment of this invention. FIG. 5 is a cross-sectional view when a reflector is installed in the tank in the same configuration as FIG. 4. FIG. 5 is a cross-sectional view illustrating a case where a powder made of a substance that transmits electromagnetic waves is provided on a wall of a tank that does not transmit electromagnetic waves, and a sensor similar to that in FIG. It is the schematic which shows one structural example at the time of using the level detection apparatus of this invention for the level switch of a liquid tank. In Example 4, it is a figure which shows the time-dependent change of a sensor output at the time of changing the level of a storage thing (ash).

  The level detection device of the present invention is a level detection device in which a level sensor for detecting the level of the stored item using a microwave is provided on the outer wall of a tank for storing the stored item. Hereinafter, a level detection apparatus according to an embodiment of the present invention will be described with reference to the drawings. In addition, in each drawing, the same code | symbol is attached | subjected to a corresponding structure and description is abbreviate | omitted.

  FIG. 1 is a conceptual diagram showing a configuration of a level detection apparatus according to an embodiment of the present invention. The level detection device 1 according to the present embodiment is installed on the outer wall surface 20a of the wall 20 of the tank 2 and the level sensor 10 exposed to the outside of the tank wall 20 is sandwiched between the tank storage unit and the level sensor 10. A reflector (reflector) 13 is provided on the outer wall surface of the tank at a position facing the sensor 10.

  The level sensor 10 includes a sensor positioning member (sensor guide) 12 installed on the tank outer wall 3 and a sensor main body 11 held by the sensor positioning member 12. A predetermined gap (air layer) G is provided between the antenna surface 11c on the front surface of the sensor body 11, that is, the emission surface, and the outer wall surface 20a of the tank, and the sensor positioning member 12 sets an interval z between the gaps G. It is configured to be adjustable. The sensor body 11 includes an oscillator 11d that generates a high frequency, a transmitting antenna 11a, a receiving antenna 11b, and a mixer 11f. An AC input A is supplied to the oscillator 11d, and a sensor output signal S is output from the mixer 11f.

In the configuration shown in FIG. 1, microwaves transmitted from the transmitting antenna 11 a are, as shown by solid lines, broken lines, and alternate long and short dash lines in the figure, a tank outer wall surface 20 a (or a sensor side wall surface of a sensor cover described later), a tank wall 20. And the stored object 3 (or air) at the interface (tank wall inner surface 20b), the tank inner wall surface 20c facing the storage portion 21, and the reflector (reflector) 13 attached to the outer tank outer wall surface. Each is reflected and received by the receiving antenna 11b. The output S from the sensor is a DC component of the product of the transmission voltage E _e (t) and the reception voltage E _r (t), and the component of the frequency 2f represented by this product is removed by a filter (not shown). . The output DC voltage E _m when the tank contains items and the output DC voltage E ₀ when the tank is empty are expressed by the following equations (1) and (2), respectively.

In the above equation, f is the carrier frequency, E _e is the transmission voltage, E _ro is the reception voltage from the tank wall (or sensor cover), E _rc , E ^* _rc are the reception voltages from the storage, and E ^* _rm is Received voltage from the reflector, 2D is the distance between the antennas, c ₀ is the speed of light, c _c is the speed at which the microwave passes through the tank wall, cm is the speed of the microwave in the storage, lc is the thickness of the tank wall, and l _T Is the thickness of the stored item (inner diameter of the tank).

As an example, when each parameter is set as shown in Table 1 below, the values of E _m (broken line) and E _o (solid line) and the difference ΔE (dotted line) = E _m −E ₀ are expressed as displacement z 2 is plotted on the horizontal axis.

  As shown in FIG. 2, the magnitude of ΔE can be adjusted by adjusting the gap z of the gap G, and the presence or absence of stored items can be detected by the output signal S (DC voltage) from the sensor. Can do.

Although the above formula describes the case where a reflector is installed on the outer wall surface of the tank, E ^* _rm may be set to 0 when no reflector is used. In actual use of the device, the gap may be adjusted so as to maximize ΔE according to the stored items, and used as a level detection device. As an example, FIG. 3 shows examples of E ₀ (solid line), Em (dashed line), and ΔE (dotted line) actually measured in Example 2 described later.

  FIG. 4 shows a cross-sectional view of a portion where the level sensor 10 according to the present invention is installed in a tank (a side view of the sensor body). In the present embodiment, the tank wall 20 is made of a resin such as acrylic. The sensor positioning member 12 is fixed to the outer wall surface 20a of the tank. Fastening means 12a such as a bolt may be used for fixing. For example, a male screw 11 e may be formed on a part of the outer surface of the sensor body 11 and screwed into a female screw 12 e formed on the positioning member 12. At that time, the gap z of the gap G between the antenna surface 11c and the outer wall surface 20a is adjusted according to the screwing depth, and is adjusted so as to maximize the signal strength when detecting the signal strength of the stored object as the subject. .

  If the tank is made of a material that passes electromagnetic waves (in the present invention, microwaves) such as resin and ceramic, a sensor may be installed outside the tank as in the above-described embodiment. If the tank is made of a material that does not pass through, an opening may be provided in the tank wall and the opening may be closed with a window made of a material that allows electromagnetic waves to pass through, or a sensor with a cover made of a material that allows electromagnetic waves to pass through may protrude into the tank. You may let them. That is, the level sensor 10 may be attached to the tank wall so as to be exposed from the tank wall 20 to the outside. Since the level sensor 10 is exposed to the outside of the tank, the level sensor can be easily maintained and inspected, and the gap G can be adjusted according to the contents stored in the tank. However, if necessary, the antenna surface of the sensor may be arranged inside the tank. 4 shows the case where the level sensor and the reflection plate are installed on the outer wall surface of the tank, the reflection plate may be arranged inside the tank as necessary.

  FIG. 5 shows a state in which the reflection plate 13 is installed in the tank. Further, as described above, the reflector is not an essential configuration, and in some cases, the reflector may not be used. When the relative permittivity of the stored item in the tank is relatively high, the stored item can be detected without the reflector. Further, when the tank wall is made of a material that does not transmit electromagnetic waves, the reflection intensity when the microwave from the level sensor is reflected by the tank wall on the opposite side of the sensor is high, and a reflecting plate is unnecessary.

  FIG. 6 shows a state in which the level sensor 10 is mounted by providing a window 21 made of a material (for example, resin) that allows electromagnetic waves to pass through the opening of the tank wall 20 made of a material that does not transmit electromagnetic waves. Here, the level sensor 10 has the same configuration as the level sensor shown in FIG. The electromagnetic wave (broken line) transmitted through the window 21 is reflected by the stored item 3 (powder) and received by the receiving antenna of the level sensor 10. When there is no stored item 3, the microwave reflected from the inner wall surface 20 c on the opposite side of the level sensor 10 is received by the receiving antenna of the level sensor 10.

  In each configuration shown in FIGS. 4 to 6, the output signal S from the level sensor 10 differs (except for a specific z value) between when there is a stored item and when there is no stored item. The presence / absence of a stored item at the site can be determined. That is, in each embodiment, the output voltage from the level sensor 10 with and without storage is measured, and the position of the sensor body 11 is adjusted so that the voltage difference is maximized by the positioning member 12. What is necessary is just to use it as a level detection apparatus.

As the level sensor 10 used in the level detection apparatus 1 of the present invention, a microwave Doppler sensor can be used. As a sensor having a microwave transmitting antenna and a receiving antenna, a Doppler sensor has been developed for detecting an operation of an automobile or a person.
The frequency of the microwave used may be, for example, 10.5 GHz to 10.55 GHz, or 24.05 GHz to 24.25 GHz. Although it is not limited in terms of the configuration of the invention, it is necessary to use a frequency that is permitted to be used in accordance with laws and regulations. In Japan, the above frequency is permitted for sensor applications. In countries where other frequency bands are allowed, other frequencies may be used.

The level detection device can also be used as a level switch for stopping or starting the loading of stored items when the stored items in the tank reach a predetermined level.
FIG. 7 is a schematic cross-sectional view showing an example when the level detection device of the present invention is installed in the liquid tank 2. The upper side of the tank 2 is connected to the inflow path 5A via the first valve 4A, and the lower side is connected to the discharge path 5B via the second valve 4B. Two level detection devices 1A and 1B (in this case, sensors 10A and 10B) of the present invention are installed at predetermined positions on the tank wall 20, and the detection device and the valve are connected to the controller 6. In the detection devices 1A and 1B, the installation interval 2D is adjusted so that the sensitivity of the level sensors 10A and 10B is maximized. For example, when the second valve 4B is opened to discharge the liquid 3 in the tank, when the liquid level falls below the measurement level of the second detection device 1B, the controller 6 detects a change in the output voltage, A command to close the second valve 4B is issued. Next, the first valve 4 </ b> A is opened, and the liquid 3 is replenished in the tank 2. When the liquid level exceeds the measurement level of the first detection device 4A, the controller 6 detects a change in the output voltage and closes the first valve 4A. In this way, the level of the stored item 3 in the tank 2 can be held so as to be between the sensors 10A and 10B.

[Example 1]
The specimen 1 is foamed polystyrene (thickness 150 mm) having a foaming rate of 99% and a relative dielectric constant of 1.006, and the specimen 2 is water (relative dielectric constant 80) in an acrylic tank having a volume of 144 mm × 144 mm × 144 mm (width 150 mm). Prepared what was collected. Further, a copper plate having an area of 365 mm × 365 mm and a thickness of 0.3 mm was placed at a position of 0.15 m, 0.30 m, 0.60 m, and 3.00 m from the outer surface of the polystyrene foam on the sensor side or the outer wall surface of the acrylic tank. In addition, when the sensor was directly installed on the outer surface of the polystyrene foam or the outer wall surface of the acrylic tank, the experiment was performed under three conditions: a 1 mm thick polytetrafluoroethylene cover was provided, and a 3 mm thick acrylic cover was provided. As a sensor, a microwave Doppler sensor with a frequency of 24.15 GHz (manufactured by Kansai Automation) is used, and the output voltage when the antenna surface is moved to a position of 15 mm every 0.5 mm from the sensor front end surface, depending on the presence or absence of storage items The voltage difference was determined. The results are shown in Table 2.

  In Table 2, T1 uses 1 mm-thick polytetrafluoroethylene as a sensor cover, A3 uses 3 mm-thick acrylic, and T1A3 uses 1 mm-thick polytetrafluoroethylene in front of the 3 mm-thick acrylic sensor cover. When A3a1A3 is installed, 3 mm acrylic (tank wall) is spaced from the 1 mm interval (air layer), and 3 mm thick acrylic is installed.

  In the case of water having a relatively high dielectric constant, the average value of the maximum value and the average value of the minimum value of the voltage difference do not change so much depending on the position of the cover, tank wall material, and reflector. Although not shown in the table, the presence of the substance could be confirmed even when the reflector was not used. This is considered to be due to the fact that most of the electromagnetic waves are reflected by the subject water. On the other hand, in the case of styrene foam having a low dielectric constant, an improvement in sensitivity is clearly recognized by installing a reflector at a position of 0.15 m near the sensor. The spatial period in which the maximum and minimum values of the voltage difference appear is 6.5 to 7 mm, which is close to a half wavelength of 6.2 mm of 24.15 (GHz). In this example, it is understood that the search for the maximum sensitivity by adjusting the position of the gap G (FIG. 1) may be performed within the adjustment range up to about 7 mm. In addition, since the experiment using styrene foam can be regarded as a simulation experiment in the case of measuring a powder having a low relative dielectric constant, it can be seen that the level detection apparatus of the present invention is also useful for measuring a powder.

[Example 2]
Water is stored in an acrylic tank (A3) with a thickness of 3 mm, and a laminate of acrylic with a thickness of 20 mm and / or natural rubber (R20) with a thickness of 20 mm is used. Then, a detection experiment from outside the tank was conducted. A reflector was not used. The results are shown in Table 3. As an example, FIG. 3 shows a graph when measurement is performed through an acrylic plate having a thickness of 20 mm and a tank wall (A23). In FIG. 3, the solid line indicates the output DC voltage when the tank is empty, the broken line indicates the output DC voltage when there is water at the level detection position, and the dotted line indicates the difference ΔE (the scale is different) between the two.

表３に見るように、タンク壁面の厚さと素材により、出力最大値は変化する。他方、ｚ＝５〜１００ｍｍの範囲で、出力が最大値となるときに、空タンクとの出力差も最大になっていた。したがって、レベル計としての使用にあたっては、タンクに水があるときに出力最大となる条件に変位（ｚ値）を設定すればよい。

As seen in Table 3, the maximum output value varies depending on the thickness and material of the tank wall. On the other hand, when the output becomes the maximum value in the range of z = 5 to 100 mm, the output difference from the empty tank was also the maximum. Therefore, in use as a level meter, the displacement (z value) may be set to a condition that maximizes the output when there is water in the tank.

[Example 3]
When a polyethylene resin tank specified in JISZ1710 is prepared and a microwave Doppler sensor is installed directly on the tank wall, when measured through a 20 mm acrylic resin (A20), measured through a natural rubber with a thickness of 20 mm Case (R20), 3 layers (A3R20A20) of acrylic resin with a thickness of 3 mm, natural rubber with a thickness of 20 mm and acrylic resin with a thickness of 20 mm are stacked on the tank wall, and a microwave Doppler sensor is installed on each outermost layer. An experiment was conducted to detect kerosene in the tank. A reflector was not used. The results are shown in Table 4. As shown in Table 4, although depending on the conditions of the tank wall, a voltage difference was detected by adjusting the displacement z.

[Example 4]
As an example of a level sensor, an experiment was conducted to detect ash in a ceramic brazier from outside the brazier. A reflector was not used. In 10 to 17 seconds after the output measurement by the sensor was started, the ash in the brazier was stacked above the sensor level, and during 34 to 44 seconds, the ash was scraped out to be lower than the sensor level. The output level of the Doppler sensor during this period is shown in FIG. In this experiment, the measurement is performed through a thick ceramic (brace wall), and the ash level is not uniform in front of the sensor, so air is also present, but as shown in FIG. A change in the level of nearby ash was detected as a change in sensor output.

[Example 5]
In order to examine the effect of the reflector when detecting an object having a low dielectric constant, a sample 1 having a foaming rate of 99% and a relative dielectric constant of 1.007, a foaming rate of 97% and a relative dielectric constant of 1.015 are used. Three types of copper reflectors of 30mm x 27mm, 30mm x 11mm, 30mm x 6mm are placed 25mm apart from the antenna surface of the Doppler sensor, and the space between the antenna surface and the reflector plate is air. The displacement z of the sensor was adjusted so that the output was 0 V, and the change in output power from 0 V when the sample was sandwiched between the antenna surface and the reflector was read. The results are shown in Table 5.

  As shown in Table 5, it can be seen that, by using the reflector, even a sample having a low relative dielectric constant can be used as a level detection device. From this result, it can be expected that level measurement can be facilitated even for a sample having a low relative dielectric constant such as powder by using, for example, the reflector 13 shown in FIGS.

  According to the level detection device of the present invention, it is possible to suitably measure the level of fluid and powder in the sealed tank from outside the tank. As a sensor of the level detection device, a Doppler sensor having a high penetration rate can be used, and a simple and inexpensive configuration can be obtained.

1 level detector 10 sensor 11 sensor body 12 positioning member 13 reflector (reflector)
11a Output antenna 11b Reception antenna 11c Antenna surface 11d High frequency oscillator 11e Thread 2 Tank 20 Tank wall 20a Tank wall outer surface 20b, 20c Tank wall inner surface 21 Window (cover)

Claims (5)

A level sensor is provided on the outer wall of the tank for storing the stored items to detect the level of the stored items by the oscillation and reception of the microwave
The level sensor is exposed and attached to the outside of the outer wall of the tank,
The first signal level of the microwave reflected by the level sensor and received by the level sensor, and the second signal of the microwave received by the level sensor reflected from the inner surface of the tank or the reflection plate provided in the tank. Based on the difference with the level,
A level detection device configured to detect the presence or absence of the stored item at a measurement position.   2. The level detection apparatus according to claim 1, wherein the level sensor includes an oscillator that oscillates a microwave, a first antenna that transmits the microwave to the outside of the main body, and a second antenna that receives the reflected microwave. A gap is provided between an antenna surface including the front surfaces of the first and second antennas and an outer surface of the tank, and the size of the gap is set so that the signal level difference is maximized. Level detector.   3. The level detection device according to claim 1, further comprising a reflection plate disposed inside the tank so as to face the level sensor and reflecting the microwaves. 4.   3. The level detection device according to claim 1, further comprising a reflecting plate disposed on an outer wall surface of the tank so as to face the level sensor and reflecting the microwave. 4.   5. The level detection device according to claim 1, wherein the level sensor is a microwave Doppler sensor. 6.

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