JP5260840B2 - Microwave densitometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microwave densitometer capable of being attached even to a measuring pipe, having a caliber smaller than those of conventional types by miniaturizing the shape of a microwave transmission antenna and that of a microwave receiving antenna and made hard to deposit a suspended substance. <P>SOLUTION: The microwave densitometer is constituted so as to calculate the concentration of a fluid to be measured from the change in the microwave propagation time. Each of a microwave transmission antenna 1a and a microwave receiving antenna 1b is equipped with a coaxial core conductor 11, the cylindrical insulating body 12 for covering the periphery of the coaxial core conductor 11 and the metal cylinder 14 for opening at part of the outer periphery opposed to the insulating body 12 and both of the microwave transmission antenna 1a and the microwave receiving antenna 1b have their respective coaxial core conductors 11 provided in a facing relation on the plane crossing or parallel to a pipe axis. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a microwave densitometer that applies microwaves and measures the concentration of a fluid to be measured including various suspended substances and soluble substances such as sludge and pulp.

  In general, when microwaves are incident on zero water (for example, tap water that can be regarded as having a concentration of 0%) as a concentration reference, the received wave has a phase lag (θ1) compared to the transmitted wave.

  In addition, when a microwave is incident on a suspension such as sludge, the received wave similarly has a phase delay (θ2) compared to the transmitted wave. The difference in phase lag (phase difference Δθ = θ2−θ1) is proportional to the sum of the concentration of the suspended substance and the concentration of the substance dissolved in the liquid.

The density X at this time is expressed as follows.
X = C · Δθ = C · (θ2−θ1)
Where C: correction coefficient,
θ1: Phase delay when microwaves are incident on zero water as a reference θ2: Phase delay when microwaves are incident on suspension

  An example of a microwave densitometer based on the measurement principle as described above is disclosed in Patent Document 1, for example.

  By the way, such a conventional microwave densitometer has a structure in which a microwave transmitting antenna and a microwave receiving antenna are arranged on the side wall of the measuring tube so as to face each other across the tube axis of the measuring tube (tube). Therefore, when the diameter of the measurement tube is large, the distance between the microwave transmitting antenna and the microwave receiving antenna increases, and the attenuation of the propagating microwave increases.

  Therefore, in the case of a measuring tube having a certain diameter or more, there is a problem that measurement is difficult with a tube axis crossing structure.

  Thus, a microwave densitometer is disclosed in which a microwave transmitting antenna and a microwave receiving antenna are inserted from one tube wall of the measuring tube when the diameter of the measuring tube is increased (referred to as side insertion type). (For example, see Patent Document 2).

  FIG. 6 shows a cross-sectional view of this side-insertion type microwave densitometer viewed from the tube axis direction. In FIG. 6, this side-insertion type microwave densitometer includes a microwave transmitting antenna 26 and a microwave receiving antenna 29 that are housed in an airtight tube and are separated by a predetermined distance necessary for concentration measurement. The receiving tube 24 of the microwave transmitting antenna 26 and the storing tube 28 of the microwave receiving antenna 29 are arranged so that the microwave emitting direction of the microwave transmitting antenna 26 and the microwave incident direction of the microwave receiving antenna 29 are opposed to each other. Is attached to the attachment base flange 23 and is fixed to the measurement tube flange portion 22 of the measurement tube 21 through which the fluid 20 to be measured flows.

  The structure of the microwave transmission antenna 26 of such a microwave concentration meter will be described. (The structure of the microwave receiving antenna 29 is the same as that of the microwave transmitting antenna 26, and the description thereof is omitted.)

  FIG. 7A is a cross-sectional view of a microwave transmission antenna 26 formed of a rectangular cavity resonator. The microwave transmission antenna 26 is a window made of an insulating material, and microwaves excited by a coaxial core wire 27a of a coaxial cable 27. 25 to the z-axis direction.

  The transmitted microwave is received by a microwave receiving antenna 30 composed of a rectangular cavity resonator having the same structure as that of the microwave transmitting antenna 26, and this received signal is sent to the measuring unit 32 via the coaxial cable 31. .

  The shape of the rectangular cavity resonator of the microwave transmission antenna 26 is shown in FIG. For example, when a resonator having a resonance frequency f (2 GHz) and a resonance wavelength λ is formed of a rectangular cavity resonator with a> b, the shape of the rectangular cavity resonator (a × b × L1) is as follows. .

  Here, if the plane parallel to the tube axis is the xy plane, the plane orthogonal to the tube axis is the yz plane, the x-axis dimension a, the y-axis dimension b, and the z-axis dimension L1, the resonance wavelength λ and dimensions a, b, and L1 have the following relationship.

4 / λ ² = m ² / a ² + n ² / b ² + p ² / L1 ²
Here, m, n, and p indicate the number of standing waves in the x-axis direction, the y-axis direction, and the z-axis direction, respectively.

In the case of a single mode cavity resonator, the z-axis dimension L1 is, for example,
In the case of TE _mnp (TE ₁₀₁ ), the shape becomes the smallest when L1 = a. At this time,
4 / λ ² = 2 / L1 ² , ∴L1 = λ / 2 ^1/2
It becomes.

When the speed of light is c (= 3 × 10 ⁸ m / sec) and the relative dielectric constant inside the cavity resonator is ε _r = 20, the dimension L1 is
L1 = ^{1/2 1/2} × c / ε _r ^1/2 × 1 / f
= ^1/21/2 * (3 * 10 < ⁸ >) / ( ^201/2 * 2 * 10 < ⁹ >)
= 23.7 × 10 ⁻³ (m)
It becomes.

Therefore, as shown in FIG. 6, the minimum diameter ^dΦ of the measurement tube 21 to which the transmission antenna and the reception antenna can be attached facing from the side surface of the measurement tube 21 is as follows.
^dΦ ≧ Lm + 2 (L1 + α)
It becomes.

  Here, (L1 + α) is a dimension in the z-axis direction that allows for a margin dimension α for housing the microwave transmission antenna, and Lm is a dimension between the storage cylinder 24 and the storage cylinder 28.

That is, the diameter d ^[Phi of this aspect insertable minimum applicable is, 40 mm and Lm, when a 10mm to alpha, is at least 107.4mm above.

  Therefore, in the microwave densitometer using this square cavity resonator, there is a problem that it is difficult to apply at a diameter of 100 mm or less in the above example.

Further, in the microwave transmitting antenna and the microwave receiving antenna in which such a rectangular cavity resonator is housed in a housing tube, the opening on the side surface of the measuring tube needs to have a dimension of (L1 + α) or more in the tube axis direction. There is also a problem that suspended substances contained in the fluid to be measured are easily deposited on the storage cylinder, and the measurement is difficult due to the deposits.
JP-A-4-238246 JP 2000-258361 A

  In the side-insertion type microwave densitometer as described above, there is a problem that only a tube having a relatively large diameter can be applied as a measurement tube that can be attached.

  In addition, there is a problem in that the portion of the storage cylinder of the microwave transmitting antenna and the microwave receiving antenna protrudes in the portion where the fluid to be measured flows, and suspended substances accumulate on this portion, making measurement impossible.

  The present invention was made in order to solve such problems, the size of the microwave transmitting antenna and the microwave receiving antenna can be reduced in size, and can be attached to a measuring tube having a smaller diameter than the conventional one. Another object of the present invention is to provide a microwave densitometer in which suspended substances do not easily accumulate.

In order to achieve the above object, a microwave densitometer according to a first aspect of the present invention includes a pair of microwave transmitting antennas and a microwave receiving antenna, which are provided to face each other, from the outer peripheral side surface of a measurement tube that allows a fluid to be measured to flow A microwave densitometer for determining a concentration of the fluid to be measured from a change in propagation time from insertion to transmission of microwave from the microwave transmission antenna to reception by the microwave reception antenna, the microwave transmission antenna and The microwave receiving antenna is a coaxial resonator type antenna, and each antenna constitutes a coaxial core conductor of a coaxial cable and an outer conductor of the coaxial core conductor. A metal cylinder opened in an angle range, a dielectric having a preset dielectric constant filling the space inside the metal cylinder, and a lid covering the surface of the dielectric The metal tube for fixing the insulator, the coaxial cable on one surface, and the metal tube including the coaxial core conductor, the dielectric, and the insulator of the coaxial cable penetrating on the other surface; A fixed holder made of the same material, and the microwave transmitting antenna and the microwave receiving antenna are connected to each other on the plane where each of the coaxial core conductors intersects the tube axis of the measuring tube. It is characterized in that the opening positions are provided facing each other.

In order to achieve the above object, a microwave densitometer according to a second aspect of the present invention includes a pair of microwave transmitting antennas and a microwave receiving antenna, which are provided to face each other, from the outer peripheral side surface of a measurement tube that allows a fluid to be measured to flow A microwave densitometer for determining a concentration of the fluid to be measured from a change in propagation time from insertion to transmission of microwave from the microwave transmission antenna to reception by the microwave reception antenna, the microwave transmission antenna and The microwave receiving antenna is a coaxial resonator type antenna, and each antenna constitutes a coaxial core conductor of a coaxial cable and an outer conductor of the coaxial core conductor. A metal cylinder opened in an angle range, a dielectric having a preset dielectric constant filling the space inside the metal cylinder, and a lid covering the surface of the dielectric The metal tube for fixing the insulator, the coaxial cable on one surface, and the metal tube including the coaxial core conductor, the dielectric, and the insulator of the coaxial cable penetrating on the other surface; A fixed holder made of the same material, and the microwave transmitting antenna and the front microwave receiving antenna, wherein each of the coaxial core conductors has a plane parallel to the tube axis of the measuring tube. It is characterized in that the opening positions are provided facing each other.

  According to the present invention, a transmitting antenna and a receiving antenna include a coaxial core conductor, a concentric cylindrical insulator that covers the periphery of the coaxial core conductor, and a metal cylinder that opens a part facing the insulator. A coaxial resonator is used.

  Therefore, by adjusting the coaxial tube dimensional ratio b / a between the coaxial core conductor diameter a of the coaxial resonator and the metal cylinder inner diameter 2b, the dimension in the direction orthogonal to the tube axis can be reduced, so that attachment is possible. The diameter of the measuring tube is reduced.

  In addition, since the cross-sectional shape of the microwave transmitting antenna and the microwave receiving antenna as viewed from the direction intersecting the tube axis of the measurement tube is a curved surface, and the fluid resistance in the tube axis direction is reduced, the microwaves in which suspended substances are difficult to deposit A densitometer can be provided.

  Embodiments of the present invention will be described below with reference to the drawings.

  Hereinafter, a microwave densitometer of Example 1 according to the present invention will be described with reference to FIGS.

  FIG. 1 shows a cross-sectional view of the measurement tube 5 of the microwave concentration meter of the present invention as seen from the tube axis direction.

  In FIG. 1, the microwave densitometer has a configuration in which an excitation signal is transmitted to a microwave transmission antenna 1a, a microwave reception antenna 1b, and a microwave transmission antenna 1a that are provided opposite to each other on the side of the tube wall of the measurement tube 5. A coaxial cable 3a, a coaxial cable 3b for transmitting a signal received by the microwave receiving antenna 1b to the measuring unit 2, a measuring unit 2 for transmitting an excitation signal to the microwave antenna 1a and processing the received microwave signal, The microwave transmitting antenna 1a and the microwave receiving antenna 1b are attached to one tip portion, the measuring portion 2 is mounted on the other rear end portion, inserted into the joint through hole portion of the measuring tube 5 from the side surface, and the measuring tube 5 The antenna mounting portion 4 is fixed to the side surface.

  Next, the configuration of the microwave transmission antenna 1a and the microwave reception antenna 1b will be described with reference to FIG. FIG. 2 is a cross-sectional view of the measuring tube 5 as seen from the tube axis direction.

  Since the microwave transmitting antenna 1a and the microwave receiving antenna 1b that are mounted symmetrically opposite to each other vertically with respect to the horizontal axis orthogonal to the tube axis have the same configuration, only one microwave transmitting antenna 1a will be described. The description of the microwave receiving antenna 1b is omitted.

  The microwave transmission antenna 1 a constitutes a coaxial resonator, and is a coaxial core conductor 11 of the coaxial cable 3 a, a metal cylinder 14 that is an outer conductor of the coaxial core conductor 11, and a ceramic that fills the space inside the metal cylinder 14. A dielectric 12 having a high dielectric constant, such as polyethylene, an insulator 13 such as polyethylene for protecting the dielectric 12, a coaxial cable 3a passing through one surface and the other surface through the coaxial core conductor 11, dielectric 12 , And a fixed holder 15 made of the same material as the metal cylinder 14 provided with the insulator 13.

  The fixed holder 15 of the microwave transmitting antenna 1a and the fixed holder 15 of the microwave receiving antenna 1b are fixed at the position of the antenna mounting portion 4 that is symmetrical in the vertical direction with respect to the horizontal axis orthogonal to the tube axis. The antenna attaching portion 4 is inserted and fixed from the outer peripheral side surface of the joint through hole provided in the side wall of the measuring tube 5.

  Further, as shown in FIGS. 2 (b) and 2 (c), a part of the outer circumference of the metal cylinder 14 is opened within a predetermined angle range, and a part of the metal cylinder 14 is connected to the microwave transmission antenna 1a. Each metal tube 14 of the wave receiving antenna 1b is fixed to the antenna mounting portion 4 from the inner peripheral direction of the measurement tube 5 at a position where the opening portions face each other.

Next, the setting of the coaxial resonator will be described. For example, assuming that the resonance frequency f of the coaxial resonator is 2 GHz, the resonance wavelength λ, and the relative dielectric constant of the dielectric 12 is ε _r = 20, the tube axis length L of the metal tube when both ends are short-circuited is generally It becomes as follows.
L = 1/2 × λ
= ^1/2 × c / ε _r ^1/2 × 1 / f
= ^1/2 × 3 × 10 ⁸ / (√20 ^1/2 × 2 × 10 ⁹ ) = 16.8 mm
It becomes. Here, c is the speed of light (3 × 10 ⁸ m / sec).

Further, in the mode TE _mn (TE ₁₁ ) having the lowest cut-off frequency of the coaxial resonator, the high-order mode is avoided by using the resonance wavelength λ to be used within the cut-off frequency or less, and the coaxial core conductor diameter 2a and the metal tube The coaxial tube dimension ratio b / a with the 14 inner diameter 2b is adjusted.

  For example, if the coaxial tube dimensional ratio b / a in which the Q of the coaxial resonator is in the range of 2 to 6 and the coaxial tube dimensional ratio b / a at which the Q of the coaxial resonator is maximum is 3.6, the coaxial tube dimensional ratio b / a When the thickness t is 1 mm and the coaxial core conductor diameter 2 a is 1 mm, the outer shape 2 (b + t) of the metal tube 14 is 5.6 mm.

  Therefore, the outer shape of the metal cylinder 14 of the coaxial resonator at this time is the tube axis length L = 18.8 mm and the tube outer shape is 5.6 mm.

Thus, tube diameter d ^[Phi applicable measuring pipe 5 at this time, when the measurement space Lm between the microwave transmitting antenna 1a and the microwave receiving antenna 1b 40 mm, and,
^dΦ ≧ Lm + 2 × 2 (b + t) ≈51 (mm)
It becomes.

  That is, even if the tube length L of the coaxial resonator is long, the dimension in the direction perpendicular to the tube axis of the measurement tube 5 can be reduced by appropriately adjusting the coaxial tube dimension ratio b / a.

  Therefore, it is possible to attach to a smaller diameter of the measurement tube, which is difficult to attach in the case of the cavity resonator.

  Further, it is not necessary to insert the entire length of the tube shaft length L into the measurement tube. For example, a length half of the tube shaft length L may be inserted and can be adjusted as appropriate.

  Therefore, since the size of the metal cylinder 11 protruding from the measuring tube 5 can be reduced, it is possible to provide a microwave densitometer that is easy to make a structure in which suspended solids are difficult to deposit with respect to the flow of the fluid 20 to be measured. I can do it.

  In addition, it is desirable to adjust suitably the shape of measurement space Lm and the metal cylinder 14 so that the received signal obtained with the microwave receiving antenna 1b may become an appropriate level by an experiment in detail.

  Further, the dielectric 12 and the insulator 13 for protecting the dielectric 12 may be integrally formed of plastic or the like, and can be appropriately selected depending on the fluid 20 to be measured.

  Furthermore, although the microwave transmitting antenna 1a has been described with respect to the case where it is constituted by a coaxial resonator, as shown in FIG. 2, one end of the metal tube 14 is capacitively coupled, that is, one end of the coaxial core conductor 11 is opened. Alternatively, a semi-coaxial resonator may be used.

  A microwave densitometer according to Example 2 of the present invention will be described below with reference to FIG. 3 that are the same as those of the microwave densitometer of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  The second embodiment is different from the first embodiment in that the temperature sensor for measuring the temperature of the fluid 20 to be measured is not provided in the first embodiment. However, in the second embodiment, the microwave transmission antenna 1a and the microwave reception are not provided. The temperature sensor 6 is provided in the vicinity of the microwave propagation of the antenna 1b.

  As shown in FIG. 3, by attaching the antenna attachment portion 4 so that the temperature sensing portion of the temperature sensor 6 comes into contact with the liquid, the liquid temperature in the vicinity of the measurement space where the microwave propagates can be easily measured.

  Accordingly, it is possible to provide a microwave densitometer capable of accurately correcting the output of the microwave densitometer with the output of the temperature sensor 6 even when the dielectric constant changes due to a change in temperature of the fluid 20 to be measured. Can do.

  Hereinafter, a microwave densitometer according to Example 3 of the present invention will be described with reference to FIG. 4 that are the same as those of the microwave densitometer of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  4A is a front view of the microwave transmitting antenna 1a and the microwave receiving antenna 1b as viewed from the inner surface of the measuring tube 5, and FIG. 4B is orthogonal to the tube axis of the microwave transmitting antenna 1a. It is sectional drawing seen from the direction to do.

  The difference between the fourth embodiment and the first embodiment is that in the first embodiment, the cylindrical portion of the metal tube 14, particularly the tip portion thereof, is suspended as a large fluid resistance in the tube axis direction in which the fluid 20 to be measured flows. In the third embodiment, the portion in contact with the flow is a metal cylinder 14f having a curved shape and a reduced fluid resistance in the direction in which the fluid to be measured flows.

  Therefore, it is possible to provide a microwave densitometer having a structure that does not disturb the flow of the fluid 20 to be measured and does not easily deposit and deposit suspended substances.

  A microwave densitometer according to Example 4 of the present invention will be described below with reference to FIG. About each part of the Example shown in FIG. 5, the same part as each part of the microwave densitometer of Example 1 is shown with the same code | symbol, and the description is abbreviate | omitted.

  FIG. 5A is a front view of the microwave transmitting antenna 1a and the microwave receiving antenna 1b as viewed from the inner surface of the measuring tube 5, and FIG. 5B is orthogonal to the tube axis of the microwave transmitting antenna 1a. FIG. 5C is a cross-sectional view seen from the tube axis direction.

  The fifth embodiment is different from the first embodiment in that in the first embodiment, the coaxial core conductor 11 of the microwave transmission antenna 1a is fixed to the antenna mounting portion 4 in a direction perpendicular to the tube axis and inserted into the measurement tube 5. However, in the fourth embodiment, the coaxial core conductor 11 is fixed to the antenna mounting portion 4 so as to be parallel to the tube axis, and is inserted into the measuring tube 5.

  That is, the coaxial core conductor 11 is bent 90 degrees with respect to the insertion direction of the coaxial cable 3 and fixed to the antenna mounting portion 4, and a part of the metal tube 14 facing in the tube axis direction is opened.

  Further, the tip of the metal tube 14 in the tube axis direction is formed into a curved surface so as not to disturb the flow of the fluid 20 to be measured.

  Thus, by providing the coaxial core conductor 11 in parallel with the tube axis direction, the attachment diameter of the measurement tube 5 is reduced, and the end surface of the metal tube 14 is curved to reduce the fluid resistance. A microwave densitometer that is difficult to deposit can be provided.

  The present invention is not limited to the above-described embodiments, and the dimensions of the coaxial resonator in the direction of the coaxial diameter as a microwave transmission antenna are appropriately adjusted by adjusting the coaxial pipe dimension ratio b / a. As long as the diameter is reduced, the external shape is curved so that the fluid resistance in the direction in which the fluid to be measured flows is small, and the dielectric and insulator of the coaxial resonator are measured. The material may be appropriately changed depending on the fluid, and various modifications can be made without departing from the gist of the present invention.

Sectional drawing seen from the tube-axis direction of the microwave densitometer of Example 1 of this invention. Explanatory drawing of the detailed structure of the microwave transmission antenna of the microwave densitometer of Example 1 of this invention, and a microwave receiving antenna. The attachment figure of the temperature sensor which measures the liquid temperature of Example 1 of this invention. Explanatory drawing of the detailed structure of the microwave transmission antenna of the microwave densitometer of Example 2 of this invention, and a microwave receiving antenna. Explanatory drawing of the detailed structure of the microwave transmission antenna of the microwave densitometer of Example 3 of this invention, and a microwave receiving antenna. The block diagram of the conventional microwave densitometer. Explanatory drawing of the detailed structure of the conventional microwave transmission antenna.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a Microwave transmitting antenna 1b Microwave receiving antenna 2 Measuring part 3a, 3b Coaxial cable 4 Antenna mounting part 5 Measuring tube 6 Thermometer 11 Coaxial core conductor 12 Dielectric 13 Insulator 14, 14f Metal cylinder 15 Fixed holder 20 Fluid to be measured 21 Measuring tube 22 Measuring tube flange 23 Mounting base flange 24, 28 Storage cylinder 25, 29 Insulator window 26 Microwave transmitting antenna 27, 31 Coaxial cable 27a Coaxial core wire 30 Microwave receiving antenna 32 Measuring unit

Claims (4)

Inserting a pair of microwave transmitting antenna and microwave receiving antenna provided opposite to each other from the outer peripheral side surface of the measurement tube through which the fluid to be measured flows, until microwaves are transmitted from the microwave transmitting antenna and received by the microwave receiving antenna A microwave densitometer for determining the concentration of the fluid to be measured from the change in propagation time of
The microwave transmitting antenna and the microwave receiving antenna are coaxial resonator type antennas, and each antenna is
A coaxial core conductor of a coaxial cable ;
Constituting an outer conductor of the coaxial core conductor, and a metal cylinder having an outer peripheral surface of the outer conductor opened within a predetermined angle range;
A dielectric having a predetermined dielectric constant filling the space inside the metal cylinder;
An insulator covering the surface of the dielectric;
The same material as the metal tube for fixing the coaxial cable on one surface and the metal tube including the coaxial core conductor, the dielectric, and the insulator of the coaxial cable penetrating on the other surface. A fixed holder having,
With
The microwave transmitting antenna and the microwave receiving antenna are characterized in that each coaxial core conductor is provided to face the opening position of the metal tube on a plane intersecting the tube axis of the measuring tube. Microwave densitometer. Propagation until the microwave transmitting antenna and the microwave receiving antenna provided opposite to each other are inserted from the outer peripheral side surface of the measurement tube through which the fluid to be measured flows and the microwave is transmitted from the microwave transmitting antenna and received by the microwave receiving antenna A microwave densitometer for obtaining a concentration of the fluid to be measured from a change in time,
The microwave transmitting antenna and the microwave receiving antenna are coaxial resonator type antennas, and each antenna is
A coaxial core conductor of a coaxial cable ;
Constitute the outer conductor before Symbol coaxially conductor, a metal cylinder that is open to the outer peripheral surface of the outer conductor at a predetermined angular range,
A dielectric having a predetermined dielectric constant filling the space inside the metal cylinder;
An insulator covering the surface of the dielectric;
The same material as the metal tube for fixing the coaxial cable on one surface and the metal tube including the coaxial core conductor, the dielectric, and the insulator of the coaxial cable penetrating on the other surface. A fixed holder having,
With
The microwave transmitting antenna and the front microwave receiving antenna are characterized in that each of the coaxial core conductors is provided to face the opening position of the metal tube on a plane parallel to the tube axis of the measuring tube. Microwave densitometer.
The dielectric and ceramics,
The insulating material, the microwave densitometer according to claim 1 or claim 2, characterized in that a positive Thich.   The metal tube of each of the microwave transmitting antenna and the microwave receiving antenna is formed so that a cross-sectional shape in a direction intersecting a tube axis of the measuring tube is a curved surface. Or the microwave densitometer of Claim 2.

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