JPH10318931A - Foreign matter detection device in transparent fluid - Google Patents

Abstract

(57) [Summary] [Problem] To reduce the space and accurately measure the presence or absence of foreign matter and its size. A transparent ring connected to a tip of an extruder and allowing a transparent polyethylene resin extruded from the extruder to pass therethrough, and video signals d ₁ and d _{2 obtained} by imaging the polyethylene resin passing through the transparent ring _2. comprising a line sensor camera 3 and 4 for converting, an image processing unit 5 for detecting foreign matter mixed in the polyethylene resin on the basis of a video signal d _1, d ₂ output from the line sensor cameras 3 and 4, each line The sensor cameras 3 and 4 are provided so that the arrangement direction of a plurality of imaging elements arranged in a line is orthogonal to the flow direction of the polyethylene resin, and are arranged in the flow direction of the polyethylene resin in a spaced state. I have. The line sensor cameras 3 and 4 are arranged so that the imaging directions intersect.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for detecting foreign matter in a transparent fluid, and more particularly to an apparatus for detecting the presence or size of foreign matter mixed in a transparent fluid.

[0002]

2. Description of the Related Art In recent years, as a high-voltage power cable,
CV cables using cross-linked polyethylene for the cable insulating layer are frequently used. This CV cable is usually extruded from an extruder with polyethylene containing a cross-linking agent and coated on the outer periphery of the inner semiconductive layer on the cable conductor, and then the outer semiconductive layer is extruded and coated on the outer periphery. It is manufactured through a step of heating in a state and reacting a crosslinking agent to crosslink polyethylene.

In general, when a long-distance power cable line is constructed using CV cables, the CV cables are laid along the cable route for each short span, and the front and rear ends thereof are sequentially connected to form a line. Install a termination connection at the end. Various methods have been developed for connecting the CV cable. Among them, an EMJ (extrusion mold joint) method and a BMJ (block mold joint) method have been developed.
Methods tend to be widely adopted in terms of insulation performance and reliability. In the EMJ method, the cable insulation layer and the inner and outer semiconductive layers are penciled, and a mold is assembled around the conductor connection portion of the power cable in which the exposed cable conductors are connected by a conductor sleeve. It is introduced into a mold from an extruder, and heated and pressed to form and crosslink polyethylene. Further, in the BMJ method, a polyethylene block containing a cross-linking agent formed in advance into a semi-cylindrical shape is assembled into a cylindrical shape around a conductor connection portion of the power cable, or the polyethylene block containing a cross-linking agent formed in advance into a cylindrical shape is used as the above-mentioned. It is inserted into a conductor connection portion of a power cable, a mold is arranged on the outer periphery thereof, and the polyethylene is molded and integrated by heating and pressurizing and crosslinked.

[0004] Since the above-described cable insulation layer of the power cable and the mold joint thereof are used under a high electric field, metal powder, dust, or burns (thermally degraded resin material) may be contained therein. ) May cause dielectric breakdown starting from these. In addition, while the power cable is used for a long period of time, water trees or the like are generated around the foreign matter, and there is a possibility that the insulation performance is gradually reduced. Therefore, before being supplied to the extruder, the insulating material used for the cable insulation layer and the mold joint of the power cable undergoes a thorough inspection for the presence of foreign substances, and also in the extrusion process and the molding process. Great care is taken to prevent the resin from becoming foreign matter due to excessive heating or stagnation, thereby lowering the insulation performance.

[0005]

Various methods have been developed and put to practical use as a method for inspecting foreign substances in a resin material used as an insulating material for such power cables, but each method has advantages and disadvantages. . For example, the resin pellets before being supplied to the extruder are extracted and visually inspected for the presence and degree (size and number) of foreign matter, or the resin material extruded from the extruder is formed into a film, and There is known a method of irradiating a laser beam to determine the presence or absence and degree of a foreign substance from a transmitted image, but there is a concern about the reliability of each of these methods because they are not all inspections.

Further, a transparent window is provided in a resin passage at the tip of the extruder, and a laser beam is irradiated from the transparent window to perform scanning, and the presence or absence and degree of foreign matter can be determined from a change in the intensity of the transmitted light. A foreign substance detection method and apparatus for voltage insulator extrusion molding (JP-A-7-325037) and a foreign substance inspection apparatus for a plastic extruder (JP-A-8-323841) are known. However, in such a detection method and a detection apparatus, since the foreign substance detection unit including the laser light source and the light receiver is used, the unit itself becomes considerably large, so that a certain amount of mounting space must be secured. .

Further, a method and an apparatus for detecting foreign matter in resin in an extruder head in which a transparent window is provided in a resin passage at the tip of the extruder and through which a foreign matter in the molten resin is detected by an image camera (JP-A-7-325037). Gazette) is known. In a detection apparatus to which such a detection method is applied, an image camera in which detection elements such as CCD pixels are generally arranged in a two-dimensional plane is used.
A foreign substance in the transparent liquid flowing through the transparent channel having a size of 50 mm can be detected at a size of 50 μm. However, the inner diameter of the transparent flow path used during extrusion of the cable insulator is 50.
mm, the detection limit is higher if the above image camera is used.

[0008]

(Equation 1)

[0009] It becomes. Therefore, there was a problem that it was not possible to clear the required detection limit of 50 μm.
SUMMARY OF THE INVENTION The present invention has been made to solve such conventional difficulties, and can save space, and can accurately measure the presence and absence of foreign matter and its size in a transparent fluid. It is an object to provide a detection device.

[0010]

According to the present invention, there is provided an apparatus for detecting foreign matter in a transparent fluid, which achieves the above object, by capturing an image of a transparent fluid passing through the transparent fluid and a transparent fluid passing through the transparent fluid. A line sensor camera that converts the
An image processing unit for detecting a foreign substance mixed in the transparent fluid based on a video signal output from the line sensor camera; And a plurality of them are arranged in the direction of flow of the transparent fluid at a distance from each other.

In the apparatus for detecting foreign matter in a transparent fluid according to the present invention, it is preferable that the plurality of line sensor cameras are arranged so that the imaging directions intersect. Further, in the apparatus for detecting foreign matter in a transparent fluid of the present invention, the image processing unit determines the presence / absence of foreign matter mixed in the transparent fluid and the size in the flow direction based on each video signal output from the plurality of line sensor cameras. An image processing circuit for obtaining foreign matter data to be shown;
A correction circuit for obtaining speed data of the foreign matter from a detection time difference of the same foreign matter obtained from the foreign matter data from the image processing circuit, and correcting foreign matter data indicating the size of the foreign matter in the flow direction based on the speed data. Are preferred.

Further, in the apparatus for detecting foreign matter in a transparent fluid according to the present invention, the correction circuit of the image processing section determines the speed data of the foreign matter from the detection time difference of the same foreign matter obtained from the foreign matter data from the image processing circuit. Is calculated, and the foreign matter data indicating the size of the foreign matter in the flow direction is corrected based on the correction coefficient. Further, in the device for detecting foreign matter in a transparent fluid of the present invention, the correction circuit of the image processing unit is configured to determine the position of the image of the foreign matter taken by the upstream line sensor camera and the position of the foreign matter taken by the downstream line sensor camera. It is preferable that the position of the image is compared with the position of the image, and the flow velocity of the foreign matter is obtained from the relationship between the difference between the positions and the difference in the detection time of the foreign matter.

[0013] Thus, for example, one row is 4000 to 50
Since a 00 pixel line sensor camera can be used, the detection accuracy in the direction perpendicular to the flow direction of the transparent fluid can be improved. Such a device for detecting foreign matter in a transparent fluid can be used for detecting foreign matter in a polyethylene material supplied to a cable insulating layer of a power cable or a mold joint thereof. Polyethylene resin is milky white translucent at room temperature and has insufficient light transmittance, but becomes transparent when heated and melted during kneading in an extruder, and when foreign matter is mixed in the molten resin Can be easily seen through from the outside. Therefore, a transparent flow path made of a transparent glass or resin material is inserted in the middle of the conduit connecting the extruder and the crosshead or between the extruder and the mold. By capturing an image, converting it into a video signal, and processing the signal, it is possible to detect the presence and size of a foreign substance in the polyethylene resin that has passed through the flow path.

When a foreign object is captured by a line sensor camera as a video signal, the foreign object moves in the direction of flow of the polyethylene resin, and the size of the foreign object is output as a video signal having a different size from the actual flow direction. Is done. Further, the distribution of the flow velocity in the polyethylene resin flowing in the transparent flow path is not uniform, and is large at the center of the flow path and small near the flow wall. For example, when the inner diameter of the transparent flow path is cylindrical and the fluid flowing through the flow path follows Newton's law of viscosity, the flow velocity distribution is as shown in the following equation. become.

Ur = K (R ² −r ² ) (2) where, Ur: flow velocity at the r position K: constant R: radius of the flow path r: radius position of the flow path Is not a Newtonian fluid completely conforming to the above, but exhibits a behavior close to that when the average flow velocity during extrusion is within a predetermined range. On the other hand, when the flow velocity is lower than that, rather, as shown by Vr in FIG.
9 shows a flow velocity distribution close to a Bingham fluid.

Therefore, in the apparatus for detecting foreign matter in a transparent fluid according to the present invention, images are taken by a line sensor camera at a plurality of positions different in the direction of flow of the transparent fluid, converted into video signals, and based on these video signals, the transparent fluid is output. In addition to obtaining information indicating the presence or absence and size of foreign matter in the inside, speed information of the foreign matter is obtained from a detection time difference of the same foreign matter detected by a plurality of line sensor cameras, and the size of the foreign matter in the flow direction is determined based on the speed information. Is corrected. Specifically, the flow velocity V of the foreign matter in the transparent fluid
As a method for determining the position, the transparent fluid flowing in the flow path is imaged by an upstream line sensor camera and a downstream line sensor camera from a direction intersecting with the flow, and the position of the image of the foreign matter imaged by the upstream line sensor camera And the position of the image of the foreign matter captured by the downstream line sensor camera, and the flow velocity of the foreign matter can be obtained from the difference between the positions.

Further, if a plurality of line sensor cameras are simultaneously imaged from different positions in the flow direction of the transparent fluid and from a plurality of different directions intersecting the flow of the transparent fluid, the presence or absence of foreign matter and Not only can the speed information be known, but also when foreign substances overlap and pass, the overlap can be identified, so that the number and size of the foreign substances can be accurately obtained.

The transparent flow path for taking an image with the line sensor camera can be constituted by inserting a transparent ring in the middle of the pipe. In this case, the transparent ring may have a rectangular cross section, but it is preferable that the transparent ring has a cylindrical shape having the same inner diameter as the pipe so as not to disturb the flow of the fluid flowing therethrough or cause stagnation. . When the transparent fluid is, for example, molten polyethylene, the transparent ring is preferably made of Pyrex glass (refractive index: 1.47) having a refractive index close to its refractive index of 1.44.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the apparatus for detecting foreign matter in a transparent fluid according to the present invention will be described below with reference to the drawings. In this embodiment, the present invention is applied to detection of foreign matter in polyethylene resin supplied to a mold when an insulating layer of a CV cable is connected by an EMJ method.

One embodiment of the apparatus for detecting foreign matter in a transparent fluid according to the present invention is, as shown in FIGS. 1 (a) and 1 (b), in the middle of a resin supply pipe 1 from an extruder to a mold. An image of a transparent ring 2 which is a transparent flow path inserted and a polyethylene resin which is a transparent fluid passing through the transparent ring 2
And two line sensor cameras 3 and 4 and an image processing unit 5 for detecting foreign substances mixed in the polyethylene resin based on the video signals d ₁ and d ₂ output from the two line sensor cameras 3 and 4. I have. Further, an output device 6 and a monitor 7 are connected to the image processing unit 5.

The transparent ring 2 is made of Pyrex glass or the like, and has the same cylindrical shape as the pipe 1 with an inner diameter of about 50 mm.
Faced between 10 Also, flange 9 and flange 1
0 is tightened by bolts and nuts 11 that are inserted through through holes provided in four places around them.
The seal is between.

The two line sensor cameras 3 and 4 are CCDs
Such a fixed image sensor is used, and the fixed image sensors are arranged in a line. Such two line sensor cameras 3 and 4 are provided such that, for example, the arrangement direction of a plurality of fixed imaging elements arranged in one row is orthogonal to the flow direction U of the polyethylene resin flowing through the transparent ring 2. Are arranged in the flow direction U of the polyethylene resin in a spaced state. Specifically, the imaging positions of the upstream line sensor camera 3 and the downstream line sensor camera 4 are shifted by, for example, S mm in the axial direction of the transparent ring 2.

Further, two line sensor cameras 3, 4
Are arranged so that the imaging directions intersect. In addition,
It is preferable that the crossing angles of the imaging directions of the two line sensor cameras 3 and 4 are orthogonal to each other in order to accurately detect a plurality of foreign substances. Accordingly, even when foreign substances pass through one another, the overlap can be identified, so that the number and the size of the foreign substances can be accurately obtained by the image processing unit 5.

The image processing section 5 indicates the presence / absence of a foreign substance mixed in the polyethylene resin and the size in the flow direction based on the video signals d ₁ and d ₂ output from the two line sensor cameras 3 and 4. an image processing circuit 12 for obtaining the foreign object data d _3, from the detection time difference of the same foreign substance obtained from a particle data d ₃ from the image processing circuit 12 obtains the velocity data of the foreign object (not shown), on the basis of the velocity data and a correction circuit 13 for correcting the foreign object data d _3.

The image processing circuit 12 outputs each video signal d ₁ ,
storing the time series data of d _{2 in} a storage circuit (not shown),
Each time predetermined time-series data is accumulated, image processing is performed and output to the output device 6 and the monitor 7. As a result, an enlarged image of a foreign substance detected by the upstream line sensor camera 3 on the screen a of the monitor 7 and an enlarged image of the foreign substance detected by the downstream line sensor camera 4 on the screen b are displayed as slowly moving images. .

The correction circuit 13 calculates a correction coefficient from the foreign substance velocity data obtained from the foreign substance data d ₃ from the image processing circuit 12, and based on the correction coefficient, the foreign substance data d indicating the size of the foreign substance in the flow direction. ₃ corrected by the seek foreign substance correction data d _4. Further, the correction circuit 13 compares the image position of the foreign object imaged by the line sensor camera 3 on the upstream side with the image position of the foreign object imaged by the line sensor camera 4 on the downstream side. The flow velocity of the foreign matter is obtained from the relationship between the foreign matter detection time differences. This is because the imaging positions of the upstream line sensor camera 3 and the downstream line sensor camera 4 are shifted by about S mm in the axial direction of the transparent ring 2, so that the same foreign matter is detected in the two line sensor cameras 3 and 4. Video signals d ₁ and d ₂ generated when
This is because information about the flow velocity of the foreign matter is included in the information.

The following method can be adopted as the correction method. (1) When foreign matter passes at the average flow velocity V ₀ , the foreign matter data d ₃ output from the image processing circuit 12 and indicating the size of the foreign matter in the flow direction is the foreign matter correction data d ₄ indicating the true size of the foreign matter. And set the correction coefficient at this time to 1
And (2) When the passing speed of the foreign matter is higher than the average flow velocity V ₀ , the foreign matter data d ₃ output from the image processing circuit 12 and indicating the size of the foreign matter in the flow direction is output smaller than the true size of the foreign matter. Therefore, in the correction circuit 13, the correction coefficient C ₁ is added to the foreign matter data d ₃ indicating the size of the foreign matter in the flow direction.
(> 1) is corrected. This correction coefficient C ₁ is as rate of passage of foreign matters is large, a large value. (3) When the passing speed of the foreign matter is smaller than the average flow velocity V ₀ , the foreign matter data d ₃ output from the image processing circuit 12 and indicating the size of the foreign matter in the flow direction is output larger than the true size of the foreign matter. Therefore, in the correction circuit 13, the correction coefficient C ₂ is added to the foreign matter data d ₃ indicating the size of the foreign matter in the flow direction.
(<1) is corrected. The correction factor C ₂ are as is the rate of passage of foreign matter is reduced, a small value. (4) The correction coefficients C ₁ and C ₂ are obtained in advance and
And is appropriately selected based on the speed information of the foreign matter.

For example, when the laser beam is 60 MHz (= 1)
In the case of scanning at 6.7 nsec / scan), if the number of “0” s indicating that foreign matter is detected in the scan data is 400000 consecutively in the vertical direction, 16.7 nsec / scan × 400000 = 6.68
msec, and the apparent magnitude in the flow direction is 6.68 msec × 7 mm / sec = 47 μm on the basis of the average flow velocity of 7 mm / sec, but the actually measured flow velocity V of the foreign matter is 10 mm / sec.
If it is c, the true size L of the foreign matter in the flow direction is 47 μm × 10 mm / 7 mm = 67 μm. Therefore, the correction coefficient C1 in this case is 10 /
That means seven.

Further, in the case of correcting the foreign object data d ₃ indicating the magnitude of foreign matter in the flow direction is not a multiplication of the above-mentioned correction coefficient, the foreign object data d ₃ indicating the magnitude of foreign matter in the flow direction of the foreign matter The correction amount determined by the passing speed may be added or subtracted. The operation of the device for detecting a foreign substance in a transparent fluid having such a configuration will be described. When detecting foreign matter in the polyethylene resin supplied to the mold when connecting a CV cable by the EMJ method, the cable insulation layer and the inner and outer semiconductive layers are pencilled, and the conductor between the exposed cable conductors is connected. A pair of power cables (not shown) connected by a sleeve are assembled with a mold (not shown) around the conductor connection part. The polyethylene resin used for the mold is kneaded with a crosslinking agent in an extruder (not shown), heated and melted to form a transparent fluid, and supplied into the mold through a resin supply pipe 1. When the polyethylene resin, which has become the transparent fluid, passes through the transparent ring 2 inserted in the conduit 1, the two line sensor cameras 3 and 4 take an image and inspect whether foreign substances are mixed. .

That is, as shown in FIG. 2, the polyethylene resin in the transparent ring 2 flows upward from the bottom in the ZZ 'direction.
If you are going to Y 'direction, assuming a case where the polyethylene resin foreign matter A are mixed goes through, the foreign matter data d ₃ when foreign material A is not in the height H of the scan line is not output there (Figure 2 (a), (c) ), the foreign matter a is that the foreign object data d ₃ is output when in the height H of the scan lines (Figure 2 (b)). Accordingly, the true size of the foreign matter A in the flow direction can be obtained if there is no flow. This is because the distribution of the flow velocity in the polyethylene resin flowing in the circular flow path differs depending on the distance from the center axis of the flow path, and foreign substances flowing near the wall of the flow path have a low speed, and the height of the scanning line is high. This is because the size of the foreign matter in the flow direction is displayed larger than the actual size because the time of staying in H is long. In addition, foreign matter flowing near the center of the flow path is displayed with a small size in the flow direction. From this, in order to know the true size of the foreign matter A in the flow direction, a correction coefficient is calculated from the flow velocity of the foreign matter A in the cross section in the polyethylene resin, and the flow direction of the foreign matter A is calculated based on the correction coefficient. it can be seen that the must be corrected foreign data d ₃ indicating the magnitude. Needless to say, the scanning by the line sensor camera 4 on the downstream side is the same as that by the line sensor camera 3 on the upstream side.

The flow rate of the foreign substance A is determined by the image position of the foreign substance A on the screen at the frame (time t = t _Z ) by the line sensor camera 3 on the upstream side and the frame (time t) by the line sensor camera 4 on the downstream side. = calculated the time difference between the image position of the foreign object a on the screen in t _Z + ΔTms), it is possible to obtain the flow rate of the foreign matter a by dividing the between the moving distance Dmm by the time difference DerutaTms of this frame.

Also, even when two foreign substances pass through the transparent ring 2 at the same time, two foreign substances are detected by taking an image from the orthogonal direction, and their sizes in the X and Y directions are identified. be able to. FIG. 3 shows the pattern and the foreign matter image on the monitor screens a and b. 1 is a spherical foreign matter A in the center of the flow path, and another spherical foreign matter B near the wall surface on the Y-axis (this foreign matter is near the wall surface, so it is enlarged in the length direction on the monitor screen. And appear in an oval shape). No. 2 shows a pattern in which spherical foreign substances A and B are located near the center of the flow path and the wall surface on the X axis.
o. 3 is a spherical foreign substance A near the wall surface on the Y axis and the X axis,
B shows a certain pattern. As described above, even when two foreign substances pass through the transparent ring 2 at the same time, their number and size can be identified.
Even if there are more than one, they can be identified.

If a plurality of foreign substances pass through the transparent ring 2 simultaneously, the line sensor camera 3 on the upstream side
It is conceivable that the first foreign substance detected by the detector has a low flow velocity, so that when passing through the line sensor camera 4 on the downstream side, the foreign substance is detected later than other foreign substances having a high flow velocity. The problem can be solved by adding a system for discriminating foreign matter.

The true size of the foreign matter A in the flow direction can be known by correcting the foreign matter data d ₁ indicating the size of the foreign matter A in the flow direction based on the correction coefficient thus obtained. The foreign matter correction data d ₁ ′ indicating the true size of the foreign matter A in the flow direction is output to the output device 6 (FIG. 1A), the output result is printed and output, and a predetermined fixed value is output. When a foreign substance having a size equal to or larger than the value (for example, when the identification level is several tens of μm or more than 100 μm) or the number of foreign substances is detected, an alarm is output and the worker is warned to take measures.

In this embodiment, the foreign substance detecting device of the present invention is applied as a transparent fluid to the foreign substance detection in the cable insulation layer of the CV cable and the polyethylene resin used for the connection thereof. The present invention is not limited to this, and can be widely applied to inspection of various transparent molten resin materials other than polyethylene resin, or various transparent objects which dislike the inclusion of foreign matter such as insulating oil or edible oil. In addition, even if the transparent fluid is a gas, it is needless to say that the foreign matter detection device of the present invention can be applied.

[0036]

As described above, according to the embodiment of the present invention, according to the apparatus for detecting foreign matter in a transparent fluid of the present invention, the space can be saved. Can be accurately detected. Also,
Since the line sensor camera is used, it is possible to improve detection accuracy in a direction orthogonal to the flow direction of the transparent fluid.

[Brief description of the drawings]

FIG. 1 is a view showing an embodiment of a device for detecting a foreign substance in a transparent fluid according to the present invention, in which (a) is an explanatory view and (b) is a cross-sectional view of (a).

FIG. 2 is an explanatory view showing a positional relationship between a scanning line of a line sensor camera and a foreign substance used in the apparatus for detecting a foreign substance in a transparent fluid according to the present invention along with time, wherein (a) and (c) are line sensors; Figure showing no foreign matter in the scanning line of the camera,
(B) is a diagram showing a state in which a foreign substance exists in a scanning line of the line sensor camera.

FIG. 3 is a diagram illustrating an apparatus for detecting foreign matter in a transparent fluid according to the present invention.
FIG. 9 is an explanatory diagram illustrating three patterns when two foreign substances pass, and foreign substance images on the monitor screens a and b in the respective patterns.

FIG. 4 is a graph illustrating a relationship between a radial position of a fluid in a flow path and a flow velocity.

[Explanation of symbols]

2 transparent ring (transparent passage) 3,4 line sensor camera 5 image processing unit 12 image processing circuit 13 the correction circuit d _1, d ₂ video signal d ₃ the foreign matter data

Claims (5)

[Claims] 1. A transparent flow path through which a transparent fluid passes, a line sensor camera which images the transparent fluid passing through the transparent flow path and converts it into a video signal, and the video output from the line sensor camera. An image processing unit that detects a foreign substance mixed in the transparent fluid based on a signal,
The line sensor cameras are provided so that the arrangement direction of a plurality of imaging devices arranged in one line is orthogonal to the flow direction of the transparent fluid, and the plurality of line sensor cameras are arranged in the transparent fluid flow direction in a separated state. An apparatus for detecting foreign matter in a transparent fluid. 2. The apparatus according to claim 1, wherein the plurality of line sensor cameras are arranged so that their imaging directions intersect.
A device for detecting foreign matter in a transparent fluid according to the above. 3. An image processing unit according to claim 1, wherein said video signal output from said plurality of line sensor cameras is used to generate foreign matter data indicating presence or absence of said foreign matter mixed in said transparent fluid and a size in a flow direction. The image processing circuit to be obtained, the speed data of the foreign matter is obtained from the same foreign matter detection time difference obtained from the foreign matter data from the image processing circuit, and the magnitude of the flow direction of the foreign matter is shown based on the speed data. 3. The apparatus for detecting foreign matter in a transparent fluid according to claim 1, further comprising a correction circuit for correcting foreign matter data. 4. The correction circuit of the image processing section calculates speed data of the foreign matter from a detection time difference of the same foreign matter obtained from the foreign matter data from the image processing circuit, calculates a correction coefficient, and calculates the correction coefficient. 4. The apparatus for detecting foreign matter in a transparent fluid according to claim 3, wherein the foreign matter data indicating the size of the foreign matter in the flow direction is corrected based on a coefficient. 5. The correction circuit of the image processing section includes: a position of an image of the foreign object imaged by the line sensor camera on the upstream side; and a position of an image of the foreign object imaged by the line sensor camera on the downstream side. 5. The apparatus for detecting foreign matter in a transparent fluid according to claim 4, wherein the flow velocity of the foreign matter is determined from the relationship between the difference between the positions and the difference in the detection time of the foreign matter.