JP5356738B2 - Optical sensor for liquid detection, liquid level sensor and liquid leakage sensor thereby - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sensor for liquid detection which detects the existence or absence of the contact of liquid in the whole perimeter of the outer peripheral surface of an outer tube containing a light emitting element and light receiving element, and to provide its application products. <P>SOLUTION: The optical sensor 1 in which the light emitting element 3 and light receiving element 4 are arranged vertically opposite to each other in a cylindrical transparent outer tube 2, and in which a disk-shaped light shielding plate 5 having contact with the inner peripheral surface of the outer wall part 7 of the outer tube 2 is arranged between the light emitting element 3 and light receiving element 4 so that the light from the light emitting element 3 is not directly received by the light receiving element 4. Annular light from the peripheral edge part of the light irradiated from the light emitting element 3 in a fixed solid angle is made to enter inside the outer wall part 7 at an incident angle larger than the critical angle, for example, given when the outside of the outer tube 2 is air, and the reflected light reflected by the outer peripheral surface of the outer wall part 7 is received by the light receiving element 4. Liquid level sensors and liquid leakage sensors are made using this optical sensor 1. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an improvement in an optical sensor for detecting the presence or absence of liquid, and a liquid level sensor and a liquid leakage sensor using the improved optical sensor.

  Conventionally, sensors based on various principles have been proposed as sensors for detecting the presence or absence of liquid and sensors for detecting the height of the liquid surface. For example, a float sensor that detects the position of the liquid surface based on the position of the float that floats on the liquid surface, an electrostatic sensor that detects the presence or absence of liquid by changing the capacitance based on the presence or absence of liquid, and the refraction of light due to the presence or absence of liquid An optical sensor that detects the position of the liquid surface by a change in the amount of light based on the change. Among them, the float type sensor has a float, so that it cannot be installed in a narrow place, and there is a problem that a trouble is likely to occur due to a malfunction of a movable part of the float. The electrostatic sensor is not suitable for detecting a liquid having a small electrostatic capacity, and a measurement value is changed when the measuring distance of the electrostatic capacity is changed, so that a trouble is easily caused.

  As one of the optical liquid level sensors disclosed heretofore, a light emitting element is installed on one end side of the bottom surface of the liquid storage tank, and the optical position of the line CCD etc. extends from one end side to the multi-end side of the ceiling surface of the liquid storage tank. The light beam emitted from the light emitting element obliquely upward is refracted at the interface between the liquid stored in the liquid storage tank and the space above it, and reaches the optical position sensor. The height of the liquid surface is detected because the position of the optical position sensor to which the light beam reaches differs depending on the height of the liquid (see Patent Document 1). Since this liquid level sensor uses a line sensor for light reception, it cannot be installed in a narrow place, and the manufacturing cost increases.

  As another optical type sensor, it consists of a light emitting element and a light receiving element arranged inside a transparent outer cylinder. Light incident on the outer peripheral surface of the outer cylinder from the light emitting element is in contact with the liquid at the incident point. When there is no incident light, the incident light is totally reflected at the incident point and returned to the light receiving element in the outer cylinder, but when the liquid is in contact with the incident point, the light is not totally reflected and travels almost straight into the liquid. There is a liquid detection optical sensor that detects the presence or absence of liquid by reducing the amount of light received by the light receiving element. There is a liquid level sensor in which a plurality of the above optical sensors are arranged inside an outer cylinder that is long in the vertical direction so that the height of the liquid level can be detected according to fluctuations in the level of the liquid level (Patent Document). 2). However, a single sensor can detect the presence or absence of liquid in contact with the incident point on the outer peripheral surface of the outer cylinder to which the light from the light emitting element arrives. Even if it is only attached, it has a weak point that it is erroneously detected if liquid is present.

JP 2006-300793 A JP 2001-033296 A

  There is an optical sensor that detects the presence or absence of liquid at the incident point on the outer peripheral surface in the same manner, although it is different from the optical sensor described in Patent Document 2 above. FIG. 10 is a cutaway perspective view of the liquid detection optical sensor 11 in which the light emitting element 13 and the light receiving element 14 are disposed inside the vertically transparent outer cylinder 2 with both ends closed. The optical sensor 11 causes the light emitted from the light emitting element 13 to enter the outer wall portion 7 of the outer cylinder 2 at a constant incident angle, and reflects the reflected light at the incident point P on the outer peripheral surface of the outer wall portion 7. The light-emitting element 13 and the light-receiving element 14 are inclined so that the light-receiving element 4 receives light, and the incident point (reflection point) P on the outer peripheral surface of the outer wall portion 7 depends on the amount of light received by the light-receiving element 4. It detects the presence or absence of liquid in contact. The principle of the detection is shown in FIG. 11 below. As will be described later, in order to simplify the explanation, the light is linear light along the optical axis.

  FIG. 11 is a cross-sectional view of the optical sensor 11 shown in FIG. 10, and the light emitting element 13 and the light receiving element 14 have side surfaces shown. FIG. 11 is a diagram conceptually showing the principle of detecting the presence or absence of liquid by the optical sensor 11. In addition, although the light from the light emitting element 13 is light which spreads within a fixed solid angle, in FIGS. 10 and 11, the light is shown as light along the optical axis. FIG. 11A is a diagram showing a case where the liquid 8 is not in contact with the incident point P on the outer peripheral surface of the outer wall 7, for example, the case where the outside of the optical sensor 11 is the atmosphere, and FIG. 11B is a diagram of the outer peripheral surface of the outer wall 7. It is a figure which shows the case where the liquid 8 is contacting the incident point P. FIG. In FIG. 11A, light from the light emitting element 3 enters the outer wall 7 toward the incident point P on the outer peripheral surface at a constant incident angle α, and is totally reflected at the same reflection angle α as the incident angle α. Is received.

  The total reflection occurs when the incident angle α is greater than or equal to the critical angle θm. The critical angle θm is an angle derived from the following formula (1) from Snell's law regarding refraction.

sinθm = nA / nB Formula (1)
In the above formula (1), nA is the relative refractive index of the medium A with respect to the vacuum, that is, the refractive index (also referred to as absolute refractive index), and nB is the refractive index of the medium B. In this case, nA <nB and light travels from the medium B to the medium A.

  In FIG. 11A, the medium B is, for example, a glass outer cylinder 2, and the medium A is, for example, air outside the outer cylinder 2. Assuming that the refractive index of glass is 1.47 and the refractive index of air is 1.0003, the critical angle θm is calculated as 43 degrees from the equation (1), and the incident point P on the outer peripheral surface of the outer wall 7 in FIG. Light incident at an incident angle α = 55 degrees is totally reflected at the incident point P, and the reflected light is received by the light receiving element 4.

On the other hand, in FIG. 11B, the medium B is the glass outer cylinder 2, but the medium A is the liquid 8 in contact with the incident point P on the outer peripheral surface of the outer wall 7, and the liquid 8 is water. Suppose there is. Since the refractive index of water is 1.333, the critical angle θm is similarly determined to be 63 degrees. Accordingly, light that is incident on the outer wall surface of the outer wall portion 7 of the outer cylinder 2 at the same incident angle α = 55 degrees is not totally reflected at the incident point P, but generates light L ^* that travels substantially straight into water. Compared to the case, the amount of light received by the light receiving element 4 decreases. That is, the presence or absence of water in contact with the incident point P on the outer peripheral surface of the outer wall 7 can be detected by the optical sensor 11 shown in FIG.

  However, the optical sensor 11 shown in FIG. 11 detects the presence / absence of water at the incident point P on the outer peripheral surface of the outer cylinder 2, and the presence / absence of water in the entire outer periphery of the same height including the incident point P is detected. It is not something to detect. Therefore, even when a water droplet is simply attached to the incident point P, there is a problem in that it is erroneously detected that water exists at the height level.

  The present invention has been made in view of the above-described problems, and a first object of the present invention is to provide liquid over the entire outer periphery of the same height on the outer peripheral surface of the outer wall portion of the outer cylinder in which the light emitting element and the light receiving element are arranged. An object of the present invention is to provide a liquid detection optical sensor capable of detecting the presence or absence of water.

  A second object of the present invention is to provide a liquid level sensor that can detect fluctuations in the liquid level of the liquid contained in the tank, for example, using the optical sensor.

  A third object is to provide a liquid leakage sensor that can detect the presence or absence of liquid leaking into the receiving container using the optical sensor.

In order to achieve the object of the present invention, a liquid detection optical sensor according to a first aspect of the present invention has a light emitting element and a light receiving element arranged in a height direction of a cylinder in a cylindrical transparent outer cylinder, and emits light from the light emitting element. Liquid detection light in which a disc-shaped light shielding plate that is in contact with the inner peripheral surface of the outer wall portion of the outer cylinder is disposed between the light emitting element and the light receiving element so that the received light is not directly received by the light receiving element A sensor,
Among the light emitted from the light emitting element within a certain solid angle, the light at the peripheral edge is incident on the outer wall, but the incident light is incident when the liquid is not in contact with the outer peripheral surface of the outer wall. The outer peripheral surface is incident at an angle greater than the critical angle that is totally reflected, and the light receiving element is configured to receive the reflected light.
When the liquid is not in contact with the reflecting surface, the light incident on the outer wall is totally reflected by the reflecting surface and received by the light receiving element. When the liquid is in contact with the reflecting surface, the light is incident on the outer wall. The light that travels into the liquid is generated and received by the light receiving element without being totally reflected by the reflecting surface, and the amount of light received by the light receiving element is reduced compared to when the liquid is not in contact with the reflecting surface. Thus, the liquid detection optical sensor is characterized by detecting the presence or absence of the liquid in contact with the reflecting surface.

  Such a liquid detection optical sensor allows incident light on the outer peripheral surface to be more than a critical angle so that when the liquid is not in contact with the outer peripheral surface of the outer wall, the incident light is totally reflected with the incident surface as the reflecting surface. Since it is made incident at an incident angle, it can be easily detected whether the liquid is in contact with the reflecting surface on the outer peripheral surface or not depending on whether the incident light is totally reflected or not totally reflected. .

The liquid detection optical sensor according to claim 2 is the liquid detection optical sensor according to claim 1, wherein the amount of light received by the light receiving element when the liquid is not in contact with the reflection surface and the light reception when the liquid is in contact. This is a liquid detection optical sensor in which the thickness of the light shielding plate is set so that the difference from the amount of light received by the element becomes large.
Such a liquid detection sensor clearly detects the presence or absence of liquid because the light-shielding plate having a set thickness has a large difference in the amount of light received by the light receiving element depending on the presence or absence of liquid in contact with the reflecting surface.

The liquid detection optical sensor according to claim 3 is the liquid detection optical sensor according to claim 1 or 2, wherein an optical path between the incident light and the reflected light in the outer wall portion of the outer cylinder is secured, and This is a liquid detection optical sensor in which an opaque tube is inserted in contact with the inner peripheral surface or a light shielding tape is wound around the outer peripheral surface of the outer wall portion.
Such a liquid detection sensor greatly suppresses intrusion of extraneous light into the liquid detection optical sensor, and the amount of light received by the light receiving element is hardly affected by the extraneous light.

A liquid level sensor according to a fourth aspect is a liquid level sensor in which a plurality of units each including the liquid detection optical sensor according to the first aspect as a unit are arranged in a vertical direction inside a transparent outer cylinder that is long in the vertical direction.
In such a liquid level sensor, when the liquid level height fluctuates significantly because multiple units with the liquid detection optical sensor as a unit are arranged in the vertical direction inside a long transparent outer cylinder In addition, the height of the liquid level can be detected by covering the range of the fluctuation.

A liquid level sensor according to a fifth aspect is the liquid level sensor according to the fourth aspect, wherein the liquid level sensor is installed and inserted on a substrate into which a plurality of units can be inserted into the outer cylinder.
Such a liquid level sensor makes it easy to arrange a plurality of units each having the liquid detection optical sensor of claim 1 as a unit in a long outer cylinder.

A liquid leakage sensor according to a sixth aspect is a liquid leakage sensor in which the liquid detection optical sensor according to the first aspect is placed in a posture lying on the bottom surface of the leakage receiving container.
In such a liquid leakage sensor, since the liquid detection optical sensor being used detects the presence or absence of liquid in contact with the reflection surface on the outer peripheral surface of the outer wall portion of the outer cylinder, the liquid leakage sensor leaks to the bottom surface of the receiving container. If there is liquid, it can be detected accurately.

According to the optical sensor for liquid detection according to claim 1, since it detects whether or not the liquid is in contact with the band-shaped reflection surface on the outer peripheral surface of the outer wall portion of the outer cylinder, the incident on the outer peripheral surface The detection of a droplet simply adhering to a point does not cause a false detection that the liquid is in contact with the outer peripheral surface.
According to the optical sensor for liquid detection according to claim 2, since the thickness of the light shielding plate is set so that the difference in the amount of light received by the light receiving element depending on the presence or absence of liquid is large, the presence or absence of liquid is clearly detected. Can do.
According to the liquid detection optical sensor of the third aspect, since the external light is prevented from entering the optical sensor, the presence or absence of the liquid can be detected without being affected by the external light.

According to the liquid level sensor according to the fourth aspect, since the plurality of units having the liquid detection photosensor according to the first aspect as a unit are arranged in the vertical direction inside the long outer cylinder, The height can be accurately detected.
According to the liquid level sensor of the fifth aspect, since the plurality of sensor units are installed on the substrate that can be inserted into the outer cylinder, it is easy to arrange the plurality of sensor units in the long outer cylinder.
According to the liquid leakage sensor of the sixth aspect, since the liquid detection optical sensor being used detects the presence or absence of liquid that contacts the reflecting surface on the outer peripheral surface, even if the liquid leaked into the receiving container is small Leakage can be detected quickly and accurately.

  As described above, an example of a conventional liquid detection optical sensor is totally reflected when the liquid is not in contact with the incident point on the outer peripheral surface of the outer cylinder on which the incident light from the light emitting element is incident. In the case of contact, the presence or absence of liquid is detected by not being totally reflected, but the liquid detection optical sensor of the present invention detects the presence or absence of liquid on an annular incident surface where incident light enters the outer peripheral surface. It can be detected. For this purpose, the optical sensor of the present invention has a light emitting element (for example, a light emitting diode) and a light receiving element (for example, a photo diode) arranged vertically inside a transparent outer cylinder in the vertical direction, and light from the light emitting element directly A disc-shaped light-shielding plate that is in contact with the inner wall surface of the outer wall is disposed between the light-emitting element and the light-receiving element so that the light-receiving element does not receive light. In this case, the light at the peripheral edge is incident in an annular shape into the outer wall of the outer cylinder, and the incident angle is totally reflected with the incident outer peripheral surface as the reflecting surface when no liquid is in contact with the outer peripheral surface of the outer wall. As described above, the angle is equal to or greater than the critical angle θm, and the reflected light is received by the light receiving element.

  In the optical sensor of the present invention as described above, when there is no liquid in contact with the reflection surface, incident light in the outer wall is totally reflected by the reflection surface and received by the light receiving element. If there is a liquid in contact with the liquid, a part of the incident light in the outer wall will almost straightly go into the liquid and not be totally reflected, and the amount of light received by the light receiving element will be reduced to detect the presence or absence of liquid .

  Also, a long outer cylinder with at least the lower end closed is prepared, and the light sensor of the present invention comprising a light emitting element and a light receiving element disposed vertically inside and a light shielding plate disposed between them is used as a unit, and a plurality of By arranging a plurality of units in the vertical direction, for example, a liquid level sensor that can detect the liquid level height even if the liquid level greatly fluctuates in the tank can be produced.

  In addition, by installing the light sensor of the present invention consisting of a light emitting element, a light receiving element, and a light shielding plate disposed between them in an outer cylinder closed at both ends in a posture lying on the bottom of the container, It is possible to produce a liquid leakage sensor that can quickly detect the presence or absence of leakage liquid.

  As the outer cylinder of the optical sensor of the present invention, a transparent cylindrical one, for example, a glass or transparent plastic outer cylinder is used. Moreover, although a light emitting diode is used suitably as a light emitting element, other light emitters may be used. On the other hand, as the light receiving element, a photodiode having wavelength matching with the light emitting diode is preferably used, but other light receiving bodies may be used.

  FIG. 1 is a cutaway perspective view of an optical sensor 1 for liquid detection according to the present invention. This optical sensor 1 is a liquid in contact with an annular incident surface on which incident light is incident on the outer peripheral surface of an outer wall portion 7 of an outer cylinder 2. The light-emitting element 3 and the light-receiving element 4 are vertically opposed to each other inside a vertically-transparent cylindrical outer cylinder 2 with both ends closed, and light from the light-emitting element 3 A light shielding plate 5 is disposed between the light emitting element 3 and the light receiving element 4 so that the light receiving element 4 does not receive light directly. For this reason, the light at the peripheral edge is incident in an annular shape into the outer wall 7 of the outer cylinder 2 among the light emitted from the light emitting element 3 within a certain solid angle, and the incident light has the incident surface as a reflecting surface. Although reflected, the reflected light is received by the light receiving element 4.

  FIG. 2 is a cross-sectional view of the optical sensor 1 of FIG. 1 and conceptually shows the principle of detecting the presence or absence of liquid by the optical sensor 1. Therefore, in FIG. 2, the light at the peripheral edge of the light from the light emitting element 3 is described as light along a cone surface having a solid angle with the light emitting element 3 as a vertex. In the optical sensor 1 shown in FIGS. 2A and 2B, the light emitted from the light emitting element 3 enters the outer wall portion 7 of the outer cylinder 2, and the incident light enters the outer periphery C of the outer wall portion 7 at an incident angle α. Then, the reflected light reflected by the outer periphery C at the same reflection angle α as the incident angle α is received by the light receiving element 4.

  FIG. 2A is a diagram showing a state where the liquid 8 is not in contact with the entire outer periphery C of the outer wall portion 7, and FIG. 2B is a diagram showing a state where the liquid 8 is in contact with the entire outer periphery C. In FIG. 2A, when the outside of the outer wall portion 7 is, for example, air, incident light that is incident on the outer periphery C at an incident angle α that is equal to or greater than the critical angle θm is totally reflected at the same reflection angle α as the incident angle α. Is received.

On the other hand, as shown in FIG. 2B, when, for example, water is in contact with the outer periphery C of the outer wall 7 as the liquid 8, the incident light incident on the outer periphery C of the outer wall 7 at the incident angle α is the outer periphery C. As a result, light L ^* that travels substantially straight into the water without being totally reflected is generated in FIG. That is, when the outside of the outer periphery C is air, the incident light is totally reflected and received by the light receiving element 4, but when the outer periphery C is in contact with water, it is not totally reflected and is received by the light receiving element 4. By reducing the amount, it is possible to detect the presence or absence of water in contact with the outer periphery C of the outer wall portion 7 of the outer cylinder 2 by the optical sensor 1 shown in FIG.

  FIG. 3 shows the relationship between the height of the liquid surface and the rate of change in the amount of light received by the light receiving element when the height of the liquid surface is increased on the outer peripheral surface of the outer wall portion 7 of the optical sensor 1 as described above. . In FIG. 3, the horizontal axis represents the height of the liquid level on the outer peripheral surface of the outer cylinder 2, and the vertical axis represents the rate of change in the amount of light received by the light receiving element 4. Since the amount of received light changes abruptly before and after the liquid surface height of 10 mm, it is recognized that the optical sensor of the present invention accurately detects a 1 mm change in the liquid surface height.

  The conventional optical sensor 11 detects only the presence or absence of water at the light incident point P on the outer peripheral surface of the outer cylinder 2, whereas the optical sensor 1 of the present invention moves to the outer peripheral surface of the outer cylinder 2. Since it is possible to detect the presence or absence of water in contact with the annular incident surface of incident light, it is falsely detected that liquid is present only when water droplets are attached to the incident point on the outer peripheral surface. Never do.

  In FIGS. 1 and 2, the light emitting element 3 is disposed above and the light receiving element 4 is disposed below, but the arrangement may be reversed. 1 and 2, the light emitting element 3 and the light receiving element 4 are arranged to face each other. However, as long as the light quantity on the incident surface and the reflecting surface on the outer peripheral surface of the outer cylinder 2 is secured, the light emitting element 3 and the light receiving element 4 are received. The element 4 does not necessarily have to oppose. Further, although the outer cylinder 2 is set in the vertical direction, the vertical direction is not required as long as the liquid can be detected.

  In the above description, the liquid 8 is described as water. However, a liquid other than water, for example, ethyl alcohol having a large polarity has a refractive index of 1.362, and n-hexane having a small polarity contained in gasoline or the like has a refractive index of 1. 37, both of which have a refractive index close to that of water, the optical sensor 1 can detect the presence or absence of the liquid 8 even if it is alcohol or gasoline.

Furthermore, although the transparent outer cylinder 2 is made of glass, the refractive index of a transparent fluororesin, for example, the abbreviation PFA (copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether) is 1.36, The critical angle θm is calculated to be 48 degrees according to the equation (1), and the outer cylinder 2 made of PFA can be sufficiently used even when the incident angle α is 55 degrees. Since the refractive index of PFA is slightly lower than that of glass, the interval between the light emitting element 3 and the light receiving element 4 is slightly increased when it is necessary to slightly increase the incident angle in relation to the fluctuation factors described later. May be. In addition, if the liquid is not corrosive, other plastic outer cylinders 2 can be used. Incidentally, the refractive index of polycarbonate having a high impact strength is 1.586, and the refractive index of polymethyl methacrylate used in a water tank or the like is 1.492.
<Thickness of light shielding plate and amount of light received by light receiving element>

  FIG. 2 schematically shows the detection principle of the liquid detection optical sensor of the present invention, and the light from the light emitting element 3 has been described as light along a conical surface having a solid angle with the light emitting element 3 as a vertex. As shown in FIG. 2, the light emitted from the light emitting element 3 is light that spreads within a certain solid angle. In practice, as shown in FIG. 4, incident light in the outer wall portion 7 of the outer cylinder 2 is incident. Is incident on the outer peripheral surface of the outer cylinder 2 in a band shape having a constant width, and the incident surface becomes the reflection surface R, and the reflected light is received by the light receiving element 4. FIG. 4 shows a case where the light receiving efficiency is the highest when all the incident light in the outer wall portion 7 is reflected and received by the light receiving element 4.

  However, as is apparent from FIG. 4, the solid angle of light emitted from the light emitting element 3, the inner diameter of the outer cylinder 2, the thickness of the outer wall 7, the solid angle that the light receiving element 4 can receive, the light emitting element 3 and the light receiving element. The distance to the element 4 and the thickness of the light shielding plate 5 are factors that can cause fluctuations in the light receiving efficiency of the light receiving element 4. Depending on the fluctuation factors, all of the incident light is not necessarily received by the light receiving element 4. It does n’t happen. 5 and 6 are diagrams in the case where the thickness of the light shielding plate 5 is varied and all other variation factors are constant. FIG. 5 is a diagram in the case where the thickness of the light shielding plate 5 is thin. Indicates a case where the light shielding plate 5 is thick.

  In FIG. 5, since the thickness of the light shielding plate 5 is thin, the amount of incident light from the light emitting element 3 is large, and the width of the reflection surface R ′ that can be received by the light receiving element 4 is large. When the band-shaped incident surface of the incident light incident on the outer peripheral surface does not coincide with the band-shaped reflecting surface that can be received by the light receiving element 4, and the liquid 8 is not in contact with the outside of the incident surface (reflecting surface) The difference in the amount of light received by the light receiving element 4 between the case where the liquid 8 is in contact with the liquid 8 is reduced. Further, in FIG. 6, since the thickness of the light shielding plate 5 is thick, the width of the band-shaped incident surface R ″ of incident light on the outer peripheral surface of the outer cylinder 2 is reduced, and the incident light quantity itself is reduced.

A transparent plastic tube with an inner diameter of 4.6 mm and a wall thickness of 1 mm is used as the outer cylinder 2, and other fluctuation factors are constant, and the thickness of the light shielding plate 5 is varied between 0.5 and 2 mm. The difference in output voltage due to the difference in the amount of light received by the light receiving element 4 that received the reflected light was measured when the liquid 8 was not in contact with the reflecting surface R of the outer wall 7 and when the liquid 8 was in contact. The measurement results were as shown in Table 1.

As seen in Table 1, the output voltage based on the difference in the amount of light received by the light receiving element 4 between the case where the liquid 8 is not in contact with the reflecting surface R of the outer wall portion 7 and the case where the liquid 8 is in contact is: A large output difference occurred when the thickness of the light shielding plate was 1 mm and 1.5 mm. That is, it is shown that the presence or absence of liquid can be accurately detected by setting the thickness of the light shielding plate 5 to 1 to 1.5 mm. As described above, in the optical sensor 1 of the present invention, the inner diameter of the outer cylinder 2 and the thickness of the outer wall 7, the solid angle of light emitted from the light emitting element 3, the solid angle that the light receiving element 4 can receive, and the light emitting element 3. Since the ability to detect the presence or absence of liquid varies depending on the distance between the light receiving element 4 and the thickness of the light shielding plate 5, etc., not only the thickness of the light shielding plate 5 but also other fluctuation factors are tested. The most appropriate one is selected.
<Eliminating the effects of extraneous light>

In an optical sensor in which the light emitting element 3 and the light receiving element 4 are opposed to each other with the light shielding plate 5 interposed therebetween, an incident optical path from the light emitting element 3 to the outer peripheral surface of the outer wall portion 7, for example, as in the optical sensor 1 shown in FIG. 13 and the reflected light path 14 from the outer peripheral surface to the light receiving element 4 is sufficiently secured, the outer cylinder 2 is transparent except for the portion where the incident light path 13 and the reflected light path 14 are formed. Will not need. Therefore, in order to prevent the influence due to the entry of extraneous light into the optical sensor 1, if the incident optical path 13 and the reflected optical path 14 are secured as in the optical sensor 1s shown in FIG. If an opaque tube that touches the wall surface and blocks intrusion of external light, for example, SUS tube 9, is inserted, the influence of external light can be eliminated. A similar effect can be obtained by, for example, winding a light shielding tape around the outer peripheral surface of the outer cylinder 2 after securing the incident optical path and the reflected optical path.
<Liquid level sensor using the optical sensor for liquid detection of the present invention>

  A liquid detection optical sensor 1 including a light emitting element 3 and a light receiving element 4 opposed to each other and a light shielding plate 5 disposed between the light emitting element 3 and the light receiving element 4 in a transparent long outer cylinder 2 having at least a lower end closed as a unit. By disposing the units in the vertical direction, even when the liquid level varies, a liquid level sensor that can detect the height of the liquid level by covering the variation can be produced.

FIG. 8 is a diagram showing an example of the liquid level sensor. 8A is a cross-sectional view showing the lower end portion of the rod-shaped liquid level sensor 21, and FIG. 8B is a cross-sectional view seen from the [B]-[B] line direction in FIG. 8A. As shown in FIG. 8B, the liquid level sensor 21 has a semi-cylindrical substrate 22 on which a unit U ₁ , U ₂ , U _{3 including} a light emitting element 3, a light shielding plate 5, and a light receiving element 4 is fixed on a plane portion. Is manufactured by being inserted into the outer cylinder 2. The light shielding plate 5 is disposed between the substrate 22 and the semi-cylindrical outer wall portion 23 located above the substrate 22. Therefore, the liquid level sensor 21 does not detect the height of the liquid level in the entire outer peripheral surface of the outer cylinder 2, but the height of the liquid level in the outer peripheral surface of the semicircular outer wall portion 23 in the outer cylinder 2. It is to be detected.

As shown in FIG. 8A and FIG. 8B, the liquid level sensor 21 has a light sensor unit U composed of a light emitting element 3, a light shielding plate 5, and a light receiving element 4 placed in a long outer cylinder 2 in the vertical direction U ₁ , U _2. , but is obtained by 3 unit arrangement of U _3, of course, may be obtained by placing more number of units. Since each optical sensor unit U can detect the presence or absence of liquid, the larger the number of optical sensor units U, the larger the liquid level sensor 21 that covers the fluctuation of the liquid level.
<Leak sensor using the optical sensor for liquid detection of the present invention>

  FIG. 9 shows a liquid detection optical sensor 1 comprising a light emitting element 3, a light shielding plate 5, and a light receiving element 4 in a transparent outer cylinder 2 whose both ends are closed, lying on the bottom surface of a drain pan 32 which is a receptacle for leaking liquid. It is sectional drawing which shows the leak sensor 31 mounted and used with the attitude | position which carried out. As described above, the optical sensor 1 of the present invention detects the presence or absence of liquid that contacts the reflecting surface R of the portion where the light shielding plate 5 of the outer cylinder 2 is disposed. It is possible to accurately detect the leaked liquid discharged without any delay.

It is a fractured perspective view of the optical sensor for liquid detection of the present invention. It is sectional drawing which shows the detection principle by the optical sensor for liquid detection of this invention. It is a figure which shows the change rate of the received light amount in the height of a liquid level, and a light receiving element when the optical sensor for liquid detection of this invention is used. It is sectional drawing which shows the case where the board | plate thickness of a light-shielding plate is appropriate and the total amount of incident light from a light emitting element is reflected by the surface of an outer cylinder, and is received with a light receiving element. It is sectional drawing which shows the relationship between incident light and reflected light when the board | plate thickness of a light shielding plate is thin. It is sectional drawing which shows the relationship between incident light and reflected light in case the plate | board thickness of a light-shielding plate is thick. It is sectional drawing which shows the optical sensor which excluded the influence by external light. It is sectional drawing which shows the lower end part of the liquid level sensor which uses the optical sensor of this invention. It is sectional drawing which shows the liquid leak sensor using the optical sensor of this invention. It is a fractured perspective view of a conventional liquid detection optical sensor. It is sectional drawing which shows the detection principle by the conventional optical sensor for liquid detection.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical sensor for liquid detection of this invention, 2 ... Outer cylinder,
3 ... light emitting element, 4 ... light receiving element,
5 ... shading plate, 7 ... outer wall,
11 ... Conventional optical sensor for liquid detection, 13 ... Light emitting element,
14 ... light receiving element, 21 ... liquid level sensor 31 ... liquid leakage sensor,
C: an outer periphery of a certain height on the outer peripheral surface of the outer cylinder,
P: Incident point of incident light on the outer peripheral surface of the outer peripheral surface of the outer cylinder,
R: Reflecting surface of incident light on the outer peripheral surface of the outer cylinder,

Claims (6)

A light emitting element and a light receiving element are arranged in a height direction of the cylinder in a cylindrical transparent outer cylinder, and the light emitting element is arranged so that light emitted from the light emitting element is not directly received by the light receiving element. A liquid detection optical sensor in which a disc-shaped light shielding plate that is in contact with the inner peripheral surface of the outer wall portion of the outer cylinder is disposed between the light receiving elements,
Among the light emitted from the light emitting element within a certain solid angle, the light at the peripheral edge is incident on the outer wall, but the incident light is not in contact with the outer peripheral surface of the outer wall. The incident light is incident at an angle greater than a critical angle that is totally reflected with the outer peripheral surface as a reflecting surface, and the light receiving element is configured to receive the reflected light.
When the liquid is not in contact with the reflective surface, the light incident on the outer wall is totally reflected by the reflective surface and received by the light receiving element, and when the liquid is in contact with the reflective surface In addition, the light incident on the outer wall portion is caused to travel into the liquid and is received by the light receiving element without being totally reflected by the reflecting surface, as compared with the case where the liquid is not in contact with the reflecting surface, An optical sensor for liquid detection, wherein the presence or absence of liquid in contact with the reflecting surface is detected when the amount of light received by the light receiving element decreases. The optical sensor for liquid detection according to claim 1,
The thickness of the light shielding plate is such that the difference between the amount of light received by the light receiving element when no liquid is in contact with the reflecting surface and the amount of light received by the light receiving element when the liquid is in contact is large. An optical sensor for liquid detection, characterized in that is set. In the optical sensor for liquid detection according to claim 1 or claim 2,
An opaque tube is inserted in contact with the inner peripheral surface of the outer wall portion after securing an optical path between incident light and reflected light in the outer wall portion of the outer cylinder, or a light shielding tape is provided on the outer peripheral surface of the outer wall portion. An optical sensor for liquid detection, characterized in that is wound around.   A liquid level sensor comprising a plurality of units each including the liquid detection optical sensor of claim 1 as a unit inside a transparent cylindrical outer cylinder that is long in the vertical direction. In the liquid level sensor of Claim 4,
The liquid level sensor, wherein the plurality of units are installed and inserted on a substrate that can be inserted into the outer cylinder.   A liquid leakage sensor, wherein the liquid detection optical sensor according to claim 1 is placed in a posture lying on the bottom surface of a receiving container for leakage liquid.