JP4464502B2 - Liquid level sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid level sensor that detects a position of a liquid level based on whether light projected obliquely from the inside toward a transparent portion provided in the case is reflected in the case or emitted to the outside.
[0002]
[Prior art]
As an example of this type of liquid level sensor, one described in Japanese Patent Application Laid-Open No. 10-300557 is shown in FIG. 10, and is applied to a substrate 4 accommodated in a transparent case 1 extending in the vertical direction. The light part 2A and the light receiving part 2B are arranged symmetrically and directed toward the peripheral wall of the case 1, and light is projected obliquely from the light projecting part 2A toward the peripheral wall of the case 1. Then, when there is no liquid around the case 1, the light from the light projecting unit 2 </ b> A is reflected inside the case 1 and received by the light receiving unit 2 </ b> B, and when there is liquid, the light is emitted outside the case 1. Thus, no light is received by the light receiving unit 2B, and these differences are output as a light receiving signal from the light receiving unit 2B. Then, the circuit on the substrate 4 determines whether or not the magnitude of the received light signal is greater than or equal to a predetermined value, and detects the presence or absence of liquid.
[0003]
[Problems to be solved by the invention]
However, in the above configuration, since the substrate 4 is accommodated in the case 1, there is a problem that the sensor head immersed in the liquid surface becomes large as a whole.
[0004]
Also, for example, there is a case in which an optical fiber is inserted into the case and a circuit board or the like is arranged outside the case, as disclosed in Japanese Utility Model Publication No. 63-168827. In order to make the light receiving portion symmetrical to be directed toward the peripheral wall of the case, the optical fiber must be greatly bent, and eventually the sensor head becomes large in order to secure the bending space.
[0005]
Further, in the conventional liquid level sensor, when the optical path or the electric circuit is disconnected, the light receiving signal is not taken into the detection unit even though there is no liquid around the case 1, and false detection is made that there is liquid. There was also a problem of end up.
[0006]
The present invention has been made in view of the above circumstances, and an object thereof is to provide a liquid level sensor capable of downsizing a sensor head and detecting an abnormality in an optical path and an electric circuit.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a liquid level sensor according to the first aspect of the present invention comprises a sensor head and a detection device connected to the sensor head, and the sensor head has a bottomed bottomed cylindrical shape extending in the vertical direction. And a cylindrical case having at least a part of the side wall as a transparent part, a light projecting and receiving optical fiber inserted inward from the upper end opening of the cylindrical case, and a predetermined vertical direction of the inside of the cylindrical case A fixed block fixed at a position, an optical fiber holding portion provided at the fixed block and holding the ends of both optical fibers facing downward, and provided at the fixed block and disposed below both optical fibers. And the optical fiber holding unit directs the end surface of the light projecting optical fiber to the mirror surface unit and directs the end surface of the light receiving optical fiber obliquely downward on the transparent unit side to project light. mirror from use optical fiber Toward part is projected light, reflected obliquely upward at the mirror surface portion is projected to the transparent portion, when there is no liquid on the outside of the transparent part, is reflected by the transparent portion, a light receiving optical While the light is received by the fiber and there is a liquid outside the transparent part, the structure is discharged outward from the transparent part , or the end face of the optical fiber for receiving light is directed to the mirror part and the light for projection By directing the end face of the fiber obliquely downward on the transparent portion side, when the light projected from the light projecting optical fiber toward the transparent portion side has no liquid outside the transparent portion, Reflected toward the mirror surface part, reflected upward at the mirror surface part and received by the light receiving optical fiber, and when liquid is present outside the transparent part, the liquid is discharged outward from the transparent part. The detection device receives the light received from the end surface on the proximal end side of the light receiving optical fiber. Based on, characterized by the outer side of the transparent portion where the detecting whether there is a liquid.
[0008]
According to a second aspect of the present invention, in the liquid level sensor according to the first aspect, the cylindrical case includes a transparent outer case formed in a cylindrical shape with a bottom end and a metal inner side inserted into the outer case. It is characterized by the fact that a window portion is formed at a predetermined position of the inner case so as to open to the side so that the fixed block can be accommodated in the inner case.
[0009]
According to a third aspect of the present invention, in the liquid level sensor according to the first or second aspect, the fixed block is provided with a recess , and a part of the light projected from the light projecting optical fiber is transparent. Regardless of the presence of liquid on the outside , the light is reflected at a portion other than the interface between the transparent portion and the outside , passes through the recess, and is received by the light receiving optical fiber. When the amount of received light received through the optical fiber for use is smaller than a predetermined amount, it is characterized in that an abnormal state is detected.
[0010]
[Action and effect of the invention]
<Invention of Claim 1>
In the configuration of claim 1, both the light projecting and receiving optical fibers are held downward by a fixing block provided in the cylindrical case, and either one of the end faces of both optical fibers is in the mirror surface portion. Come on. The light projected from the light projecting optical fiber is reflected by the transparent portion and the mirror surface portion and received by the light receiving optical fiber when there is no liquid outside the transparent portion. As described above, since both optical fibers are accommodated in a state along the cylindrical case , it is not necessary to provide a space for bending the optical fiber that is required in the conventional case, and thus the sensor head can be made compact. can do.
[0011]
<Invention of Claim 2>
According to the configuration of the second aspect, even if the transparent outer case is made of synthetic resin or glass or the like, the inner case made of metal inserted into the inner case can increase the strength of the entire cylindrical case. Can do.
[0012]
<Invention of Claim 3>
According to the configuration of claim 3, regardless of the presence or absence of liquid, a part of the light from the light projecting optical fiber is always reflected at a portion other than the interface between the transparent portion and the outside, and passes through the recess. The light is received by a light receiving optical fiber. As a result, when there is no abnormality, the amount of light received by the detection device from the light receiving optical fiber is always greater than or equal to a predetermined amount, and when this is smaller than the predetermined amount, it can be detected that some abnormality has occurred. .
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
FIG. 1 shows a sensor head 10 provided in the liquid level sensor of the present embodiment. The sensor head 10 is provided with a cylindrical case 11 having a bottom end and extending in the vertical direction, and its upper end opening. For example, three pairs of light projecting optical fibers 12 and light receiving optical fibers 13 are inserted.
[0014]
The cylindrical case 11 is formed by inserting a cylindrical inner case 15 inside a cylindrical outer case 14. The outer case 14 is made of the same material as the lower end of a cylindrical resin pipe formed of a transparent synthetic resin having chemical resistance (for example, polytetrafluoroethylene, “Teflon” under the trade name of Dupont). The plug 14B is closed. More specifically, a female screw is formed on the inner surface of the lower end of the resin pipe, while a male screw is formed on the outer periphery of the plug 14B. It is hermetically sealed by welding. In the present embodiment, the peripheral wall of the outer case 14 is entirely transparent and corresponds to the “transparent portion” of the present invention, and this peripheral wall is hereinafter referred to as “transparent portion 14A”.
[0015]
The inner case 15 includes, for example, a window portion 16 that is formed by cutting a metal pipe into a predetermined length and is opened sideways at three predetermined positions along the longitudinal direction. One of the window portions 16 is shown in an enlarged manner in FIG. 2 and has a vertically long oval shape, from which the fixed block 17 is accommodated in the inner case 15.
[0016]
The fixing block 17 is formed by applying a glossy plating to the surface of the synthetic resin. The fixing block 17 includes a protrusion 18 on the front side in the insertion direction into the window portion 16. The protrusion 18 is connected to the window portion 16 of the inner case 15. The inner case 15 is assembled so as not to move in the axial direction by passing through the engagement hole 19 formed so as to penetrate the opposing position. As shown in FIG. 6, the protrusion 18 is cut at a portion protruding outward from the inner case 15 in a state where the fixing block 17 is assembled to the inner case 15.
[0017]
Further, when the fixed block 17 is accommodated in the inner case 15, as shown in FIG. 3, the inner curved surface 20 of the inner block 15 has a rear curved surface 20 located on the inner side of the window 16. The window-side curved surface 21 positioned on the window 16 side is in close contact with the inner surface of the transparent portion 14A of the outer case 14, and the fixed block 17 is held without rattling.
[0018]
As shown in FIG. 2, in the longitudinal direction of the middle part of the window-side curved surface 21 of the fixed block 17, the concave sites 22 are recessed formed. As shown in FIG. 4, the recess 22 has a trapezoidal shape when viewed from the window-side curved surface 21 side, and the upper inner surface 23 of the recess 22 extends obliquely to the upper left in the figure. In the fixed block 17, first and second holding portions 25 and 26 are formed through the portion above the recess 22.
[0019]
The first holding part 25 penetrates the upper part above the recess 22 in the vertical direction, and is open to the upper end surface 17U of the fixed block 17 and the upper inner surface 23 of the recess 22. The optical fiber 12 is inserted from above, and its end surface 12A is fixed with, for example, an adhesive in a state of protruding from the lower opening as shown in FIG.
[0020]
On the other hand, the second holding portion 26 is formed so as to penetrate obliquely downward from the inclined surface 17T formed near the inner curved surface 20 in the upper end portion of the fixed block 17, and the lower end side thereof is formed by the window-side curved surface 21 and the upper inner surface 23. It is located on the ridgeline and is open to each of the surfaces 21 and 23 by a semicircle. Then, the light receiving optical fiber 13 is inserted from above, and the end surface 13A of the light receiving optical fiber 13 is exposed at a position that does not protrude from the window-side curved surface 21, as shown in FIG. Is fixed.
[0021]
Now, the portion of the fixed block 17 located below the recess 22 in FIG. 4 forms a mirror surface portion 28, and the reflection surface 24 constituting the upward inner surface of the recess 22 in the mirror surface portion 28 is shown in FIG. Slightly tilted to the upper right. As a result, the light projected from the end surface 12A of the light projecting optical fiber 12 is reflected by the reflecting surface 24 toward the light receiving optical fiber 13 while being inclined laterally.
[0022]
Further, as shown in FIG. 6, the reflection surface 24 is slightly inclined downward in the figure from the back side of the recess 22 toward the window portion 16 side. As a result, the light projected from the end surface 12A of the light projecting optical fiber 12 to the reflecting surface 24 is projected obliquely toward the transparent portion 14A of the upper outer case 14 as shown in FIGS. Lighted.
[0023]
As shown in FIG. 8, a detection device 34 is connected to the base end portion of each optical fiber 12, 13, and the detection device 34 is projected to the end surface on the base end side of each light projecting optical fiber 12. An optical element 30 is provided facing the light receiving element 31, and a light receiving element 31 is provided facing the end face on the proximal end side of the light receiving optical fiber 13. Reference numeral 32 in the figure denotes a light projecting / receiving control circuit, which sequentially drives each light projecting element 30 at a predetermined period, and outputs the light receiving signal output from each light receiving element 31 in synchronization therewith. A / D conversion is performed by the CPU 33 provided in the circuit 32 for capture. The CPU 33 runs the program shown in FIG. 9 every time each light receiving element 31 takes in a signal.
[0024]
Next, the function and effect of the present embodiment having the above configuration will be described.
First, in order to assemble the sensor head 10 of the present embodiment, three pairs of the light projecting optical fiber 12 and the light receiving optical fiber 13 are inserted into the upper end opening of the inner case 15, and a pair of each from the window portions 16. The light projecting optical fiber 12 and the light receiving optical fiber 13 are pulled out and are held by the holding portions 25 and 26 of the fixed block 17 as described above. Then, the fixing block 17 is pushed into the back of the window portion 16 to engage the projection 18 with the engagement hole 19 and cut the tip of the projection 18. Here, as shown in FIG. 4, optical fibers 12 and 13 held by the lower fixed block 17 are inserted into the side spaces of the upper two fixed blocks 17 among the three fixed blocks 17. . Finally, the inner case 15 is inserted into the outer case 14 and the upper ends of the cases 14 and 15 are caulked to prevent the sensor head 10 from being assembled.
[0025]
And the base end part of each optical fiber 12 and 13 extended from the sensor head 10 is connected to the detection apparatus 34 (refer FIG. 8), and the sensor head 10 of tank T (refer FIG. 1) which stored the chemical | medical agent etc., for example. Set inside.
[0026]
Thus, according to the present embodiment, as shown in FIG. 5, since both optical fibers 12 and 13 are accommodated in a state along the cylindrical case 11, the optical fiber required in the prior art is bent. It is not necessary to provide a space for making the sensor head 10 small, so that the sensor head 10 can be reduced in size. Moreover, since the cylindrical case 11 has a double structure of the outer case 14 and the inner case 15, the fixed block 17 can be attached to the optical fibers 12 and 13 outside the cylindrical case 11. The operation of attaching the to the predetermined position of the cylindrical case 11 is also facilitated. Moreover, even if the outer case 14 is made of synthetic resin, glass, or the like, the strength of the entire cylindrical case 11 can be increased by the metal inner case 15 inserted inside the outer case 14.
[0027]
Next, the operation of the liquid level sensor of this embodiment will be described.
A start switch (not shown) provided in the detection device 34 is turned on. Then, at a predetermined period, light is projected from the end face 12A of each light projecting optical fiber 12 toward the reflecting surface 24, and as shown in FIG. The transparent portion 14A is projected.
[0028]
At this time, if the liquid level is located above the transparent portion 14A that has received light, as shown in FIG. 6, the light projected obliquely to the transparent portion 14A is transmitted between the transparent portion 14A and the outer liquid. Without being reflected at the interface, it is emitted outward.
[0029]
On the other hand, when the liquid level is positioned below the transparent portion 14A that has received light, as shown in FIG. 7, the light projected obliquely to the transparent portion 14A is transmitted between the transparent portion 14A and the outside air. At the interface, the light is reflected toward the inside of the cylindrical case 11 and received by the end face 13A of the light receiving optical fiber 13.
[0030]
By the way, in this embodiment, since both end surfaces of both the light projecting and receiving fibers 12 and 13 face the recess 22 of the fixed block 17, there is no liquid outside the transparent portion 14A. Regardless of the light, a part of the light projected from the light projecting side is always reflected by the part other than the interface between the transparent portion 14A and the outside (see 14D in FIG. 6), and received through the recess 22. A predetermined amount of light is received by the optical fiber 13. As an example, as shown in FIGS. 6 and 7, a part of the reflected light of the light projected from the light projecting optical fiber 12 is on the inner surface 14E of the outer case 14 regardless of the position of the liquid level. The light is reflected in the cylindrical case 11 and received by the light receiving optical fiber 13.
[0031]
Accordingly, when the sensor head 10 of the present embodiment is used, when there is a liquid outside the light receiving portion of the transparent portion 14 </ b> A, a slight predetermined amount of light is detected via the light receiving optical fiber 13. The light receiving element 31 outputs a light receiving signal of a low level (hereinafter referred to as “first reference level V1”). On the other hand, when there is no liquid, the projected light is not emitted to the outside of the outer case 14, but a lot of light is received by the light receiving element 31 through the light receiving optical fiber 13, and a high level (hereinafter referred to as this). (Referred to as “second reference level V2”). Then, the CPU 33 provided in the detection device 34 performs A / D conversion and capture of the light reception signal of the light receiving element 31 in synchronization with the light projection timing of the corresponding light projecting element 30, and executes the program shown in FIG. .
[0032]
In STEP 1 of the program, first, it is determined whether or not the light reception signal V3 received from the light receiving element 31 is lower than the first reference level V1. Here, for example, when a problem on the circuit such as the light emitting element 30 or the light receiving element 31 not starting up normally or a problem on the optical path such as disconnection of the optical fiber occurs, the CPU 33 Receives a light reception signal V3 smaller than the first reference level V1. Then, the process proceeds from STEP 1 to STEP 2, and a warning signal indicating that an abnormality has occurred is output to, for example, the display 35 provided in the detection device 34.
[0033]
When there is no problem on the circuit and the optical path as described above, the light reception signal V3 is equal to or higher than the first reference level V1, so that the process proceeds from STEP1 to STEP3. It is determined whether or not it is smaller than the second reference level V2. Here, when there is liquid outside the transparent portion 14A, the reception signal V3 is the same as the first reference level V1 and smaller than the second reference level V2. The detection result that there is is output to the display 35. On the other hand, when there is no liquid outside the transparent portion 14A, the reception signal V3 becomes the same as the second reference level V2, and the process proceeds from STEP3 to STEP5, and the detection result that there is no liquid is output to the display 35.
[0034]
Thus, according to the liquid level sensor of the present embodiment, a part of the light projected from the light projecting optical fiber 12 is always other than the interface between the transparent portion 14A and the outside regardless of the presence or absence of liquid. Since a predetermined amount of received light is taken into the detection device 34 from the recess 22 through the light receiving optical fiber 13, it is detected that some abnormality has occurred when this is smaller than the predetermined amount. can do.
[0035]
<Other embodiments>
The present invention is not limited to the above-described embodiment. For example, the embodiments described below are also included in the technical scope of the present invention, and various other than the following can be made without departing from the scope of the invention. It can be changed and implemented.
[0036]
(1) In the embodiment described above, the light projecting optical fiber 12 and the light receiving optical fiber 13 may be attached to the holding portions 25 and 26 of the fixed block 17 in the opposite arrangement. Then, the traveling direction of light is opposite to that of the above embodiment, but even in this case, the same effect as that of the above embodiment can be obtained.
[0037]
(2) In the above-described embodiment, whether or not the received light amount is equal to or greater than the predetermined amount is determined by software processing by the CPU 33, but may be determined by a comparison circuit.
[0038]
(3) In the above embodiment, in step 1 of the program, the light receiving signal V3 received from the light receiving element 31 is determined to be lower than the first reference level V1, but instead of this, A first setting value slightly smaller than one reference level V1 may be provided, and it may be configured to determine whether or not the light reception signal V3 is lower than the first setting value.
[0039]
(4) In the above embodiment, in step 3 of the program, it is determined whether or not the light reception signal V3 is smaller than the second reference level V2, but instead, it is larger than the first reference level V1. A second setting value slightly smaller than the second reference level V2 may be provided, and it may be configured to determine whether or not the light reception signal V3 is lower than the second setting value.
[Brief description of the drawings]
1 is a side view showing a sensor head of a liquid level sensor according to an embodiment of the present invention. FIG. 2 is a perspective view showing a part of the sensor head. FIG. 3 is a plan sectional view of the sensor head. FIG. 5 is a perspective view of the fixed block. FIG. 6 is a side sectional view of the sensor head in a state where there is liquid outside the transparent portion. FIG. 7 is a side view of the sensor head in which there is no liquid outside the transparent portion. Side cross-sectional view [FIG. 8] Block diagram of the detection device [FIG. 9] Flow chart showing the operation of the CPU provided in the detection device [FIG. 10] Cross-sectional view of a conventional liquid level sensor
DESCRIPTION OF SYMBOLS 10 ... Sensor head 11 ... Cylindrical case 12 ... Optical fiber for light emission 12A, 13A ... End face 13 ... Optical fiber for light reception 14 ... Outer case 14A ... Transparent part 15 ... inner case 17 ... fixed block 22 ... recess 25 ... first holding part (optical fiber holding part)
26. Second holding part (optical fiber holding part)
28 ... Mirror surface part 34 ... Detection device V1 ... First reference level V2 ... Second reference level

Claims (3)

A sensor head and a detection device connected to the sensor head;
The sensor head is
A cylindrical case having a bottomed bottom end extending in the vertical direction and having at least a part of the side wall as a transparent portion;
An optical fiber for projecting and receiving light inserted inside from the upper end opening of the cylindrical case,
A fixed block fixed at a predetermined position in the vertical direction of the inside of the cylindrical case;
An optical fiber holding portion provided on the fixed block and holding the ends of the two optical fibers facing downward;
Provided on the fixed block, and provided with a mirror surface portion disposed below the two optical fibers,
The optical fiber holding unit directs an end face of the light projecting optical fiber toward the mirror surface part, and directs an end surface of the light receiving optical fiber obliquely downward on the transparent part side, thereby projecting the light projecting light. When the light projected from the optical fiber toward the mirror surface part is reflected obliquely upward at the mirror surface part , is projected onto the transparent part, and when there is no liquid outside the transparent part, A configuration in which the light is reflected by the transparent portion and received by the light receiving optical fiber, and when there is a liquid outside the transparent portion, the liquid is discharged outward from the transparent portion .
Or
The end surface of the light receiving optical fiber is directed to the mirror surface portion, and the end surface of the light projecting optical fiber is directed obliquely downward on the transparent portion side, so that the transparent portion is separated from the light projecting optical fiber. When there is no liquid on the outside of the transparent portion, the light projected toward the side is reflected toward the lower mirror surface portion by the transparent portion, reflected upward at the mirror surface portion, and While being received by the optical fiber for light reception, when there is a liquid outside the transparent portion, it is configured to be discharged outward from the transparent portion ,
The liquid level sensor, wherein the detection device detects whether or not there is a liquid outside the transparent portion based on an amount of received light received from an end surface on a proximal end side of the light receiving optical fiber.   The cylindrical case is composed of a transparent outer case formed in a cylindrical shape with a bottom end and a metal inner case inserted inside the outer case, and a predetermined position of the inner case includes: The liquid level sensor according to claim 1, wherein a window portion is formed to open to a side so that the fixed block can be accommodated in the inner case. The fixing block is provided with a recess, and a part of the light projected from the light projecting optical fiber has a liquid outside the transparent part, regardless of whether there is liquid outside the transparent part. And is reflected at a portion other than the interface with, and is configured to be received by the light receiving optical fiber through the recess .
3. The liquid level sensor according to claim 1, wherein the detection device detects an abnormal state when the amount of light received through the light receiving optical fiber is smaller than a predetermined amount.

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