JP2007278870A - Liquid detection element, liquid detection sensor, liquid detection system, and liquid detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To miniaturize the sensor, to secure real-time properties, to secure sensor reusability, to secure sensor independence, and to secure ease of wiring with respect to a liquid detection system. <P>SOLUTION: A liquid detection element, constituting this liquid detection system, is equipped with optical fiber having an end which causes light, having thereto propagated to propagate in the reverse direction by Fresnel reflection. This liquid detection sensor that uses a plurality of such liquid detection elements is equipped with a connection part to be connected to a measuring instrument, optical couplers disposed in one or a plurality of stages, and an optical fiber for connection used to make adjustment so that the distances from the connection part to the ends of the detection elements differ from each other. Also, this detection sensor can be equipped with an extra length housing part, housing an extra length of the optical fiber for connection. This liquid detection system using this detection sensor is equipped with a measuring instrument, connected to the connection part and is capable of measuring the distribution of reflection amounts or of return losses in the optical fiber. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid detection element, a liquid detection sensor, a liquid detection system, and a liquid detection method using an optical fiber that detects the presence or absence of liquid.

  As a system for detecting liquid, there is a system using a transmission type sensor as shown in FIG. 1 (Patent Document 1). FIG. 1A shows a state where there is no liquid, and FIG. 1B shows a state where there is a liquid. This water detection system includes an optical fiber 901, a water detection sensor 902, and a bending loss measurement device 903. The water detection sensor includes a case 921, a bending jig 922 having a convex portion 9221, an expansion body 923 that absorbs liquid and expands, and a holding jig 924. The bending loss measuring device 903 is a loss measuring device, a pulse tester (OTDR: Optical Time Domain Reflectometer), or the like. The water detection sensor 902 is installed with the optical fiber 901 sandwiched therebetween. When the liquid enters the place where the water detection sensor 902 is installed, the expansion body 923 expands and the optical fiber 901 is bent. Bending loss occurs in the optical fiber due to the bending, and the intrusion of liquid is detected by observing the change in the loss with the bending loss measuring device 903. However, since the expansion body 923 was used, it was difficult to reduce the size. Further, in order for the liquid to enter and the expansion body 923 to expand, a sufficient amount of water and time are required for the expansion body 923 to expand. Therefore, it takes several minutes to several tens of minutes from the ingress of liquid until it can be detected. And once the expansion body 923 expands, it does not contract even if the liquid disappears, so it is necessary to replace the water detection sensor 902 itself. Further, there is a problem that the liquid cannot be detected unless the expanding body 923 can absorb (react).

Since the water detection sensor 902 is a transmission type (a type in which the optical fiber passes through the sensor), the water detection sensor 902 can be attached to one optical fiber in a column as shown in FIG. However, when one water detection sensor 902 operates, the loss of the optical fiber increases, and the state of the water detection sensor 902 installed at a position farther than the water detection sensor 902 may not be measured.
Further, in order to identify which water detection sensor 902 has increased in loss, the interval between the water detection sensors 902 needs to be sufficiently wider than the measurement accuracy (distance resolution) of the bending loss measurement device 903. For example, when the OTDR is measured using a pulse having a pulse width of 10 nsec, the distance resolution is 1 m. Therefore, even if the place where the two water detection sensors 902 are installed is close, it is necessary to provide the extra length 911 so that the distance between the water detection sensors 902 can be secured about 5 m. FIG. 3 shows a state of wiring when a conventional water detection sensor is used. This system includes an optical fiber 901-i (i = 1 to 3), a water detection sensor 902-j (j = 1 to 6), a bending loss measuring device 903, and a surplus length 911-k (k = 1 to 5). It is configured. It is assumed that the water detection sensors 902-1, 902-2, and 902-3 are installed at locations close to each other, and the water detection sensors 902-4, 902-5, and 902-6 are installed at locations close to each other. At the time of wiring, it is first installed in a place where the water detection sensor 902-j is to be placed (a place where liquid intrusion is to be confirmed). . However, since a place for fixing the extra length 911-k must be secured near the water detection sensor 902-j and the optical fiber must be handled carefully, wiring work is complicated.
JP 2004-45220 A

  The object of the present invention is to reduce the size of the liquid detection element in the liquid detection system, to be able to detect even a small amount of liquid, to shorten the time until the liquid can be detected after entering the liquid (ensuring real-time properties), the liquid To enable the sensor to be reused when it runs out (ensures reusability), to enable detection independent of the type of liquid, even if one liquid detection element operates, other liquid detection elements System that does not affect the measurement of the liquid (ensuring the independence of the liquid detection element) and ensuring the ease of wiring.

The liquid detection element constituting the liquid detection system of the present invention includes an optical fiber having a tip that propagates the propagated light in the reverse direction by Fresnel reflection. Further, the optical fiber and the tip of the optical fiber are reinforced so that bending loss of a certain degree or more does not occur even when a lateral pressure is applied.
A liquid detection sensor using a plurality of the liquid detection elements includes a connection part for connecting to a measuring instrument, an optical coupler arranged in one or more stages, and from the connection part to the tip of each liquid detection element. A connecting optical fiber for adjusting the distance to be different is provided. Moreover, you may provide the surplus length accommodating part which accommodates the surplus length of the said optical fiber for a connection.

  A liquid detection system using the liquid detection sensor includes a measuring device connected to the connection portion and capable of measuring a distribution of reflection amount or reflection attenuation amount in an optical fiber.

  In the liquid detection element of the present invention, since the expansion body is not used, the size of the sensor can be reduced. Since the structure is simple, reinforcement is easy. Since the reflection amount (or reflection attenuation amount) changes at the moment when the refractive index of the medium in contact with the tip changes, it responds to a small amount of liquid and has a high real-time property. When the liquid is exhausted, the refractive index of the medium in contact with the tip part returns to the original state (air becomes air) and can be reused. Any liquid can be detected because its refractive index is higher than air. Further, light that propagates to each sensor, is reflected, and returns to the measuring instrument does not pass through other sensors. Therefore, even if one sensor operates, it does not affect the measurement of other sensors, so that independence can be ensured. Further, the extra length of the optical fiber for securing the distance between the sensors can be concentrated around the optical coupler. Therefore, it is not necessary to process the extra length of the optical fiber near the sensor, and wiring is easy.

Hereinafter, embodiments of the present invention will be described. In addition, in order to avoid duplication of description, the same number is given to the component which has the same function, and description is abbreviate | omitted.
[First Embodiment]
FIG. 4 shows a simplest system configuration example of the liquid detection system of the present invention. This liquid detection system includes a reflection amount measuring device 110 or a reflection loss measuring device 110 ′, an optical fiber 120, and a liquid detection element 130. The measuring device of this system may be the reflection amount measuring device 110 or the reflection loss measuring device 110 ′. This is because the strength of the Fresnel reflection at the liquid sensing element 130 can be determined by measuring the amount of reflection or the amount of return loss. A typical example of the measuring instrument is a pulse tester (OTDR), but it is not necessary to be limited to this. When only one liquid sensing element 130 is used, the reflection amount measuring device 110 or the reflection loss measuring device 110 ′ may simply know the reflection intensity. Further, when two or more liquid detection elements 130 are connected, the reflection amount measuring device 110 or the reflection attenuation amount measuring device 110 ′ is satisfied that the reflection intensity can be recognized and each liquid detection element can be discriminated. That's fine.

The scattered light intensity distribution in FIG. 4 shows the state of the backscattered light of the optical fiber 120 and the Fresnel reflected light of the liquid detection element 130 measured by OTDR. The reflectivity r of Fresnel reflection in the case of normal incidence is r = (n ₁ −n ₂ ) / (n ₁ + n ₂ ). Here, n ₁ is the effective refractive index (about 1.5) of the optical fiber 120, and n ₂ is the refractive index of the medium (air or liquid) in contact with the tip of the optical fiber 120. In a state where there is no liquid (air state), n ₂ = 1.0 and r≈0.2. For example, when water enters, n ₂ ≈1.3 and r≈0.07. When the liquid enters in this way, the reflectance r at the liquid detection unit 133 decreases. Therefore, a large difference appears between the Fresnel reflected light without the liquid (FIG. 4A) and the Fresnel reflected light with the liquid (FIG. 4B). By measuring this difference with the reflection amount measuring device 110 or the reflection attenuation amount measuring device 110 ′, the presence or absence of liquid can be determined.

  A configuration example of the liquid detection element 130 is shown in FIG. The light propagating through the optical fiber 120 is Fresnel-reflected by the liquid detection unit 133 at the tip of the optical fiber 120 and propagates in the opposite direction. The liquid detection unit 133 (tip of the optical fiber 120) is cut or polished so that the normal of the cut surface of the tip of the optical fiber and the light propagation direction substantially coincide so that the reflected light propagates in the opposite direction. Has been. In this example, the optical fiber 120 and the liquid detection unit 133 in the liquid detection element 130 are reinforced by a protective metal outer cylinder 131 and a ferrule 132. Further, the optical fiber 120 outside the liquid sensing element 130 is reinforced by coding. The degree of reinforcement depends on the environment where the liquid sensing element 130 is installed. In particular, when a side pressure is applied to the optical fiber cord 121 or the liquid detection element 130, the optical fiber 120 may be bent and a loss may occur. When such a loss occurs, the intensity of the Fresnel reflected light measured by the reflection amount measuring device 110 or the reflection loss measuring device 110 'becomes small, as if the liquid has entered. Therefore, in the reinforcement design of the optical fiber cord 121 and the liquid detection element 130, it is necessary to determine a side pressure that may be applied in advance, and to prevent bending loss that would be mistaken for liquid intrusion under the side pressure. On the other hand, in an environment where almost no external force is applied, it is not necessary to reinforce the optical fiber 120, and the optical fiber 120 may be left as it is. With this configuration, the liquid detection element can be reduced in size. Further, since the reflection amount (or reflection attenuation amount) changes at the moment when the refractive index of the medium in contact with the tip changes, it responds to a small amount of liquid and has high real-time properties. Furthermore, when the liquid runs out, the refractive index of the medium in contact with the tip part returns (becomes air) and can be used as it is. In addition, when the tip is contaminated with liquid, cleaning is necessary, but it is not necessary to replace the liquid detection element, so that reuse is possible. And any liquid can be detected because its refractive index is higher than air.

[Second Embodiment]
FIG. 6 shows a system configuration example when a plurality of liquid detection elements are attached. The liquid detection sensors of this system include optical fibers 120 and 124-a (a = 1 to 4), extra lengths 121-b (b = 1 to 4) of optical fibers, and liquid detection elements 130-c (c = 1 to 4). 4), an optical coupler 140-d (d = 1 to 4), and a connection unit 160. The optical coupler 140-d is a component for distributing measurement light to each liquid detection element 130. For example, the optical coupler 140-1 may be an optical coupler that distributes 2% light to the liquid detection element 130-1 side and distributes 98% light to the next optical coupler 140-2 side. If such an optical coupler is used, several tens of liquid sensing elements 130-c can be attached to one optical fiber. The light distribution ratio can be changed in consideration of the number of liquid sensing elements 130-c to be used. The connection unit 160 is a component for connecting the reflection amount measuring device 110 or the reflection attenuation amount measuring device 110 ′ and the liquid detection sensor, and is an optical connector such as an SC connector.

  The light generated by the reflection amount measuring device 110 or the return loss measuring device 110 ′ for measurement is distributed by the optical coupler 140-1, and one of the light propagates to the liquid sensing element 130-1 via the optical fiber 124-1. Is done. The other light is input to the next optical coupler 140-2 via the extra length 121-1 of the optical fiber. The optical coupler 140-2 also distributes light, and the distributed light is input to the liquid detection element 130-2 and the optical coupler 140-3. In this way, the light distribution is repeated.

  The light input to the liquid detection element 130-4 is Fresnel-reflected at the tip of the liquid detection element 130-4 and returns to the optical coupler 140-4. In the optical coupler 140-4, the light returned from the extra length 121-4 side and the light returned from the liquid detection element 130-4 are added and propagated in the direction of the optical coupler 140-3. Similarly, light reflected by Fresnel at the tips of the liquid detection elements 130-3, 130-2, and 130-1 is added by the optical couplers 140-3, 140-2, and 140-1, and the direction of the connection portion 160 is also added. To propagate. The light generated by the reflection amount measuring device 110 or the reflection attenuation measuring device 110 ′ in this manner returns to the reflection amount measuring device 110 or the reflection attenuation measuring device 110 ′.

  When OTDR is used as the reflection amount measuring device 110 or the return loss measuring device 110 ′, the Fresnel reflected light of each liquid detection element 130-c is located at a position corresponding to the distance between the OTDR and each liquid detection element 130-c. Is detected. Here, as described above, when the OTDR is used to measure a pulse having a pulse width of 10 nsec, the distance resolution is 1 m. Therefore, the extra length 121-b is adjusted so that the length of the optical fiber between the OTDR and each liquid sensing element 130-c differs by at least about 5 m. If the lengths of the optical fibers are the same, Fresnel reflected light from the two liquid detection elements overlap, and it becomes impossible to know which liquid detection element has been submerged.

With the system configuration as shown in FIG. 6, neither the light input to the liquid detection element 130-c nor the light reflected by the liquid detection element 130-c passes through the other liquid detection element 130-c. Therefore, even if one liquid sensing element 130-c is submerged, it does not affect the measurement of Fresnel reflection at the other liquid sensing element 130-c. Therefore, in this system, independence between the liquid detection elements can be ensured.
6 that the extra length 121 is not in the vicinity of the liquid detection element 130. Therefore, it is not necessary to fix the extra length of the optical fiber at the place where the liquid detection element 130-c is installed, and the wiring work can be facilitated.

[Modification 1]
FIG. 7 shows a configuration example of a liquid detection system in which the extra length is provided in the optical fiber that connects the liquid detection element. The difference from FIG. 6 is that the distance (the length of the optical fiber) between the reflection amount measuring device 110 or the reflection loss measuring device 110 ′ and each liquid sensing element 130-c (c = 1 to 4) is adjusted. This is because the extra length 123-e (e = 1 to 4) of the optical fiber is provided between the optical coupler 140-d (d = 1 to 4) and the liquid detection element 130-c. Also in this case, the extra length 123-e can be fixed in the vicinity of the optical coupler 140-d, so that the wiring work is easy. Moreover, the same effect as 2nd Embodiment is acquired also about another effect.

[Modification 2]
FIG. 8 shows a configuration example of a liquid detection system in which the extra length is provided to both the optical fiber connecting the optical couplers and the optical fiber connecting the liquid detection element. The only difference from FIG. 6 and FIG. 7 is the place where the extra length is given. This configuration can be said to be a general configuration example including the second embodiment and Modification 1 in that any optical fiber may have a surplus length. Also in this case, the extra length 121-b (b = 1 to 4) and the extra length 123-e (e = 1 to 4) can be fixed in the vicinity of the optical coupler 140-d, so that the wiring work is easy. is there. Moreover, the same effect as 2nd Embodiment is acquired also about another effect.

[Modification 3]
FIG. 9 shows a configuration example of the liquid detection system in the case where a 3 dB coupler is used as the optical coupler. The 3 dB coupler (optical coupler 141-f (f = 1 to 3)) distributes light evenly in two directions. For example, the optical coupler 141-1 distributes ½ of the light from the reflection amount measuring device 110 or the reflection attenuation amount measuring device 110 ′ to the optical coupler 141-2, and distributes the other ½ to the optical coupler 141-3. Allocate to The optical coupler 141-1 returns light from the optical coupler 141-2 (the sum of reflected light from the liquid detection element 130-1 and reflected light from the liquid detection element 130-2) and the optical coupler 141-3. The return light (the sum of the reflected light from the liquid detection element 130-3 and the reflected light from the liquid detection element 130-4) is synthesized. Further, since the extra length 121-b can be secured at a location away from the liquid detection element 130-c, wiring work is also easy. Therefore, the same effect as the second embodiment can be obtained. In this modification, the configuration is shown in which three 3 dB couplers are used and light is divided into four equal parts, but the branching ratio of the couplers may be different, and the number of couplers may be freely changed.

[Modification 4]
FIG. 10 shows a configuration example of a liquid detection system in which a storage unit is added to the configuration of FIG. The only difference between FIG. 10 and FIG. 8 is that the storage unit 150 is added. FIG. 11 shows a configuration example of a liquid detection system in which a storage unit is added to the configuration of FIG. The only difference between FIG. 11 and FIG. 9 is that the storage unit 150 is added. FIG. 12 shows a configuration example of a liquid detection system in which a storage unit is provided for each optical coupler. The configuration as shown in FIG. 12 can be used when it is desired to disperse the optical coupler. In this example, the optical couplers are dispersed one by one, but may be dispersed two by two. In that case, two optical couplers are accommodated in each accommodating portion.

  As an example of the storage units 150, 150-1, and 150-2, a cabinet or the like generally used for optical fiber communication in a building can be considered. Such a cabinet is originally intended to accommodate optical components and connecting portions and the extra length of the optical fiber. Therefore, if the optical coupler and the extra length are stored in this cabinet, wiring can be efficiently performed. This is an effect obtained because the extra length can be arranged in the vicinity of the optical coupler by the structure and system configuration of the liquid detection element of the present invention.

[Third Embodiment]
FIG. 13 shows the difference between the conventional wiring of FIG. 3 and the wiring using the present invention. 3 and 13 illustrate a case where three liquid detection elements 130-c or three water detection sensors 902-j are installed close to each other.

  An example of such wiring is a river water level detection system. For example, a liquid detector is installed at each of the water depth level to be warned, the water depth level to be warned, and the water level level to be evacuated, such as a pillar indicating the water depth installed in the river (may be a bridge or a dike wall). Install. In this way, it is possible to arrange three liquid detection elements 130-c on one pillar and observe the water level with several pillars from upstream to downstream. In the conventional method (FIG. 3), since the surplus length 911-k is in the vicinity of the water detection sensor 902-j, the surplus length must be gathered around the pillar and fixed. This is not only difficult for wiring work but also a problem from the viewpoint of protection (failure prevention) of optical fibers. However, according to the method of the present invention, there is no extra length in the vicinity of the liquid detection element 130-c, and all are stored in the storage unit 150. Also from this figure, it can be seen that wiring work is facilitated by the present invention. Moreover, when using for such a use, it is important from the surface of maintenance that the liquid detection element is small and can be reused.

  Further, in the conventional method, when one water detection sensor is immersed in water, there is a possibility that the water detection sensor beyond that cannot be identified. Therefore, it cannot be used for a system that assumes that a plurality of water detection sensors are immersed in water, such as a river water level detection system. In the case of the liquid detection system of the present invention, since the system can be designed on the assumption that a plurality of liquid detection elements are in contact with the liquid, the range of applications can be expanded.

[Experimental example]
FIG. 14 shows a configuration of an experimental example of the liquid detection system of the present invention. In this experiment, the OTDR 111 was used as the reflection amount measuring device 110 or the reflection loss measuring device 110 ′. The pulse width of OTDR was measured at 10 nsec (distance resolution 1 m). The extra length for adjusting the distance between the OTDR 111 and each liquid sensing element 130-c (c = 1 to 6) (the length of the optical fiber therebetween) is between the optical couplers 140-d (d = 1 to 4). I gave it to. Then, the difference in distance between the liquid detection elements is adjusted to 20 m. In addition, on the assumption that the three liquid detection elements are arranged at close positions, three optical couplers were stored in the storage units 150-1 and 150-2, respectively. The light distribution of the optical coupler 140-d was 98% and 2%.

  FIG. 15 shows a measurement waveform at OTDR111. (A) is a waveform in the state where all the liquid detection elements 130-c are not in contact with the liquid. (B) is a waveform when the liquid detection elements 130-4, 130-5, and 130-6 are immersed in water. The waveform numbers in FIG. 15 correspond to the numbers of the components in FIG. The vertical axis indicates the intensity of the reflected light, the convex portion indicates the Fresnel reflection at the connection portion 160, the liquid detection element 130-c, the connection point 161, and the cutting point 170, and the other portions indicate the light. The intensity of backscattered light from the fiber 120 is shown. The horizontal axis indicates the distance, and the left side of the waveform is closer to the OTDR 111 and the right side is farther from the OTDR 111. The interval between the liquid detection elements 130-1 and 130-2 corresponds to 20 m. On the right side of the cut point 170 is noise.

As can be seen from FIGS. 15A and 15B, the only difference between the two waveforms is the intensity of Fresnel reflection at the liquid sensing elements 130-4, 130-5, and 130-6, and the other parts of the waveform. Has not changed. That is, it shows that the measurement accuracy of each liquid detection element does not depend on the state of other liquid detection elements.
In the above-described system, only the reflection amount measuring device 110 or the return loss measuring device 110 ′ is illustrated, but it is also possible to perform measurement using a computer by connecting the measuring device directly or via a network. is there. If a computer is used in this way, various measurements according to the purpose of use, such as periodic measurement, automatic measurement, and real-time measurement, can be performed.

The figure which shows the structure of the conventional water detection sensor. The figure which shows the structure of the conventional water detection system. The figure which shows the mode of wiring at the time of using the conventional water detection sensor. The figure which shows the simplest system structural example of the liquid detection system of this invention. The figure which shows the structural example of the liquid detection element. The figure which shows the system structural example at the time of attaching a some liquid detection element. The figure which shows the structural example of the liquid detection system at the time of giving the extra length to the optical fiber which connects a liquid detection element. The figure which shows the structural example of the liquid detection system at the time of giving surplus length to both the optical fiber which connects between optical couplers, and the optical fiber which connects a liquid detection element. The figure which shows the structural example of the liquid detection system at the time of using a 3 dB coupler as an optical coupler. The figure which shows the structural example of the liquid detection system which added the accommodating part to the structure of FIG. The figure which shows the structural example of the liquid detection system which added the accommodating part to the structure of FIG. The figure which shows the structural example of the liquid detection system which provided the accommodating part for every optical coupler. The figure which shows the difference between the conventional wiring of FIG. 3, and the wiring using this invention. The figure which shows the structure of the experiment example of the liquid detection system of this invention. The figure which shows the measurement waveform in OTDR111.

Claims (9)

A liquid detection element using an optical fiber for determining the presence or absence of liquid,
The liquid detection element, wherein the optical fiber has a tip for propagating light propagating through the optical fiber in the reverse direction by Fresnel reflection. The liquid sensing element according to claim 1,
The liquid detection element, wherein the optical fiber and the tip of the optical fiber are reinforced so that a bending loss of a predetermined value or more does not occur even when a predetermined lateral pressure is applied. A liquid detection sensor for determining the presence or absence of liquid,
A connection for connecting to the measuring instrument;
Optical couplers arranged in one or more stages;
A liquid sensing element having an optical fiber that propagates the light branched by the optical coupler that has propagated in the reverse direction by Fresnel reflection at the tip;
An optical fiber for connection between the connection part and the optical coupler, between the optical couplers, and between the optical coupler and the liquid detection element, adjusted to have different distances from the connection part to the tip of each liquid detection element A liquid detection sensor comprising: The liquid detection sensor according to claim 3,
A liquid detection sensor comprising a surplus length storage portion for storing a surplus length of the connection optical fiber. A liquid detection system for determining the presence or absence of liquid,
A measuring instrument capable of measuring the distribution of reflection or return loss in an optical fiber;
A liquid sensing element having an optical fiber that propagates the light branched by the optical coupler that has propagated in the reverse direction by Fresnel reflection at the tip;
A liquid detection system comprising: an optical fiber connecting the measuring device and the liquid detection element. A liquid detection system for determining the presence or absence of liquid,
A measuring instrument capable of measuring the distribution of reflection or return loss in an optical fiber;
Optical couplers arranged in one or more stages;
A liquid sensing element having an optical fiber that propagates the light branched by the optical coupler that has propagated in the reverse direction by Fresnel reflection at the tip;
Light for connection between the measuring instrument and the optical coupler, between the optical couplers, and between the optical coupler and the liquid detecting element, adjusted so that the distance from the measuring instrument to the tip of each liquid detecting element is different. A liquid detection system comprising a fiber. The liquid detection system according to claim 6,
A liquid detection system comprising a surplus length storage unit for storing a surplus length of the connecting optical fiber. A liquid detection method for determining the presence or absence of liquid,
Connect an optical coupler to one or more stages directly or via an optical fiber to a measuring instrument that can measure the distribution of reflection or return loss in the optical fiber.
A liquid sensing element having an optical fiber that propagates the propagated light in the reverse direction by Fresnel reflection at the tip is connected so that the light branched by the optical coupler can propagate,
Adjust the length of the optical fiber for connection between the optical coupler and between the optical coupler and the liquid detection element so that the distance from the measuring device to the tip of each liquid detection element is different,
A liquid detection method, wherein the presence or absence of liquid is confirmed by measuring the reflection amount or reflection attenuation amount of Fresnel reflection of each liquid detection element by the measuring device. The liquid detection method according to claim 8,
After adjusting the length of the connecting optical fiber,
A surplus length of the optical fiber for connection is stored in a surplus length storage section.

Images