JP2014035321A - Optical fiber application liquid level measurement device - Google Patents

Abstract

An optical fiber applied liquid level device capable of reducing a maintenance burden is provided.
An optical pulse signal is incident on a sensor unit 2 made of an optical fiber laid in the depth direction of the liquid, and a temperature distribution along the laying direction of the sensor unit 2 is calculated based on return light from the sensor unit 2. Measurement is performed, and the liquid level at the position where the sensor unit 2 is laid is detected based on the change point in the temperature distribution. This eliminates the need for a device having a complicated structure such as a conventional liquid level sensor. That is, with respect to temperature sensing, since the measurement principle is that the optical fiber itself detects the temperature, the burden of maintenance can be reduced.
[Selection] Figure 1

Description

  The present invention relates to an optical fiber applied liquid level measuring apparatus for measuring a liquid level.

  In sewers that transport domestic wastewater, sewage, rainwater, etc. (hereinafter referred to as “sewage”) to a sewage treatment plant using pipes buried underground, the sewage can be quickly treated or localized torrential rain, etc. A monitoring system is used to monitor the liquid level in the pipes in order to advise residents to evacuate when there is a possibility of flooding. In this monitoring system, the liquid level in the pipe tube is measured by a liquid level sensor (for example, refer to Patent Document 1). In this liquid level sensor, a detection unit for detecting water pressure is installed in water, and the liquid level is measured from the differential pressure between the water pressure detected by the detection unit and atmospheric pressure.

JP 2008-039787 A

  However, since conventional liquid level sensors are installed in water to detect differential pressure, they are required to have a waterproof structure and water resistance, and therefore a complicated structure must be adopted. Was needed. In addition, since sewer pipes are generally buried underground, it takes time to prepare for maintenance such as workers entering the basement to perform maintenance on the detection part of the liquid level sensor. When the maintenance of the position sensor itself is combined, it requires a considerable amount of work as a whole. Furthermore, since sewers are buried over long distances in sewers, liquid level sensors must be provided at various locations, and the above-described maintenance is required at the respective locations where these liquid level sensors are installed. It was a thing. For this reason, a liquid level sensor capable of reducing the maintenance burden has been desired.

  Then, an object of this invention is to provide the optical fiber applied liquid level measuring apparatus which can reduce the burden of a maintenance.

  In order to solve the problems as described above, an optical fiber applied liquid level measuring device according to the present invention includes an optical fiber laid in the depth direction of the liquid, an optical pulse incident unit that injects an optical pulse into the optical fiber, A measurement unit that measures the temperature distribution along the laying direction of the optical fiber based on the return light from the optical fiber on which the optical pulse is incident, and detects the liquid level based on the temperature distribution measured by the measurement unit And a detecting unit that performs the above operation. The measurement principle is that the optical fiber itself can sense temperature, and the structure is simple and maintenance is not required.

  The above-mentioned optical fiber applied liquid level measuring device further includes a cable laid in the longitudinal direction of the pipe in the pipe through which the liquid flows, and a plurality of optical fibers are provided and connected to the cable at predetermined intervals. The optical pulse incident unit outputs an optical pulse signal to the cable, the measurement unit measures the temperature distribution along the laying direction of each optical fiber based on the return light from the cable, and the detection unit You may make it detect the liquid level of the liquid level in the position which laid the fiber.

  According to the present invention, an optical pulse signal is incident on an optical fiber laid in the depth direction of the liquid, a temperature distribution along the laying direction of the optical fiber is measured based on return light from the optical fiber, and this temperature By detecting the liquid level based on the distribution, a complicated structure as in the conventional liquid level measuring device is not required, and the maintenance burden can be reduced.

FIG. 1 is a diagram schematically showing the configuration of an optical fiber applied liquid level measuring apparatus according to an embodiment of the present invention. 2A is an enlarged view of a main part of FIG. 2B is a cross-sectional view taken along the line II of FIG. 2A. FIG. 3 is a block diagram showing the configuration of the measuring device. FIG. 4 is a diagram for explaining a liquid level detection method. FIG. 5 is a flowchart for explaining a method of extracting change points.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present embodiment, the case where the liquid level in the sewer pipe is measured will be described.

[Configuration of optical fiber applied liquid level measuring device]
As shown in FIG. 1, FIG. 2A, FIG. 2B, the optical fiber applied liquid level measuring device according to the present embodiment includes a cable 1 laid in the length direction of the pipe 100 in the pipe 100 of the sewer, A plurality of sensor units 2 a to 2 d connected to the cable 1 at predetermined intervals, and a measuring device 3 connected to the cable 1 via an optical coupler 11 are provided. The pipe rod 100 is provided with manholes 101a to 101d in the laying direction.

  The cable 1 is made of a known optical fiber, and is laid in the length direction of the pipe rod 100 in the pipe rod 100. One end of the cable 1 is led to the ground from a manhole 101 a that connects the tube 100 and the ground, and is connected to the measuring device 3 via the optical coupler 11. Such a cable 1 is laid in the length direction of the tube 100 via the repeaters 12a to 12d provided for the manholes 101a to 101d. The repeaters 12 a to 12 d are interface devices for connecting the cables 1 and connecting other optical fibers to the cable 1.

  The sensor parts 2a to 2d are made of a known optical fiber sensing cable made of an optical fiber whose outer surface is covered with metal, and are suspended from the repeater 12a with both ends connected to the repeater 12, thereby It is laid in the depth direction of the sewage that circulates in the tub 100. The sensor units 2a to 2d have the same configuration.

  Here, the sensor units 2a to 2d are laid in a loop from the repeater 12a disposed in the manhole 101 to the bottom of the pipe rod 100 as in the sensor unit 2a shown in FIGS. 2A and 2B. . Specifically, the sensor unit 2a extends from one end connected to the repeater 12a to the bottom of the pipe rod 100, folds back at the bottom and extends vertically upward, and the other end is connected to the repeater 12a. ing. Thus, since the sensor part 2a is provided across the inside of the pipe tub 100 in the depth direction, the liquid level of the sewage flowing through the pipe tub 100 comes into contact with the sensor part 2a. Here, the lengths of the sensor units 2a to 2d are stored in the measuring device 3 in advance.

  The measuring device 3 includes a temperature distribution measuring unit 31 that measures the temperature distribution of each of the sensor units 2a to 2d, a storage unit 32 that stores the length of each of the sensor units 2a to 2d, and the sensor units 2a to 2d. The liquid level detection part 33 which detects the liquid level of the tube 100 and the liquid level output part 34 which outputs the detection result by this liquid level detection part 33 are provided.

  Here, the temperature distribution measurement part 31 consists of a well-known optical fiber sensor, and measures the temperature distribution along the laying direction, ie, the depth direction of sewage, about each sensor part 2a-2d. Such a temperature distribution measuring unit 31 includes an optical pulse incident unit 311, an incident light detection unit 312, a return light detection unit 313, and a temperature distribution detection unit 314.

  The light pulse incident part 311 is made of a semiconductor laser or the like and generates a light pulse. The generated light pulse enters the cable 1 through the optical coupler 11 and enters the incident light detection unit 312.

  The incident light detection unit 312 includes the frequency spectrum waveform of the light pulse incident from the light pulse incident unit 311 (hereinafter referred to as “incident light”) and the time when the incident light is incident (hereinafter referred to as “incident time”). .). The detected frequency spectrum waveform and incident time are output to the temperature distribution measuring unit 312.

  The return light detection unit 313 reaches the sensor units 2a to 2d via the optical coupler 11, the cable 1, and the repeaters 12a to 12d, and scatters at each position in the longitudinal direction of the sensor units 2a to 2d. This is a light receiving element that detects the waveform of the frequency spectrum of light returning through the repeaters 12a to 12d, the cable 1, and the optical coupler 11 (hereinafter referred to as “returned light”). The detected frequency spectrum waveform of the return light is output to the temperature distribution detector 314.

  The temperature distribution detection unit 314 compares the frequency spectrum waveforms of the incident light and the return light input from the incident light detection unit 312 or the return light detection unit 313 based on the optical pulse reflection method (Optical Time Domain Reflectometer). It is an arithmetic circuit that detects the temperature distribution of the sensor units 2a to 2d made of optical fibers by analyzing the distance distribution of light intensity. Here, the positions of the sensor units 2a to 2d that detect the temperature distribution are set by matching the delay time from the incident time to the time when the return light is received with the positions of the sensor units 2a to 2d. Therefore, the temperature distribution of each of the sensor units 2a to 2d can be detected by appropriately setting the delay time. In the present embodiment, in the case of the sensor unit 2a, a plurality of measurement points are set from the lowest point L0 to the highest point Ln as shown in FIG. 2B, and the sensor is measured by measuring the temperature at each measurement point. The temperature distribution of the part 2a can be detected. Further, the temperature of the sensor units 2a to 2d is affected by the temperature in the vicinity of the sensor units 2a to 2d. Therefore, measuring the temperature distribution of the sensor units 2a to 2d means measuring the temperature distribution in the pipe rod 100 at the position where the sensor units 2a to 2d are provided.

  The memory | storage part 32 consists of memory devices which memorize | store the length of each sensor part 2a-2d. The length of each of the sensor units 2a to 2d is stored by a user operation input or the like.

  Based on the temperature distribution of each of the sensor units 2 a to 2 d measured by the temperature distribution measurement unit 31 and the length of each of the sensor units 2 a to 2 d stored in the storage unit 32, the liquid level detection unit 33 It is an arithmetic circuit which detects the liquid level in the pipe rod 100 in the position where 2a-2d was laid. Details of the liquid level detection method by the liquid level detection unit 33 will be described later.

  The liquid level output unit 34 is an interface device that outputs the detection result of the liquid level detection unit 33 to the user.

[Method of judging the presence or absence of sewage]
Next, a method for detecting the liquid level by the liquid level detection unit 33 will be described with reference to FIG.

  In general, liquids and gases have different temperatures even when they are close to each other. Therefore, when measuring the temperature distribution at a location where the liquid and gas are continuous, the change point at which the temperature rapidly changes at the interface between the liquid and gas, that is, the liquid level. (See change point β in FIG. 4). Therefore, in the present embodiment, the change point is detected as a liquid level.

  Specifically, first, the liquid level detection unit 33 receives and acquires the temperature distribution of each sensor unit 2 as indicated by the symbol α in FIG. 4 from the temperature distribution measurement unit 31.

  Next, a change point at which the temperature rapidly changes is extracted from the received and acquired temperature distribution, such as a change point β in the temperature distribution α. This change point can be extracted, for example, by taking a difference or differentiation between adjacent points in the temperature distribution. An example of this extraction method will be described later.

  When the change point is extracted, the actual lengths of the sensor units 2a to 2d are acquired from the storage unit 32, and the actual length and temperature distribution are compared to detect the actual water depth position of each point of the temperature distribution. The actual water depth position of the extracted change point is detected. Then, the actual position of the change point is determined as the liquid level. For example, in the case of the temperature distribution α shown in FIG. 4, since the actual position of the change point β is 4 [m], it is determined that the liquid level is 4 [m].

  The liquid level determined in this way is output by the liquid level output unit 34. For example, on the display screen of the measuring device 3, the liquid level of the tube 100 provided with the sensor units 2a to 2d is displayed. Thereby, the user can confirm the liquid level of the sewage in the position in which the sensor part 2 in the tube 100 is provided by looking at the display screen of the monitoring device 2.

  Such determination of the liquid level is performed for each of the sensor units 2a to 2d. As described above, the sensor units 2 a to 2 d are provided at predetermined intervals in the length direction of the tube rod 100. Therefore, since the liquid level detection unit 33 also determines the liquid level of the tube tub 100 at predetermined intervals, the liquid level output unit 34 outputs the liquid levels at a plurality of points of the tube tub 100. . As a result, the user can monitor the liquid level throughout the tube 100.

[Change point extraction method]
Next, an example of a method for extracting change points by the liquid level detector 33 will be described with reference to FIG.

  First, the liquid level detection unit 33 sets La to the lowest point L0, which is the lowest measurement point (step S1). In addition, Lb is set to a measurement point located immediately above La (step S2). Therefore, in the first measurement, Lb becomes the measurement point L1, as can be seen from FIG. 2B.

  When La and Lb are set, the liquid level detection unit 33 calculates β, which is the difference between the temperature of Lb and the temperature of La (step S3), and determines whether β is 0 (step S4).

  When β is 0 (step S4: YES), since the temperatures of La and Lb are equal, Lb is not a liquid surface, so the liquid level detection unit 33 has determined whether or not all the measurement points of the sensor unit 2a have been determined. To confirm whether or not Lb is the uppermost measurement point, that is, the highest point Ln (step S6).

When Lb is not the highest point Ln (step S6: NO), the liquid level detection unit 33 means that there is a measurement point further above the current Lb, so the next measurement point is the liquid level. In order to check whether the current measurement point is Lb or not (step S7), the process returns to step S2.
On the other hand, when Lb is the highest point Ln (step S6: YES), since the temperature of all the measurement points is the same, the air temperature and the water temperature are the same, or the liquid level is 0 or exceeds the upper limit value. This means that the liquid level detection unit 33 outputs the same value as the previous measurement value (step S8).

  If β is not 0 (step S4: NO), the liquid level detection unit 33 determines that the measurement point corresponding to Lb is the liquid level and outputs it because the temperatures of La and Lb are different (step S5). .

  By adopting such an extraction method, the change point can be extracted. Note that the above-described extraction method is an example, and it goes without saying that various methods can be applied. Moreover, in the extraction method mentioned above, since the sensor part 2a is formed in the left-right symmetric circle, the liquid level can be detected by sensing only one side.

  As described above, according to the present embodiment, a light pulse is incident on the sensor unit 2 made of an optical fiber laid in the depth direction of the sewage, and the sensor unit 2 is based on the return light from the sensor unit 2. The temperature distribution along the laying direction is measured, and the sewage liquid level at the position where the sensor unit 2 is laid is detected based on the change point in the temperature distribution, so that a complicated structure like a conventional liquid level sensor is obtained. Therefore, the maintenance burden can be reduced.

  In particular, in the present embodiment, only the sensor units 2a to 2d made of optical fibers are in contact with sewage. Since the sensor units 2a to 2d have a much simpler configuration as compared with the conventional liquid level sensor, maintenance is also easy. Therefore, this embodiment can reduce the manufacturing cost and the maintenance burden as compared with the conventional liquid level sensor.

  In recent years, communication optical fibers and repeaters that connect sewage treatment facilities and the like are laid in sewer pipes. For this reason, it becomes possible to detect the liquid level of the pipe tub simply by connecting the sensor units 2a to 2d in the present embodiment to the repeater and connecting the measuring device 3 to the optical fiber for communication.

  In the present embodiment, the case where the sensor units 2a to 2d, the repeaters 12a to 12d, and the manholes 101a to 101d are provided has been described as an example. Can do.

  In the present embodiment, the case where the present invention is applied to a sewer system has been described as an example. However, it is needless to say that the present invention can be applied to various systems as long as a fluid circulates in a pipe such as a water supply, a river, or a crude oil pipeline.

  Moreover, in this Embodiment, although the case where the sensor parts 2a-2d which consist of optical fibers were suspended from the repeater 12 was demonstrated to the example, if the position of the sensor parts 2a-2d can be pinpointed, the sensor parts 2a-2. The method of laying 2d is not limited to this, and can be set freely as appropriate, for example, laying along the inner periphery of the tube 100.

  Moreover, in this Embodiment, although the case where the several sensor parts 2a-2d were provided in the cable 1 was demonstrated to the example, it is possible to measure the liquid level of a water tank by making the sensor parts 2a-2d into one. Needless to say. In this case, the sensor unit 2 may be directly connected to the measuring device 3 without providing the cable 1 and the repeater 12.

  Furthermore, although the case where the sensor units 2a to 2d are provided at predetermined intervals has been described as an example in the present embodiment, it goes without saying that the interval at which the sensor units 2a to 2d are provided can be set as appropriate.

  The present invention can be applied to various processes in which liquid and gas circulate in pipes such as waterworks and sewers and liquid level measurement in water tanks and the like.

  DESCRIPTION OF SYMBOLS 1 ... Cable, 2a-2d ... Sensor part, 3 ... Measuring device, 11 ... Optical coupler, 12a-12d ... Repeater, 31 ... Temperature distribution measurement part, 32 ... Memory | storage part, 33 ... Liquid level detection part, 34 ... Liquid Position output section, 100 ... tube rod, 101a to 101d ... manhole, 311 ... light pulse incident section, 312 ... incident light detection section, 313 ... return light detection section, 314 ... distribution detection section, L0 to Ln ... measurement points.

Claims (2)

An optical fiber laid in the depth direction of the liquid;
An optical pulse incident part for injecting an optical pulse into the optical fiber;
A measurement unit for measuring a temperature distribution along a direction in which the optical fiber is laid based on return light from the optical fiber on which the optical pulse is incident;
An optical fiber applied liquid level measuring device comprising: a detecting unit that detects a liquid level of the liquid based on the temperature distribution measured by the measuring unit. Further comprising a cable laid in the length direction of the tube in the tube through which the liquid flows,
A plurality of the optical fibers are provided and connected to the cable at predetermined intervals,
The light pulse incident part outputs the light pulse signal to the cable,
The measurement unit measures the temperature distribution along the laying direction of each optical fiber based on the return light from the cable,
The said detection part detects the liquid level of the said liquid in the position which laid each said optical fiber. The optical fiber applied liquid level measuring apparatus of Claim 1 characterized by the above-mentioned.

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