JPS61288298A - Multipoint monitoring system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a multi-point monitoring system capable of collecting information at multiple points along an optical fiber using a single optical fiber.

[Conventional technology] A conventional multi-point monitoring system is shown in FIGS. 6 and 7.

FIG. 6 shows the most common system that individually connects information measurement points and solid equipment that are distributed at various locations.

That is, the output of the bus monitoring device @1 at each point is optically transmitted by an optical transmitter 2 through an optical fiber 3, and the transmitted optical signal is converted into an electrical signal by a central optical receiver 4. Input into device 5. The solid device 5 reads the input electrical signals and displays the monitoring results at each point.

FIG. 7 shows an example in which the optical fibers are integrated into one, and the optical output of the optical transmitter 2 of each process monitoring device @1 is coupled to the same optical fiber 3 via the optical branch/combiner 6. It is sent to the solid device 5 through. In this case, some kind of wavelength multiplexing is required to prevent optical signals from colliding.

[Problem to be solved by the invention] However, the above two systems have the following problems.

First, both systems require an optical transmitter 2.

Therefore, a power supply device is essential. Also, when used in high pressure systems (e.g. power plants), the optical transmitter 2
There is also the problem of interference with induction, and furthermore, when used in chemical factories, etc., there is a risk of explosions caused by sparks generated by the power supply. Furthermore, the system shown in FIG. 6 uses a large number of optical fibers 3, which complicates the system and increases costs, while the system shown in FIG. is large, making multipoint monitoring difficult.

[Object of the Invention] This invention was devised to solve the problems of the prior art described above, and an object of the invention is to enable monitoring of multiple points using a single optical fiber, and to An object of the present invention is to provide a multi-point monitoring system capable of monitoring without installing an optical transmitter on the monitoring side.

[Summary of the Invention] In order to achieve the above object, the present invention provides an optical loss changer that increases or decreases the loss of light transmitted through the optical fiber in accordance with the condition to be monitored, which is installed at appropriate intervals in the optical fiber. A mechanism is provided to perform optical TDR (Time [) oa+ai
The present invention attempts to detect the state of the monitored object at each point where the optical loss changing mechanism is installed using the n Reflectmeter (time domain reflection measurement) method.

[Example] Prior to describing the example, the basic principle of the optical TDR method will first be explained with reference to FIGS. 4 and 5.

In FIG. 4, 7 is a light emitting element, and the light emitting element 7 generates pulsed light in response to a pulse signal from a pulse generator 8. Pulsed light from the light emitting element 7 enters the optical fiber 3 via the directional coupler 9.

The optical fiber 3 has optical discontinuities, such as an optical connector 10, a splice 11, and an II end 12, at which the light propagating through the optical fiber 3 is reflected and returns to the incident side.

Further, there is also return light due to Rayleigh scattering from continuous points of the optical fiber 3. These returned lights are extracted by the directional coupler 9, sent to the optical receiver 13, and photoelectrically converted.

Figure 5 (a) shows pulse generation! 8, (b) is the output waveform of the return light detected by the light receiving element 13, (c)
is an enlarged view of the output waveform of the return light in (b),
In both cases, time is measured in the horizontal direction and voltage is measured in the vertical direction.

In FIG. 5(C), 31 is Fresnel reflection and loss at the input end face of optical fiber 3, 32 is Fresnel reflection and loss at optical connector 10, 33 is loss at splice 11, and 34 is a level change due to Fresnel reflection at terminal end 12. shows. Since pulsed light is periodically incident from the light emitting element 7, if synchronization is achieved with the period of the pulse generator 8, a stationary waveform as shown in FIG. 5(C) can be seen on the oscilloscope 14. If the time interval between the point of incidence and the point of loss of the incident pulsed light (for example, T in FIG. 5(c)) is measured, then X=T/2V (V is the propagation speed of light in the optical fiber 3, X is the distance from the input tJJ end of the optical fiber 3 to the point where the optical loss occurs), it can be determined at which position the discontinuity point is located.

Next, FIG. 1 shows the basic configuration of an embodiment of the present invention using the above optical TDR method.

As shown in the figure, the optical fiber 3 is provided with a plurality of optical loss changing mechanisms 17 at appropriate intervals along its longitudinal direction. The solid device 16 has the same configuration as the solid device 16 shown in FIG. 4 described above. The optical loss changing mechanism 17 increases or decreases the local optical loss of the optical fiber 3 depending on the state of the monitored object or physical quantity (for example, whether a relay is ON or OFF, or whether a weight has fallen or not). . The optical loss changing mechanism 17 includes an optical loss increasing mechanism that normally has no loss (or little loss) but increases the loss when the state changes, and conversely, an optical loss increasing mechanism that normally has no loss but increases the loss when the state changes. Then, there is an optical loss reduction mechanism that reduces the loss.

FIG. 3 shows an example of a shell with optical loss change 1111417.

FIG. 3(a) shows a bundle of optical fibers 3 in a loop shape held between pressure receiving plates 18 and 18. FIG. 3(b) shows a mechanism in which optical fibers 3 bundled in a loop are heated with flame or a heater 19 or the like. Third
In Figure (C), an optical fiber 3 is cut to form a gap, and this gap is filled with a filler 20 whose loss changes depending on the temperature. In FIG. 3(d), the optical fiber 3 is broken so that the loss changes depending on the axis deviation d. In FIG. 3(e), the optical fiber 3 is broken so that the loss changes depending on the gap distance l. Finally, in FIG. 3(f), the optical fiber 3 is surrounded by an elastic material 21 that expands and contracts greatly depending on the temperature, and the loss is changed by the expansion and contraction of the elastic material 21. (B) indicates the presence or absence of pressure; (B), (C), and (F) indicate the presence or absence of heat or flame; and (D), (BO) indicates the presence or absence of mechanical changes.

The pulsed light emitted from the solid device 16 enters the optical fiber 3 and undergoes Rayleigh scattering at each point of the optical fiber 3. The returned light due to this scattering is detected by the solid device 16. FIG. 2 shows the waveform (part of it) of the returned light. The horizontal direction represents time, and the vertical direction represents the return light level or the output voltage of the optical receiver 13. If the optical loss changer 4117 is an optical loss increasing mechanism, the light that has passed through the optical loss changer 17 of the optical fiber 3 will undergo a loss due to a change in state and its power will be weakened, so that the optical fiber 3 that is further away than this
As shown in FIG. 2, a step 30 is formed in the return light due to Rayleigh scattering. Whether there is a step 30 (FIG. 2, broken line) or whether there is no step 30 (FIG. 2, real #) represents the state of the object or physical quantity to be monitored. When the portion of the optical fiber 3 that undergoes a loss change in the optical loss change mechanism 17 is short (for example, in the case of a gap), the waveform change of the returned light appears as a step, and when it is long, the waveform change appears as a slope change. Note that not only ON-OFF information but also analog information can be obtained from waveform changes.

Further, depending on how much time has passed since the pulsed light was sent from the solid device 16 when the step 30 occurs, it can be determined at which position of the optical fiber 3 the loss (information) in the optical loss changing mechanism 17 occurs. Note that it is easier to observe the waveform of the returned light once it is logarithmically transformed. This is because if this is done, the waveform of the return light from the portion of the optical fiber 3 where the optical loss is uniform becomes a linearly inclined waveform. In addition, as shown in FIG. 4, the middle mounting @16 is provided with a waveform analysis circuit 15 in addition to the oscillation scope 14. The waveform analysis circuit 15 detects, determines, and displays the condition to be monitored along the optical fiber 3 rather than detecting at what point the loss changes.

[Effects of the Invention] Medium Since the optical TDR method is used to detect the state of the monitored object from changes in the waveform of the return light from the optical fiber, multiple points can be monitored using only one optical fiber.

(2) There is no need to install an optical transmitter on the monitored side;
There is no need to install a power supply for this, making it possible to save energy and prevent explosions, and eliminate detection errors due to induction disturbances in the optical transmitter.

+31 Optical loss change Vs4M as sensor 4 section is a passive device that changes the loss of light transmitted through the optical fiber, which can promote miniaturization and is suitable for monitoring narrow spaces.

(4) If a long wavelength laser diode is used as a light source, monitoring of 10 KmN degrees is possible.

(5) Optical fiber breakage accidents can be detected.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the multi-point monitoring system according to the present invention, FIG. 2 is a waveform diagram showing an example of returned light detected by the system, and FIG. 3 is a light loss according to the present invention. A diagram showing an example of the change mechanism, FIG. 4 is a configuration diagram of a system for explaining the optical TDR method which is the basic principle of the present invention, FIG. 5 is a waveform diagram in the same system, and FIGS. 6 and 7 are FIG. 1 is a configuration diagram of a conventional multipoint monitoring system. In the figure, 1 is a process monitoring device, 2 is an optical transmitter, 3 is an optical fiber, 4 is an optical receiver, 5 is a solid device, 6 is an optical branch/combiner, 7 is a light emitting element, 8 is a pulse generator, 9 is a directional coupler, 10 is a connector, 11 is a splice, 12 is a terminal,
13 is a light receiving element, 14 is an oscilloscope, 15 is a waveform analyzer, 16 is a solid device, 17 is an optical loss changing mechanism, 18
1 is a pressure receiving plate, 19 is a heater, 20 is a filling material, and 21 is an elastic material. Patent Applicant Hitachi Cable Co., Ltd. Representative Patent Attorney Nobuo Kinutani Figure 2 R Nino
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Claims (1)

[Claims] A light source that emits pulsed light, a directional coupler that sends out the pulsed light from the light source to an optical fiber and takes out the return light from the optical fiber, and a plurality of directional couplers that are installed at appropriate intervals on the optical fiber and are used to monitor targets. An optical loss changing mechanism that increases or decreases the loss of light transmitted through an optical fiber depending on the state, and a monitoring target at each point where the optical loss changing mechanism is installed based on changes in the waveform of the return light extracted by a directional coupler. A multi-point monitoring system characterized by comprising: a signal processing system that detects the state of the system.