JPS62157526A - Multipoint monitoring system - Google Patents

Abstract

PURPOSE:To facilitate the estimation of the point to be monitored, by providing a position display unit close to a light loss changing mechanism. CONSTITUTION:Light emitted from a central unit 1 receives a Rayleigh scattering at each point of an optical fiber 5 and the return light thereof is detected with a receiver 9. Light passing through position display units 12a-12c of the optical fiber 5 suffers a specific loss and losses 21a-21c are created on the return light due to the Rayleigh scattering from a farther optical fiber 5. Light passing through a light loss changing mechanisms 7a-7c suffers a loss due to a change in the state, which causes steps 22a-22c in the return light. This condition is shown on a display unit 12 and no change in the step 22b is observed. Thus, the mechanism 7b is determined to be OFF.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a system for monitoring the status of multiple points, and in particular, a system that can collect information at multiple points along an optical fiber using one optical fiber. Optical TDR method (time domain reflectometry)
Concerning a multi-point monitoring system.

[Conventional technology] One of the methods for collecting information from multiple points is the optical TDR method.

FIG. 4 shows a configuration diagram of a conventional multi-point monitoring system using this optical TDR method. This system installs optical loss changing mechanisms at appropriate intervals in the optical fiber to increase or decrease the loss of light transmitted through the optical fiber depending on the condition of the monitored object, and uses the optical TDR method to create an optical loss changing mechanism. The system attempts to detect the status of the monitored object at each point where the system is installed. That is, the light emitting element 2 in the solid device 1 generates pulsed light in response to a pulse signal from the pulse generator 3, and this pulsed light enters the optical fiber 5 via the directional coupler 4. The optical fiber 5 has an optical discontinuity point, for example, an optical connector 6.
- There is an optical loss changing mechanism 7, a terminal end 8, etc., where the light propagating through the optical fiber 5 is reflected and returns to the incident side. Also,
There is also return light due to Rayleigh scattering from the continuous points of the optical fiber 5. These returned lights are extracted by the directional coupler 4, sent to the optical receiver 9, and photoelectrically converted.

Figure 5 (a) shows the output waveform of the pulse generator 3, (b) shows the output waveform of the return light detected by the optical receiver 9, and (c) shows 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), 51 is Fresnel reflection and loss at the input end face of optical fiber 5, 52 is Fresnel reflection and loss at optical connector 6, 53 is loss at optical loss changing mechanism 7, and 54 is Fresnel reflection at terminal end 8. shows the level change due to Since pulsed light is periodically incident from the light emitting element 2, if synchronization is achieved with the period of the pulse generator 3, a stationary waveform as shown in FIG. 5(c) can be seen on the oscilloscope 10. Furthermore, if the waveform analysis circuit 11 measures the time interval (for example, T in FIG. 5(c)) between the point of incidence of the incident pulsed light and the point of loss,
is the propagation speed of light in the optical fiber 5, × is the propagation speed of the optical fiber 5
(distance from the incident end to the point where optical loss occurs),
You can see where the discontinuity point is.

The optical loss changing mechanism 7 changes the optical fiber 5 depending on the state of the object or physical quantity to be monitored (for example, whether a relay is ON, whether a weight has fallen, etc.).
For example, as shown in FIG. 6, it is made up of a loop-shaped bundle of optical fibers 5 held between two pressure-receiving plates 61. In this case, optical loss is increased or decreased depending on whether or not pressure is applied.

[Problems to be Solved by the Invention] The multi-point monitoring system described above has the advantage of being able to perform analog measurement or on/off measurement of physical quantities at a large number of monitoring points using only one optical fiber. are doing.

However, when there are many monitoring points and these points are arranged irregularly, it is time-consuming to determine from the reflected waveform which monitoring point the optical loss has occurred, and the accuracy of the judgment is difficult. There was a problem that the

Furthermore, when performing on/off measurement, there is no optical loss in the reflected waveform unless a predetermined phenomenon (on or off phenomenon) occurs, so it is difficult to determine where the monitoring target point is on the reflected waveform. This results in inconvenience for observation.

[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 provide a multi-point monitoring system that can easily determine the position of a point to be monitored. Our goal is to provide the following.

[Summary of the Invention] In order to achieve the above object, the present invention includes a light source that emits pulsed light, and a directional coupling for transmitting the pulsed light from the light source to an optical fiber and extracting the returned light from the optical fiber. a plurality of optical loss changing mechanisms that are provided at appropriate intervals on the optical fiber and that increase or decrease the loss of light transmitted through the optical fiber depending on the state of the monitored object; The position indicator has a predetermined optical loss, and the position of each point where the optical loss changing mechanism is installed is determined based on the waveform change of the return light taken out by the directional coupler, using the optical loss due to the position indicator as a landmark. It is equipped with a signal processing system that detects the state of the monitored object at these points.

[Example] Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a configuration diagram of a multi-point monitoring system according to an embodiment of the present invention. In the figure, reference numeral 1 denotes a solid device, which has the same configuration as the solid device in the conventional example shown in FIG. That is, light emitting element 2. Pulse generator 3, directional coupler 4, optical receiver 9, oscilloscope 10, and waveform analysis circuit 11
It consists of Further, an optical fiber 5 is connected to the directional coupler 4, and a plurality of optical loss changing mechanisms 7a to 7 are provided at appropriate intervals along the longitudinal direction of the optical fiber 5.
C is provided, and position indicators 12a to 13C are provided on the optical fiber 5 near each of the optical loss changing mechanisms 7a to 7C, respectively, to always indicate a predetermined optical loss. Each of the optical loss changing mechanisms 7a to 7C is configured to cause an optical loss when the installation point thereof is in the on state, and not to cause an optical loss when the installation point is in the off state.

Next, the operation of this embodiment will be explained.

First, the pulsed light emitted from the solid device 1 is transmitted to the optical fiber 5.
and undergoes Rayleigh scattering at each point of the optical fiber 5. The returned light due to this scattering is detected by the optical receiver 9 in the solid device 1. 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 9. In the figure, 21a~
21C are losses in the position indicators 12a to 12c, respectively, and 22a to 22c are optical loss changing mechanisms 78 to 7, respectively.
It shows the loss in C. The light that has passed through the position indicators 12a to 12c of the optical fiber 5 undergoes a predetermined loss and its power weakens.
As shown in FIG. 2, a step 218.21b, 2IC is always formed in the return light due to Rayleigh scattering from the light source.

Further, the light that has passed through the optical loss changing mechanisms 7a to 7C undergoes loss due to the state change, and a step is produced in the returned light, so the presence or absence of the step represents the state of the object or physical quantity that is desired to be monitored.

In the example shown in FIG. 2, there is a step at 22a and 220, so it can be seen that the optical loss changing mechanisms 78 and 7C are in the on state at each installation point. On the other hand, in 22b- of FIG. 2, no step is formed. Therefore, the position of 22b is apparently unclear. However, since a step 21b is generated in the returned light by the position indicator 12b installed near the optical loss changing mechanism 7b, it can be easily determined that there is no step 22b using this step 21b as a landmark. That is, it is observed that the optical loss changing mechanism 7b is in an OFF state at its installation point.

By monitoring multiple points in this way, the delay time T is measured on the time axis of the waveform of the returned light.
Even without using the method of determining the position X from the position X, the position of the monitoring target point can be uniquely specified by counting the number of position indicators.

Note that when the portion of the optical fiber 5 that undergoes the loss change in the optical loss change mechanisms 78 to 7C is short (for example, in the case of a gap), the waveform change of the returned light becomes a step as described above, but when it is long, the waveform change does not occur. This appears as a slope change, and from these waveform changes, not only on/off information but also analog information can be obtained.

Furthermore, once the waveform of the returned light is transformed logarithmically, it is easier to observe. In this way, the optical fiber 5 with uniform optical loss
This is because the waveform of the return light from the portion becomes a linearly inclined waveform.

As the position indicators 12a to 12c, (2) splices having a predetermined loss are provided.

■ Apply external force to the optical fiber 5.

■ Bend the optical fiber 5 to a small diameter This can be realized by methods such as.

Further, in the above embodiment, the position indicator was installed in a one-to-one correspondence with the optical loss changing mechanism, but the present invention is not limited to this, and one position indicator may be installed in correspondence with a plurality of optical loss changing mechanisms. Good too. For example, when one position indicator is associated with three optical loss changing mechanisms, a waveform of the returned light as shown in FIG. 3 is obtained. That is, following the step 31 due to the position indicator, the waveform change 32.3 due to each optical loss changing mechanism
3.34 results. In the example shown in this figure, it can be seen that the three optical loss changing mechanisms are in an OFF state, an ON state, and an ON state at each installation point.

[Effects of the Invention] As explained above, according to the present invention, the following profound effects are achieved.

(1) Since the position indicator is provided close to the optical loss changing mechanism, it is easy to determine the position of the monitoring target point.

Therefore, accurate monitoring can be performed even when there are many points to be monitored.

(2) Therefore, it is possible to increase the number of points to be monitored and realize a 1B denser monitoring system.

Furthermore, when the optical fiber is broken, the location of the break can be easily detected.

[Brief explanation of drawings]

Fig. 1 is a block 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 waveform diagram showing an example of return light detected by the system. Figure 4 is a configuration diagram of a conventional multi-point monitoring system, Figure 5 is a waveform diagram of the system shown in Figure 4,
FIG. 6 is a configuration diagram showing an example of an optical loss changing mechanism. In the figure, 1 is a solid device, 2 is a light emitting element, 3 is a pulse generator, 4 is a directional coupler, 5 is an optical fiber, 7a to 7C are optical loss changing mechanisms, 9 is an optical receiver, and 10 is an oscilloscope. ,
11 is a waveform analysis circuit, and 12a to 12c are position indicators. Patent Applicant: Hitachi Cable Co., Ltd. Representative Patent Attorney Nobuo Kinutani Figure 2 Figure 3

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, a position indicator provided near the optical loss changing mechanism and having a predetermined optical loss, and a directional coupler. It is equipped with a signal processing system that determines the position of each point where the optical loss changing mechanism is installed using the optical loss caused by the position indicator as a mark from the waveform change of the returned light taken out, and detects the state of the monitored object at these points. A multi-point monitoring system characterized by: