JPH0551089B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a system that monitors the status of multiple points, and in particular, a system that monitors the status of multiple points along the optical fiber. This paper relates to a multi-point monitoring system using optical TDR (time domain reflectometry).

[Prior Art] 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 uses an optical TDR method to install an optical loss changing mechanism at appropriate intervals on the optical fiber to increase or decrease the loss of light transmitted through the optical fiber depending on the condition of the monitored object. 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 central device 1 generates pulsed light according to the pulse signal from the pulse generator 3,
This pulsed light enters the optical fiber 5 via the directional coupler 4. The optical fiber 5 has optical discontinuities, such as an optical connector 6, an optical loss changing mechanism 7, and
There is a terminal end 8, etc., where the light propagating through the optical fiber 5 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 5. These returned lights are extracted by the directional coupler 4, sent to the photoreceiver 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, all of which are shown in the horizontal direction. The time is taken in the vertical direction, and the voltage is taken in the vertical direction. In FIG.
is Fresnel reflection and loss in optical connector 6, 5
3 shows the loss in the optical loss changing mechanism 7, and 54 shows the level change due to Fresnel reflection at the terminal end 8. 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. 5C can be seen on the oscilloscope 10. Further, if the waveform analysis circuit 11 measures the time interval between the point of incidence of the incident pulsed light and the point of loss (for example, T in FIG. From the propagation speed of light inside the optical fiber 5 (x is the distance from the input end of the optical fiber 5 to the point where optical loss occurs), it can be determined where the discontinuity point is located.

Note that the optical loss changing mechanism 7 changes the state of the object or physical quantity to be monitored (for example, whether a relay is ON or OFF).
This method increases or decreases the local optical loss of the optical fibers 5 depending on whether the weight has fallen or not. For example, as shown in FIG. 6, the optical fibers 5 are bundled into a loop. The two pressure receiving plates 61
It is made up of something held between two. In this case, optical loss is increased or decreased depending on whether pressure is applied or not.

[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 points to be monitored and these points are arranged irregularly, optical TDR is used, so it is difficult to detect where optical loss occurs in the optical fiber in terms of signal processing. However, in general, optical fibers are never laid in a completely straight line between the optical TDR device and the optical loss changing mechanism, and between each optical loss changing mechanism. Unless the length of the optical fiber up to the changing mechanism is accurately known, optical
It is not possible to correlate the optical loss generating device of the optical fiber detected by TDR with the position of the optical loss changing mechanism. Therefore, there is a problem in that it takes time and effort to determine from the reflected waveform at which monitoring target point the optical loss has occurred, and the accuracy of the determination decreases.

Furthermore, as mentioned above, it is difficult to match the optical loss occurrence position of the optical fiber detected by optical TDR with the position of the optical loss changing mechanism 7, so when performing on/off measurement, a predetermined phenomenon (on/off Since no optical loss occurs in the reflected waveform (or off phenomenon), it is not possible to determine where the monitoring target point is on the reflected waveform, causing inconvenience in 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 provided at appropriate intervals on the optical fiber and increasing or decreasing the light loss in the coil of the optical fiber according to the state of the physical quantity to be monitored; A position indicator that constantly generates a predetermined loss of light, and an optical loss changing mechanism that uses the waveform change of the return light taken out by the directional coupler as a guide to determine the location of each point where the optical loss changing mechanism is placed. The device is equipped with a signal processing device that determines the position and detects the state of the physical quantity to be monitored at these points.

[Examples] Examples 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 central device, which has the same configuration as the central device in the conventional example shown in FIG. That is, it is composed of a light emitting element 2, a pulse generator 3, a directional coupler 4, an optical receiver 9, an oscilloscope 10, and a waveform analysis circuit 11. Further, an optical fiber 5 is connected to the directional coupler 4, and a plurality of optical loss changing mechanisms 7a to 7c are provided at appropriate intervals along the longitudinal direction of the optical fiber 5. Position indicators 12a to 12a that always indicate a predetermined optical loss are located near each of the optical loss changing mechanisms 7a to 7c.
13c is provided. The optical loss changing mechanisms 7a to 7c are configured to cause optical loss when the respective installation points are in the on state, but not to cause optical loss when the respective installation points are in the off state.

Next, the operation of this embodiment will be explained.

First, pulsed light emitted from the central device 1 enters 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 central 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 to 21c
are the losses in the position indicators 12a to 12c, respectively, and 22a to 22c are the optical loss changing mechanisms 7, respectively.
The losses in a to 7c are shown. The light that has passed through the position indicators 12a to 12c of the optical fiber 5 undergoes a certain amount of loss and its power is weakened, so the return light due to Rayleigh scattering from the optical fiber 5 farther away is always reflected as shown in Figure 2. Step 21a, 2
1b and 21c are possible.

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 indicates 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 between 22a and 22c, so the optical loss changing mechanism 7a
It can be seen that each of the installation points 7c and 7c is on-response. In contrast, 22b in Figure 2
There is no difference in level. Therefore, apparently 2
The position of 2b becomes unclear. However, the position indicator 1 installed near the optical loss changing mechanism 7b
2b causes a step 21b in the returned light, so using this step 21b as a mark, it can be easily determined that 22b does not have a step. That is, it is observed that the optical loss changing mechanism 7b is in an OFF state at its installation point.

By performing multi-point monitoring in this way,
Even if you do not use the method of measuring the delay time T on the time axis of the return light waveform and determining the position X from this delay time T, you can uniquely monitor the position by counting the position indicator. The position of the target point can be specified.

Note that when the portion of the optical fiber 5 that undergoes a loss change in the optical loss change mechanisms 7a to 7c is short, the waveform change of the returned light becomes a step as described above, but when it is long, the waveform change appears as a slope change, Not only on/off information but also analog information can be obtained from these waveform changes.

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

Note that the position indicators 12a to 12c are as follows: Provide a splice with a predetermined loss.

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 caused by the position indicator, the waveform changes 32, 3 caused by each optical loss changing mechanism occur.
3,34 occurs. 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 excellent effects are exhibited.

(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 even if the optical fiber is laid along a non-linear path. 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 more detailed monitoring system.

Furthermore, if the optical fiber is disconnected, the location of the disconnection can be easily detected.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example 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 same system, and Fig. 3 is a waveform diagram showing an example of return light detected by the same system. Waveform diagram of the returned light, 4th
This figure is a block diagram of a conventional multi-point monitoring system, FIG. 5 is a waveform diagram in the system of FIG. 4, and FIG. 6 is a block diagram showing an example of an optical loss changing mechanism. In the figure, 1 is a central 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; 1
0 is an oscilloscope, 11 is a waveform analysis circuit, 12
a to 12c are position indicators.

Claims (1)

[Claims] 1. 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 return light from the optical fiber, and a directional coupler that is installed on the optical fiber at appropriate intervals. an optical loss changing mechanism that increases or decreases the optical loss in the coil of the optical fiber according to the state of the physical quantity to be monitored, and a position provided near the optical loss changing mechanism to constantly generate a predetermined optical loss. Determining 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 return light taken out by the indicator and the directional coupler, and monitoring at these points. A multi-point monitoring system comprising: a signal processing device that detects the state of a target physical quantity.