JPH1151784A - Optical fiber-type multipoint physical-quantity detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber-type multipoint physical-quantity detector in which an erroneous judgment is not generated even when the output of a light source is lowered or even when an optical fiber is disconnected. SOLUTION: In an optical fiber-type multipoint physical-quantity detector, the shape of an optical fiber system which is composed of an optical fiber 1, of optical branching filters 311 to 313 and of optical physical-quantity sensors 2a to 2n or of reflectors 411 to 414, 41a to 41n is a ladder shape or a comb shape, optical pulses are incident on the optical fiber 1 from a light source 4, and the optical pulses which are passed through the optical fiber system are received by a photodetector 5 so as to be signal-processed by a signal processor 9. In the optical fiber-type multipoint physical-quantity detecting apparatus, the existence of the optical pulses is detected in the optical fiber system by using a near-end reference 6a, a far-end reference 6b, a high-level reference 7a and a low-level reference 7b. Thereby, an erroneous judgment is not generated even when the output of the light source 4 is lowered or even when the optical fiber 4 is disconnected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical fiber type multipoint type physical quantity detection device.

[0002]

2. Description of the Related Art There is an optical fiber type multipoint type physical quantity detection apparatus as an apparatus for collectively measuring physical quantities such as temperature, humidity, liquid leakage and the like and distribution thereof using an optical fiber.

FIG. 9 is a block diagram of a conventional optical fiber type multi-point physical quantity detecting device.

The device shown in FIG. 1 is provided with optical splitters 31a-31 at corresponding positions of two parallel optical fibers 1a and 1b.
n, 32a to 32n, respectively, and each optical branching device 31a
Between the optical physical quantity sensors 2a to 31n and 32a to 32n.
2n, an optical pulse generator is connected to one end of the optical fiber 1a, a light receiver is connected to one end of the optical fiber 1b, a signal processing device is connected to the light receiver, and an optical pulse generator 4 and a light receiver 5 are connected. Between the optical splitters 310 and 320 closest to the optical fiber 6a and between the optical splitters 31n and 32n farthest from the optical fiber 6a,
6b.

In an apparatus having such an optical fiber system, an optical pulse sent from the optical pulse generator 4 to one optical fiber 1a is split by optical splitters 31a to 31n, respectively, and each optical physical quantity sensor 2a 2n or the optical splitters 32a to 32n through the optical fibers 6a and 6b.
Are returned to the optical receiver 5 through the other optical fiber 1b again, and the signal is processed by the signal processing device 9.

[0006] Each of the optical physical quantity sensors 2a to 2n has a transmittance that changes in accordance with a change in a physical quantity at a position where the sensor is provided. In particular, since the operation is a binary operation of ON / OFF, the transmittance is changed. Is about 0% or about 100%.

As shown in FIG. 11, in the photodetector 5, light pulses 16a, 12a to 12n, 1 are provided for each delay time corresponding to the distance from the measuring unit 8 of each of the optical physical quantity sensors 2a to 2n.
6b is detected, and an optical pulse is obtained as a time-series pulse train at the sensor unit. Each sensor output (physical quantity) can be obtained from the magnitude of each of the light pulses 12a to 12n. FIG. 11 shows a waveform of a received pulse train measured by the conventional optical fiber type multi-point physical quantity detection device shown in FIG. 9, in which the horizontal axis indicates time and the vertical axis indicates light receiver output.

The apparatus has two self-diagnosis functions of soundness. One is that it is possible to confirm whether or not the optical pulse generator 4 emits light normally by confirming the presence of the optical pulse 16a passing through the optical fiber 6a. That is, when the optical pulses 12a, 12b,... Are no longer confirmed, it can be determined from the presence of the optical pulse 16a whether or not an abnormality has occurred in the optical pulse generator 4. Two, by confirming the presence of the light pulse 16b passing through the optical fiber 6b,
The point is that it is possible to confirm whether or not a and 1b are disconnected during the process. That is, when the optical pulses 12a, 12b,... Are no longer confirmed, it can be determined from the presence or absence of the optical pulse 16b whether or not the optical fibers 1a, 1b are disconnected.

Such an optical fiber type multipoint type physical quantity detection device has an advantage that it is possible to prevent a problem that a sensor output is erroneously determined due to a device failure such as a light source failure or an optical fiber disconnection.

FIG. 10 is a block diagram of a conventional optical fiber type multipoint type physical quantity detection device using a reflection type time division multiplexing method (Nelson, AR, Mchon, DHand Gravel, RL: "Passive").
Multiplexing System for Fiber-Optical Sensors ", App
l.Opt, Vol 19, No17, pp2917-2920). Note that the same members as those in the conventional example shown in FIG.

In the apparatus shown in FIG. 1, optical splitters 31a to 31n are provided in the middle of one optical fiber 1, and each of the optical splitters 31a to 31n is provided.
One end of the optical physical quantity sensor 1 is connected to the branch side of a to 31n, and the reflectors 41a to 41n are connected to the other end of each optical physical quantity sensor and one end of the optical fiber 1, respectively. The optical pulse generator 4 that emits an optical pulse and the optical receiver 5 are connected via the optical splitter 310, and the signal processor 9 is connected to the optical receiver 5.

In an apparatus having such an optical fiber system, an optical pulse generated by the optical pulse generator 4 is sent out to the optical fiber 1 via the optical splitter 310 and split by the optical splitters 31a to 31n. Is done. Thereafter, the light passes through each of the optical physical quantity sensors 2a to 2n, and passes through the reflectors 41a to 41a.
The light is reflected by 1n, passes through the optical physical quantity sensors 2a to 2n again, and is sent back to the optical fiber 1 via the optical splitters 31a to 31n. Receiver 5 via optical splitter 310
, And the signal is processed by the signal processing device 9.

The device shown in FIG. 3 is similar to the device shown in FIG. 9 and includes a measuring unit 8 for each of the optical physical quantity sensors 2a to 2n.
Light pulses 12a to 12g for each delay time corresponding to the distance from
12n is detected, and an optical pulse is obtained as a time-series pulse train at the sensor unit. Each sensor output (physical quantity) can be obtained from the magnitude of each of the light pulses 12a to 12n (see FIG. 11).

[0014]

However, FIG.
The device shown in FIG. 10 has the following problems.

(1) When the light receiving level is reduced due to a decrease in the output of the light source or the like, the signal level becomes lower than the determination threshold even if the optical physical quantity sensor is not operating. Will be misjudged.

(2) When the S / N ratio decreases due to a decrease in the output of the light source or the like, even if the optical physical quantity sensor operates, noise is superimposed on the signal and becomes higher than the determination threshold value. Erroneously determines that is not operating.

(3) When the light receiving level is reduced due to the disconnection of the optical fiber, the signal level becomes lower than the determination threshold even if the optical physical quantity sensor is not operating. Misjudgment.

An object of the present invention is to solve the above-mentioned problems and to provide an optical fiber type multipoint type physical quantity detection device which does not make an erroneous determination even if the output of the light source is reduced or the optical fiber is disconnected. is there.

[0019]

In order to achieve the above object, the present invention provides an optical system in which a plurality of optical splitters are provided in the middle of two parallel optical fibers, and the optical loss or the like changes due to a change in physical quantity. An optical fiber type in which a physical quantity sensor is connected between the corresponding optical splitters of both optical fibers, a light source that emits a light pulse is connected to one end of one optical fiber, and an optical receiver is connected to one end of the other optical fiber. In the multi-point type physical quantity detection device, at least one portion between the optical splitters of both optical fibers has a portion that transmits an optical pulse having a level lower than the optical pulse and a portion that transmits an optical pulse having a level higher than the noise level. Either or both.

According to the present invention, a plurality of optical splitters are provided in the middle of an optical fiber, and one end of an optical physical quantity sensor whose optical loss changes due to a change in physical quantity is connected to the branch side of each optical splitter. A reflector is connected to the other end of the physical quantity sensor and one end of the optical fiber, respectively, and a light source that emits a light pulse via a light splitter and a light receiver connected to the other end of the optical fiber are optical fiber multipoint type physical quantity detection. In the device, at least one of the optical splitters provided in the middle of the optical fiber is a portion that simply reflects without connecting an optical physical quantity sensor, a portion that reflects an optical pulse of a lower level than an optical pulse, and noise. Any or all of the portions that transmit light pulses of a higher level than the level.

In addition to the above configuration, the present invention provides a pulse train having a length of 2 · L · n / C (where
L may be a pseudo-random pulse train having a distance from the light source to the farthest optical splitter, C being the speed of light in a vacuum, and n being a refractive index or more.

According to the present invention, a plurality of optical splitters are respectively provided in the middle of two parallel optical fibers, and an optical physical quantity sensor is connected between the corresponding optical splitters of both optical fibers.
A light source that emits a light pulse is connected to one end of one optical fiber, and an optical receiver is connected to one end of the other optical fiber, and the light pulse emitted from the light source is a light pulse having a lower level than the light pulse. In the case where the light passes through a portion that transmits light (high-level reference ladder) or a portion that transmits light pulses having a level higher than the noise level (low-level reference ladder), the light from the optical physical quantity sensor that is not operating is output. Where the light pulse should be determined to be high level is erroneously determined to be low level due to a decrease in the output of the light source, or where the light pulse from the operated optical physical quantity sensor should be determined to be low level is determined by the decrease in S / N. It is possible to prevent erroneous determination of a high level.

According to the present invention, a plurality of optical splitters are provided in the middle of the optical fiber, one end of the optical physical quantity sensor is connected to the branch side of each optical splitter, and the other end of each optical physical quantity sensor is connected. And a reflector connected to one end of the optical fiber, and a light source and a light receiver that emit a light pulse via an optical splitter to the other end of the optical fiber.The light pulse emitted from the light source is simply reflected, In the case of passing through any or all of a part that reflects a light pulse of a level lower than the light pulse (high-level reference) and a part that transmits a light pulse of a level higher than the noise level (low-level reference), Monitors the level of the light pulse reflected by the reflector (near-end reference) closest to the light source in the light pulse time-series light-receiving signal obtained by the light receiver. It is possible to determine whether or not the light.

By monitoring the signal level of the light pulse reflected by the reflector (far end reference) farthest from the light source, it is possible to determine whether or not the optical fiber is broken. Further, by monitoring the high-level reference signal level, it is possible to prevent a light pulse from an inactive optical physical quantity sensor from being determined to be at a high level from being erroneously determined to be at a low level due to a decrease in light source output.

By monitoring the low-level reference signal level, the level of the light pulse from the operated optical physical quantity sensor is determined to be low level by the S / N.
Can be prevented from being erroneously determined to be a high level due to a decrease in

As described above, by using the near-end reference, the far-end reference, the high-level reference, and the low-level reference, it is possible to stop the light emission of the light source, disconnect the optical fiber, decrease the output of the light source, and determine the device based on the decrease in S / N. Errors can be prevented.

[0027]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an embodiment of an optical fiber type multipoint type physical quantity detecting device according to the present invention.

A plurality of optical splitters 310, 311, 312, 31a to 31n are provided in this order in the middle of the optical fiber 1a, and the optical splitters 320, 321 and 322 are provided in the optical fiber 1b parallel to the optical fiber 1a. , 32a to 32n are provided at positions corresponding to the optical splitters 310, 311, 312, 31a to 31n. Each optical splitter 31a-31
n, 32a to 32n, optical physical quantity sensors 2a to 2n
Is connected. These optical physical quantity sensors 2a to 2a
n is a sensor that outputs a signal indicating either the transmittance of about 100% or about 0% according to the degree of temperature, humidity, liquid leakage or the like.

An optical pulse generator 4 as a light source for emitting an optical pulse is connected to one end (left end in the figure) of one optical fiber 1a, and a light receiver 5 is connected to one end (left end in the figure) of the other optical fiber 1b. Is connected. A signal processing device 9 is connected to the light receiver 5, and the optical pulse generator 4, the light receiver 5 and the signal processing device 9 constitute a measuring unit 8.

The optical splitter 310 and the optical splitter 320 closest to the measuring unit 8 and the optical splitter 31 farthest from the measuring unit 8
n and the optical fiber 6a, 6
b (referred to as connection portions 6a and 6b, respectively). An optical attenuator 10a is connected between the optical splitters 311 and 321 between the optical fiber 6a and the optical physical quantity sensor 2a, and an optical attenuator 10b is connected between the optical splitters 312 and 322. The optical splitters 311 and 321 and the optical attenuator 10a constitute a high-level reference ladder 7a, and the optical splitters 312 and 322 and the optical attenuator 10b constitute a low-level reference ladder 7b.

When the optical fiber type multipoint type physical quantity detecting device having such an optical fiber system operates, an optical pulse is emitted from the optical pulse generator 4 to the optical fiber 1a, and one end (the left end in the figure) of the optical fiber 1a. Is incident on. The optical pulse from the optical pulse generator 4 is converted into an optical splitter 31 × (× =
0, 1, 2; a,..., N), and each of the optical physical quantity sensors 2a to 2n, the connection part 6a or the connection parts 6b, 7a,
7b, the optical splitter 32 × (× = 0, 1, 2; a,
.., N), again enters the light receiver 5 through the optical fiber 1b, and is signal-processed by the signal processing device 9.

When the light pulse emitted from the light pulse generator 4 propagates through one of the optical fibers 1a, the light splitter 3
The optical pulse component is branched into the optical fiber components 1a to 31n and propagates as it is in the optical fiber 1a, and the optical pulse component is branched and propagates to the other optical fiber 1b.

The light pulse branched and propagated on the optical fiber 1b side passes through optical physical quantity sensors 2a to 2n and optical splitters 32a to 32n provided between the optical fiber 1a and the optical fiber 1b. Through the optical fiber 1b. The signal obtained by the signal processing device 9 is
Each of the optical splitters 310, 311, 312, 31a to 31 is delayed by a time corresponding to the distance from the optical pulse generator 4 to the light receiver 5 via each of the optical physical quantity sensors 2a to 2n.
n, 320, 321, 322, and 32a to 32n are obtained as a time-series signal of optical pulses obtained by superimposing the optical pulses.

FIG. 2 is a diagram showing a waveform of a received pulse train measured by the optical fiber type multi-point physical quantity detecting device shown in FIG. That is, the figure shows the optical physical quantity sensor 2b.
Operates to have a transmittance of about 0%, the other optical physical quantity sensors 2a, 2c to 2n do not operate, and have a transmittance of about 100%.
FIG. 6 shows a waveform of a received signal in a situation where no device failure such as a decrease in output of the optical pulse generator 4 or a decrease in S / N occurs. 16a is an optical pulse that has passed through the connection portion 6a for determining whether the optical pulse generator 4 is emitting light,
16b is an optical pulse that has passed through the connecting portion 6b for determining whether or not the optical fiber 1a and the optical fiber 1b are disconnected, 17a is an optical pulse that has passed through a high-level reference ladder, and 17b is an optical pulse that has passed through a low-level reference ladder. The optical pulses are shown respectively.

Numerals 12a, 12b and 12n are light pulses passing through the optical physical quantity sensors 2a, 2b and 2n, respectively.
As shown in the figure, although there is a small noise 21, the S / N of the light source output and each light pulse is sufficiently large, and each light pulse 12a, 12b,
.., 12n can be reliably determined to be a high level or a low level.

If there is a device failure such as a decrease in light source output, as shown in FIG.
The levels of 2a, 12b,..., 12n are lowered as a whole.
For example, the optical physical quantity sensor 2a does not operate and the optical pulse 12a
May be erroneously determined to be at a low level below the threshold level 22 even though is at a high level. However, before the output of the optical physical quantity sensor 2a is erroneously determined to be at the low level, the level 17a of the optical pulse from the high-level reference ladder 7a slightly lower than the level of the optical pulse 12a is changed from the high level. Since it changes to a low level (41), it is possible to detect a decrease in the output of the light source before a determination error occurs. FIG. 3 shows FIG.
FIG. 7 is a diagram showing a received pulse train waveform measured when the output of the light source of the optical fiber type multi-point physical quantity detection device shown in FIG.

If a failure of the apparatus such as a decrease in S / N occurs, the noise 21 increases as shown in FIG. 4, and the large noise 21 is superimposed on the optical pulse 12b. As a result, the optical physical quantity sensor 2b operates and the optical pulse 12b is at a low level, but the threshold level 22
There is a possibility that an incorrect determination is made that the level is higher than the high level. However, before the output of the optical physical quantity sensor is erroneously determined to be at the high level, the noise 21 is superimposed on the level 17b of the optical pulse from the low-level reference ladder slightly higher than the level of the optical pulse 12b, and the low level is obtained. To a high level (42), it is possible to detect a decrease in S / N before erroneous determination occurs. FIG. 4 is a diagram showing a received pulse train waveform measured when the S / N of the optical fiber type multi-point physical quantity detection device shown in FIG. 1 is reduced.

Thus, the output of the light source is reduced and the S /
Since the failure of the device can be detected before the output of the sensor is erroneously determined due to the failure of the device such as a decrease in N, high reliability can be obtained.

In this embodiment, the optical pulse generator 4
Connection section 6 for determining whether or not the LED emits light normally
Although the high-level reference ladder 7a for detecting the output decrease of the optical pulse generator 4 is provided separately from the high-level reference ladder 7a, the role of the connection part 6a may be combined with the high-level reference ladder 7a. Also, a high level reference ladder 7a
The low-level reference ladder 7b and the low-level reference ladder 7b may be inserted at any place between the two optical fibers 1a and 1b.

Further, in order to make the signal from the high-level reference ladder smaller than the light pulse returning from another ladder, or to make the low-level reference ladder a level higher than the noise level, Instead of inserting the optical attenuator into the reference ladder, the branching ratio of the optical branching units 311, 321 and 322 may be adjusted, and both the adjustment of the branching ratio and the adjustment of the attenuation rate of the optical attenuator may be performed. .

Furthermore, the pulse train emitted from the optical pulse generator is not limited to a system that generates a single pulse,
A method of generating a pseudo random code pulse train may be used. Here, in the single-pulse system, the distance between the optical pulse generator and the farthest optical branching device from the optical pulse generator is L,
Assuming that the speed of light in a vacuum is C and the refractive index of the optical fiber is n, the time interval for generating a single pulse from the optical pulse generator is 2
-It is preferable to send out at least L · n / C. Also,
In the pseudo-random system, it is preferable to transmit a pulse train defined as a pseudo-random code pulse train having a pulse train length of 2 · L · n / C or more. When using the pseudo-random method, a function for demodulating the pseudo-random signal is added to the signal processing device.

FIG. 5 is a block diagram showing another embodiment of the optical fiber type multipoint type physical quantity detecting device according to the present invention.
The same members as those in the apparatus shown in FIG. 1 are denoted by the same reference numerals.

The difference from the embodiment shown in FIG. 1 is that the shape of the optical fiber system of the device shown in FIG. 2 is a ladder type whereas the shape of the optical fiber system of the device shown in FIG. Is a comb shape.

The optical fiber type multipoint type physical quantity detecting device shown in FIG. 5 has one optical fiber 1 and a plurality of optical splitters 310, 311, 312, 3 provided in the middle of the optical fiber 1.
1a to 31n, an optical pulse generator 4 connected to one end (the left end in the figure) of the optical fiber 1, a photodetector 5 connected to the branch side of the optical splitter 310, and a signal connected to the photodetector 5 Processing device 9, optical physical quantity sensors 2a to 2n having one end connected to the branch side of optical splitters 31a to 31n, and reflectors 41a to 41d connected to the other ends of optical physical quantity sensors 2a to 2n.
41n, optical attenuators 10a and 10b, one ends of which are connected to optical splitters 312 and 313, respectively, and optical attenuators 10a and 10b.
Reflectors 412 and 41 respectively connected to the other end of 10b
3, an optical fiber (connection portion) 6a connected to the branch side of the optical branching device 311, a reflector 411 connected to the other end of the optical fiber 6a, and one end connected to the transmission side of the optical branching device 31n. Optical fiber (connection part) 6b and a reflector 414 connected to the other end of the optical fiber 6b. The optical pulse generator 4, the optical splitter 310, the light receiver 5, and the signal processing device 9 constitute the measuring unit 8.
2. A high-level reference is composed of the optical attenuator 10a and the reflector 412, and the optical branching unit 313 and the optical attenuator 10b
The reflector 413 forms a low-level reference. The optical fiber 6a closest to the measuring unit 8 is set as a near-end reference, and the optical fiber 6b farthest from the measuring unit 8 is set as a far-end reference.

When such an optical fiber type multipoint type physical quantity detecting device is operated, the optical pulse generated by the optical pulse generator 4 is incident on one end of the optical fiber 1 via the optical splitter 310 and is split. Branches at the units 311 to 313 and 31a to 31n. The branched optical pulses are supplied to the optical physical quantity sensors 2a to 2n, the near-end reference, the far-end reference,
The light passes through the high-level reference and the low-level reference, is reflected by the reflectors 411 to 414, 41a to 41n, and again passes through the optical physical quantity sensors 2a to 2n, the near-end reference, the far-end reference, the high-level reference, and the low-level reference. , Each optical splitter 31a-3
The light is sent back to the optical fiber 1 via 1n. The optical pulse sent back to the optical fiber 1 reaches the optical receiver 5 via the optical splitter 310, and is subjected to signal processing by the signal processor 9. The signals obtained by the signal processing device 9 are output from the optical pulse generator 4 to the respective optical splitters 311, 312, 313, 31a to 3a.
1n, optical physical quantity sensors 2a to 2n and reflector 411
414, 41a to 41n, each of the optical splitters 311, 31 delayed by a time corresponding to the distance to the light receiver 5 via the light receiver 5
It is obtained as a time-series signal of an optical pulse in which optical pulses that have passed through 2,313,31a to 31n are superimposed.

FIG. 6 is a diagram showing a received pulse train waveform measured when the optical fiber type multipoint physical quantity detection device shown in FIG. 5 is in a healthy state. That is, the optical physical quantity sensor 2b is activated to have a transmittance of about 0%, the other optical physical quantity sensors are not activated and the transmittance is about 100%, and the light emission of the optical pulse generator 4 is stopped, the optical fiber is disconnected, and the like. FIG. 6 shows a waveform of a received signal in a state where no device failure such as a decrease in output of the optical pulse generator 4 and a decrease in S / N occurs.

Reference numeral 116a denotes an optical pulse that has passed through the connection portion 6a for determining whether or not the optical pulse generator 4 emits light. Reference numeral 116b denotes a connection portion for determining whether the optical fiber 1 is disconnected. The light pulse passing through 6b 117a is the light pulse passing through high-level reference 7a, 117a
b is an optical pulse that has passed through the low-level reference 7b. 112a, 112b, and 112n are light pulses that have passed through the optical physical quantity sensors 2a, 2b, and 2n, respectively.
Although there is a small noise 121, the output of the optical pulse generator 4 and the S / N of each optical pulse are sufficiently large, and the optical pulse levels 112 a and 11 are based on the threshold level 122.
.., 112n can be reliably determined to be a high level or a low level.

Here, if a device failure such as light emission stop of the optical pulse generator 4 occurs, the near-end reference 6
It can be detected by the disappearance of the level 116a of the light pulse from a. Further, when a device failure such as an optical fiber disconnection occurs, the optical pulse 116b from the far-end reference 6b disappears, which can be detected.

If a device failure such as a decrease in the output of the optical pulse generator 4 occurs, as shown in FIG. 7, the levels of the time-series pulse trains 112a, 112b,... The optical physical quantity sensor 2a does not operate, and the optical pulse 112a is at the high level, but may be erroneously determined to be at the low level lower than the threshold level 122. However, before the output of the optical physical quantity sensor 2a is erroneously determined to be low, the optical pulse 112a
High level reference 7 slightly lower than
Since the level 117a of the optical pulse from a changes from the high level to the low level (141), it is possible to detect a decrease in the output of the optical pulse generator 4 before erroneous determination occurs. FIG. 7 is a diagram showing a received pulse train waveform measured when the output of the light source of the optical fiber type multipoint physical quantity detection device shown in FIG. 5 is reduced.

If a failure of the device such as a decrease in S / N occurs, the noise 121 increases as shown in FIG. 8 and a large noise is superimposed on the optical pulse 112b. As a result, the optical physical quantity sensor 2b operates, and although the light pulse 112b is at a low level, the threshold level 1
There is a possibility that a high level higher than 22 is erroneously determined. However, before the output of the optical physical quantity sensor is erroneously determined to be at the high level, the noise 121 is superimposed on the level 117b of the optical pulse from the low-level reference 7b, which is slightly higher than the optical pulse 112b, and the level changes from low to high. Since the level changes to (142), a decrease in S / N can be detected before an erroneous determination occurs. FIG. 8 shows the S / S of the optical fiber type multipoint type physical quantity detection device shown in FIG.
FIG. 9 is a diagram showing a received pulse train waveform measured when N has decreased.

In this manner, the output of the optical physical quantity sensor is erroneously determined due to a device failure such as stoppage of light emission of the optical pulse generator 4, disconnection of the optical fiber, decrease in output of the optical pulse generator 4, and decrease in S / N. An optical fiber type multipoint type physical quantity detection device which can detect a failure of the device beforehand can be obtained.

In this embodiment, the light pulse generator 4
Connection section 6 for determining whether or not the LED emits light normally
a and a high-level reference 7 a for detecting a decrease in the output of the optical pulse generator 4 are separately provided.
The role of a may also serve as the high-level reference 7a. Further, the high-level reference 7a and the low-level reference 7b may be inserted at arbitrary positions in the optical fiber 1.

Further, in order to make the signal from the high-level reference smaller than the light pulse returning from another ladder, or to make the low-level reference a level larger than the noise level, the high-level reference and the low-level reference are used as optical signals. Instead of inserting an attenuator, the branching ratio of the optical branching units 31a to 31n may be adjusted, and both the adjustment of the branching ratio and the adjustment of the attenuation rate of the optical attenuator may be performed.

Further, the pulse train emitted from the optical pulse generator is not limited to the method of generating a single pulse,
A method of generating a pseudo random code pulse train may be used. Here, in the single-pulse system, the distance between the optical pulse generator and the farthest optical branching device from the optical pulse generator is L,
Assuming that the speed of light in a vacuum is C and the refractive index of the optical fiber is n, the time interval for generating a single pulse from the optical pulse generator is 2
-It is preferable to send out at least L · n / C. Also,
In the pseudo-random system, it is preferable to transmit a pulse train defined as a pseudo-random code pulse train having a pulse train length of 2 · L · n / C or more. When using the pseudo-random method, a function for demodulating the pseudo-random signal is added to the signal processing device.

[0056]

In summary, according to the present invention, the following excellent effects are exhibited.

In the optical fiber type multipoint type physical quantity detecting device, the output of the light source is reduced by detecting the presence or absence of an optical pulse using the near end reference, the far end reference, the high level reference and the low level reference. It is possible to provide an optical fiber type multi-point physical quantity detection device that does not make an erroneous determination even if the optical fiber is disconnected.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an optical fiber type multipoint physical quantity detection device according to the present invention.

FIG. 2 is a diagram showing a received pulse train waveform measured when the optical fiber type multipoint physical quantity detection device shown in FIG. 1 is in a healthy state.

3 is a diagram showing a received pulse train waveform measured when the output of the light source of the optical fiber type multipoint physical quantity detection device shown in FIG. 1 is reduced.

4 is a diagram showing a received pulse train waveform measured when the S / N of the optical fiber type multi-point physical quantity detection device shown in FIG. 1 is reduced.

FIG. 5 is a block diagram showing another embodiment of the optical fiber type multipoint type physical quantity detection device of the present invention.

6 is a diagram showing a received pulse train waveform measured when the optical fiber type multipoint physical quantity detection device shown in FIG. 5 is in a healthy state.

7 is a diagram showing a received pulse train waveform measured when the output of the light source of the optical fiber type multipoint physical quantity detection device shown in FIG. 5 is reduced.

8 is a diagram showing a received pulse train waveform measured when the S / N of the optical fiber type multi-point physical quantity detection device shown in FIG. 5 is reduced.

FIG. 9 is a block diagram of a conventional optical fiber type multipoint physical quantity detection device.

FIG. 10 is a block diagram of a conventional optical fiber type multipoint type physical quantity detection device using a reflection type time division multiplexing method.

11 is a reception pulse train waveform measured by the conventional optical fiber type multipoint physical quantity detection device shown in FIGS. 9 and 10. FIG.

[Explanation of symbols]

 1, 1a, 1b Optical fiber 2a-2n Optical physical quantity sensor 310-313, 31a-31n Optical splitter 4 Light source (optical pulse generator) 411-414, 41a-41n Reflector 5 Light receiver

Claims (3)

[Claims] 1. A plurality of optical splitters are respectively provided in the middle of two parallel optical fibers, and an optical physical quantity sensor whose optical loss or the like changes due to a change in physical quantity is provided between the optical splitters corresponding to the two optical fibers. In a fiber-optic multipoint physical quantity detection device in which a light source that emits a light pulse is connected to one end of one optical fiber and an optical receiver is connected to one end of the other optical fiber, the optical splitter of both optical fibers is connected. At least one portion between the optical fiber type multi-layered optical fiber and the optical fiber type multi-layered optical fiber is characterized in that one or both of a portion that transmits a light pulse having a level lower than the light pulse and a portion that transmits a light pulse having a level higher than the noise level are provided. Point type physical quantity detection device. 2. An optical physical quantity sensor comprising: a plurality of optical splitters provided in the middle of an optical fiber; and one end of an optical physical quantity sensor whose optical loss or the like changes due to a physical quantity change connected to a branch side of each optical splitter. A reflector is connected to the other end of the optical fiber and one end of the optical fiber, and a light source that emits a light pulse through a light splitter to the other end of the optical fiber and a light receiver are connected to an optical fiber type multipoint physical quantity detection device. At least one of the optical splitters provided in the middle of the optical fiber is a portion that simply reflects without connecting an optical physical quantity sensor, a portion that reflects an optical pulse of a lower level than an optical pulse, and a noise level. An optical fiber type multi-point physical quantity detection device, characterized in that any or all of the portions that transmit higher-level light pulses are used. 3. Instead of emitting a light pulse from the light source, a pulse train length of 2 · L · n / C (where L is the distance between the light source and the light source farthest from the light source, C is the speed of light in vacuum, and n is the speed of light in vacuum) 3. The optical fiber type multi-point physical quantity detection device according to claim 1, wherein a pseudo random pulse train having a refractive index of not less than is transmitted.