JPH0712655A - Measurement system - Google Patents

Abstract

PURPOSE:To heighten measurement precision and position resolution by continuously laying down a transmission route of an optical fiber at each measurement point of an area to be measured, applying a signal for reference and continuously and exactly measuring temperature, humidity and temperature distribution of a lot of measurement points. CONSTITUTION:A conduit 15 is hung from a ceiling 21 as a thermal partition wall in a room which is an area to be measured, arranged in the room, optical fibers 13 are passed therein, the optical fibers are loosely drawn from branch pipes 161-16n of the conduit 15 respectively provided at a plurality of temperature measurement points and temperature measurement parts 171-17n which indicate the same wound method as a non-inductive resistance are pulled from the branch pipes 161-16n to the outside. An operation instruction is received from CPU of a signal processor 14 of a thermometer body 20, and a light pulse emitted from a light source 11 is made incident on the optical fibers 13 through a beam splitter 12. Back scattered light is returned from each temperature measurement part 171-17n, introduced to the signal processor 14 through the beam splitter 12 and temperature is measured from the intensity of the back scattered light at the positions of the temperature measurement parts and therefrom.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention lays an optical fiber in a region to be measured in a building such as a building, receives an optical signal from an incident end which is one end of the optical fiber, and directs it toward the other end. By analyzing the backscattered light returning from all parts of the optical fiber to the incident end, the temperature at an arbitrary place in the measured region,
The present invention relates to a measurement system that measures humidity or temperature distribution.

[0002]

2. Description of the Related Art A thermometer using an optical fiber of this type includes an OTDR (Optical Time Domai).
n Reflectometry) type thermometer and OFD
R (Optical Frequency Domai)
n Reflectometry) type thermometer.
Both of these thermometers use a Raman scattering method and a Rayleigh scattering method. The difference between these two methods is that Raman scattering has a scattering wavelength different from that of the emitted light. Is that the scattered wavelength is the same wavelength as the emitted light.

Here, an example in which an OTDR type thermometer is used as a thermometer and a Raman scattering method with high temperature measurement sensitivity is used will be described. This OTDR type thermometer consists of two principles: temperature measurement using Raman scattering in an optical fiber and position measurement using an optical pulse reflection method.

Raman scattering is a physical phenomenon in which photons incident on a substance interact with an optical mode of molecular vibration to cause inelastic collision, whereby light having a wavelength different from the incident light is scattered. There are two types of Raman scattered light: one that shifts to the long wavelength side (Stokes light) and one that shifts to the short wavelength side (anti-Stokes light) with respect to the incident light. Is λ, the wavelength of Stokes light is λ _S , and the wavelength of anti-Stokes light is λ _A ,

[Equation 1] The following relationship holds. Here, ν is the wave number. The wave number is a quantity determined by the properties of matter, and is called Raman shift.

The intensity of Raman scattered light depends on temperature. The ratio of anti-Stokes light to Stokes light at temperature T is R
Assuming (T), the following relationship holds.

[0006]

[Equation 2] Here, h is Planck's constant, c is the speed of light, and h is Boltzmann's constant. In Raman scattering, it is known that the scattering intensity of anti-Stokes light greatly changes with temperature,
This is used for temperature measurement. On the other hand, the OTDR method
The distance is measured by injecting pulsed light from one end of the optical fiber and measuring the time of the component that is backscattered and returned in the medium of the optical fiber. Therefore, 2 mentioned above
The temperature distribution can be measured by combining the two methods.

This Raman scattering is considered to be difficult to use for temperature measurement because it is affected by minute substances and various molecules in the environment in the environment of air or gas. However, since then, with the development of optical fiber manufacturing technology, various methods of using the optical fiber have been studied, and as part of the research and development, the use of the thermometer has been researched and developed. In particular, it has been found that the optical fiber is suitable for temperature measurement, although it is gradually different from the environment of air or gas because only the fixed fiber component exists. OTDR measures temperature using high-speed pulses, while OFDR measures temperature using frequency-modulated light.

However, in the OTDR type thermometer which is a typical model to which the Raman scattering method is applied at present, the position resolution length L _{t of the} temperature measuring portion (temperature measuring portion) of the optical fiber is 20.
m, minimum measured temperature T _b is 5 ° C., maximum measured temperature T _c is 15
0 ° C, maximum measurement length L _max is 1 km (0.1 GHz at 0.1
Since it corresponds to m, the resolution is about 0.1 m, which is the limit of the measurement range. However, due to academic conference and other circumstances, L _t will be 0.5 m, T _b will be −50 ° C., and T _c will be 500 ~
It is considered that the _{Lmax at} 600 ° C. is improved to about 10 km. The Rayleigh scattering method may be used, and these scattering methods will be referred to as an OTDR type thermometer.

Therefore, at present, L _t is 20 m.
Since it is larger than that, it is difficult to measure the temperature of the point, and only researches to measure the temperature distribution along the optical fiber have been made. Moreover, the backscattered light from each point on the long optical fiber is weak, and since noise is mixed in this, the optical signal is repeatedly emitted several thousands to tens of thousands of times, and the obtained backscattered light is emitted. It is configured to average and remove noise and measure the desired signal, but high fidelity measurements are very difficult.

The OTDR originally has a function of detecting a position, and an optical signal is made incident from the light source to the incident end of the optical fiber, and of the Raman scattering generated in the optical fiber by this optical signal. It is configured to measure the temperature detection position from the time until the backscattered light returning to the incident end is returned, but the optical fiber is changed depending on the difference in the minute components that make up the optical fiber, the configuration, and the like. This is often different from the case where the length from the outside to the temperature detection position is measured with a length meter. In addition to that, the optical fiber, which is the temperature detecting portion of the OTDR, has a problem that it is very difficult to measure the length of the optical fiber from the outside of the optical fiber because the shape of the optical fiber adapts flexibly to the mounting place.

One of the reasons why L _t requires a length larger than 20 m is that it is due to a change in the transmission speed of light. Therefore, when measuring an abnormal temperature that is used in a certain temperature environment at a predetermined measurement location and partially occurs, the temperature detection location and the temperature at that location should be fairly accurate while considering these known conditions. However, in the case of general temperature measurement for measuring the temperature of an unspecified place, various problems as mentioned above occur.

[0012]

As described above, it is difficult to measure the temperature of a point because the position resolution length L _t of the temperature measuring portion of the optical fiber is larger than 20 m under the present circumstances.
In addition, since the backscattered light from each point on the long optical fiber is weak and noise is mixed therein, the optical signal is repeatedly emitted tens of thousands of times, and the obtained backscattered light is averaged to generate noise. However, there is a problem that it is very difficult to measure with high fidelity.

Therefore, according to the present invention, it is possible to continuously and accurately measure the temperature and humidity at a large number of measurement points in a wide range of the measured area, or the temperature distribution of the measured area, and to improve the measurement accuracy and position resolution. The purpose is to provide a measuring system.

[0014]

According to the measurement system of the present invention, an optical signal is input from a light source to an incident end of an optical fiber, and Raman scattering generated in the optical fiber by the incidence of the optical signal is measured at the incident end. In the measurement system that measures the temperature, humidity, or temperature distribution by analyzing the time until the backscattered light going back and the strength of the returned signal are measured by the signal processing device, each measurement of the measured area The transmission path of the optical fiber is continuously laid over a portion, and a reference signal application unit for applying a reference signal is applied to a part or the whole area of the transmission path, and the transmission path of the optical fiber is thermally Laying on the back side of the partition wall as a reference signal applying section, and pulling out the optical fiber to the front surface of the partition wall in a slack shape in a single stroke at each of the measurement points, and using it as a temperature measuring section, using the boundary between the front and back sides. Characterized in that so as to clarify the measurement point position.

[0015]

In the measuring system of the present invention, the main transmission line of the optical fiber is laid behind the thermal partition wall over each measurement point in the measured region to serve as the reference signal application section, and the optical signal is applied at each measurement point. By slackening the fiber to the surface of the partition wall in a slack-like manner and using it as a temperature measurement unit, when an environment change occurs in the measurement area, the temperature measurement unit on the surface of the partition wall shows a sensitive temperature change. , Since the temperature change on the back side of the partition is slow, use the clarification of the boundary position between the front and back,
Even if the length of the optical fiber bundle of the temperature measuring unit is small, the measurement point position and the temperature can be accurately measured.

[0016]

The present invention will be described in detail below with reference to the embodiments shown in the drawings.

First, the measurement principle of a thermometer using an OTDR, which is a base for explaining the measurement system of the present invention, will be described with reference to FIGS. 4 to 6.

Now, for example, as shown in FIG. 4, a light source 1 such as a laser oscillator or a light emitting diode for generating an optical pulse.
When the optical pulse S is generated from 1 and is incident on the incident end of the optical fiber 13 through the beam splitter 12 (a device that performs the same function as the beam splitter, for example, a beam splitter including the optical branch), The transmission position of the optical pulse S in 13 is, for example, t ₁ , ... T
_{From n-1} , t _n ,

[Equation 3] Raman scattering of a certain frequency is generated one after another, whereby the backscattered light returns from each position t ₁ , ..., t _n-1 , t _n to the optical fiber entrance end side and is reflected or branched by the beam splitter 12. And is introduced into the signal processing device 14. Therefore, after the above-described light pulse S is generated, in the signal processing device 14, the temperature T ₁ , ..., Which is the intensity of the backscattered light scattered from each position t ₁ , ..., t _n-1 , t _n .
T _n-1 and T _n are detected, and T ₁ = T ₂ = ... = T _n-1
= T _n , the signal level decreases because the loss due to the transmission increases as the temperature is farther away. That is, the measurement result by the signal processing device 14 is as shown in FIG. Since the signal processor 14 issues an optical pulse emission command to the light source 11, in the present embodiment, an electrical signal capable of processing the emission command and the backscattered light scattered and returned from the optical fiber 13. Converted to, measure the time that the backscattered light returns with reference to the launch command time, measure the intensity of the backscattered light on the measurement time axis, and calculate the speed of light in the optical fiber as known, The temperature is measured from the measurement position and the intensity of the backscattered light at the measurement position.

That is, this measurement principle is a method of measuring the time from the generation of the optical pulse S to the return from the inside of the optical fiber 13 and knowing at which position the Raman scattering occurred. Effective for relatively long optical fibers.

On the other hand, in the OFDR, when an AC continuous wave (modulation wave) is used, Raman scattering occurs at any position due to the phase shift between the AC waveform optical signal and the AC waveform optical signal returning from the optical fiber. This is a method of knowing whether or not a problem has occurred, and in this case, even a relatively short optical fiber can be accurately measured. In either case, the temperature is measured from the size of the backscattered light. Other wavelength lambda of the light pulses S generated from the light source 11 in this backscattered light, λ _A, λ since _S etc. are mixed, lambda by characteristic filter or the duplexer of the signal processing apparatus 14 _A, lambda Separate _S and measure the temperature. λ
_{Since A} has a high sensitivity to temperature and λ _S has a low sensitivity to temperature, it is divided like λ _A / λ _S , and λ _S is used to compensate for variations in the light source and the transmission line. By performing such compensation, highly sensitive temperature measurement using λ _A can be performed without being greatly affected by a change in the light amount of the light source, a change in the loss of the transmission line, and the like. On the other hand, it is desirable to utilize λ _A and λ _S for the temperature at which the position is detected.
The beam splitter is not required when using an element that also serves as a light source that generates an optical signal and a detector.

Next, FIG. 6 is a diagram showing a specific example of the signal processing device 14, in particular. That is, this signal processing device 14
Has a CPU 141 which outputs various commands based on a sequence program, receives an operation command from the CPU 141, and transmits an optical pulse of wavelength λ from a light source 11 via a beam splitter 12 composed of, for example, two prisms. When the light is incident on the optical fiber 13, the backscattered light including the wavelengths λ, λ _A , λ _S, etc. returning to the light incident end side of the Raman scattering generated inside the optical fiber 13 is the characteristic filter or the demultiplexer 142. Incident on.

When 142 is a characteristic filter, a filter that passes one of wavelengths λ _A or λ _S is used. As described above, temperature measurement is performed at λ _A and fluctuations of the light source and transmission line are performed at λ _S. As detected, for example, λ _A / λ _S is a compensated process quantity corresponding to temperature. Or λ
_A filter that passes both _A and λ _S is used, and λ _A and λ _S are used as temperature signals.

On the other hand, when 142 is a duplexer, λ _A , λ
After separating into light of wavelength _S , the subsequent opto-electric converter 1
At 43 and 144, they are converted into electric signals. Then, the electric signal converted by the optical-electrical converter 144, that is, the signal caused by Raman scattering is sent to the high-speed time series processing means 146 directly or through the switch circuit 145, where the operation from the CPU 141 to the light source 11 is performed. Time (position) based on the timing signal input in synchronization with the command output
And the signal strength corresponding to the temperature for that time are measured and sequentially stored in the built-in memory. A processing unit 147 performs desired data processing by using the data stored in the high-speed time series processing unit 146 and the data of the file 148 in which, for example, a temperature transmission source of the measured region is mapped as necessary. .

Next, a measuring system according to an embodiment of the present invention will be described with reference to FIG.

As shown in FIG. 1, a conduit (steel, vinyl chloride, etc.) 15 as a thermal barrier is hung from a ceiling 21 in a room, which is an area to be measured, and an optical fiber 13 is passed through the conduit 15 to form a plurality of conduits. The optical fiber 13 is drawn out from the branch pipes 16 _{1 to} 16 _{n of} the conduits respectively provided at the temperature measurement points in a slack shape, and the temperature measuring units 17 _{1 to} 17 _n wound in the same manner as the non-inductive electric resistance are externally provided from the branch pipes. A heat-insulating plug (eg glass wool, putty, etc.) inside the open end of each branch pipe.
(Rubber viscosity, cement, etc.) 19 is provided, and the measuring portions 17 _{1 to} 17 _n protruding from the branch pipe are covered with a cover 18 having a large number of small holes distributed therein, and this cover 18 is attached to the branch pipe. Thus, the fire alarm system is configured. A sufficiently long interval L (having a length necessary for temperature measurement) between the temperature measuring units is used as a reference signal applying unit.

An optical pulse emitted from the light source 11 in response to an operation command from the CPU of the signal processing device 14 (see FIG. 6) in the separately placed OTDR type thermometer main body 20 is transmitted through the beam splitter 12 to the optical fiber. It is incident on 13. Backscattered light returns from each of the temperature measuring units 17 _{1 to} 17 _n and is introduced into the signal processing device 14 via the beam splitter 12, and the temperature is determined from the position of the temperature measuring unit and the intensity of the backscattered light at that position. To be measured.

In the measurement system configured as the fire alarm system of this embodiment, the main transmission line of the optical fiber 13 is laid inside the conduit 15, and the optical fiber 13 is laid at each measurement point by conduit branch pipes 16 _{1 to} 16 _n. Was drawn as a slack in a single stroke, and the temperature measuring parts 17 _{1 to} 17 _n wound in the same manner as the non-inductive electric resistance were covered with a cover 18 having a porous structure, and heat was cut off from the inside of the conduit 15 by a plug 19. Therefore, when a fire occurs at the measurement point, the temperature changes of the temperature measurement units 17 _{1 to} 17 _n appear sensitively and remarkably, and the temperature change of the optical fiber 13 of the reference signal application unit in the conduit 15 is slow. Therefore, even _if the length of the optical fiber 13 bundle of the temperature measuring units 17 _{1 to} 17 _n is small, the measurement point position and the temperature can be accurately measured. As a result, a large number of optical fiber bundles can be formed from the optical fiber having a limited length of 1000 m, and the temperature measuring unit can be arranged in a wide area.

In the embodiment shown in FIG. 1, the temperature measuring portion is constructed by winding the optical fiber 13 drawn out in a slack shape in a non-inductive manner like the non-inductive electric resistance. The fibers 13 may be bundled in a crumpled shape and covered with a cover to form a temperature measuring unit.

An experimental example of the relationship between the length of the optical fiber 13 of the temperature measuring section and the measurement accuracy will be described with reference to FIGS. 3 (a) and 3 (b). As shown in FIG.
The optical fiber 13 is placed in the thermostatic chamber 31 set to 20 ° C.
Temperature measuring section is installed, the required reference temperature application section of the optical fiber 13 is taken out of the thermostatic chamber, and when a reference temperature of 20 ° C. is applied, the width of the optical pulse, the material of the optical fiber, and the data processing method. 3b
It becomes a relationship like. That is, after setting the reference temperature application part (i) of the optical fiber 13 to 20 ° C.,
When the temperature is introduced into the constant temperature bath 31 to form a temperature measuring section (a) having a length of 1 m, the set temperature of 120 ° C. inside the constant temperature bath 31 should be measured, but only 80 ° C. is obtained as the measurement result. Hereinafter, similarly, the reference temperature 20 ° C. is applied to the reference temperature applying portions (ro) to (to) of the optical fiber 13 by extending it to the outside in the constant temperature bath 31 in the same manner, and thereafter, the reference temperature is applied to the inside of the constant temperature bath 31 to change the length. If 2m, 5m, 10m, and 50m temperature measuring parts (b) to (e) are installed, each of the measure measuring parts (b), (c), (d), and (e) has 1
06 ° C, 119.5 ° C, 120 ° C, 120 ° C are obtained,
The reproducibility was found to be sufficient. Therefore, with respect to the measurement results obtained by the respective temperature measuring units (a) to (e),
By multiplying by a correction coefficient of 1.5 in (a), 1.132 in (b) and 1.004 in (c), 120 ° C. can be obtained as a correction value, and the correction value of the optical fiber of the temperature measurement unit can be obtained. If the length is known, it is possible to obtain the correct temperature by correction. That is, there is no problem even if the optical fiber bundle of the temperature measuring unit is shortened to about 1 m.

Next, another embodiment of the measuring system of the present invention will be described with reference to FIG. In this embodiment, the ceiling 21 is used as a thermal partition, and the optical fiber 13 is routed over the ceiling 21, and the optical fiber 13 is slackened from the holes 23 formed in the ceiling at a plurality of temperature measurement points. In the same manner as in the case of FIG. 1, the temperature measuring parts 17 _{1 to} 17 _n are formed by applying a visual treatment such as a cover to the slack portion. The main transmission line of the optical fiber 13 between the temperature measuring units on the ceiling 21 is a reference signal (temperature) applying unit, and the lengths of the optical fiber bundles of the temperature measuring units 17 _{1 to} 17 _n are shortened. Can also accurately measure the measurement point position and temperature.

The measurement system of the present invention is calibrated by comparing the temperature measured in a part or the whole area of the optical fiber with the temperature measured by another reference thermometer. Alternatively, a bundle of sufficiently long optical fibers may be placed in a constant temperature bath having a known temperature, and the value read by the OTDR may be adjusted to match the known temperature.

[0032]

As described above in detail, according to the present invention, a transmission line of an optical fiber is continuously laid over each measurement point in a region to be measured, and a reference line is used over a part or the whole region of this transmission line. A reference signal applying section for applying a signal is provided, and a transmission path of the optical fiber is laid behind a thermal partition wall to serve as a reference signal applying section, and the optical fiber is arranged at each measurement point on the partition wall table. By implementing a measurement system that draws a slack in a single stroke as a temperature measurement section and uses the boundary between the front and back to clarify the measurement point position, the measured area When an environmental change occurs in the temperature measurement section on the front side of the partition wall, the temperature change appears sensitively and the temperature change on the back side of the partition wall is slow, so the length of the optical fiber bundle in the temperature measurement section is small. Even measuring point position and temperature It can be accurately measured. In addition, since the optical fiber is drawn out in a slack shape in a single stroke at each temperature measurement unit, there is no need for connection, facilitating construction,
The number of man-hours can be reduced, the loss of light can be minimized, and the number of measurement points can be increased.

[Brief description of drawings]

FIG. 1 is a schematic elevation view showing the configuration of a measuring system according to an embodiment of the present invention.

FIG. 2 is a schematic perspective view showing the configuration of a measuring system according to another embodiment of the present invention.

3A and 3B are views for explaining the relationship between the length of the optical fiber bundle of the temperature measuring unit and the measured value.
FIG. 3A is an equivalent configuration diagram when a reference temperature device is provided outside the measured region, and FIG. 3B is a diagram showing a measured temperature when the equivalent configuration of FIG. 3A is used. .

FIG. 4 is a configuration diagram for explaining the measurement principle of the measurement system of the present invention.

5 is a diagram illustrating a relationship between time and intensity of backscattered light after a light pulse is generated from the light source in the configuration of FIG.

FIG. 6 is a block diagram showing a specific configuration example of the signal processing device in FIG.

[Explanation of symbols]

 11 ... Light source 12 ... Beam splitter 13 ... Optical fiber 14 ... Signal processing device 15 ... Conduit 16 ... Conduit branch pipe 17 ... Temperature measuring part 18 ... Cover 19 ... Stopper 20 ... OTDR type thermometer main body 21 ... Ceiling

Claims (3)

[Claims] 1. An optical symbol is incident from a light source to an incident end of an optical fiber, and backscattered light, which is directed to the incident end, of Raman scattering generated in the optical fiber due to the incidence of the optical signal is returned. In a measurement system in which the signal processing device analyzes the time and the strength of the returned signal to measure temperature, humidity, or temperature distribution, the optical fiber transmission line is continuously connected over each measurement point in the measured region. And a reference signal applying section for applying a reference signal over a part or the whole area of the transmission line, and the reference signal is provided by laying the optical fiber transmission line behind a thermal partition wall. As a voltage application section, at each of the measurement points, the optical fiber is drawn out in a slack shape in a single stroke to the front surface of the partition wall to serve as a temperature measurement section, and the position of the measurement point is clarified using the front and back boundaries. What you did Measuring system. 2. The thermal partition wall is any one of a ceiling, a wall, a floor of a building, and a conduit suspended from the ceiling and installed at a fixed interval from the ceiling.
The described measurement system. 3. The temperature measuring unit comprises an optical fiber drawn in a slack shape from a hole of a partition wall, wound in a non-inductive manner or bundled in a crumpled manner, and the hole is closed with a heat-insulating stopper and wrapped or bundled. The measuring system according to claim 1, wherein the optical fiber is covered with a cover.