JPS63132138A - Distribution type humidity sensor - Google Patents

Abstract

PURPOSE:To vary the lateral pressure of a temperature sensing body to an optical fiber according to temperature variation and to accurately measure the temperature variation and the varying position of temperature by attaining the temperature sensing body to the outer peripheral part of the optical fiber under the state where the lateral pressure with which the optical fiber has high loss at low temperature. CONSTITUTION:A distribution sensor 1 is structured by strongly stranding the optical fiber 2 and a temperature sensing fiber bundle 3, and clamping the fiber 2 by the fiber bundle 3. Then this fiber 2 is obtained by forming a primary coating layer 2b and a secondary coating layer 2c around the outer peripheral part of a normal fiber 2a. This coating layer 2b prevents humidity from entering the fiber 2 and the coating layer 2c protects the optical fiber 2a from external force. Then the lateral pressure of the sensor 1 to the fiber 2 is varied according to temperature variation and the loss of the fiber 2 also varies according to variation in the lateral pressure, so that a trouble point detector connected to an end part of the sensor 1 measures the partial loss variation.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a distributed humidity sensor suitable for use in a hygrometer or the like capable of measuring humidity distribution.

"Conventional technology" In recent years, for example, factories equipped with clean rooms for producing electronic circuit parts such as VLSIs, or high-rise buildings, have begun to remove dust and other substances in order to maintain a suitable and constant environment inside the building. Humidity control is carried out along with removal and temperature control.

Hygrometers such as electrical resistance hygrometers have conventionally been used for such humidity control. This electrical resistance hygrometer is
The humidity sensor is a moisture sensing element that easily absorbs ambient moisture, and the humidity is determined by measuring the change in electrical resistance of this humidity sensor before and after moisture absorption. For example, carbon particles that swell upon absorption of moisture are dispersed in an aqueous solution of hydroxyethyl cellulose, and this is applied onto a substrate and then dried.

To control humidity using such electrical resistance hygrometers, the above-mentioned hygrometers must be installed in each controlled area, and the humidity data obtained from these hygrometers must be collected by a central control device. I try to manage it.

``Problems to be Solved by the Invention'' However, in hygrometers used for such humidity control, it is not possible to manufacture large-scale humidity sensing elements as humidity sensors, so the measurement area that can be measured with one hygrometer is limited. There was a problem that only so-called one-point measurement could be performed. Therefore, in order to measure humidity in the entire managed area, it is necessary to set up many measurement points within the managed area and install one of the above hygrometers at each of these measurement points, especially in large managed areas. In this case, it was difficult to perform detailed humidity control.

Under these circumstances, it has been desired to develop a humidity sensor for use in a hygrometer that can perform multi-point measurements.

``Means for Solving the Problems'' Therefore, as a result of intensive studies in view of the above circumstances, the inventors have determined that changes in humidity can be interpreted as changes in lateral pressure on optical fibers, and that changes in optical fibers due to changes in lateral pressure. By determining the change in loss, we have come to the idea of optically measuring humidity at multiple points along the length of the optical fiber. That is, the feature of the present invention is that a moisture sensitive body is attached to the outer circumferential portion of the optical fiber while applying lateral pressure so that the optical fiber has a high loss under low humidity.

"Function" The distributed humidity sensor of the present invention, having the above-described configuration, exhibits the following function.

That is, by attaching a moisture sensitive body to the outer periphery of the optical fiber in advance under low humidity, lateral pressure is applied to the optical fiber, and this lateral pressure causes partial microbending in the optical fiber, causing the optical fiber to bend. As the humidity increases, the moisture-sensitive body expands in response to the humidity, weakening the lateral pressure on the tip fiber, and eliminating the partial microbending of the optical fiber that occurs at low temperatures. and losses are reduced.

Therefore, the loss change due to the above-mentioned optical fiber microbending can be calculated by inputting light from the input end of the optical fiber.
By measuring the reflected light such as backscattered light of this light, it is possible to detect the amount of loss change and the position where microbending disappears.
Therefore, the humidity change and the position where the humidity change occurs can be easily and accurately detected from these.

"Example" Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a first embodiment of the present invention, and reference numeral 1 in the figure indicates a distributed humidity sensor (hereinafter simply referred to as a sensor). This sensor 1 is made by tightly twisting an optical fiber 2 and a moisture-sensitive fiber bundle 3 together, and tightening the optical fiber 2 with the 1aNfi bundle 3.

The above-mentioned optical fiber 2 is formed by providing a primary coating layer 2b and a secondary coating layer 2c on the outer periphery of an ordinary bare optical fiber 2a such as a silica-based glass fiber.

The primary coating layer 2b is for preventing moisture from penetrating into the optical fiber 2 from the surface of the optical fiber 2. and,
Suitable materials for forming this IE 12b include, but are not limited to, amorphous silicon such as silicon nitride glass and silicon oxynitride glass, amorphous carbon, and amorphous metals such as aluminum and iron. It's not something you can do.

In addition, the film thickness of this second coating layer 2b is determined by the moisture sensitivity described below.ノ<91, -1 dimension A
at can be transmitted to the optical fiber 2 with precision;
It is determined in consideration of preventing moisture from entering the surface of the optical fiber 2, and it is usually sufficient if the amount is about 0.05 μm or more.

A secondary coating layer 2c is formed on the outer peripheral surface of the primary optical fiber 2b to protect the bare optical fiber 2a from external forces.

The material used to form this secondary coating H2c is one that can reliably transmit the lateral pressure caused by twisting the moisture-sensitive fiber bundles to the optical fiber 2, which will be described later. Specifically, low-density polyethylene (LDPE), high Density polyethylene (HDPE)
), polypropylene (PP), ethylene/vinyl acetate copolymer (EVA), ethylene/ethyl acrylate resin (
EEA), polyurethane resin, polyester resin, thermoplastic resin such as nylon, thermosetting resin such as silicone resin, urethane resin, ultraviolet curable resin such as epoxy acrylate resin, urethane acrylate resin, silicone acrylate resin, etc. are preferably used. It will be done. Further, the thickness of the secondary coating layer 2c is sufficient as long as it can protect the optical fiber 2 from unnecessary external forces, and is usually in the range of about 5 to 20 microns.

The optical fiber 2 and the moisture-sensitive fiber bundle 3 are as follows:
are twisted together. The moisture-sensitive fiber bundle 3 becomes wet when the humidity is high, and its tension is released, thereby weakening the partial lateral pressure on the tip fiber 2. This moisture-sensitive fiber bundle 3
The moisture-sensitive material forming the moisture-sensitive fiber bundle 3 is selected from a material having a small Young's modulus along the longitudinal direction of the fibers of the moisture-sensitive fiber bundle 3 under low humidity and a large Young's modulus along the longitudinal direction when moistened under high humidity. ,
Specifically, cellulose derivatives such as methylcellulose, hydroxyethylcellulose, carboxymethylcellulose (CMC), cellulose sulfate, cellulose phosphate, aminodeoxycellulose, and chlorodeoxycellulose are preferably used, but are not limited thereto. The above-mentioned cellulose derivatives have a high degree of polymerization with a large amount of moisture absorption, since the outer diameter of the moisture-sensitive fiber bundle 3 can be made smaller and the resulting sensor 1 can be made more compact as the amount of moisture absorbed per unit volume is larger. It is desirable that the Furthermore, the outer diameter of the moisture-sensitive fiber bundle 3 is as follows:
It is determined in consideration of the type of moisture sensitive body, the moisture absorption characteristics of the moisture sensitive body, etc., and is usually in the range of about 20 to 100 μ blades.

Next, a method for manufacturing the sensor 1 having such a configuration will be described. First, the tip fiber 2 is produced. That is, by depositing solid carbon, which is obtained by rapidly cooling and solidifying gaseous carbon, on the outer peripheral surface of the bare optical fiber 2a made of silica-based glass, for example, a primary wave (! [layer 2b is formed) made of amorphous carbon is formed. Next, the optical fiber wire on which the secondary coating layer 2b has been formed is passed through, for example, a melting tank of an ultraviolet curable epoxy acrylate resin, and the resin is applied onto the primary coating 12b of the wire, and then, By irradiating ultraviolet rays, a secondary coating HJ 2 a having a predetermined thickness is formed on the secondary coating layer 2b to obtain an optical fiber 2.

On the other hand, a moisture-sensitive material made of, for example, hydroxyethyl cellulose is spun into fibers, and these fibrous moisture-sensitive materials are longitudinally attached to each other along the same direction and bundled to form a moisture-sensitive fiber bundle 3 having a predetermined outer diameter. Create.

Next, the desired sensor 1 is obtained by twisting this moisture-sensitive fiber bundle 3 and the optical fiber 2 together under low humidity. Here, the optical fiber 2 and the moisture-sensitive fiber bundle 3 are connected to the optical fiber 2 at a rate of about 5 dB/min under low humidity of about 20 to 30%.
The fibers are twisted together so that a loss of about 11% occurs.

In the sensor 1 obtained in this way,
Since the optical fiber 2 and the moisture-sensitive fiber bundle 3 are twisted together, lateral pressure is applied to the optical fiber 2 during manufacturing, causing microbending loss in the optical fiber 2 and causing a high loss of about 5 dB/&*. Leave it as a loss fiber. Thus, when the optical fiber 2 is placed under high humidity, the moisture sensitive body becomes wet and expands, thereby weakening the lateral pressure on the optical fiber 2. Therefore, in this sensor 1, the lateral pressure on the optical fiber 2 changes as the external humidity changes, and the loss of the optical fiber 2 changes due to this lateral pressure.
For example, an optical fiber failure point detector is connected to the end of the sensor 1, and this detector is used to measure the loss change of the optical fiber 2 due to the lateral pressure as 0TCrt (Optical Time
The amount of change in loss and the position of loss change can be detected by measuring using the Domain Rerrectoa+etry method, etc., and the change in humidity and the position of humidity change can be easily and accurately detected from these detected data.

FIG. 2 shows a second embodiment of the invention. The sensor 1 in this example is roughly composed of an optical fiber 2, a moisture-sensitive fiber layer 4, and a jacket 5.

The above-mentioned moisture-sensitive fiber layer 4 is obtained by spinning the above-mentioned moisture-sensitive material into fibers under low humidity, and longitudinally attaching these fibrous moisture-sensitive materials along the longitudinal direction of the optical fiber 2 while applying a tensile force. Something,
This applies lateral pressure to the optical fiber 2, causing a microbending loss of 5 dB in the optical fiber 2.
/Jcx high loss fiber is used. Thus,
When the optical fiber 2 is placed under high humidity, the moisture sensitive body becomes wet, thereby weakening the lateral pressure on the optical fiber 2.

Jacket 5 has the above-mentioned moisture-sensitive edge [! 14 from external forces, and has breathability to the outer surface of the moisture-sensitive fiber layer 4. The jacket 5 is made of a braid made of synthetic resin fibers or metal fibers, a hard foam made of polystyrene resin, polyurethane resin, phenol resin, urea resin, epoxy resin, acrylic resin, etc., and a hard foam made of polystyrene resin, polyvinyl chloride resin, etc. Porous coating layers such as semi-rigid foam, tapes made of viscose rayon such as cellophane, etc. are preferably used, but are not limited to these. Note that the jacket 5 may be provided loosely on the moisture-sensitive fiber layer 4.

In the sensor l of this example, since the jacket 5 is provided on the outside of the moisture-sensitive fiber layer 4, the moisture-sensitive fiber layer 4 made of a moisture-sensitive element can be protected from external force. Since changes in the loss of the optical fiber 2 due to changes in humidity can be distinguished from changes in loss in the optical fiber 2 due to external forces, changes in humidity can be measured more accurately.

FIG. 3 shows a third embodiment of the invention. In the sensor l of this example, a plurality of moisture-sensitive fiber bundles 3 are formed around the optical fiber 2 on the outer peripheral surface of the optical fiber 2 under low humidity.
... are strongly twisted together, and these moisture-sensitive fiber bundles 3
. . . It has a structure in which a jacket 5 is provided on top.

The moisture-sensitive fiber bundle 3 is sandwiched between the outer circumferential surface of the optical fiber 2 and the inner 11 surface of the jacket 5 under low humidity conditions, and when the humidity increases, the moisture-sensitive fiber bundle 3 becomes wet and the binding force on the optical fiber 2 becomes loose. Therefore, the loss of the optical fiber 2 is reduced due to the reduction in the binding force on the moisture-sensitive fiber bundle 3. Therefore, in this example as well, a change in external humidity can be interpreted as a change in loss in the optical fiber 2, so by measuring the amount of change in loss in the optical fiber 2 and its position, the humidity can be easily and accurately determined. Changes and their measurement locations can be detected.

[Experiment example]

(Example 1) On the outer peripheral surface of a bare optical fiber (relative refractive index difference of about 1.0%) with a cladding diameter of 125μ11 and a core diameter of 80μ, a film with a thickness of 0
．． After forming a primary coating layer made of amorphous carbon having a thickness of 1 μm, a secondary coating layer made of an ultraviolet curable epoxy acrylate resin and having a thickness of approximately 20 μm was formed on this secondary coating layer to obtain an optical fiber.

On the other hand, as a moisture sensitive material, hydroxyethyl cellulose with a high degree of polymerization was spun into fibers, and these fibers were longitudinally attached to each other along the same direction and bundled to obtain a moisture sensitive fiber bundle having an outer diameter of about 165 μm.

Next, this moisture-sensitive fiber bundle and the above-mentioned optical fiber were heated at a humidity of 30°C.
A sensor as shown in FIG. 1 with a loss of 5 dB/&x was produced by twisting each other with each other while applying back tension at a twisting speed of 6 leaks/min and a pitch of 20 JIJ.

(Example 2) Humidity level 3 was applied on the outer peripheral surface of the optical fiber obtained in Example 1 above.
A large number of hydroxyethyl cellulose fibers with a high degree of polymerization under 0% are vertically attached with a back tension of 500 g/cm'' to form a moisture-sensitive fiber layer with a film thickness of 20tIR, and then cellophane is further applied on this moisture-sensitive fiber layer. The sensor shown in Figure 2 with a loss of 5 dB/&z was obtained by wrapping a piece of tape to form a jacket.The sensor thus obtained had an outer diameter of about 190 μ It was agriculture.

(Example 3) Centering on the optical fiber obtained in Example 1 above, nine pieces with an outer diameter of 100 μm were placed on the outer periphery of the optical fiber under 30% humidity.
1 of moisture-sensitive fiber bundles twisted at a speed of 6 blades/min, 40J11
The fibers were twisted in a pinch while applying back tension, and a synthetic resin braid was wound around these moisture-sensitive fiber bundles to obtain a sensor with a loss of 5 dB/km as shown in FIG. 3.

Next, the length of about 1001 obtained in each of Examples 1 to 3 above is
I tried measuring humidity using this sensor. That is,
A fiber optic fault detector was connected to one end of each sensor.

This detector is a device for investigating loss changes in optical fibers, and consists of a light-emitting section consisting of a pulse generator and a light-emitting diode that input light pulses from the input end of the optical fiber, and a Fresnel reflection from the optical fiber. A light detection unit that receives reflected light pulses such as light and backscattered light, a calculation unit that processes the time delay of the reflected light pulses received by this light detection unit, and a display unit that displays the processing results. It is composed of.

Then, from the other end of the sensor connected to this detector, 10
A section of ~30 m was placed in a humidity adjustment tank with an internal temperature of 24°C, and the humidity in this humidity adjustment tank was varied in the range of 30 to 80%, and the relationship between this humidity change and the loss change of the tip fiber was investigated. The results are shown in the graph of FIG.

As is clear from the graph in FIG. 4, in Examples 1 to 3, the optical fiber was formed under 30% humidity by lateral pressure on the optical fiber by winding the moisture-sensitive fiber bundle or longitudinally supporting the moisture-sensitive fiber layer. It was found that a loss of about 5 dB/km occurs, but as the humidity gradually increases, the loss decreases, and that the decrease in loss becomes extremely small when the humidity is about 70% or more. Therefore, in each of these Examples, it was found that if the humidity was in the range of 30 to 70%, the humidity data could be measured as a change in the loss of the optical fiber.

Next, connect the above detector to one end of the sensor with a sensor length of 10001, set the humidity environment of this detector and the senna to 30%, and then
Humidity is 40%, 5 only at each point x, 800+t, respectively.
It was set to 0% and 60%.

Then, when we measured the loss change m of the optical fiber and its position using a detector and referring to the graph in Figure 4, we found that the point where the humidity change was observed was 10 minutes from the detector.
0.2II, 499.8g, 798.8R, and the humidity at each point is 39.5%, 50.5%, 60
%Met.

"Effects of the Invention" As explained above, the sensor of the present invention has a moisture-sensitive element attached to the outer periphery of an optical fiber while applying lateral pressure so that the optical fiber has a high loss under low humidity. Therefore, the lateral pressure exerted by the moisture sensitive body on the optical fiber changes in accordance with changes in humidity, and the loss of the optical fiber changes as the lateral pressure changes. Therefore, if an optical fiber failure point detector is connected to one end of this sensor, and the sensor's local loss change is measured by this detector, the humidity change and the loss change position can be determined from the loss change amount and loss change position. The position of change in humidity can be easily and accurately measured.

Furthermore, according to this sensor, it is possible to measure humidity at multiple points along the longitudinal direction of the optical fiber. Therefore, when used for humidity control, for example, even if the controlled area is wide, the humidity of the entire controlled area can be measured. Distribution can be easily and accurately measured.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view showing a first embodiment of the invention, FIG. 2 is a schematic sectional view showing a second embodiment of the invention, and FIG.
The figure is a schematic sectional view showing a third embodiment of the invention, and FIG. 4 is a graph showing an example of humidity measurement using the distributed humidity sensor of the invention. I...Senna (distributed humidity sensor), 2...Optical fiber, 3...Moisture sensitive fiber bundle (humidity sensitive body), 4...Moisture sensitive fiber layer (humidity sensitive body).

Claims (1)

[Claims] A distributed humidity sensor characterized in that a moisture sensing element is attached to the outer periphery of an optical fiber in a state where lateral pressure is applied so that the optical fiber has a high loss under low humidity.