JPS62204143A - Optical fiber type humidity sensor - Google Patents

Abstract

PURPOSE:To enable measurement which is high in stability and accuracy and widely applicable by scattering and sticking a fine moisture-absorptive material which has a higher refractive index than the quartz core of an optical fiber in a low humidity range on the surface of the quartz core. CONSTITUTION:The fine moisture-absorptive material A which has the higher refractive index than the surface-treated quartz core is scattered and stuck on the surface of the core, which is arranged in a measurement area 8 which is filled with gas to be measured such as air. A photodetector 10 detects the intensity of light from a light source 9 which is incident on the fiber core 7. Light which is reflected and propagated in the quartz core strikes on the interface between the core and material A to have optical loss. When this material A contains a little water, the refractive index decreases and the leak of water increases by water absorption until the quartz core and material A become equal in refractive index and scattered light propagated components into the quartz core increase. Consequently, the transmitted light in the fiber core 7 varies in intensity according to variation in the humidity of the gas to be measured and the temperature of the gas to be measured is found from the intensity of the transmitted light of the photodetector 10.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical fiber humidity sensor in which the optical fiber itself is used as a dampening sensor.

[Prior art 1] Conventional humidity measurement is mostly based on a method that utilizes changes in resistance and resistance to humidity of materials such as ceramics and plastics, and detects these electrically to determine humidity.

In addition, as a method using an optical fiber, as shown in FIG. Using changes in the infrared absorption intensity due to changes in the humidity of the air in the light source 4, the light from the hk and others is transferred to the light transmitting optical fiber 1.
There is a method in which the light is transmitted through a space 3 and an optical fiber 2 for receiving light, and the intensity thereof is detected by a light receiver 5. Furthermore, as an improvement on this method, a method has been proposed in which a moisture-sensitive resin whose absorption coefficient of a specific wavelength changes depending on humidity is interposed between the transmitting and receiving optical fibers (Japanese Patent Laid-Open No. 56-67738).
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[Problems to be Solved by the Invention] However, in the above-mentioned method of electrically detecting the resistance change shade with respect to humidity, there are many problems such as electrical noise due to the application of humidity detection using J3 in a high voltage environment. Furthermore, with this method, humidity can only be detected within a very limited area where the sensor is installed. It is necessary to install a sensor.

The optical method shown in Fig. 6 can be applied even under high voltage, but due to changes in humidity, etc., the light transmission optical fiber 1
The optical axis of the light-receiving optical fiber 2 is easily misaligned, or it is easily affected by dust in the outside air, making stable measurement difficult, and it can only be used in limited environments. Furthermore, high rIli degree processing is required for the jigs and the like that support the optical lens 6 and the optical fiber 1.2.

On the other hand, in a method in which a moisture-sensitive resin is interposed between optical fibers for transmitting and receiving light, the optical system can be easily fixed and is less susceptible to influences other than humidity, such as dust.

However, due to moisture absorption and swelling of the moisture-sensitive resin, microbent occurs at the joint between the moisture-sensitive resin and the optical fiber, and this causes J.
The l'l loss increases, making stable measurement difficult.

In addition, the resin deteriorates over time, making it impossible to obtain sufficient long-term performance. Furthermore, it is a method that does not insert a moisture-sensitive resin into the optical transmission path, and if you try to increase the sensitivity to humidity changes by thickening the moisture-sensitive resin,
There is a problem that the attenuation of light inevitably increases and the received light W decreases.

In addition, since the method detects only light of a specific wavelength,
The equipment becomes expensive.

[Object of the Invention] The present invention was devised to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide high stability.

An object of the present invention is to provide an optical fiber type humidity sensor that can measure humidity with high accuracy and a wide range of applications at low cost.

[Summary of the Invention] In order to achieve the above object, the present invention provides a quartz core surface of an optical fiber with a
A fine hygroscopic substance with a refractive index, such as carbide of silicone polymer, is scattered and deposited to form a surface-treated optical fiber core,
The surface-treated optical fiber core is arranged so that its outer periphery is surrounded by a gas to be measured whose humidity is to be measured, and the humidity of the gas to be measured is determined from the change in the intensity of light when light is incident on the surface-treated optical fiber core. It has the configuration you are looking for.

Examples] Specific examples of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a humidity detection device using an optical fiber type humidity sensor V of the present invention. In the figure, 7 is a surface-treated optical fiber core in which a fine hygroscopic substance having a higher refractive index than the quartz core in a low humidity region is scattered and adhered to the surface of the quartz core.
The surface-treated optical fiber core 7 is arranged in a measurement region 8 filled with a gas to be measured such as air. A light source 9 is installed at one end of the surface-treated optical fiber core 7, and a light receiver 10 is installed at the other end.

Light incident on the surface-treated optical fiber core 7 from the light source 9 propagates through the surface-treated optical fiber core 7, and its intensity is detected by the light receiver 10. However, in the surface-treated optical fiber core 7, fine hygroscopic substances having a higher refractive index than the quartz core in a low temperature region are scattered and attached to the surface of the quartz core.
When light reflected and propagated within the quartz core hits the interface between the quartz core and the fine hygroscopic material, light leakage and Fresnel reflection occur at this interface, resulting in optical loss. When this fine hygroscopic material absorbs a small amount of moisture due to moisture absorption, its refractive index decreases, and as shown in FIG. Accordingly, the leakage of light increases according to region (3) in FIG. 4, and the leaked light is scattered at the moisture interface in the fine hygroscopic material, and the scattered light propagation component into the quartz core also increases. Therefore, the intensity of light transmitted through the surface-treated optical fiber core 7 changes in accordance with changes in the humidity of the gas to be measured, and the humidity of the gas to be measured can be determined from the intensity of light transmitted through the light receiver 10.

In addition, since the refractive index change due to humidity of the fine hygroscopic substance is significantly smaller than the refractive index change due to temperature, it is possible to accurately detect the change in IG.Experiments have shown that the fine hygroscopic substance mentioned above is silicone polymer. It was confirmed that carbides of silicone rubber and silicone resin are suitable.

In this way, in the present invention, the surface-treated optical fiber core 7 itself is used as a humidity sensor, so it can be used not only under high voltage but also in a wide range of environments, and it can also be used in a wide range of environments due to aging, optical system misalignment, etc. Humidity measurement can be performed with stable accuracy without any errors. Furthermore, there is no restriction on the measurement wavelength and it can be carried out at low cost.

FIG. 2 shows that when light is incident on a surface-treated optical fiber core 7 in which measurement areas 8 are formed at intervals along the axial direction,
This figure shows a measuring device that determines the humidity of a gas to be measured from the intensity of backscattered light that returns to the incident side of the scattered light. The light source 9 is modulated by the pulse generator 11 to generate pulsed light, which is incident on the surface-treated optical fiber core 7. There are a plurality of measurement regions 8 surrounded by the gas to be measured in the axial direction of the surface-treated optical fiber core 7, and a plurality of measurement regions 8 surrounded by the gas to be measured in the axial direction of the surface-treated optical fiber core 7, The pulsed light incident on the surface-treated optical fiber core 7 changes in the leakage light and its scattering at the trace moisture interface in response to changes in the humidity of the gas to be measured in each measurement region 8, and the backscattered light changes. The intensity is detected by a photoreceiver 10 via a directional coupler 12.

The pulse generation time of the pulse generator 11 is monitored by the timing generator 13, and the humidity detection position and humidity are determined by the signal processing circuit 14 from this pulse generation time and the backscattered light pulse detection time and intensity detected by the light receiver 10. It is calculated and displayed on the display device 15.

This humidity measurement is a multi-point measurement with multiple measurement areas 8,
It is possible to measure each humidity distribution.

When the optical fiber type humidity sensor of the present invention was used to change the relative humidity of the air in the range of 20 to 80% and measure the change in backscattered light intensity using the method shown in Figure 2, the results were as shown in Figure 5. It was confirmed that there was an intensity change of 3 (18 or more), and that the sample had good sensitivity and high-speed response.

[Effects of the Invention] To summarize, according to the present invention, the following excellent effects are achieved.

(1) The optical fiber itself is q t = center, and there is no need for any optical elements other than the optical fiber, and there is no need to measure at a specific wavelength such as infrared rays. Therefore, the measurement system can be simplified, handling is easy, and costs can be reduced.

(2) Furthermore, since the optical fiber itself is used as a humidity sensor, there is no loss caused by intervening optical lenses or the like due to deterioration over time, and stable measurement can be performed over a long period of time.

(3) It is possible to sense not only one point but also long-distance sensing of humidity and moisture distribution along the length of an optical fiber.

(4) Highly sensitive detection over a wide humidity range due to the use of significant refractive index changes due to moisture absorption of fine hygroscopic substances scattered on the quartz core surface or changes in scattered light intensity at trace moisture interfaces I can do it.

(5) Rather than detecting humidity by using the change in characteristics due to moisture absorption of a moisture-sensitive element such as a ceramic or moisture-sensitive resin,
The surface of the quartz core is treated with a fine hygroscopic material that has a higher refractive index than the quartz core in the low humidity ffi range to avoid adhesion.The gas to be measured is detected by directly contacting the outer periphery of the optical fiber core. , has good responsiveness and can quickly detect humidity changes.

[Brief explanation of drawings]

Figures 1 and 2 are schematic configuration diagrams showing devices for measuring humidity according to the present invention, and Figure 3 shows the refractive index of a surface-treated optical fiber core of an optical fiber type humidity sensor to be incorporated into these devices. Distribution diagram, Figure 4 is a characteristic diagram showing the relationship between changes in refractive index and transmitted light intensity, Figure 5 is a diagram showing the measurement results of backscattered light-humidity dependence using the device in Figure 2, and Figure 6 1 is a schematic configuration diagram showing a conventional humidity measuring device. 1... Optical fiber for light transmission. 2...Optical fiber for light reception. 3...Space. 4...Light source. 5... Light receiver. 6...Optical lens. 7...Surface treated optical fiber core. 8...Measurement area. 9...Light source. 10... Light receiver. 11...Pulse generator. 12... Directional coupler. 13...Timing generator. 14...Signal processing circuit. 15...Display device. Agent Patent Attorney Fujio Sato No. 3 n AJ Shiiyakuchikagenogu'Core T Guide) Emachi 廝Fig. time

Claims (6)

[Claims] (1) A fine hygroscopic substance having a higher refractive index than the quartz core in a low humidity region is scattered and adhered to the surface of the quartz core of the optical fiber to form a surface-treated optical fiber core, and the outer periphery of the surface-treated optical fiber core is formed. is arranged so that it is surrounded by the gas to be measured whose temperature is to be measured, and the humidity of the gas to be measured is determined from the change in the intensity of light when the light is incident on the surface-treated optical fiber core. Optical fiber type humidity sensor. (2) The surface-treated optical fiber core has the fine hygroscopic substance scattered and adhered to the surface of the quartz core at appropriate intervals along the axial direction of the quartz core. Optical fiber type temperature sensor according to scope 1. (3) The optical fiber type humidity sensor according to any one of claims 1 to 2, wherein a carbide of a silicone polymer is used as the fine hygroscopic substance. (4) The humidity of the gas to be measured is determined from the intensity of transmitted light when the light is incident on the surface-treated optical fiber core. Optical fiber type humidity sensor. (5) Claims 1 to 3 are characterized in that the humidity of the gas to be measured is determined from the intensity of backscattered light when light is incident on the surface-treated optical fiber core. Optical fiber type humidity sensor. (6) The humidity distribution of the gas to be measured along the axial direction of the surface-treated optical fiber core is determined from the temporal change in backscattered light when pulsed light is incident on the surface-treated optical fiber core. An optical fiber type temperature sensor according to any one of claims 1 to 3.