CN101424630A

CN101424630A - Optical fibre grating sensor

Info

Publication number: CN101424630A
Application number: CNA2008102322396A
Authority: CN
Inventors: 杜兵
Original assignee: Xian Jinhe Optical Technology Co Ltd
Current assignee: Xian Jinhe Optical Technology Co Ltd
Priority date: 2008-11-12
Filing date: 2008-11-12
Publication date: 2009-05-06

Abstract

The invention relates to a fiber grating sensor which comprises a light source, optical fibers, a probe and a fiber grating, wherein the fiber grating is mounted on the optical fibers in a measuring point, is used for monitoring the change of humidity, and is plated with polyimide. The fiber grating sensor is characterized in that a probe light signal output by a light source is injected from the incident ends of the optical fibers, and the wavelength of probe light is not in a selective function wavelength brand of the fiber grating and forms a preset wavelength difference value with the selective function wavelength band. When the monitored humidity changes to a quantitative value, the selective function wavelength band of the fiber grating in the measuring point at least drifts away to the preset wavelength difference value so that the selective function wavelength band is crossed and overlapped with a probe light signal wavelength brand. At the time, the wavelength band in the measuring point generates a certain reflection or dissipation of the probe light signal, the probe detects the intensity change of the probe light signal at the emergent ends so as to probe the change of the humidity.

Description

A kind of fiber-optic grating sensor

Affiliated technical field

The present invention relates to a kind of fiber-optic grating sensor, is to survey the sensor that humidity changes by optical fiber and fiber grating, and this method belongs to field of sensing technologies.

Background technology

The measurement of humidity is used very extensive in industrial and agricultural production and daily life, greenhouse as agricultural production, the dry run of tobacco, tealeaves, wood working, artificial environments such as medicament compartment, hospital, operating room, bacteria growth chamber, important places such as museum, library, archive office, laboratory, machine room all need to carry out moisture measurement and control.Especially in Minepit environment, water layer caves in to easy initiation of infiltration of rock, by the monitoring that ambient humidity is changed, can avoid the generation of this type of mine disaster effectively.

The most frequently used moisture instruments is a psychrometer at present, utilizes the wet bulb water evaporates to absorb latent heat greater than dry bulb, makes near the temperature of wet bulb be lower than near the temperature of dry bulb, obtains rh value according to temperature difference.But in order correctly to obtain wet-bulb temperature, air should have enough wind speed near the wet bulb.This method is difficult to realize digitizing long-distance transmissions result simultaneously, can't satisfy the actual needs of a lot of productive lifes.

Summary of the invention

The present invention is directed to the deficiencies in the prior art, proposed a kind of measuring accuracy height, be easy to the humidity sensor equipment based on Fiber Bragg Grating FBG integrated and encapsulation.

For this reason, the present invention proposes a kind of fiber-optic grating sensor, comprise light source, optical fiber, detector and be placed in the fiber grating that humidity changes that is used for that is positioned at measurement point on the optical fiber, it is characterized in that:

One this fiber grating surface is coated with one deck polyimide,

The detection light signal of one light source output injects from an end that is called the incident end of optical fiber, and the wavelength of surveying light signal and has the preset wavelength difference with described selectively acting wavelength not in the selectively acting wavelength band of fiber grating,

One when monitored humidity variation reaches certain value, be positioned at the preset wavelength difference that the selectively acting wavelength band of the fiber grating of measurement point has drifted about above-mentioned at least, thereby make this selectively acting wavelength band cover the part of described detection wavelength of optical signal band at least, at this moment, the fiber grating of this measurement point is just to certain reflection or dissipation of having surveyed light signal generating, promptly survey the part reflection or the dissipation of light signal, thereby other end exit end at the incident end of optical fiber, then detect the variation of transmitted light, thereby detect the variation of humidity.

The present invention surveys to be monitored a kind of fiber-optic grating sensor that humidity changes, be to be coated with one deck polyimide on the fiber grating surface, its thickness is the 20-50 micron, when absorbing airborne water vapor, polyimide can expand, thereby make fiber grating generation axial strain, cause fiber grating selectively acting wavelength band position excursion, if variation has taken place near the humidity of being monitored a fiber grating, and the variation that takes place has reached the degree that we are concerned about, at this moment the selectively acting wavelength band of the fiber grating preset wavelength difference of having drifted about at least, thereby make this selectively acting wavelength band cover a part of surveying the wavelength of optical signal band at least, at this moment, the fiber grating of this measurement point is just to certain reflection or dissipation of having surveyed light signal generating, promptly survey the part reflection of light signal or dissipate, detector detects the variation of transmitted light, and this explanation has stress to exist, thereby may detect the variation of corresponding humidity.

In actual engineering, we usually only need obtain the data that a part of humidity changes, just can reach our target, in the humidity warning system in the workshop that needs electrostatic prevention at, we press for understanding to the moisture condition between the 65%RH to 75%RH the time, we only need to set a monitoring, alarming humidity, as 60%RH, then as the fiber grating on the optical fiber of sensor, measure this fiber grating when 60%RH the selectively acting wavelength band and choose a wavelength as the wavelength of surveying light signal, select light source according to this wavelength then, described fiber grating is when 70%RH, its selectively acting wavelength band has wavelength difference with the wavelength of the detection light signal of selecting, this sensor is installed in the place of monitoring, under normal conditions, ambient humidity is between 65%RH to 75%RH the time, the detection light signal that injects sensor fiber loss less passed through optical fiber and fiber grating, can record intensity at the detector of the exit end of optical fiber through light signal, and as benchmark, have only when the humidity of measurement point near or when reaching 60%RH, the fiber grating selectively acting wavelength band of this measurement point will drift about and with the wavelength band juxtaposition of surveying light signal, and to surveying suitable reflection or the dissipation of light signal generating, at this moment, can monitor obvious variation on the detector through the intensity of light signal, thereby triggered the humidity alert if, reached the purpose of monitoring.

Under actual engineering specifications, a value of only monitoring humidity usually is not enough, so the different a plurality of detection light signals of wavelength can be set, just can monitor a plurality of values of humidity, the trend that changes of measurement point humidity as can be seen simultaneously is so that better monitoring.

Description of drawings:

Fig. 1 is the reflectance spectrum of a Bragg grating of expression, the spectrum of a detection light signal and both graphs of a relation;

Fig. 2 is the transmitted spectrum of a long period fiber grating of expression, the spectrum of a detection light signal and both graphs of a relation;

Fig. 3 is the structured flowchart of the fiber-optic grating sensor of relevant first embodiment of the present invention of expression;

Fig. 4 is the structured flowchart of the fiber-optic grating sensor of relevant second embodiment of the present invention of expression;

Fig. 5 is the structured flowchart of the fiber-optic grating sensor of relevant the 3rd embodiment of the present invention of expression;

Among the figure: 3,3a, 3b, 3n one light source,

9a, 9b one optical branching device,

5 one are coated with the fiber grating of polyimide

6,6a, 6b, 6n one photo-detector,

7 one optical fiber,

8 one photoswitches,

10a, 10b, 10n one fixed wave filter.

Embodiment

Curve 1 among Fig. 1 has schematically shown the reflectance spectrum of a Bragg grating, λ ₁And λ ₂Be respectively the lower limit and the upper limit wavelength of this Bragg grating reflection wavelength, all wavelength all are the wavelength that Bragg grating can reflect in these two wavelength, are called the reflection wavelength band here.Curve 2 has schematically shown a spectrum of surveying light signal, λ ₃And λ ₄Be respectively the lower edge and the upper edge wavelength of this detection light signal, λ ₂And λ ₃Between distance be exactly that described preset wavelength is poor.

Curve 11 among Fig. 2 has schematically shown the transmitted spectrum of a long period fiber grating, λ ₁And λ ₂Be respectively the lower limit and the upper limit wavelength of this long period fiber grating coupling attenuation wavelength, long period fiber grating all has decay to all wavelength in these two wavelength, is called the dissipation wavelength band here.Curve 2 has schematically shown a spectrum of surveying light signal, λ ₃And λ ₄Be respectively the lower edge and the upper edge wavelength of this detection light signal, λ ₂And λ ₃Between distance be exactly that described preset wavelength is poor.

First embodiment

Fig. 3 is the structured flowchart of the fiber-optic grating sensor of expression first embodiment.The fiber-optic grating sensor of first embodiment by light source 3, photo-detector 6, be positioned at measurement point and be used to monitor fiber grating that is coated with polyimide 5 and the optical fiber 7 that humidity changes and constitute.Connect with optical fiber between each parts.

Detection light signal from light source 3 outputs, the wavelength of surveying light signal is not in the selectively acting wavelength band of fiber grating 5, and default wavelength difference arranged with it, survey light signal by optical fiber 7 and fiber grating 5, and detect the intensity of surveying light signals by photo-detector 6, at monitored humidity no change or change when not reaching the degree that we are concerned about, the wavelength of surveying light signal is not at the selectively acting wavelength band of the fiber grating 5 that is positioned at measurement point, be that fiber grating 5 is not to surveying light signal reflection or consume, at this moment to detect be zero-decrement substantially light signal to photo-detector 6, and with this intensity as benchmark, when the humidity of monitored point changes to the degree of our care, the selectively acting wavelength band that is positioned at the fiber grating 5 of the described measurement point described preset wavelength difference of having drifted about at least, at this moment described selectively acting wavelength band has covered a part of surveying the wavelength of optical signal band at least, this fiber grating 5 is just to suitable reflection or the dissipation of having surveyed light signal generating, at this moment photo-detector 6 detects the intensity of surveying light signal obvious variation, thereby detects the variation of humidity.

Second embodiment

Fig. 4 is the structured flowchart of the fiber-optic grating sensor of expression second embodiment.The fiber-optic grating sensor of second embodiment by light source 3a, light source 3b, light source 3n, photo-detector 6, photoswitch 8, be positioned at measurement point and be used to monitor that humidity changes is coated with polyimide fiber grating 5 and optical fiber 7 constitutes.Connect with optical fiber between each parts.

From light source 3a, light source 3b, the detection light signal of the different wave length of light source 3n output, the wavelength of surveying light signal is not all in the selectively acting wavelength band of fiber grating 5, and different preset wavelength differences arranged with it, photoswitch 8 can select the detection light signal of Different Light by optical fiber 7 and fiber grating 5, arrive photo-detector 6, at this moment to detect be zero-decrement substantially light signal to photo-detector 6, and with this intensity as benchmark, the variation of monitored humidity can cause the drift of the selectively acting wavelength band of fiber grating 5, when preset wavelength difference that the selectively acting wavelength band has drifted about different, we can detect the Strength Changes of the different detection light signal of input, so just can detect a plurality of values that humidity changes.

The 3rd embodiment

Fig. 5 is the structured flowchart of the fiber-optic grating sensor of expression the 3rd embodiment.The fiber-optic grating sensor of the 3rd embodiment by light source 3a, light source 3b, light source 3n, wave filter 10a, wave filter 10b, wave filter 10n, photo-detector 6a, photo-detector 6b, photo-detector 6n, optical branching device 9a, optical branching device 9b, be positioned at measurement point and be used to monitor that humidity changes is coated with polyimide fiber grating 5 and optical fiber 7 constitutes.Connect with optical fiber between each parts.

From light source 3a, light source 3b, the detection light signal of the different wave length of light source 3n output, the wavelength of surveying light signal is not all in the selectively acting wavelength band of fiber grating 5, and different preset wavelength differences arranged with it, survey light signal by optical branching device 9a, again by optical fiber 7, fiber grating 5 and optical branching device 9b, enter into different detectors by different wave filters respectively, each wave filter and light source are one to one, and only allow the detection light signal of corresponding wavelength to pass through, other detection filtered optical signal is fallen, and when humidity do not changed each intensity of surveying light signal as benchmark, the variation of monitored humidity can cause the drift of the selectively acting wavelength band of fiber grating 5, when the selectively acting wavelength band has drifted about described different preset wavelength difference, will cause the variation of different detection light signal strengths, all detection light signals see through optical fiber 7 and optical branching device 9b, enter into different detectors by different wave filters respectively, detector will be at this moment each intensity of surveying light signal and corresponding benchmark strength ratio, we just can detect a plurality of values of humidity variation like this.

As seen, the method according to detection of the present invention is simpler than the method for prior art.

Certainly, the present invention is not limited to the embodiment that the front is introduced, and we can replace whole device with another kind of equivalent arrangements, and do not exceed scope of the present invention.

Claims

1. fiber-optic grating sensor, comprise light source, optical fiber, detector and be placed on the optical fiber be positioned at measurement point be used to monitor the fiber grating that humidity changes, it is characterized in that:

One this fiber grating surface is coated with one deck polyimide,

One when monitored humidity variation reaches certain value, be positioned at the preset wavelength difference that the selectively acting wavelength band of the fiber grating of measurement point has drifted about above-mentioned at least, thereby make this selectively acting wavelength band cover the part of described detection wavelength of optical signal band at least, at this moment, the fiber grating of this measurement point is just to certain reflection or dissipation of having surveyed light signal generating, promptly survey the part reflection of light signal or dissipate, detector detects the variation that the optical fiber exit end is surveyed light signal strength, thereby detects the variation of described humidity.

2. a kind of fiber-optic grating sensor according to claim 1, it is characterized in that: a plurality of light sources inject a plurality of detection light signals from an end that is called the incident end of optical fiber, its wavelength is not all in described reflection wavelength band, and have different preset wavelength differences, thereby can detect a plurality of values that measurement point humidity changes with reflection wavelength.