CN104848927A - Vibration detection system based on chirped grating sensing and wavelength division multiplexing technology - Google Patents

Abstract

The invention provides a vibration detection system based on chirped grating sensing and a wavelength division multiplexing technology. The vibration detection system comprises a broadband light source, an optical coupler, a fiber grating vibration sensor group, a wavelength division multiplexing device, a photoelectric detector array and a signal acquisition processor. Light emitted by the broadband light source penetrates into the fiber grating vibration sensor group via the optical coupler, returned optical signals penetrate into the wavelength division multiplexing device via the optical coupler, and the output ends of the wavelength division multiplexing device are input to the signal acquisition processor through the photoelectric detector array; the fiber grating vibration sensor group is composed of multiple groups of fiber gratings on one optical fiber, and each group of gratings comprises two chirped fiber gratings; and the wavelength division multiplexing device comprises one input end and the n output ends. The vibration detection system provided by the invention can enlarge the detection scope of a fiber grating vibration detection system and improves the detection capability.

Description

Vibration detection system based on chirped grating sensing and wavelength division multiplexing technology

technical field

The invention belongs to the technical field of optical fiber sensing and detection, and in particular relates to a vibration detection system based on chirped grating sensing and wavelength division multiplexing technology.

Background technique

Vibration is an inherent characteristic of all moving objects, and the vibration signal contains a wealth of object state information. Therefore, vibration signal detection technology is one of the foundation and key technologies for understanding and grasping the state of motion of objects. In the detection and diagnosis of mechanical equipment, vibration detection technology plays an important role and develops rapidly. It can be said that vibration detection is one of the most promising methods in state detection and fault diagnosis of mechanical equipment.

In the field of vibration detection of mechanical equipment, the monitoring method based on electromagnetic sensors is widely used at present. For example, Harbin Institute of Technology has developed a representative mechanical condition monitoring and fault diagnosis system - MMMD system. The team of Academician Gao Jinji of Beijing University of Chemical Technology has monitored more than 5,700 sets of pumps, and established a remote monitoring network for equipment and an intelligent platform for maintenance and safety assurance information based on SOA architecture. However, these systems are all developed based on electromagnetic sensing technology. The eddy current displacement vibration sensor developed by Bentley Corporation of the United States has been widely used in the field of mechanical equipment monitoring. However, for mechanical equipment testing in special environments, such as high temperature, high pressure, flammable, explosive and other dangerous occasions, the above-mentioned testing instruments and methods are not competent.

Due to the characteristics of non-electric detection and intrinsic safety, optical fiber sensing technology has become a new and important detection method in the field of danger detection. For the detection of vibration signals of mechanical equipment, sensors and their detection methods are the key. The vibration detection methods of fiber grating mainly include: wavelength detection method, phase detection method, light intensity detection method and so on. For the detection of high-frequency vibration signals, the main problem of the wavelength detection method is that the demodulation speed is difficult to meet the detection requirements. However, the phase detection method has the problem of poor detection accuracy. The light intensity detection method has become one of the most used methods because of its advantages such as fast demodulation speed, simple detection device, and low manufacturing cost.

The light intensity detection method is a vibration signal method based on double grating matching and edge filter demodulation. It makes use of the approximately linear feature of the grating reflection spectrum edge to allow two gratings with similar wavelengths to form a match in the edge area, convert the wavelength change caused by the vibration signal into light intensity approximately linearly, and measure the vibration signal by detecting the light intensity. frequency and amplitude. Although this method has the above-mentioned advantages, it also exposes some shortcomings in application: first, the detection accuracy is not high. The detection result is greatly affected by light source fluctuation and line loss, and the detection accuracy is not high. Aiming at this point, the invention patent CN201010104541.0 introduces a reference grating, and uses a light intensity ratio algorithm to solve this problem skillfully. Second, the dynamic detection range is small. When the vibration amplitude of the mechanical equipment under test is large, it will exceed the dynamic detection range of the system; third, the detection capability is insufficient. The single channel of the system detection instrument can only demodulate one vibration sensing signal, and when there are many detection points, it cannot perform synchronous detection. So far, there is still no effective solution for the last two problems of the light intensity detection method.

Contents of the invention

The technical problem to be solved by the present invention is to provide a vibration detection system based on chirped grating sensing and wavelength division multiplexing technology, which can increase the detection range of the fiber grating vibration detection system and improve the detection capability.

The technical solution adopted by the present invention to solve the above technical problems is: a vibration detection system based on chirped grating sensing and wavelength division multiplexing technology, characterized in that it includes a broadband light source, an optical coupler, and a fiber grating vibration sensor Group, wavelength division multiplexer, photodetector array and signal acquisition processor, wherein the light emitted by the broadband light source enters the fiber grating vibration sensor group through the optical coupler, and the optical signal returned by the fiber grating vibration sensor group passes through the optical coupler and enters the wave A division multiplexer, the output of the wavelength division multiplexer converts the optical signal into an electrical signal through a photodetector array and then inputs it to the signal acquisition processor;

The fiber grating vibration sensor group is a plurality of groups of fiber gratings on an optical fiber, and each group of gratings contains two chirped fiber gratings;

The wavelength division multiplexer includes an input port and n output ports, and outputs n lights in different wave bands, the bandwidth of the light wave is greater than the maximum bandwidth of the reflection spectrum of the fiber grating vibration sensor group, and each output port is connected to a photodetector , n photodetectors constitute the photodetector array.

According to the above solution, the optical coupler is a 3dB optical coupler, the 3dB bandwidth of the chirped fiber grating is greater than 2nm, and the center wavelength difference is less than 0.5nm.

The beneficial effects of the present invention are as follows: the use of chirped fiber grating as the sensing element expands the linear matching range of the sensing grating, and can significantly improve the dynamic detection range of the fiber grating vibration sensor; using a wavelength division multiplexer, multiple The fiber grating vibration sensor is multiplexed on one optical fiber, and the signals of each sensor are separated and detected independently during detection. Therefore, after adding a wavelength division multiplexer in the demodulation optical path, the single channel of the fiber grating demodulation instrument carries the sensor The quantity has been significantly improved, and the detection ability of the system has been enhanced; by adopting the system of the present invention, the difficulty of making the fiber grating vibration sensor and the comprehensive manufacturing cost of the system have been reduced, and it is suitable for popularization and application in engineering practice.

Description of drawings

Fig. 1 is a schematic structural diagram of an embodiment of the present invention.

Fig. 2 is a structural schematic diagram of a fiber grating vibration sensor.

In the figure: 1-broadband light source, 2-optical coupler, 3-wavelength division multiplexer, 4-photodetector array, 5-fiber grating vibration sensor group, 6-signal acquisition processor.

Detailed ways

The present invention will be further described below in conjunction with specific examples and accompanying drawings.

Fig. 1 is a structural schematic diagram of an embodiment of the present invention, and the vibration detection system based on chirped grating sensing and wavelength division multiplexing technology includes a broadband light source 1, an optical coupler 2, a fiber grating vibration sensor group 5, and a wavelength division multiplexer 3. The photodetector array 4 and the signal acquisition processor 6, wherein the light emitted by the broadband light source 1 enters the fiber grating vibration sensor group 5 through the optical coupler 2, and the optical signal returned by the fiber grating vibration sensor group 5 enters through the optical coupler 2 The wavelength division multiplexer 3 , the output terminal of the wavelength division multiplexer 3 converts the optical signal into an electrical signal through the photodetector array 4 and then inputs it to the signal acquisition processor 6 .

The fiber grating vibration sensor group is multiple groups of fiber gratings on one optical fiber, as shown in Figure 2, each group of gratings contains two chirped fiber gratings.

The wavelength division multiplexer includes an input port and n output ports, and outputs n lights in different wave bands, the bandwidth of the light wave is greater than the maximum bandwidth of the reflection spectrum of the fiber grating vibration sensor group, and each output port is connected to a photodetector , n photodetectors constitute the photodetector array.

In this embodiment, the optical coupler is a 3dB optical coupler, the 3dB bandwidth of the chirped fiber gratings is greater than 2nm, the center wavelength difference is less than 0.5nm, and their reflection spectra are mostly in an overlapping state, that is, matching. Using a chirped fiber grating as a sensing grating increases the dynamic detection range of the fiber grating vibration sensor several times. The reflection spectrum of each group of gratings is within the spectrum of the broadband light source, and a certain interval is maintained between the reflection spectra of each group of gratings (the wavelength interval is greater than 2nm), so as to avoid interference between signals from different sensors and improve measurement accuracy and reliability. . Each set of gratings corresponds to an output of the wavelength division multiplexer.

The present invention takes the water pump as an example, and installs 4 groups of gratings on the non-coupling side of the water pump unit (one vertical, one horizontal and one axial) and one anchor bolt on the same side. Connect the end to end of four groups of gratings sequentially and multiplex them onto one optical fiber. Since the water pump unit is on site and the detection equipment is placed in the operating room, a 200-meter transmission optical cable is needed to transmit the signal to the operating room. In this embodiment, the bandwidth of the broadband light source is 1280-1325 nm, and the optical power is 18 μw. The wavelength division multiplexer is a 1×4 structure, with 4 available bands, the center wavelengths are 1290nm, 1300nm, 1310nm, 1320nm, the wavelength range of each band is 5nm, and the band interval is 5nm. The light emitted by the broadband light source passes through the 3dB optical coupler and then irradiates the fiber grating vibration sensor group. The light that meets the conditions is reflected and then enters the wavelength division multiplexer through the 3dB optical coupler. The light of different wavelengths is multiplexed from the wavelength division multiplexer The corresponding output port of the device is output, and the output light enters the photodetector array and is converted into a corresponding electrical signal, and then sent to the signal acquisition processor.

The detection principle of the fiber grating vibration detection system: when the fiber grating vibration sensor vibrates together with the water pump, the reflection spectrum of the sensing grating will move, and the envelope area of the reflection spectrum will change periodically, that is, the output light intensity of the sensor will also produce periodic changes. The change frequency is equal to the vibration frequency of the pump unit, and the change range indirectly reflects the amplitude of the pump unit. The light intensity signal is converted into an electrical signal by the detection device 6, and sent to the computer for collection and processing to directly display the vibration parameters of the water pump unit. In this embodiment, the rated rotational speed of the water pump unit is 1200 rpm, the rotational frequency is 20 Hz, and the collection frequency of the system is set to 2560 Hz. When the water pump unit is working, the four groups of gratings all respond, and their time domain responses are similar, but through frequency domain analysis, it is found that the amplitudes of different frequency components are different. It can be seen that the vibration acceleration spectrum of the bearing seat is a synthesis of multi-order harmonic components dominated by the fundamental frequency, which better reflects the state characteristics of the pump unit under working conditions. The effective value of the maximum acceleration is 18.45ms ^-2 , which is basically consistent with the result obtained by the hand-held measuring instrument. This example verifies the feasibility of the present invention.

According to actual needs, the space division multiplexing technology system can be used to realize expansion, forming a detection system with 1, 2, 4, 8, 16 channels, etc., which improves the detection ability of the system and can meet the simultaneous detection of multiple mechanical equipment (groups) It can realize remote and online monitoring of vibration signals of multiple large-scale mechanical equipment.

The above embodiments are only used to illustrate the design concept and characteristics of the present invention, and its purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The protection scope of the present invention is not limited to the above embodiments. Therefore, all equivalent changes or modifications based on the principles and design ideas disclosed in the present invention are within the protection scope of the present invention.

Claims (2)

1. the vibration detecting system based on chirp grating sensing and wavelength-division multiplex technique, it is characterized in that: it comprises wideband light source, photo-coupler, optical fiber raster vibration sensor group, wavelength division multiplexer, photodetector array and signal acquisition process device, the light that wherein wideband light source sends enters optical fiber raster vibration sensor group through photo-coupler, the light signal that optical fiber raster vibration sensor group returns enters wavelength division multiplexer through photo-coupler, light signal is converted to electric signal by photodetector array and inputs to signal acquisition process device again by the output terminal of wavelength division multiplexer,

Described optical fiber raster vibration sensor group is the many groups fiber grating on an optical fiber, often organizes grating and comprises 2 chirped fiber gratings;

Described wavelength division multiplexer comprises an input end and n output terminal, export the light that n is positioned at different-waveband, band of light is wider than the maximum bandwidth of optical fiber raster vibration sensor group reflectance spectrum, each output terminal connects a photodetector, the photodetector array described in n photodetector is formed.

2. the vibration detecting system based on chirp grating sensing and wavelength-division multiplex technique according to claim 1, it is characterized in that: described photo-coupler is 3dB photo-coupler, described chirped fiber grating three dB bandwidth is all greater than 2nm, and central wavelength difference is less than 0.5nm.