CN202975044U - High-reliability fiber bragg grating acceleration sensor with automatic temperature compensation function - Google Patents

Abstract

The invention relates to a highly reliable fiber grating acceleration sensor with self-warming compensation function, which belongs to the technical field of optical fiber sensing. It solves the problems of low sensitivity and poor reliability of traditional fiber grating sensors. It includes a rhomboid beam, a vibrating beam, a mass block and an optical fiber grating. The rhomboid beam includes a rhombus tube and four square beams; the cross section of the rhombus tube is rhombus; the four square beams are fixed clockwise on the four corners of the rhombus tube. On the outer wall, and all on the same plane; the upper surface of the two square beams located at the two acute angles of the rhombus corresponding to the outer wall is provided with a U-shaped groove; the vibrating beam includes a sensitivity-increasing groove, a vibrating arm and a fixed seat; The seat is fixedly connected with the vibrating arm through the sensitization groove; the end of the vibrating arm is stuck in the groove on the upper surface of the mass block; On the sensitive groove, the fiber grating is embedded in the groove of the diamond beam and extends out of the groove. It is suitable for the technical field of optical fiber sensing.

Description

Highly Reliable Fiber Bragg Grating Acceleration Sensor with Self-warming Compensation Function

technical field

The utility model relates to an optical fiber grating acceleration sensor, which belongs to the technical field of optical fiber sensing.

Background technique

At present, fiber Bragg Grating (Fiber Bragg Grating, FBG, referred to as fiber grating) sensing technology has been widely used at home and abroad, such as temperature and stress deformation monitoring of civil engineering structures such as bridges, dams, tunnels, buildings, landslides, debris flows, etc. Geological disaster monitoring, online temperature measurement of switch cabinets, transformers, cables, overhead lines and other power transmission and transformation equipment, automatic fire alarms for oil tanks and tunnels, structural safety monitoring of special equipment such as pressure vessels and hoisting machinery, and mine structure safety monitoring, etc. wait.

The research and testing of vibration is a basis for the development of modern industry, and has a wide range of applications in the fields of science and technology, national economy and national defense. The vibration signal measured by the vibration sensor can be characterized by vibration acceleration or vibration amplitude. Therefore, the detection of vibration signals has two schemes: vibration detection based on vibration acceleration and vibration detection based on vibration amplitude, and the former is the main detection scheme. According to the different physical detection methods of vibration signals, it can be divided into electric detection type acceleration sensor and optical detection type acceleration sensor.

The electric detection acceleration sensor uses the vibration sensitive mechanism to sense the vibration acceleration, and the vibration sensitive mechanism is mainly composed of a sensitive mass block, an elastic element and a conversion element. Electric detection acceleration sensors mainly include electromagnetic induction type, capacitive type and piezoelectric type. Under the action of vibration acceleration, the sensitive mass senses the vibration acceleration and produces motion or stress changes, which drives the conversion elements connected to it, such as electromagnetic coils, capacitor plates to move or produce stress changes in piezoelectric wafers. The electromagnetic coils in the permanent magnet The movement in the magnetic field cuts the magnetic force lines to generate induced voltage, the position change of the capacitor plate changes the capacitance value, and the piezoelectric signal is generated by the stress change of the piezoelectric chip, so that the vibration signal is perceived through the change of the electrical signal. The electrical output signal of the sensor of the electrical detection acceleration sensor is generally very weak, and the amplification circuit in the electrical signal detection unit is required to provide gain. Therefore, the electrical signal detection unit and the vibration sensor must usually be packaged in the same package structure to form an acceleration sensor. That is to say The electrical signal detection unit and the vibration sensor are inseparable. The electrical detection acceleration sensor must also have its own power supply or external power supply. The electrical detection acceleration sensor is characterized by being susceptible to electromagnetic interference, short signal transmission distance, and requiring power supply, which limits the application of the electrical detection acceleration sensor in some occasions such as the presence of electromagnetic interference, difficulty in on-site power supply, and long-distance transmission.

The light detection type acceleration sensor uses the light signal to detect the vibration of the object, including two main forms of non-contact type and contact type. The non-contact acceleration sensor mainly uses the optical signal to directly detect the vibration amplitude (ie displacement) of the surface of a certain part of the object to sense the vibration. It belongs to the absolute vibration measurement. There are methods such as optical fiber displacement detection, laser triangulation method, and laser external cavity oscillation method. Another way of the non-contact acceleration sensor is to use the optical signal to detect the Doppler frequency shift of the reflected or scattered light signal caused by the vibration velocity of the surface of a certain part of the object to sense the vibration. The contact acceleration sensor is fixedly connected with the vibrating object, and uses the vibration sensitive mechanism to sense the vibration acceleration of the object. The vibration sensitive mechanism is mainly composed of a sensitive mass block, an elastic element and a conversion element. Because the fiber optic sensor has small size, light weight, corrosion resistance, anti-electromagnetic interference, and is suitable for flammable and explosive environments, it is usually realized by using optical fiber, which is called an optical fiber acceleration sensor or an optical fiber accelerometer. Optical fiber acceleration sensors can be divided into phase modulation type, wavelength modulation type and light intensity modulation type according to the sensitive principle. The phase-modulated fiber optic acceleration sensor mainly uses a variety of methods to convert vibration signals into optical phase changes, and then uses fiber optic interferometers, such as Fabry-Perot (F-P) interferometers, Michelson interferometers, Mach-Zehnder ( M-Z) interferometer to detect phase changes. This fiber optic acceleration sensor has the advantage of high sensitivity, but the fiber optic interferometer has a complex structure and stability problems, making it difficult to be practical and costly.

The wavelength-modulated fiber-optic acceleration sensor is mainly based on fiber-optic grating (FBG) sensing technology. The FBG stress deformation is driven by the sensitive mechanism, resulting in the change of the FBG reflection wavelength, and the acceleration signal is obtained by wavelength demodulation. In addition to the inherent advantages of fiber optic sensors, the fiber grating acceleration sensor has excellent transmission characteristics (not subject to light source fluctuations and attenuation introduced by long-distance transmission fibers) because its output signal is the central wavelength of the optical signal reflected by the grating, which is a digital quantity impact), and quasi-distributed measurement can be easily realized by multiplexing different wavelengths. It can be widely used in nuclear explosion tests, aerospace engineering and other cutting-edge national defense technology fields, as well as acceleration monitoring and measurement of water conservancy and hydraulic structures, bridges and building structures, mechanical equipment, etc.

Since the fiber grating itself is sensitive to temperature and strain at the same time, when the fiber grating is used as the sensitive element of the acceleration sensor, it will be affected by the temperature and the measurement accuracy will be greatly reduced; in addition, although the fiber grating has good axial tensile fatigue resistance, But once its force direction deviates from the axial direction, it is easily broken by shear force. Aiming at these practical engineering application problems, the utility model proposes a highly reliable fiber grating acceleration sensor with self-warming compensation function which can eliminate temperature influence and avoid fiber grating fracture.

Utility model content

The purpose of the utility model is to provide a highly reliable fiber grating acceleration sensor with a self-warming compensation function for the problems of low sensitivity and poor reliability of traditional fiber grating sensors.

Highly reliable fiber grating acceleration sensor with self-heating compensation function, the sensor includes diamond beams, vibrating beams, mass blocks and fiber gratings;

The rhomboid beams include rhombus tubes and four square beams;

The cross-section of the rhomboid tube is rhombus; the four square beams are fixed clockwise on the outer walls corresponding to the four corners of the rhomboid tube;

The rhomboid tube and the four square beams are located on the same plane;

U-shaped grooves are arranged on the upper surfaces of the two square beams located on the two acute angles of the diamond-shaped cylinder corresponding to the outer walls;

The vibrating beam includes a sensitivity-increasing groove, a vibrating arm and a fixing seat;

The fixing seat is fixedly connected with the vibrating arm through the sensitization groove;

The mass block is a cuboid structure with a groove on the center line of the upper surface, and the end of the vibrating arm of the vibrating beam is stuck in the groove;

The ends of the two square beams located at the two obtuse angles of the rhomboid cylinder corresponding to the outer side walls are fixed on the sensitization grooves of the vibrating beam,

Fiber gratings are embedded in and extend out of the grooves of the diamond beams.

The utility model has the advantages that: the sensor is processed with a sensitivity-increasing groove on the vibrating beam, which improves the detection sensitivity of the acceleration.

The utility model realizes the coordinate axis orthogonal conversion between the force deformation direction of the fiber grating and the force deformation direction of the vibration beam by adding a rhombus beam, isolates the shear force generated by the bending deformation of the vibration beam, and ensures that the fiber grating is always in a linear stretching state , which improves the long-term reliability of the fiber grating acceleration sensor.

The utility model can offset the temperature drift of the fiber grating acceleration sensor by changing the respective thermal expansion coefficients of the vibrating beam and the rhombic beam, and improve the detection accuracy of the acceleration in actual engineering.

Description of drawings

Fig. 1 is the structural representation of the utility model rhombic beam 1;

Fig. 2 is the structural representation of the utility model vibrating beam 2;

Fig. 3 is a structural schematic diagram of the utility model.

Detailed ways

Specific Embodiment 1: The present embodiment will be described below in conjunction with FIG. 1 to FIG. 3 ,

The high-reliability fiber grating acceleration sensor with self-warming compensation function described in this embodiment includes a rhombic beam 1, a vibrating beam 2, a mass block 3 and a fiber grating 5;

The rhomboid beam 1 includes a rhombus tube 1-1 and four square beams 1-2;

The cross section of the rhomboid tube 1-1 is rhombus; the four square beams 1-2 are fixed clockwise on the outer side walls corresponding to the four corners of the rhomboid tube 1-1;

The rhomboid tube 1-1 and the four square beams 1-2 are located on the same plane;

U-shaped grooves are arranged on the upper surfaces of the two square beams located at the two acute angles of the rhombus tube 1-1 corresponding to the outer side walls;

The vibrating beam 2 includes a sensitizing groove 2-1, a vibrating arm 2-2 and a fixing seat 2-3;

The fixing seat 2-3 is fixedly connected with the vibrating arm 2-2 through the sensitization groove 2-1;

The mass block 3 is a cuboid structure with a groove on the center line of the upper surface, and the end of the vibration arm 2-2 of the vibration beam 2 is stuck in the groove;

The ends of the two square beams located at the two obtuse angles of the rhombus tube 1-1 corresponding to the outer side walls are fixed on the sensitization groove 2-1 of the vibrating beam 2,

The fiber grating 5 is embedded in the groove of the diamond beam 1 and extends out of the groove of the diamond beam 1 .

Specific embodiment two: The present embodiment will be described below in conjunction with Fig. 1 to Fig. 3. This embodiment is a further description of the first embodiment. There are two screw holes on the side.

working principle:

The utility model can realize the automatic temperature compensation function, and eliminate the temperature drift effect of the fiber grating acceleration sensor based on the difference of the bimetallic thermal expansion coefficient between the vibrating beam and the rhombic beam; at the same time, the force deformation direction of the fiber grating and the force of the vibrating beam are realized by means of the rhombus beam The coordinate transformation of the deformation direction eliminates the problem of fiber grating fracture caused by the shear force generated by the bending deformation of the vibrating beam.

The optical signal reaches the fiber grating fixed on the vibrating beam through the transmission fiber. Since the fiber grating has wavelength selective characteristics, when the incident wavelength satisfies the Bragg reflection condition, part of the forward transmission light will be coupled into the reverse transmission mode, and It is reflected back to the fiber along the original optical path. The key of this technology is that the vibrating beam has a sensitizing groove, the fiber grating is pre-fixed on the diamond-shaped beam, and then the rhomboid beam is fixed on both sides of the sensitizing groove of the vibrating beam. When the mass block at the end of the vibrating beam produces a reverse inertial force under the action of acceleration, the rhomboid beam fixed on the intensifying groove will undergo greater stress deformation, so that the fiber grating fixed on the rhombus beam has a More sensitive detection capability. In the utility model, the diamond beam and the vibrating beam adopt two kinds of metal materials with different thermal expansion coefficients, thereby realizing automatic compensation for the temperature drift of the fiber grating acceleration sensor; at the same time, the force direction of the diamond beam and the fiber grating The force direction is perpendicular to each other, so that the fiber grating always works in a straight-line tension state, avoiding the problem of fiber grating fracture caused by the shear force generated by the bending of the vibrating beam, and greatly improving the reliability of the fiber grating acceleration sensor. Therefore, the utility model fundamentally solves the problem of temperature drift and long-term reliability of the fiber grating acceleration sensor, thereby meeting the application requirements of practical engineering.

Fiber Bragg grating sensing technology is a sensing technology with high reliability, strong practicability and wavelength division multiplexing in optical fiber sensing. It adopts the laser irradiation method, and the laser spot with the center wavelength of 235nm to 248nm is adjusted by the lens and mirror for multiple times to form a rectangular laser spot with uniform distribution of light intensity, and then the laser spot is patterned with the help of a phase mask. Light and dark equiperiod diffraction fringes are formed along the axial direction of the quartz single-mode fiber, which eventually leads to periodic changes in the refractive index of the fiber in the area irradiated by the patterned spot In 8mm-15mm), after the irradiation is completed, the irradiated and processed area of the single-mode fiber has Bragg reflection characteristics - when the narrow-band light of a specific wavelength that meets the Bragg condition is incident, it will be reflected by the area and return along the original path of the incident light path , while optical signals of other wavelengths are normally transmitted, this area of the fiber is usually called Fiber Bragg Grating (Fiber BraggGrating), referred to as Fiber Bragg Grating (FBG). The central wavelength of the FBG narrow-band reflection spectrum is determined by the equivalent refractive index and the period of the refractive index change of the grating. Physical quantities such as strain and temperature will change the equivalent refractive index and the period of the refractive index change of the grating through the elastic-optic effect and thermo-optic effect, so that The central wavelength of the FBG reflection spectrum drifts, and the demodulation of the physical quantity information can be realized by detecting the change of the central wavelength of the FBG reflection spectrum with a spectrometer or a fiber grating wavelength demodulation device. In this technology, only the gate region of the fiber is sensitive to strain and temperature, and other parts of the fiber are not sensitive to its physical quantity. Therefore, based on the FBG wavelength coding characteristics, the FBG and the fiber itself are integrated, and the light source intensity and other factors cause light Attenuation will not affect the FBG measurement accuracy, and multiple FBG sensors with different central wavelengths can be connected in parallel or in series on one optical fiber for multi-point distributed sensing measurement.

Light intensity modulated fiber optic acceleration sensors have the advantages of simple structure and low cost, and can be divided into three types: transmission type, polarization type and reflection type. The usual structure of the transmission optical fiber acceleration sensor is that the transmitting optical fiber is fixedly connected to the sensitive mass, and the receiving optical fiber connected to the detector is fixedly connected with the measured body. Under the action of the vibration acceleration, the relative displacement of the transmitting optical fiber and the receiving optical fiber occurs, and the optical signal intensity of the receiving optical fiber is modulated by the vibration acceleration. Its receiving optical fiber can be single-path or double-path, and the influence of light source fluctuation can be eliminated by adopting dual-path receiving optical fiber.

Claims (2)

1. A highly reliable fiber grating acceleration sensor with self-warming compensation function, characterized in that: the sensor includes a diamond beam (1), a vibrating beam (2), a mass (3) and a fiber grating (5); The rhomboid beam (1) includes a rhomboid tube (1-1) and four square beams (1-2); The cross section of the rhomboid tube (1-1) is rhombus; the four square beams (1-2) are fixed clockwise on the outer walls corresponding to the four corners of the rhomboid tube (1-1); The rhomboid tube (1-1) and the four square beams (1-2) are located on the same plane; U-shaped grooves are arranged on the upper surfaces of the two square beams located at the two acute angles of the rhombus tube (1-1) corresponding to the outer side walls; The vibrating beam (2) includes a sensitizing groove (2-1), a vibrating arm (2-2) and a fixing seat (2-3); The fixing seat (2-3) is fixedly connected with the vibrating arm (2-2) through the sensitization groove (2-1); The mass block (3) is a cuboid structure with a groove on the center line of the upper surface, and the end of the vibration arm (2-2) of the vibration beam (2) is stuck in the groove; The ends of the two square beams corresponding to the outer sidewalls of the two obtuse angles of the rhombus (1-1) are fixed on the sensitization groove (2-1) of the vibrating beam (2), The optical fiber grating (5) is embedded in the groove of the diamond beam (1) and extends out of the groove of the diamond beam (1). 2. The highly reliable fiber grating acceleration sensor with self-warming compensation function according to claim 1, characterized in that: the two sides of the upper surface center line of the fixed seat (2-2) of the vibrating beam (2) are opened There are two screw holes.

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