Fabrication of cascaded fiber grating pressure sensor for annulus of rod pumping wells

In order to realizethe pressure measurement with wide range in narrow sapce of annulus of rod pumping wells, a cascaded fiber grating pressure sensor has been developed. First, according to the actual working condition, a packaging structure of optical fiber grating pressure sensor is designed based on the combination of flat diaphragm and equal-strength beam. Using the method of cascading, the measuring range is expanded without changing the performance index of optical fiber grating, and the contradiction between pressure measurement range and sensitivity is solved. Then the rationality and feasibility of this structure are verified through mechanical analysis, and the temperature compensation method of cascaded pressure sensor is expounded. Finally, the experimental results show that the pressure measuring range is from 0 to 30 MPa, sensitivity is 329 pm/MPa, and linear degree is above 98%. The sensor is simple and small in structure, easy to realize, and the actual thickness is only 17 mm after assembling to the tube, which can satisfy requirements of pressure monitoring in annulus of rod pumping wells.