Prototype fiber-optic pressure cell for stress monitoring

A fiber-optic pressure cell (FOPC) device for measurement of real stress in the construction and mining industries, which is miniature, completely free from electromagnetic interference (EMI), and directly compatible with optical data transmission systems, is presented. The sensing element is based on a highly birefringent polarization-maintaining optical fiber. The instrumentation of the sensor consists of a HeNe linearly polarized laser, polarization controllers, input and output optical fibers, analyzer, and a computer-controlled synchronous detection system based on a lock-in amplifier. An all-fiber configuration was also developed and studied. For calibration purposes, the pressure cell was placed inside a large pressure chamber designed to simulate the real environment. The device hysteresis, selectivity, and sensitivity were characterized for pressures up to 7 MPa and for ambient temperature. The sensor is simple, cost-effective, and safe in electrically dangerous and explosive environments.