Prototype fiber-optic pressure cell for stress monitoring

A fiber-optic pressure cell (FOPC) device is presented for measurement of real stress in the construction and mining industries. The device is miniature, completely electromagnetic-interference (EMI) -free and directly compatible with optical data transmission systems. The sensing element of the device is based on a highly birefringent (HB) polarization-maintaining optical fiber. The instrumentation of the sensor consists of an HeNe linearly polarized laser, polarization controllers, input and output optical fibers, an analyzer, and a computer-controlled synchronous detection system based on a lock-in amplifier. An all-fiber configuration employing a semiconductor pigtailed laser without any bulk optical components was developed and studied. For calibration purposes, the pressure cell was placed inside a large pressure chamber designed to simulate the real environment. The chamber was connected to a Harwood deadweight tester with an attainable accuracy of 0.01%. The device hysteresis, selectivity, and sensitivity, were determined for pressures up to 70 bar and for ambient temperature