Through the use of a proprietary process, Luna has developed a fiber optic pressure sensor based upon Extrinsic Fabry-Perot Interferometer (EFPI) technology that can operate up to 1050˚C (1922˚F) in extremely harsh environments. A key, enabling technology that has been recently developed is the high-temperature packaging of silica optical fibers within high-temperature alloy housings. Previously, the large mismatch in the coefficient of thermal expansion (CTE) of these materials has prevented the successful joining of silica to stainless steel at high temperatures, thus limiting the maximum operating temperature of fiber optic pressure sensors. Luna’s proprietary manufacturing process has overcome this limitation. An integral temperature sensor also provides active thermal compensation.
Prototype Status: Beta Prototype  A prototype sensor is shown in Figure 1. In a laboratory calibration procedure, pressure and temperature were varied from 0-500psi and 25-1050ËšC (77 – 1922ËšF), respectively, to produce a two dimensional (2-D) test matrix. The experimental setup, shown in Figure 2, consisted of a small box furnace, fitted with a ceramic door which simulated the temperature gradient across a pressure boundary, and a specially designed pressure chamber. The experimental setup was thermally characterized to ensure that the gas temperature at the probe tip was maintained at 1050ËšC (1922ËšF). Figure 3 shows some of the results for one set of pressure cycles to 500psi at a gas temperature of 1050ËšC (1922ËšF). This same design has been tested in a test combustion chamber (Figure 4) and an operating Pratt & Whitney JT-15D gas turbine engine (Figure 5).
