Extreme Range Temperature Sensor
Luna has developed an extremely high frequency fiber optic temperature sensor. These sensors have been shown to be highly repeatable over multiple high temperature cycles beyond 1100˚C (2012˚F) and cycles as low as -269˚C (-452.2˚F). The sensors have been demonstrated to survive short excursions to 1400˚C (2552˚F) and have demonstrated high frequency performance of 2.4×106 ˚C/s. Luna Innovations’ fiber-optic temperature sensors are robust, immune to Electro-Magnetic Interference (EMI), and extremely sensitive (better than 0.1˚C (0.05˚F) resolution). The small size of the sensing element (<200um) enables high frequency response, large dynamic range, and high resolution measurements.
Prototype Status: Beta Prototype Thermal shock tests have been conducted to verify the durability of the sensor construction. Temperature sensors, such as the one shown in Figure 1, were rapidly immersed in a hot air environment in a box furnace and then withdrawn repeatedly. The air temperature in the furnace was 665˚C (1229˚F), and the maximum heat-up and cool-down rate was 23˚C/s. Figure 2 shows the data from passing the sensor through a propane torch flame multiple times generating a thermal shock of 38,000˚C/s. A photograph of the test is shown in Figure 3. To test the frequency response limit of these sensors, sensors were placed into a CNC laser micro-machining system that utilizes a 100W CO2 laser. The beam was focused to a 150mm spot with a varied pulse width of 10ms to 24ms. The sensor survived 16 tests before the signal began to degrade due to fiber ablation. This sensor has also been utilized in field trials in which it was rapidly heated with a high intensity laser providing a 2.4×106 ˚C/s transient response (Figure 4). Cryogenic testing has also been conducted by immersion into LN2 at -196˚C (-321˚F).
High Temperature Pressure Sensor
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 25-1050˚C (77 – 1922˚F), 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 1050˚C (1922˚F). Figure 3 shows some of the results for one set of pressure cycles to 500psi at a gas temperature of 1050˚C (1922˚F). 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).
- Figure 1: High-temperature pressure sensor.
- Figure 2: Schematic of high temperature test configuration