Remote Measurement of High Temperatures in the Presence of a Strong Magnetic Field
Abstract
The environment inside a railgun makes conventional temperature sensing techniques ineffective. Large time-varying magnetic fields induce noise into sensors with electrical connections. The high rate of change of temperature requires a fast thermal response and a fast sampling rate. Finally, the intense heat generated requires a sensor that is thermally stable over a large range of temperatures. To overcome such environmental challenges, this project utilized an interferometric technique where the temperature is measured remotely with a low power laser and a thin sapphire sensor. A sapphire sensor with a semi-reflective coating on one side and a near totally reflective coating on the other side was designed, constructed, and evaluated. To design the sensor for maximum sensitivity a computational model was developed to determine optimal coating thicknesses. To construct the sensor, nickel and nickel oxide coatings were deposited onto a sapphire dye with the use of electron-beam metal vapor deposition. A laser was directed at the sensor at normal incidence, and the reflection from the sensor was collected with a photodiode. As the sensor s temperature was manipulated between 26 C and 355 C its reflectance changed due to variations in the optical properties of the sapphire, nickel oxide, and nickel. The data indicated the sensor responded in a manner similar to the theoretical model. Based on that data, an algorithm was developed to convert the collected optical signal into temperature data, creating a functional temperature sensing system. The system was then taken to the Naval Research Laboratory in Washington D.C. where it was used to monitor the temperature of a hollowed stainless steel cylinder through which high density current pulses were forced. The optical system s performance under such conditions was compared against a type K thermocouple, and the system demonstrated superior time response and relative immunity to electromagnetically induced noise.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 07, 2007
- Accession Number
- ADA473328
Entities
People
- Scott F. Lord
Organizations
- United States Naval Academy