Fabrication, Testing, and Evaluation of Prototype Fluidic Capillary Pyrometer Systems

Abstract

Protype fluidic capillary pyrometers (FCP) were designed and fabricated to measure elevated temperatures for several field applications. The device utilizes a viscosity and, hence, temperature-sensitive fluid resistor or capillary tube as the sensing probe combined with a simple fluid resistor bridge. Small pressure changes due to temperature are then amplified to a useable level with fluidic laminar amplifier circuitry. Monolithic FCP sensors for low thermal stress applications were constructed from several refractory oxides. Other sensors, for high thermal shock duty, were constructed from molybdenum protected with ceramic oxide coatings. This demonstrated that fabrication is feasbile and permitted the evaluation of performance at elevated temperature. Two monolithic sensors were installed at the Scranton Army Ammo Plant and have, to date, successfully operated for over 5000 hr. A coated molybdenum sensor was tested in various environments which included rapid immersion in an inductively heat molten gray iron bath. This sensor accumulated over 48 hr at temperatures up to 1550°C and made measurements for 6 hr in the molten iron. Materials and design options for high temperature probes are outlined and pertinent fluid circuitry is detailed.