HIGH TEMPERATURE CAPACITIVE STRAIN GAGE

OUR APPROACH TO STRAIN MEASUREMENT ABOVE 2000 DEGREE FAHRENHEIT IS TO MINIATURIZE AND 'RUGGEDIZE' THE NASA SPONSORED, BOEING DEVELOPED DIFFERENTIAL CAPACTIVE STRAIN GAGE. 1 THIS GAGE, INTRODUCED AROUND 1973, HAS NEVER BEEN REDESIGNED OR UPDATED. THE BASIC GAGE HAS DEMONSTRATED ABILITY TO MEASURE STATIC STRAINS ACCURATELY AT TEMPERATURESUP TO 1500 DEGREE FAHRENHEIT. THIS LIMITATION OF 1500 DEGREE FAHRENHEIT IS DUE TO ELECTRICAL LEAKAGE IN THE INSULATORS AND CABLE. THE GAGE ITSELF IS STABILIZED AT 2000 DEGREE FAHRENHEIT DURING MANUFACTURING, AND COULD OPERATE AT LEAST FOR A SHORT TIME AT THIS TEMPERATURE. MORE RECENT MODIFICATIONS TO THE SIGNAL CONDITIONING 2 INCREASE THE INSTRUMENTS CAPACITY TO TOLERATE MORE SEVERE ELECTRICAL LEAKAGE. WITH THIS IMPROVEMENT COMBINED WITH BETTER INSULATION, THE GAGE SHOULD OPERATE WELL ABOVE 2000 DEGREE FAHRENHEIT USING CURRENT TECHNOLOGY. THE FIRST PHASE OF THE PROJECT WOULD STUDY METHODS OF IMPROVING GAGE COMPONENTS SUCH AS IMPROVED FLESURE DESIGNS, POSSIBLE USE OF CERAMIC BEARINGS IN PLACE OF FLEXURES, AND AN OVERALL MINIATURIZATION OF THE GAGE. THE USE OF CERAMIC COMPONENTS SUCH AS ALUMINA, SILICON CARBIDE, AND SILICON NITRIDE WITH SPUTTERED INSULATION AND SPUTTERED THIN FILM CAPACITOR PLATE COULD SUBSTAINTIALLY INCREASE RUGGEDNESS AND PROVIDE MINIATURIZATION. THE END RESULT OF PHASE II WOULD BE A MINIATURE, RUGGED DIFFERENTIAL CAPACITIVE STRAIN GAGE WHICH COULD MEASURE LARGE OR SMALL STRAINS AT TEMPERATURES WELL ABOVE 2000 DEGREE FAHRENHEIT. THE GAGE WOULD BE INSENSITIVE TO SHOCK LOADS OR MECHANICAL VIBRATIONS AND LESS EXPENSIVE THAN PRESENT MODELS. ITS PRIMARY USE WOULD BE TO MEASURE STRAIN ON ADVANCED AEROSPACE STRUCTURES, TURBOJET AND RAM JET ENGINE COMPONENTS. IT WOULD ALSO HAVE LIMITED APPLICATIONS ON NUCLEAR AND CONVENTIONAL POWER PLANT COMPONENTS, REFINERIES, ADVANCED AUTOMOTIVE GAS AND DIESEL ENGINES AND IN MATERIAL TESTING APPLICATIONS.