CHALLENGES IN VALIDATING FLIGHT DATA FROM A DIGITAL DAMAGE DOSIMETER

摘要

The Air Force Research Laboratory (AFRL) sponsored development of on-board state-of-the-art digital datarnrecorders called damage dosimeters to measure temperature and vibration data in areas of acoustic fatigue on aging aircraftrnsuch as the B-52, F-15, F-18, MD-88 and C-130. The Boeing Company designed the damage dosimeter to measure structuralrnstrains and temperatures on in-service aircraft to diagnose difficult-to-analyze structural conditions, such as acoustics andrnhigh cycle fatigue, requiring design of damped durability patches. The damage dosimeter is a rugged, small (fits in palm ofrnhand), battery powered, lightweight (weighs less than 1.5 lb. (.69kg) without battery), data acquisition system that runsrnautonomously. The dosimeter measures 3 channels of strain at rates as high as 15 kilo-samples per second and a singlernchannel of temperature at a rate of 1.3 samples per second. It only acquires data above a programmer defined rms strainrnthreshold. For most tests, the dosimeter program stores 42 records of time history data each 0.3 seconds long and records andrnstores third octave records until its 4-Megabyte memory is filled. The damage dosimeter merges the functionality of both thernanalog signal conditioning, and a digital single board computer. Since the dosimeter requires installation of standard bondedrnstrain gages and uses a series implementation of the Anderson Current Loop (ACL), a dosimeter measurement presents somerntechnical calibration challenges. This paper shows AFRL investigated techniques to perform a system and physicalrn(mechanical) end-to-end calibration of the three bonded strain gages connected in series. Techniques include inserting shuntrncalibration resistors in line for a system calibration and exciting the strain gages with a remote control structural exciter for arnphysical end-to-end calibration. The paper will present results from laboratory and C-130 calibration experiments.