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