Several aspects of mechanical transfer evaluation for an electronic package from flight and vibration tests (Part 1 - Test results)

摘要

An electronic device installed in an airborne system on a vibration isolation device was flight tested several times. Vibration data were measured at the device's mounting location (input) and on the device itself (output). Between the flight tests transfer functions were calculated that relate the output to the input, assuming linearity. The calculated transfer functions were noted to differ from one flight test to another (this should not happen for a linear system, for which the excitation conditions do not affect the transfer function). When the changes in flight test transfer functions were identified, it was decided to perform a laboratory vibration test, in order to investigate under controlled conditions the vibration isolation device's transfer function. While installed on the shaker in a configuration that simulated the flight mounting, the system was excited at several levels with a similar spectral content to that of the input measured during the flight test. Transfer functions were calculated for the different vibration excitation levels. The results varied slightly between the different vibration tests, but differed significantly between the laboratory vibration tests and the flight tests. Under these circumstances it was decided to investigate the measurements accumulated in the laboratory and flight tests and to try to understand the discrepancies that were surfaced during the transfer evaluation process. The results of the investigation are summarized in two papers. The first paper presents the results of the measured data analysis, both in flight and the laboratory, and the second paper presents a statistical analysis of these results. The factors that affect the amplification are identified, the results are modeled as a function of these factors, and the extent of the effects of the different factors are identified. The paper begins with a schematic description of the system under test. Representative examples of the transfer functions evaluated by different methods are presented. The examples highlight the discrepancies between the results of the laboratory and flight tests. To help understand these discrepancies the principles of the different analysis methods are described briefly. Next the results of application of these methods are presented, followed by modeling and statistical analysis of the results. Effects of the different factors on the amplifications are identified. Finally several remarks are presented with respect to the relation between the laboratory testing and flight test results.