Development of the Second Generation NRC Acoustic Spectrum Control System for High Intensity Noise Testing
Abstract
NRC conducts high-intensity noise testing using a reverberant chamber that measures 6.9 x 9.75 x 8m. This is the only facility in Canada capable of vibroacoustic testing of full-size spacecraft and large spacecraft components at high sound pressure levels (SPL) to ensure that they withstand exposure to the intense acoustic environment during launch. Within this chamber, testing at SPLs of greater than 150dB with accurate spectrum shaping is routinely performed.
From 1984 until 1993, the target acoustic spectrum for test articles was achieved through the real-time manual adjustment of 1/3-octave spectrum shapers. Over time, with ever tighter target tolerances, the ability of human operators to achieve the target spectrum over the duration of tests became severely challenged. In response, NRC developed an in-house closed-loop system for spectrum control. The key components of the first generation controller are a B&K-2131 spectrum analyzer, a Norsonic-731 noise-shaper, and a PC executing the control algorithm. Data flow between the analyzer, computer and shaper was achieved using the IEEE-488 interface. The system worked extremely well, providing accurate and reliable performance, and was used in the testing of major satellites (RADARSAT-1 and -2, and CASSIOPE amongst others).
In order to eliminate the risk due to obsolescence, ageing hardware and reliance on an unsupported operating system and development environment, a plan was developed to migrate the control algorithm to a current hardware and software. After a review of available hardware and software, the National Instruments PXI platform and Labview-RT development system was chosen. A control system that provided the baseline functionality of the First Generation controller with additional features and performance was developed and benchmarked against the original system as well as two commercial acoustic control systems. A more detailed discussion of the system, along with information on its performance will be provided in the full paper.
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