Apparatus and method utilizing signal modulation detection for analyzing the internal pressure of containers

摘要

A method for analyzing the internal pressure of a closed container includes inducing vibration in a surface of the container; detecting sound resulting from the vibration; deriving information representing the detecting sound; and determining whether this information corresponds to a predetermined spectral frequency condition and a predetermined spectral amplitude condition. To ensure that the test results are not affected by modulating distortion which may be present in the information, the information is tested for the presence of a modulating distortion, and if so processed to compensate for the effects of this modulating distortion, prior to being tested against the predetermined spectral conditions. Alternatively or in addition, one or both of the upper and lower amplitude limits which define the spectral amplitude condition may be reset periodically to allow for slow changes in manufacturing conditions by accumulating amplitude data from a plurality of containers judged to have an acceptable internal pressure, analyzing this amplitude data to derive an average value and a deviation therefrom, and resetting one or both of the amplitude limits in dependence upon the derived average value and deviation.