Method of inspecting internal pressures in sealed containers

A method of inspecting the internal pressures in sealed containers comprising the steps of:

• exerting an impulsive force to a metallic end surface of each sealed container;
• detecting vibration of the end surface of said sealed container generated by said impulsive force, by means of one of a plurality of vibration detectors;
• supplying an output electric signal of said detector to a plurality of band-pass filters having substantially adjacent pass-bands;
• comparing the levels of the output signals of said band-pass filters;
• selecting two filters through which signals having the highest and second highest levels based on such comparison, pass;
• designating the signal passing through the filter having a lower frequency out of said two filters, as a fundamental frequency signal;
• selecting the filter having a frequency equivalent to a value obtained by multiplying the frequency of said fundamental frequency signal by a specific numeral from 2 to 3;
• designating the signal passing through said last-mentioned filter, as a higher harmonic signal;
• and
• judging said sealed container as defective when said fundamental frequency signal and said higher harmonic signal are applicable to at least one of following conditions;
• (a) the level of said fundamental frequency signal is smaller than a predetermined standard level;
• (b) the frequency of said fundamental frequency signal deviates from a predetermined frequency range;
• and
• (c) the ratio of said higher harmonic signal level to said fundamental frequency signal level is larger than a predetermined standard ratio.