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Acoustic technology is used to measure pressure or vacuum in containers that do not have a measurable lid deflection such as beer bottle, coffee bricks and aerosol cans.
The acoustic sensor works by applying a “tap” to the top of each container, then listens to the resulting “tone.” The tap is produced by an electromagnetic pulse which excites the container lid. The lid vibrates at a natural resonant frequency tone based on internal pressure or vacuum. The tone signal is sensed by a microphone, digitally sampled and stored in memory for processing. A digital signal processor (DSP) produces a real-time signal spectrum and calculates the resultant frequency of the tone for that container lid. This frequency value is then compared to user set limits where containers with a frequency response outside these limits are rejected. | 
