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Under pressure?

It is the aim of every drinks producer to supply the best quality. In the case of products containing carbon dioxide it is particularly important that this does not escape. The HEUFT sonic internal pressure detection can identify faulty bottles in the stream of production contact-free at an output of up to 80,000 containers per hour.

The idea behind this detection was surprisingly inspired by music. The sound of a drum changes when the tension of the drumhead is altered. In the bottling hall the drumhead corresponds to the metal crown cork of a bottle. This tension is produced by the internal pressure of the bottle. The closure is struck by a short electromagnet pulse which leads to a mechanical deflection of the closure. It then oscillates in its characteristic waveform.

These oscillations are recorded by a microphone, amplified, filtered and analysed electronically. The internal pressure can be determined on the basis of these values.

However the waveform also depends on other parameters:

• closure material (drumhead material)
• force applied by the closer head (drumhead tension)
• finish shape of the bottle (shape of the hollow space of the drum)
• fill level of the bottle (size of the hollow space of the drum)

All these parameters have to be taken into account in order to carry out a correct measurement. A relative measuring method is necessary. The pitch of the bottles is compared. A bottle that sounds faulty, i.e. its pressure is not within the norm, is detected and rejected. In other words to return to our original example different drums are compared and those that sound bad are sorted out.

However the "bad sound" always depends on the surroundings. In the world of music semitones only sound harmonious in the correct sound environment. It is similar in the case of bottles. There are also "badly sounding" crown corks which can only be evaluated as being good by using information from their surroundings.
This is the exact point at which the development of information transfer via the HEUFT magnetic tracking starts. The HEUFT O₂ inspection checks the waveform of the closure immediately after the filling process in order to detect bottles with an oxygen content which is too high in the headspace. At this point the internal pressure of the bottle is nearly the same as the external one.

The information received here has to be transported container-related along the line. For this we use the magnetic properties of the closure and use it as a diskette. The result of the HEUFT O₂ measurement is coded on the closure. The HEUFT sonic measures the pressure again after the pasteurizer where the nominal pressure is built up. The two measurements are compared afterwards. There are two different tones in the case of a correctly closed bottle due to the difference in pressure. The faulty bottles do not change their tone. The individual character of each bottle is taken into consideration in the result by means of this measuring method and the precision of the measurement can be decisively improved.