When the Delta P measurement becomes inoperative, distortion sensors can be used to advantage to identify the stresses on the packaging. This packaging is generally heat sealed (peelable seam, pouch, doy pack, tray, etc.). Another use of the distortion measurement concerns readings on pull rings and bulging of jar caps or flat can lids/bottoms. These more technical aspects will be dealt with separately.
The standard use of the distortion sensor aims to give the operator information on the fine balance existing between the autoclave pressure (Pext) and the packaging pressure (Pint). We use the term ∆D since it is the variation in position in relation to the start of measurement that is of interest to us. A bulge (positive distortion) is the result of excess Pint, a hollow (negative distortion) excess Pext. This simplicity of interpretation allows autoclave management with appropriate process control. However, certain plastic packaging reacts locally in the opposite way. It is therefore essential to remain vigilant with this type of process control. To be fully operational, it must be possible to fit a distortion sensor on all faces of the packaging, without exercising any mechanical stress (spring systems must not be used) and to have a wide measurement range.