Method of detecting wrapping material in a packaging machine

The wrapping material used by a packaging machine is advanced along a set feeding path by applying a subsidiary material, typically an adhesive, in a dotted pattern to a station in selected areas of the surface of the material. A static charge is applied to the material at a first station, and a distribution of charges is displayed at a second station; electrostatic charges are more densely displayed on and around the points so as to be measured by measuring the rest of the surface. Any change in density, the substandard application of the adhesive can be identified so that the base material can be inspected before it reaches the wrapping station of the machine.