The invention relates to methods of testing the wrappers of rod-shaped articles produced or used in the tobacco-processing industry, particularly methods of a type wherein for example a pressure drop between an interior space surrounded by the wrapper and an exterior space outside the wrapper is created by pneumatic means, and wherein for example for the purpose of generating defect signals pressure changes are detected by converting pneumatic test signals into electrical test signals and then evaluating them.
The invention also relates to arrangements for testing the wrappers of rod-shaped articles produced or used in the tobacco-processing industry, particularly arrangements wherein the articles are transported in a direction transverse to their elongation in recesses of a test conveyor, with the recesses having associated with them sealing means for closing off the front end of the article relative to the environment outside the wrapper. The arrangements in question usually also have means for feeding testing air into the article, to generate between the interior of the article and the exterior of the article a pressure drop, and are further provided with means for detecting testing pressure changes attributable to the permeability of imperfectly formed wrappers, e.g., wrappers having tears, cracks, holes, and the like, with measuring means being provided, the measuring means including for example a measurement value transducer and an evaluating arrangement.
Testing methods and apparatus such as just described produced a test result, for example in the form of a measurement or test signal, which is often erroneous or very inaccurate due to the effect of disturbances, such as atmospheric pressure, humidity and temperature changes, the effect of such atmospheric changes upon mechanical, electromechanical and electronic measurement system components, aging of such components, and the like. The erroneous or very inaccurate measurement or test signals could prevent the testing arrangement from recognizing defective articles as such, or alternatively could cause the testing arrangement to automatically discard articles which are in fact non-defective.
Two particularly important disturbances are disturbances of the pneumatic part of the testing system and fluctuations of the porosity of the wrapper material. Such fluctuations are in general not distinguishable from changes in the total air permeability of the wrapper attributable to structural imperfections of the wrapper.