method and apparatus for electrically perforating strip of dielectric material

摘要

A system is provided for controlling the porosity of a web or film issuing from an electric spark perforating apparatus in accordance with an operator-set reference porosity regardless of variations in web speed, inherent web porosity, spark discharge energy and spark repetition frequency by controlling the frequencies of the electrical sparks applied to the web in accordance with the product of two signals, one a difference signal obtained by comparing the porosity of the web leaving the perforator and the reference porosity and the other signal derived from the speed of the web.