On-line sensing of paper machine wet-end properties: dry-line detector

This paper is concerned with the task of sensing in web-forming process control loops. Conventional and newly proposed measurement techniques are discussed and a new type of measurement is suggested. The new measurement method adresses the problem of paper machine "wet-end" sensing and is based on a CCD camera system which can detect the dry-line. Both the theoretical and practical aspects of the invention are investigated and the sensing system is developed into a portable measurement system which is applied to a paper machine. The paper machine measurements are analyzed and presented using nonparametric techniques based on analysis of variance. Compared to traditional scanning gauge systems the dry-line detector allows for a large reduction in the transport delay, higher data density and sampling rate, and better machine directional (MD), and cross-directional (CD) signal decomposition.