[IEE IEE Colloquium on `Applications of Plasma Technology to Surface Processing - Recent Developments in Modelling and Diagnostics for Process Control and Optimization' - London, UK (30 March 1995)] IEE Colloquium on `Applications of Plasma Technology to Surface Processing - Recent Developments in Modelling and Diagnostics for Process Control and Optimization' - Dusty plasmas - a theoretical charge model and industrial applications