1. Department of Measurement and Control, Gerhard-Mercator-Universität -GH Duisburg, Bismarckstrasse 81 BB, 47048 Duisburg, Germany
2. Department of Electrical Engineering, Lausitz University of Applied Sciences, 01968 Senftenberg, Germany,
3. Department of Automatic Control, Technical University of Iasi, Blvd D.Mangeron 53A, RO-6600 Iasi, Romania