Achieving Bilateralism in Electroheat Stability Evaluations

The stability criteria for controlled electroheat processes, i.e., plastic extruders, arc furnaces, induction furnaces, plasma torches, fluidized beds, etc., is studied. A previous geometric approach was unilateral, in that stability criteria could be evaluated if the electroheat gain and the controller sensitivity were known, but the reverse procedure was not possible. Subsequent experience has shown that this lack of bilateralism was unacceptable. Now the earlier geometric method is extended so that these stability criteria can be evaluated bilaterally. This covers almost all stability evaluations encountered in design-office and on-site situations. The presentation is practical, rather than mathematical, and is intended for the professional engineer concerned with the practical electroheat control problems of industry.