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| After first calling up the program part NYQUIST-DIAGRAM, the position of the critical point Pk=[+1;j0] or Pk=[-1;j0] must be entered. After this selection has been made, it is retained and shown in the graph until the program part has been reset. Scale factor changes are always based on the scale of the first graph; thus Re=+6 and Im=+j6 corresponds to scale factor 1. If the scale selected is on interval M:=[2;12], then the unit circle appears additionally in the Nyquist-diagram. This way the viewer can compare the RESULTS with the graph more easily. If the locus has not been completely calculated after more than 10^8Hz or 1200 values (Re(Fo)), a corresponding warning will appear in the lower window of the screen. If, for example, the quadrant for the actual start of the locus (given through Fo(w->o) of the result list) and the quadrant for the "Graph Start" just shown do not coincide, the scale factor or the coordinate`s zero point should definitely be changed. The exactness of the RESULTS is thereby increased and the processing time is considerably reduced. All RESULTS then stands in relation to the screen window shown. If the parameter dead time Tt in the order of magnitude is given for the other control-loop time constants involved, the accompanying locus describes a spiral or loop. The number of value-pairs then can easily exceed the given maximum. This is indicated by a corresponding statement. | However, such a control is frequently unstable, making a correction of the parameter necessary all the same. Thus, there is no disadvantage resulting from this for the user. If the phase margin is between 0ø and 1ø, the text "Stab-Gr" (stability boundary) is issued. The exactness of the calculated RESULTS is around 0,01% and stands in relation to the respective frequency domain presented. If all remaining parameters of a control are reset, the locus of the remaining control-loop member can be immediately shown. |