of the disturbance is actually exacerbated if : of frequencies -of the Nyquist stability theorem - if IG(eiW)P(e if the loop gain is rather it can be of more than 2 (approximately). This suggests that one should

doi:10.4324/9780203814628-132

Chapter

of the disturbance is actually exacerbated if

ABSTRACT

This occurs if the point of the Nyquist locus corresponding to the frequency w lies inside the circle which has centre at - 1 + Oi and radius 1. This circle is shown by the solid line in Figure XIII.10. In practice it is impossible to prevent the Nyquist locus entering the circle for some range of frequencies - because of the Nyquist stability theorem - so there are always some potential disturbances whose effect is worse than it would be if no regulation were attempted.