A new chart relating open-loop and closed-loop frequency responses of linear control systems

CONTROL ENGINEERS generally adhere to the use of frequency response as the fundamental tool for feedback control systems. Through the use of the Nichols chart,1 the open-loop characteristics can be quickly converted to the closed-loop characteristics. The performance of control systems can be estimated according to the gain and phase margins and the magnitude of peak M. Although actual performance may be quite different from that predicted by a certain value of a particular specification, yet by means of Meerov´s method2 it should not be difficult for engineers to determine the limits of applicability and to evaluate its effectiveness.