Abstract: The two-channel relay feedback of SISO systems is analyzed in-depth. With the use of the describing function method and Nyquist stability criterion, the existence and stability conditions for-corresponding limit cycle oscillation are presented. Furthermore, the relation between the information of the limit cycle and the frequency characteristic of the forward path is built. On the basis of these conclusions, two ways to apply two-channel relay feedback——extracting multi point frequency characteristics in multiple quadrant and closed-loop performance monitoring——are given. Simulations show satisfying results and verify the method presented in this paper.

Key words: two-channel relay, frequency characteristic, performance monitoring, describing function, limit cycle oscillation