The relay feedback method is one of the easiest identification methods to obtain the ultimate information of the process. Therefore, this method is widely used to automatically tune the PID controller in industry, and many applications of this method have been developed. It uses a square signal to obtain a continuous oscillatory response. However, since the square signal is totally different from the sinusoidal signal, the accuracy of the obtained ultimate information can be poor. Therefore, we propose a new relay feedback identification method to find more accurate ultimate information. The proposed method reduces the harmonics of the test signal so that the test signal becomes more similar to the sinusoidal signal.