A new closed-loop process activation method is proposed to reduce the harmonics and obtain more accurate frequency data compared with the previous methods. It has another advantage that the effect of the input nonlinearity can be removed by the proposed method combined with disturbance rejection techniques. The proposed method combines 10 pulses to generate one period of the relay signal. The 10 pulses are combined in an optimal way by solving a constrained nonlinear optimization problem to reduce the harmonics as much as possible. In the implementation step, this study uses the obtained optimal solution without continuing to solve the optimization problem. So, the implementation is almost as simple as that of the previous methods. The proposed method shows significantly smaller harmonics compared with the conventional relay feedback method. The previous approaches, which use a sinusoidal signal, multi-step signal, saturation-relay signal or preload relay signal to reduce the harmonics, cannot manipulate the input nonlinearity. However, the proposed method can estimate the frequency data set of the process effectively for the case where the process has an input nonlinearity because the proposed method uses pulse signals. (C) 2008 Elsevier Ltd. All rights reserved.