This method is convenient when a rod motion controller is used to change the power to satisfy a change in a power-demand set point. The binary
pulse chain is fed into the control system as a power-demand set point. The controller changes reactivity to attempt to satisfy this demand. Figure 7.1c shows the power-demand rod control system. In this case, the output would have a power spectrum that approximates the power spectrum of the binary pulse chain (approximation depends on control-system perform­ance). The input power spectrum would approximate the reciprocal of the square of the reactor gain. This is completely acceptable for frequency response measurement purposes. Of course, if the rod-position controller uses some other signal rather than reactor power, then the method will also work if that demand signal is used.