[en] This study proposes an innovative method for the monitoring the nuclear power plant. In this field, false detection of the trouble, both 'false negative' and 'false positive' will become a serious problem. In the other hand, since its complexity of nuclear power plant, simplicity of monitoring system is strongly required. Here, we propose a new simple and reliable health monitoring sensor network system. Our pulse width modulation technique realizes a self-maintenance function in single signal line (token ring shaped). (author)