Long discharges have been demonstrated by lower hybrid current-drive experiments on some tokamak devices. Discharges of longer than 1000 s are also planned for the International Thermonuclear Experimental Reactor (ITER) and Tokamak Physics Experiment (TPX) projects. In the case of long-time or steady-state operation, it is important to monitor the plasma parameters continuously and change the operational conditions during the discharge to maintain the plasma current. However, a conventional data acquisition and analysis system cannot follow these operations because it must show the results after each pulse. A new system that can continuously monitor and support steady-state operation is necessary. A new system is developed in which the signal flow is divided into branches, and one series of processing is made to switch alternately among the groups in every regular desired interval. An application of this system has been demonstrated on a 1-h discharge by TRIAM-1M.