Mitsubishi analog controller MELNAC

For recent power generating plants, high reliability is more and more required, while their capacity is increasing and they are becoming more complicated and sophisticated. Especially in nuclear power plants, in addition to the keen requirement for high reliability, high aseismatic property and signal selectivity are the specific requirements. MELNAC, an analog controller, has been developed as the process control system used for nuclear power plants. The main features are high reliability, high aseismatic property, reduction of required floor space, and shortening of the periods for wiring, field adjustment and testing. Next, the outline of the system is described, such as signal and power supply systems and the specifications of each card, which are listed in a table. The performance was confirmed by the two-stage test of card and system levels, respectively. For the card level, accuracy, frequency characteristics, drift, supply voltage variation, temperature characteristics, humidity endurance, aseismatic property, isolation and others were tested, and the excellent performance was confirmed. For the system level, the primary coolant temperature difference/mean temperature protection system was selected as a typical system, and the type test was carried out. As described above, various performance checking tests were now completed, and the systems have been delivered to many loops in nuclear power plants. (Wakatsuki, Y.)