Yokogawa Electric Works, Ltd.

Susumu Nagata

Hisayuki Uchiike

Yutaka Wakasa

Mutsuaki Nakagawa

A process control system of the type arranged to accept sensing signals from field sensing devices, to digitally process data represented thereby, and to supply control signals to field control devices. The system is characterized by a centralized maintenance backup system for supplying backup control signals to selected field control devices while their normal control signals are interrupted during servicing of various system components, e.g., signal conversion units. A maintenance backup device, centrally located at a control station, includes means for providing an adjustable backup control signal, a selector unit having jack terminals connected through prewired leads to a plurality of field control devices, and jack plug means for connecting the backup control signal means to a selected jack terminal and the field control device corresponding thereto. Servicing of circuit boards used, e.g., for signal conversion purposes, is facilitated by providing ready and simplified access to the different field control devices through the selector unit, and by utilizing data available at the system's central operating location to continue control of the field device in the manner prescribed by the digital processing unit.

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Musashino, Japan

Susumu Nagata