Abstract: A process control system of the type arranged to accept varied forms of analog sensing signals from field sensing devices, to digitally process data represented thereby, and to supply varied forms of analog control signals to field control devices. The system is characterized by signal converter means which convert data between the varied analog forms generated by the field devices and a standard form of intermediate signal, e.g., a pulse-width signal, which carries data as a function of duration. The intermediate signals facilitate signal transmission, editing, and isolation, and permit the process control system to have a simple, noise-free, easily adaptable structure. Digital interface means then convert data between the intermediate signals and digital signals in a form suitable for use by digital data processing means.

Abstract: 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.