Abstract: Novel method and system for controlling input/output in a process control wherein state signals of object processes to be controlled are applied to a CPU via a process input/output unit and operated in the CPU in accordance with a logic programmed and stored in advance, and results of the operation are delivered out to the object processes to control the same. A buffer memory is interposed between the CPU and the process input/output unit. While reception and delivery of data are performed between the CPU or processor unit and the buffer memory, fetching of the state signals of the object processes or delivery of the process controlling signals is performed between the buffer memory and the object processes, thereby attaining a high rate processing as viewed from the overall processing of the system.

Abstract: In measuring analog input voltages through isolation transformers, an analog input voltage V.sub.in is applied across a primary winding of the isolation transformer, voltages V.sub.A and V.sub.B developing across the secondary winding of lapses of time T.sub.A and T.sub.B (T.sub.A < T.sub.B) from application of the analog input voltage are detected, and by using measured times T.sub.A and T.sub.B and secondary winding voltages V.sub.A and V.sub.B, the analog input voltage V.sub.in is calculated in accordance with an expression ##EQU1## whereby influence of sag due to the isolation transformer is compensated for.