Real-Time Backup Systems for Programmable Controllers

Programmable controllers (PC's), conceived in 1968 by a team of engineers at G. M.'s Hydramatics Division, have experienced a revolutionary development and gone through four generations of design in a decade. The exponential increase of functional capability was accompanied by a similar development trend in the I/O area from passive I/O modules to intelligent I/O and distributed I/O systems. As these programmable controllers became larger, their chip count increased substantially and, thus, their meantime between failures (MTBF) was lowered despite use of LSI and highly reliable components (λ-values substantially above industrial grade) with elevated temperature ratings (85°C) and adherence to conservative component stress levels.