Abstract :
The power of programmable controllers having greatly increased has given much enhanced capability but in return needs attention to program structure, status and error information automatically provided by the products and a much higher level of visibility of the condition and effectiveness of automation systems. There is continuing pressure to maximise up-time of plant, and also maintain a consistently high product quality through analysis of production tolerances and trends. Therefore the implementation of diagnostic functions within the PLC and its program for commissioning, plant operation, and maintenance is a primary concern in many industries. This is designed-in diagnostics (or D2 for short). D2 can be applied in three ways according to the facilities provided by the PLC manufacturer within the processor and its I/O structure: fault display routines; structured relay ladder programming; and the graphical program definition and structure
