Development in the direction of open architecture and downsizing in distributed control systems can be noticed in the factory systems popularity implemented by programmable logic controllers (PLCs) and personal computers networks. This article describes on the PLC designed of Q4AR redundant to meet the requirements of distributed control while providing the reliability and high performance required for control applications of “mission critical” factory.
The Q4AR has a backup network interfaces and encouragement processor for better reliability, and features a full match of progression programming instructions for POLs (problem-oriented languages) together with derivative proportional and integral functions. The base unit has structured power-supply modules symmetrically, network interface modules CPU modules, and system control modules. A supplementary base unit is linked through a centrally positioned the module of bus switching to let I/O control and modules of special-function.
The modules of CPU have functions and performance similar to the top-end CPU of MELSEC Q4A. A floating point coprocessor operation executes basic arithmetic 4X faster than similar modules of single-processor CPU. The central CPU and backup CPU execute data tracking through a dedicated bus, and arithmetic consequences from the central CPU are relocated to the backup CPU so that, if the central CPU shut down, the backup CPU can replace processing in the same position. The modules of system control check the modules of CPU and power-supply. They transfer a switch command to the switching bus unit and turn on a relay contacts set when they notice a fault.
The module of bus switching connects the central CPU bus to the supplementary base unit in reaction to switch commands. The modules of network interface offer redundant the compatible interfaces of MELSECNET/10 and a function of switching to choose between them. The hardware is backward compatible, permitting redundant apparatus to be established in existing networks. The backup CPU is turned on to substitute the central CPU when satisfying failure phenomena criteria happen. Switching is started automatically by a failure of power-supply, network unit failure or diagnostic abnormality.