Safety PLC offers redundancy according to IEC 61508 SIL 2

29 June 2018

Mitsubishi Electric’s modular PLC series MELSEC iQ-R is now available as a fully redundant pair of controllers for high performance and extra reliability. To help reduce the total cost of ownership (TCO), the system also integrates various features into the PLC for monitoring and managing safety.

Many key production applications now require full redundancy conforming to the IEC 61508 SIL 2 standard, so critical systems can still operate in case of a failure or accidental damage to the primary CPU unit.

The MELSEC iQ-R redundant pair of PLCs comply with the functionality requirement of this standard. The guidelines within the redundancy standard require a full duplicate PLC rack with all modules, which the primary set will switch-over to instantaneously. 

The programming platform, GX Works3 engineering software integrates both process and safety-control programming in one environment. This enables the execution of integrated process-and safety-control programs with a single CPU module, eliminating the time and cost associated with purchasing and installing a separate safety controller. 

Process integrity and dependability are the main reasons for plant operators to install redundant automation controllers into their systems, which is why another layer of protection has been added to the basic redundancy architecture of the iQ-R. The safety version includes a SIL2-process CPU module and a separate SIL2-function module as a set, sitting alongside the power supply module, basic base unit and network module. This ensures continuous operation by switching to standby operation if an error occurs in the control system.

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