Intelligent Hot Standby System iHS+
RFL has a reputation for engineering smart solutions for critical control and network systems. Considerable investment has been made into the design and evolution of a fault tolerant control system, based around the industry standard Hot Standby PLC.
Typical Hot Standby systems only provide failover resilience for the PLC, whilst the RFL iHS+system has been designed to tolerate, both PLC failure and a range of faults outside of the control system itself. This high level resilience has been achieved by using information received from a combination of triplicated signals and dual I/O units to remove all single points of failure (SPOF) in the control system. Any non-critical inputs or outputs can be accommodated in “simplex” form focusing capital outlay on the critical items, thus reducing systems costs.
Inputs - Remote I/O
For critical items, dual signals input to the PLC via a local “main” I/O unit. Should a fault cause these two signals to disagree, the PLC will look at the 3rdcontact which inputs to the “reference” I/O unit, and acts according to this information. The faulty input is identified and logged on the system, for correction at a convenient time. By this means a single point of failure is avoided.
For analogue inputs, these can be read by either the main or reference I/O units, or both, dependent on criticality.
For non-critical digital inputs, these can go to either of the I/O units.
Outputs - Remote I/O
Critical outputs come from either of the I/O units. Normally, the main I/O controls the required item, but if this I/O unit develops a problem, the main PLC controls the item from the “ref” I/O, and flags up the problem.
Non-critical outputs can be arranged to come via either of the I/O units.
PLCs – Main and Hot Standby
The PLCs are installed in a Hot Standby arrangement providing a bump less transfer of information should the main PLC fail.
Network – Resilient Fully Rugged Hardware
The network is run as a ring which is “self-healing”. Should the fibre be broken the flow of information is automatically reversed on the ring with no impact on operation.
Due to the available bandwidth capacity in the fibre ring, other items can also be installed on the network in addition to the control system. SCADA, Metering, CCTV, Access Systems and IP Telephony are some examples of the extra systems that can be added to the network.
Incorporating all the above, iHS+provides unprecedented levels of resilience for a Hot Standby system whilst allowing scalability dependent on criticality or cost
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