Written by Tony Deane, CST Technical Manager

Cost Effective High Availability / Hot Standby PLC System

How many existing applications cry out for a high availability solution, but because of cost restrictions a compromise solution to the application has been arrived at? Or worse still, how many projects are never even realised for the same cost driven reasons?

At Phoenix Contact, we have a concept that offers high availability at the following levels:

• Processor level
• I/O level
• Network level

This is achieved at a very competitive cost whilst delivering on all three of the above criteria.

By using Applicative System Redundancy (ASR) Phoenix Contact’s ASR Solution can dramatically lower the cost of achieving Hot Standby / Hi Availability, making it a realistic proposition in small to medium control systems.

ASR works by handling the redundancy between the controllers using the application function blocks rather than firmware in the controllers. This means that standard components are utilised with no requirement for special versions of controller.

Both controllers have identical programs. Both read the inputs, but only the Primary CPU writes to the outputs. The Standby CPU monitors the Primary CPU and takes over writing to the outputs if the Primary fails. This is achieved by function blocks in the application. The I/O are connected to the CPUs via a Profinet Network on a Media Redundancy Protocol (MRP) ring.

Change over times are 700ms when the AXC 1050 CPUs are used and 200ms when using the AXC 3050 CPUs.

For more information, contact Tony on 07824 437393 or email tdeane@phoenixcontact.com