Tuesday, March 15, 2011

When to Utilize Safety PLCs





The self-checking and redundancy features of safety PLCs come with a price tag. Safety PLC cost around 25% to 30% more than their standard PLC counterparts. However, they do provide a significant savings cost when compared to the total cost of dual cross-wired PLCs. When compared with safety relay-based systems, is offset by reduced wiring costs and panel space as well as improved flexibility, likewise, this cost differential.

Developers suppose to be aware that specific control architectures based on standard PLCs have been certified by safety governing bodies for use in specific applications. In specific examples, it may prove more cost effective to use the certified package versus taking new control architecture through the certification process. End users also need to evaluate the additional training, stocking and maintenance costs incurred by implementing a new system as opposed to the cost of creating a safety system using the standard software and hardware with which they are familiar.

Scope
In other article already highlights some of the fundamental differences between PLCs and safety PLCs. Other differences which aren’t elaborated upon in the other article include the use of power supplies designed specifically for use in safety control systems and redundant backplane circuitry between the controller and I/O modules.

While standard PLCs, safety PLCs, and safety relays all have their niche, final selection of the appropriate control system will be determined by a variety of factors. Engineers developing safety systems suppose evaluate each control approach in an effort to determine the appropriate solution for their specific application. Whatever control architecture is chosen when implementing safety systems, it is important to work with a control supplier that can support and supply multiple approaches.

The GuardPLC controller from Rockwell Automation is a new safety rated PLC. It is designed to meet the requirements of this standard.



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