I/O card, the power is disengaged. Similarly, at the communications level, if the correct data are not received at the right time, the controller enters a safe mode. With so many advantages, it simply makes more sense, technically, to consider an integrated approach.

Examining the bottom line: Total cost of ownership

It also makes sense economically: integrated safety compliance positively impacts the bottom line. A look at the total cost of ownership (TCO) shows why. When evaluating an investment, many manufacturers fail to consider the softer expenses, making a decision purely on the basis of product cost. However, the significant additional cost of installing and maintaining two separate systems should not be overlooked. (The two accompanying graphs visually reflect cost of ownership and product cost vs. functionality.)

For companies who find an integrated approach outside their comfort zone, integrated control technologies-for example, those from major automation suppliers such as Siemens Energy and Automation-are available to embrace both standalone and integrated philosophies. The same hardware platform can be fully dedicated to safety while sending diagnostics to standard PLCs. Such an installation offers the economic benefits of using the same programming, open Ethernet for communications, and the same hardware and engineering-all from the same supplier.

Notes Michel Jabbour, Manager, Safety Business for Siemens: "Although not necessary, we still see a lot of companies buying two controllers from two different suppliers to perform these functions. Even though a safety integrated approach has many benefits, if a company feels it must maintain a separate PLC for general machine control in parallel to a safety PLC, Siemens offers a PLC platform that can simplify the application by providing one hardware platform, one engineering tool, and a certified safety bus."   

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