Machine safety: PLC versus PAC, is there a difference for safety?

Is PAC the newest PLC? Is there less risk for machine safety in using one or the other?


Is PAC the newest PLC? And, what’s that got to do with machine safety? What does PAC stand for? The answer is, programmable automation controller. What does PLC stand for? Everyone should know by now; that's programmable logic controller. So what’s the difference, and does a PAC have the capability to include safety logic?


In recent times, PLCs have grown to include unique safety certified PLCs with the capability to perform safety-related functions. We’ve also seen over the past 10 years the addition of safe controllers for various applications such as drives, motion, vision, communication, wireless, and many others. Each of these devices have, for years, been application-specific devices with unique capabilities, programming tools, and so forth. As a result, each safety-related device also required its own safety certification. Integrating these devices into one architecture on a machine was touted as easy because they would all “plug and play” on the same communications network for general automation and safety automation.


Then came the PAC parade. In my words, a PAC platform is designed to provide a universal capability to combine all these typical application devices plus safety-rated control for safety-related functions on a common platform. Typically this might be represented as optional modules configuring a controller (control system architecture) and programming the entire application with one tool. This advancement from automation suppliers greatly simplifies the life of manufacturers because of savings in components, spare parts inventory, training, unplanned machine downtime, re-development time for multiple machines, to mention a few.


A PAC solution is usually a complete machine control architecture, so it would naturally find its way to manufacturers via new machines and complete controls retrofits of legacy machines.


J.B. Titus, CFSE

But, do you see application possibilities about how PACs can find their way onto other installed machines? Has this presented you with any new perspectives? Add your comments or thoughts to the discussion by submitting your ideas, experiences, and challenges in the comments section below.


Related articles:

Siemens – PACs

Rockwell Automation – PACs


Opto 22 – PACs

PACs – Plant Engineering’s Product Of The Year

Contact: for “Solutions for Machine Safety”.

ESMOND , Non-US/Not Applicable, Singapore, 05/09/13 07:40 PM:

I don't see how the machine safety and PAC relation, mostly machine safety signal are using digital and with the specific design of the safety function, a simple safety PLC can do the work. It could be over kill if to PAC for safety purpose but of its part of the machine application.. I do agree with you.
JB , GA, United States, 05/10/13 03:15 PM:

Esmond - you are correct in that there are small applications where a simple programmable safety relay or small safety PLC are a best fit perhaps creating a safety layer in the architecture. Whereas, larger applications could benefits via a safety PAC with safety modules for a safe drive, safe motion, safe wireless, etc. on a common backplane. All of these technologies could then be programmed with one software programming tool versus several.
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