Safety PLC Impact On Software vs. Hardware Debate

After working on several projects with Siemens S7-300 Safety PLCs, I was given the opportunity to contribute to an article for that presents cases for and against replacing hardware components with software solutions in machine control.

From my experience, I have seen some direct advantages of replacing hardware such as a safety relay with a safety program in a safety-rated PLC.

Some benefits of going this direction are:

Wiring Advantage

  1. Single pair of contacts as PLC inputs rather than wiring to both input card and safety relay
  2. By wiring only to the PLC, you get both safety functionality and monitoring/diagnostics
  3. Simplifies wiring layout, saving time during commissioning and future wiring troubleshooting


  1. Safety logic and conditions can usually be quickly modified programmatically without physical modifications to system
  2. Custom variations to safety logic are possible in software that are impossible or limited with hardware alternatives


  1. Machine guarding or manufacturing line e-stop zoning can be done in software rather than multiple safety relays. Safety zones can also easily be dynamically modified based on machine operating status.
  2. Intelligent devices such as laser scanners and light curtains are usually made to integrate smoothly into the software development environment of a safety PLC.

Read the full article at

Software Replaces Machine Hardware, but Mechanical Solutions Still Have Their Places

A article written by Mike Bacidore and featuring comments by Nick Shea from DMC.

Where Has All the Hardware Gone?: As More and More Mechanical Systems Are Replaced, Is Software the Final Frontier?


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