The purchase price is declining, and safety PLC options are even more attractive at installation because the long cable home runs get decreased. Instead of having all safety device cables return to the central location where the safety relays reside, the devices can land locally at distributed Ethernet IO locations which communicate via regular Ethernet cable. The Ethernet IO cable already must be pulled back to the central PLC; this gives a significant cost savings for cabling and installation time.
The drawback to SafetyPLC option is the complexity for post-acceptance troubleshooting. The skill level required to maintain and troubleshoot such a system is much higher. Trouble-shooting a system using regular safety relays can be much simpler.
Interesting piece, TJ. With safety becoming more an integral part of the integrated architecture/product line-ups for many automation control vendors, it will be interesting to see how the pricing trends play out over the next few years. Would expect that the premium will be heading downward but it's impossible to know how fast.
Beth, I have to write a correction here. I realize I neglected to SUBTRACT the cost of the standard PLC from my safety PLC figure (the safety PLC performs both the safety function and the regular PLC function in one unit and thus replaces the standard PLC).
This would adjust the total safety PLC cost down to around $7000. The safety PLC decision becomes even more attractive for the next system.
I love this real-world example of how one simple design decision and component change can have real impact on the cost of the BOM and the ultimate performance of the product. This is a classic example of what happens every day in design iteration. It really shines a spotlight on how a more holistic view and big-picture thinking can really have impact on design results not to mention, costs. Thanks for sharing, TJ.
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