Programmable Logic Controllers, PLCs, Reliability.

PLCs are not about all the long list that gets hauled out about their speed and ease of programming and all the issues of "how they work". PLCs are about reliability. PLCs are expensive... for reasons that many are too late in understanding.

You can make your own PLC if you work out how to get the hardware and ecosystem up to or better than the standards for existing PLC reliability. Most will never understand what this requires until they fail. Nor will they have the self awareness to get past their own flaws and look outwards (and maybe even bypass failure?).

Am I challenging you? Yes. Am I challenging you to "self sufficiency" or "rugged individualism"? Look at how ecosystem plays to reliability and then ecosystems like the open source and maker movement and then decide.

Are PLC use cases what is driving the massive reduction of costs in underpinnings of their function?  Spoiler: It is the glass screen in your pocket, and the search bar everywhere.

"Come now, let us reason together". You want to build one? Yes you do! *grin* Let's see how.

Continuous Monitoring Based Commissioning.

Article regarding Continuous Monitoring Based Commissioning.
http://w3.usa.siemens.com/buildingtechnologies/us/en/Smart_Buildings/Documents/the-12-things-you-need-to-know-about-monitor-based-commissioning-a-siemens-white-paper-final.pdf

Most everyone knows about commissioning. For most systems the concept is straightforward, and the goal is universal - optimization - chiefly for reliability (be it economic or functional.. and this is not really an "or" at transcendence).

It is more nuanced what happens with re-commissioning a system... Is it a snapshot? Does one stop the process? etc.

Then after one gets the before/after understood... one is faced with understanding ongoing versus batch/jump. The real winners (sometimes better termed "non-losers") are the ones who can harness the power of continous improvement.

Here is Contiuous Improvement with a large "C". 
http://en.wikipedia.org/wiki/Continual_improvement_process