i see no reason why it cant run for several years provides it has a good stable power supply?
This is true.
The ATMEL microcontroller and other chips on an Arduino are good industrial quality.
The PC Board quality and manufacturing processes are the same as used in Industrial equipment.
You do need to pay attention to:
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External connections: protection against voltage spikes and induced currents. What happens if lighting hits the building? Where is real "Ground".
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Software testing, especially if there is any potential danger from a failure. This is a significant area of expertise. I once was in a meeting with the guys who wrote the code that ran in the Lunar Lander. There were error conditions (Hear the alarms, and "go" in the landing tape), but there were successful error handlers. We wanted to learn from them when we automated factories with Bad Stuff gases and high-level Plasma generators.
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