Excellent article, very thorough and detailed. Few people realize how difficult it can be to specify a simple resistor. It's also quite common to use two resistors in series to satisfy redundant failure analysis.
Resistor consideration is related to instantaneous or repeated peak MOV power dissipation, too. Few engineers realize that a lightning stroke does not consist of just one pulse, but five or more together. I proved this years ago with a camcorder, and viewing a lightning strike frame by frame I saw separate bolts of lightning in every other video frame.Our eyes perceive a lightning strike as flickering, but in reality each strike is a series of discharges until the cloud voltage drops low enough to stop altogether.
Consider each meter is also sealed environment with a glass cover, much like a greenhouse but without ventilation. Now consider a typical meter sitting on a outside, south-facing wall on a home in the deep south. Internal temperatures can easily rise up near the upper operating limits for most electronic components.
Both MOV and resistor power ratings must be greatly de-rated to insure long term reliablility of both. De-rating is also required for other electronic components. Proper testing of components requires both good equipment and use of an environmental chamber during testing. This type of testing reveals flaws and design issues with components not previously apparent or even considered as a problem.
With record-breaking temperatures around the country, it's hard to find a more punishing environment for electronic components. Perhaps a oil well probe lowered down to the botton of an oil to make temperature and resistance measurements might be a worse environment, but that's just a temporary high temperature environment, while a electric meter is on-going day after day A wall ona building is even worse than the passenger compartment in most vehicles. At least in the case of vehicles, electronics can be located under car seats or behind the dashboard, away from direct sun exposure.
New versions of BASF's Ecovio line are both compostable and designed for either injection molding or thermoforming. These combinations are becoming more common for the single-use bioplastics used in food service and food packaging applications, but are still not widely available.
For industrial control applications, or even a simple assembly line, that machine can go almost 24/7 without a break. But what happens when the task is a little more complex? That’s where the “smart” machine would come in. The smart machine is one that has some simple (or complex in some cases) processing capability to be able to adapt to changing conditions. Such machines are suited for a host of applications, including automotive, aerospace, defense, medical, computers and electronics, telecommunications, consumer goods, and so on. This radio show will show what’s possible with smart machines, and what tradeoffs need to be made to implement such a solution.