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.
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.
From design feasibility, to development, to production, having the right information to make good decisions can ultimately keep a product from failing validation. The key is highly focused information that doesn’t come from conventional, statistics-based tests but from accelerated stress testing.
There’s a good chance that a few of the things mentioned here won't fully come to fruition in 2015 but rather much later down the line. However, as Malcolm X once said, "The future belongs to those who prepare for it today."
Pressure vessels are part of common equipment utilized in plants to store liquids and gases under high pressure. It is certain that pressurized fluids will develop stresses in the vessel, which when exceeds failure limits, will lead to hazardous incidents and fatalities.
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