HOME  |  NEWS  |  BLOGS  |  MESSAGES  |  FEATURES  |  VIDEOS  |  WEBINARS  |  INDUSTRIES  |  FOCUS ON FUNDAMENTALS
  |  REGISTER  |  LOGIN  |  HELP
Blogs
Guest Blogs
Design Decisions: Choosing the Right Resistor for Energy Metering
8/2/2012

Image 1 of 2      Next >

Figure 1: A typical transformerless power supply section for an energy meter.
Figure 1: A typical transformerless power supply section for an energy meter.

Image 1 of 2      Next >

Return to Article

View Comments: Oldest First|Newest First|Threaded View
tedtw
User Rank
Iron
Electric meter current measurement
tedtw   8/30/2012 1:12:51 PM
NO RATINGS
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.

tekochip
User Rank
Platinum
Excellent Article
tekochip   8/30/2012 1:47:21 PM
NO RATINGS
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.


Partner Zone
More Blogs from Guest Blogs
Was Steve Job’s signature outfit of a black turtleneck, jeans, and sneakers the secret behind his success? Maybe, or maybe not, but it was likely an indication of a decision-making philosophy that enabled him to become one of the most successful innovators of all time.
Electromechanical actuators and propulsion system enable the first controlled landing and ascent from a solar system body other than the moon.
Combining energy-saving product design and advanced lithium batteries enables wireless devices to operate maintenance-free for up to four decades.
Hardware-in-the-loop test platforms enable manufacturers to deal with increasing software complexity.
Remember when design decisions for optimizing low-power MCU applications were simple? All you needed to do was select when to put the MCU into the low-power mode and when to wake it up. Once it was awake, you just ran the required code as quickly as possible. Simple, right? Well, these days designing for power efficiency isn’t so simple. Why is that the case?
Design News Webinar Series
2/25/2015 11:00 a.m. California / 2:00 p.m. New York
12/11/2014 8:00 a.m. California / 11:00 a.m. New York
12/10/2014 8:00 a.m. California / 11:00 a.m. New York
11/19/2014 11:00 a.m. California / 2:00 p.m. New York
Quick Poll
The Continuing Education Center offers engineers an entirely new way to get the education they need to formulate next-generation solutions.
Feb 23 - 27, Baremetal C Programming for Embedded Systems
SEMESTERS: 1  |  2  |  3  |  4  |  5  |  67


Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.
Learn More   |   Login   |   Archived Classes
Twitter Feed
Design News Twitter Feed
Like Us on Facebook

Sponsored Content

Technology Marketplace

Copyright © 2015 UBM Canon, A UBM company, All rights reserved. Privacy Policy | Terms of Service