Breaking News
News & Analysis

More accurate readings of total energy promised with metering ICs

11/20/2003 03:07 AM EST
1 Comment
NO RATINGS
More Related Links
View Comments: Newest First | Oldest First | Threaded View
kendallcp
User Rank
Rookie
re: More accurate readings of total energy promised with metering ICs
kendallcp   10/18/2010 1:12:34 PM
NO RATINGS
Actually, the data sheet for the ADE7753 doesn't mention total energy anywhere! These devices, like most other electrical energy measurement chips, give an apparent energy reading that's rms-computed from the real energy measurement and a 'reactive' energy measurement obtained through a 90deg shift of one of the input variables. This was fine in the old days when the main non-resistive contribution was a pure reactance leading to a phase-shifted fundamental current. In the modern environment of non-PFC'd power supplies and triac-controlled loads, the main contribution to non-resistive load current is harmonics. These are just as much trouble as reactive currents (sometimes more) but are not correctly measured by most energy measurement chips. As a result, such chips display an incorrect, overoptimistic power factor reading on a range of common loads, if the standard apparent rms calculation is used. It's easy to show just with a spreadsheet that a standard power supply with a narrow conduction angle has a close-to-perfect reactively measured power factor but a terrible PF based on a proper calculation of the apparent load implied by the spiky harmonic-rich current. As more and more non-expert new companies pour into the 'smart meter' space and rely on the chip suppliers for the accuracy of their results, we could be sleepwalking into widespread inaccuracy in the installed meter base.

Flash Poll
Radio
LATEST ARCHIVED BROADCAST
Join our online Radio Show on Friday 11th July starting at 2:00pm Eastern, when EETimes editor of all things fun and interesting, Max Maxfield, and embedded systems expert, Jack Ganssle, will debate as to just what is, and is not, and embedded system.
Like Us on Facebook

Datasheets.com Parts Search

185 million searchable parts
(please enter a part number or hit search to begin)
EE Times on Twitter
EE Times Twitter Feed
Top Comments of the Week