[time-nuts] Simple AC mains zero-cross detector

Charles Steinmetz csteinmetz at yandex.com
Sat Dec 20 16:56:55 EST 2014

Magnus wrote:

>So, I do not completely agree that a through-zero measurement with a 
>TIC has all the information

No, a series of time-stamped zero crossings doesn't have all of the 
information in the original signal, and a small glitch that occurs 
during the middle of a cycle (far away from a zero cross) could hide 
and show nothing more than a slight displacement of one or two zero 
crosses.  Grid-nuts can ignore such short glitches.  Utilities can't, 
particularly in today's cybersecurity environment.  Horses for courses.

 From my observations of the AC mains while I was testing the simple 
ZCD, I would expect such hidden glitches [that are real grid-related 
phenomena, not just someone starting a motor downstairs] to be very 
rare.  The grid phenomena I saw typically last more than one grid 
cycle and thus affect more than one zero cross, and/or are large in 
magnitude and cause serious displacement of at least one zero 
crossing, or several extra zero crossings.

Best regards,


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