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

[Mike Garvey]

>From a Time-Nut perspective, isn't phase/frequency of the (nominal) 60 Hz
all we'd be interested in?  Phase is best measured at a zero crossing as
this is the (only) phase measurement point which is independent of
amplitude.
Mike

-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Charles
Steinmetz
Sent: Saturday, December 20, 2014 4:57 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Simple AC mains zero-cross detector

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,

Charles



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