[time-nuts] 60 Hz power glitch, US West coast (Silicon Valley)

Jimmy Burrell jimmydburr at gmail.com
Thu Feb 6 01:21:20 UTC 2014


Tom,

You sound like a guy who just might have experimented with different core materials for your transformer? Any suggestions for rolling your own?

I'd love to hear more about your pulse monitoring/measuring setup if it's something you can share.

Thanks,

Jimmy...
N5SPE

> On Feb 5, 2014, at 4:40 PM, Tom Harris <celephicus at gmail.com> wrote:
> 
> For your setup measuring mains there will be a large phase difference
> across the transformer. This is due to very many physical properties of the
> materials, the largest being the magnetic succeptability of the core. Now,
> this does show a slight temperature dependance. So how do you know that you
> are not getting a slow variation in the phase showing up as a frequency
> shift, since you are measuring such tiny variations. I know that the
> transformer is probably in thermal equilibrium with it's surroundings, so
> is at a steady temperature, but this problem  (of getting an accurate idea
> of mains frequency & phase) has exercised me over the years. I currently
> use an opto and voltage reference to get mains frequency, phase & and
> voltage (computed by lookup table from pulse width) which I found was more
> stable than a transformer. And cheaper as well, since this is for a
> commercial product.
> 
> I'm just surprised that you get such results with a cheap transformer.
> 
> Just remembered, we got a tiny change in phase shift across a transformer
> due to its orientation, we could turn it 90 Deg and get a tiny change (less
> than a milliradian), we never got to the bottom of it, maybe the Earth's
> magnetic field?
> 
> 
> Tom Harris <celephicus at gmail.com>
> 
> 
>> On 6 February 2014 04:39, Hal Murray <hmurray at megapathdsl.net> wrote:
>> 
>> 
>> jimmydburr at gmail.com said:
>>> Interesting.. I'm assuming the green graph is actual voltage and the red
>>> graph is..?
>> 
>> The green is the frequency as measured over the last 10 seconds.
>> 
>> The red is the long term clock offset in cycles relative to what it would
>> be
>> if the frequency was exactly 60 Hz.  It's the error you would see if you
>> looked at a clock that was tracking the power line.  The 0 point is
>> arbitrary
>> since I can't see the reference clock the power system is using.  For those
>> graphs, I used the start of the day/file as 0.
>> 
>> 
>>> I've never done any mains monitoring/measuring and was wondering, what's
>>> your equipment setup?
>> 
>> It's simple.  The hardware is an AC wall wart and a couple of resistors as
>> a
>> divider connected to a modem control pin.  I forget which one.  It's the
>> one
>> that ntpd expects to use with a PPS input.
>> 
>> There was a discussion on that topic here a year or 3 ago.  It's in the
>> archives, but I couldn't find it with a quick look.
>> 
>> The software is a simple python hack.  It runs on Linux.
>>  http://www.megapathdsl.net/~hmurray/time-nuts/60Hz/pps.py
>> 
>> Linux has a back door to the PPS info.  Things like
>> /sys/class/pps/pps0/assert give text like this:
>>  1391619268.999925084#1125070
>> The number left of the # is the time of the last PPS.  The number to the
>> right is the pulse count.  The software above just waits 10 seconds, grabs
>> another sample, and writes a line of text to a log file and switches to a
>> new
>> file every day.  It's 1/2 megabyte per day.
>> 
>> If you have FreeBSD or NetBSD rather than Linux, it shouldn't be too hard
>> to
>> use the same API as ntpd uses.  I don't know how PPS works on Windows.
>> 
>> Another approach would be to feed it into the audio input and scan for zero
>> crossings.  I captured the raw binary for a while when I was chasing some
>> noise glitches.  It's a lot of data.
>> 
>> 
>> --
>> These are my opinions.  I hate spam.
>> 
>> 
>> 
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