[time-nuts] 60 Hz frequency and phase measurement

[Paul Theodoropoulos]

This stuff is fascinating to a time-nut-level:Novice such as myself. 
While falling down the rabbit-hole searching on all the various bits of 
the info below, I ran across this - not sure if you're aware of it, or 
if it's old news, but it seems at least peripherally interesting:

http://fnetpublic.utk.edu


On 7/3/19 08:56, Tom Van Baak wrote:
> Bob,
>
> Several of us do long-term measurement of mains frequency. We tend to 
> time-stamp cycles and then compute period or frequency, rather than 
> measuring frequency or period directly. Traditional counters in gated 
> frequency or time interval mode have dead time and this will skew 
> results.
>
> In my case I just run a 5 VAC wall-wart through a 10k resistor 
> directly to the input pin of a PIC. No scaling, no filtering, no opto, 
> no ZCD, no nothing. If I measure every cycle I get 155 million samples 
> per month. If I extract one cycle each second (decimate by 60) it's 
> only 2.5 million samples a month. Many months there is not a single 
> glitch in the data in spite of all the FUD about power line noise. 
> Once in a while a month contains an extra or missing sample but the 
> beauty of timestamp data is that this can be detected and repaired as 
> part of data processing with no loss of phase.
>
> Here's a page where Kevin (in New Mexico) and I (in Seattle) both used 
> picPET's to measure mains for a few days and then we compared the 
> results. Although thousands of miles apart, we're both on the same 
> grid so the agreement was astonishing. It was milliseconds in time and 
> ADEV down to e-8 over a day:
>
> http://leapsecond.com/pages/mains-cv/
>
> See also: http://leapsecond.com/pic/mains-adev-mdev-gnuplot-g4.png
>
> /tvb
>
>
> On 7/2/2019 10:09 PM, Bob Albert via time-nuts wrote:
>>   I have tried to measure the power line frequency with spotty 
>> success.  My best results came from a period measurement, as many 
>> periods as the counter can accumulate.  Due to noise, one is never 
>> sure at quite what point the source is measured.  Perhaps a brick 
>> wall filter would clean it up for a more reliable measurement.
>> Of course, at 60 Hz the period is 16-2/3 milliseconds.  So the 
>> counter should properly show a 1 followed by a row of 6s, with the 
>> last digit bouncing between 6 and 7 most of the time.
>> If there is a filter used, it will not only remove noise but also 
>> short term variations.  But generatlly speaking you don't want to 
>> measure those, unless you are trying to evaluate a rotary generator.
>> Getting this reading can be a challenge.
>>      On Tuesday, July 2, 2019, 10:01:03 PM PDT, jimlux 
>> <jimlux at earthlink.net> wrote:
>>     On 7/2/19 4:09 PM, Dana Whitlow wrote:
>>> I've always noted that casual attempts to pick up 60 Hz with small 
>>> antennas
>>> etc see more harmonics and other trash than actual line frequency.  
>>> But if
>>> you're in an office environment, why not plug something in? It's 
>>> quite easy
>>> to build a simple passive diode clipper/filter that will plug into a 
>>> wall
>>> outlet and
>>> which will provide a sort of soft (but clean) squarewave at a 
>>> voltage level
>>> convenient for lab instruments and with good protection against big 
>>> spikes
>>> and
>>> other trash riding on the line.
>>
>> Safety approvals are one obstacle (of course one could use a AC wall 
>> wart).
>>
>> Actually, it's because someone asked me about a science experiment where
>> you'd place them in a neighborhood outdoors.
>>
>>
>>
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>
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-- 
Paul Theodoropoulos
www.anastrophe.com