[time-nuts] 60 Hz line quirks, anybody recognize this stuff?

Peter Gottlieb nerd at verizon.net
Sat Sep 1 13:50:42 UTC 2012


I concur with John, the grid doesn't do that.  To me it looks like line noise 
and/or a software issue is causing your setup to give false results.    I have 
seen a lot of instrumentation get fooled by line noise, especially around zero 
crossings.  Measuring the power line accurately in the presence of all the 
variations and possible kinds of noise and phase shifts turns out to be more 
difficult than it seems at first.

Peter


On 9/1/2012 9:30 AM, J. Forster wrote:
> IMO, you have an instrumentation issue. I don't think the power grid can
> do anything like that.
>
> YMMV,
>
> -John
>
> ===============
>
>
>
>> The context is using the 60 Hz line for timing.
>>
>> I'm feeding 60 Hz from a wall wart transformer into a modem control signal
>> that the kernel PPS stuff watches.  Mostly, it works as expected, but
>> occasionally, it picks or drops a cycle.
>>
>> In order to understand what was going on, I fed the same signal into the
>> audio input and setup a job to capture the audio.  Here is an example of a
>> pick:
>> http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Aug-09-a-pick.png
>> http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Aug-09-a0.png
>> http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Aug-09-a1.png
>>
>> OK, that somewhat makes sense.
>>
>>
>> Something happened several days ago.  I used to get picks/drops rarely,
>> say
>> ballpark of 1 a month.  Now I'm getting 10 or 20 per day.  So I started
>> looking closer.
>>
>> I'm now seeing stuff like this.  I've got lots and lots of examples.  I
>> added
>> a second PC with different hardware.  It sees the same stuff.
>>
>> Does anybody recognize this?
>>
>> http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Sep-01-a0.png
>> http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Sep-01-b0.png
>> http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Sep-01-c0.png
>> http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Sep-01-d0.png
>> http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Sep-01-e0.png
>>
>>
>> --
>> These are my opinions.  I hate spam.
>>
>>
>>
>>
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>
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