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

[Magnus Danielson]

On 09/03/2012 11:11 PM, Bob Smither wrote:
> On 09/03/2012 12:00 PM, Graham / KE9H wrote:
>> On 9/1/2012 1:35 AM, Hal Murray wrote:
>>> 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
>>>
>>>
>> Hal:
>>
>> Two ideas:
>>
>> 1.) You could have some process in Windows that is causing aperiodic
>> blocking of the OS's ability to process real time data.  Can be many,
>> many causes.
>
> Hmmm - but wouldn't that result in missing samples and an abrupt phase jump?
> The waveforms reported appear phase continuous (right number of samples) but the
> sample values are somehow forced to a constant value.  I would guess that the
> waveform being sampled actually looks like that.

Indeed. What I was stroked by was the repetitive levels and their 
tendency (except for one case) to strive towards zero with a small 
slope. For me the source is in the analogue domain rather than digital 
domain. Phase continuity and restoration of phase rather implies 
disturbance of the analogue signal, and the fault behaviour looks like 
some form of intermittent glitch and discharge mechanism. Try to see if 
you can find some intermittent part of the design.

Cheers,
Magnus