[time-nuts] Logging the grid frequency....

Tom Van Baak (lab) tvb at leapsecond.com
Thu Feb 28 18:03:08 EST 2013


Yes, correct, sometimes the power line goes faster than 60 Hz in which case the zero-crossings occur before you "expect them"; so time error can be negative, on average, as often as it is positive.

You cannot design a PLL that always expects phase error to be unidirectional.

The data I provided is time error relative to an ideal 60 Hz; this data can be both positive and negative; and both gaining and losing, as well as both accelerating and decelerating. Welcome to the interesting world of time & frequency, even at 60 Hz.

/tvb (iPhone4)

On Feb 28, 2013, at 10:42 AM, Daniel Mendes <dmendesf at gmail.com> wrote:

> Em 28/02/2013 13:37, Tom Van Baak escreveu:
>> Daniel,
>> 
>> I've placed two log files for you under http://leapsecond.com/pages/mains/
>> 
>> log1932.dat.gz -- timing of every 60 Hz zero-crossing (1.296 million samples)
>> log97312.dat.gz -- timing of every 60th zero-crossing (21.6 thousand samples)
>> 
>> Each represents 6 hours of collection time. Units are seconds (elapsed time), resolution is 100 ns, granularity is 400 ns. This data was collected with a picPET (http://leapsecond.com/pic) using an accurate 10 MHz reference.
> 
> This isn´t very clear to me. First few lines say:
> 
> 0.0000000
> 
> -0.0000029
> 
> -0.0000071
> 
> -0.0000064
> 
> 0.0000027
> 
> -0.0000099
> 
> -0.0000176
> 
> 
> Time went backwards?
> 
> 
> Daniel
> 
> 
> 
> 
> 
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