[time-nuts] Line Frequency

Tom Van Baak (lab) tvb at leapsecond.com
Sun Feb 9 16:34:11 EST 2014


It depends of your goals. If you want a 60 Hz time/frequency standard then using a mains disciplined oscillator is good. Like AN12 shows.

But if your goal is to measure mains itself, warts and all, then measure mains as it is, not a pure oscillator tied to mains by PLL or FLL.

See this Atmel app note: http://www.atmel.com/images/doc2508.pdf

Also: http://leapsecond.com/pages/ac-detect/

/tvb (i5s)

> On Feb 9, 2014, at 12:04 PM, "M. Simon" <msimon6808 at yahoo.com> wrote:
> 
> I kind of like the synchronized oscillator on page 6 of this pdf
> 
> http://cds.linear.com/docs/en/application-note/an12fa.pdf
> 
> 
> They claim good results. I may have to build one and see. 
> 
>  
> 
> 
> 
> Engineering is the art of making what you want from what you can get at a profit.
> 
> 
> 
> On Sunday, February 9, 2014 7:44 PM, Chris Albertson <albertson.chris at gmail.com> wrote:
> 
> All you need to monitor line frequency is a small transformer connected to a computer's DCD pin on a serial port.   You can get fancier and use comparator, opto isolation and so on but a simple 5V transformer is enough.  This takes advantage of the electronics inside the RS232 port that is designed to handle positive and negative voltages up to about +/- 12 volts.  
>> 
>> 
>> Then the linux pulse per second driver will time stamp and log every cycle with the internal clock.  It is accurate to a couple microseconds.  
>> 
>> 
>> Don't worry about line noise because that is what you are measuring and it averages out after a few cycles.   You might try a >60Hz RC filter to remove noise but I think to do any better you will have to treat the signal as if it were audio frequency.  So scale it to 1 volt peak to peak and read it with an audio interface and then use an FFT.     But the transformer on the DCD pin of any normal computer with the Linux PPS driver works.  People are doing just fine with the simple transformer and time stamping the transitions.   And then it is just pure luck that Linux will already do this out of the box.
>> 
>> 
>> 
>> On Sun, Feb 9, 2014 at 5:53 AM, M. Simon <msimon6808 at yahoo.com> wrote:
>> 
>> This probably came up during the recent discussion of Line Frequency Monitoring but I may have missed it.
>>> 
>>> 
>>> Does any one have a circuit (tested - operational) for monitoring line frequency? I'd like something that checks zero crossing so that it is relatively insensitive to line voltage variations.
>>> 
>>> 
>>> Simon
>>> 
>>>  
>>> Engineering is the art of making what you want from what you can get at a profit.
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>> 
>> 
>> 
>> -- 
>> 
>> Chris Albertson
>> Redondo Beach, California
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