[time-nuts] Recommendations for Mains Power Monitor / Logger

[d.schuecker at avm.de]

Hi,

I did my recordings of grid frequency and cycle count with my homebrew
device.

https://www.tindie.com/products/DetlefS/mains-ac-frequency-meter/
http://www.dschuecker.de/

The heart is a STM ARM processor, which samples the grid voltage at 160ks/s
behind a step-down transformer, slow enough to handle the data in realtime.
It is clocked with a TCXO, off 0.4ppm. I do a sinewave-fit on any single
cycle. Measured precision on an artifical 50Hz sine wave is 1.4E-4 Hz,
which comes close to a jitter of 60ns. Precision is heavily affected by
transients and harmonics, so an aggressive digital filtering is necessary,
analog filtering is not sufficient. The step response of this filter limits
the response of the device to changing frequency.

Cycle count should not be affected by glitches. I use hysteresis and time
windowing on the sampled and filtered data for counting.

The data is presented on a RS232 interface and pumped to the cloud by a
Raspberry running a Python script.

I knew a bit about FNET but I was not aware of www.naspi.org. Are there
similar initiatives in Europe?

Cheers
Detlef
DD4WV


"time-nuts" <time-nuts-bounces at febo.com> schrieb am 11.03.2018 23:13:26:

> Von: Attila Kinali <attila at kinali.ch>
> An: Discussion of precise time and frequency measurement
<time-nuts at febo.com>
> Datum: 11.03.2018 23:30
> Betreff: Re: [time-nuts] Recommendations for Mains Power Monitor / Logger
> Gesendet von: "time-nuts" <time-nuts-bounces at febo.com>
>
> On Sun, 11 Mar 2018 14:41:23 -0500
> Dana Whitlow <k8yumdoober at gmail.com> wrote:
>
> > I'll have to take a look around to see if there isn't something cheap
that
> > can run
> > standalone so I don't have to tie up (or wear out) a whole PC for the
> > acquistion
> > process.
>
> Blub... I should the whole mail....sorry about that.
>
> How about this: get a uC board (e.g. STM32discovery), replace
> the crystal with a 10MHz input from your frequency reference.
> Use the on-chip 12bit (really just 6bit) ADC to sample the
> sine wave from your mains. Do phasor measurement in software.
>
> Probably any sampling frequency between 200Hz and 1kHz should
> do the job, Which is slow enough so you can still handle the
> samples with the uC alone and don't need any fancy DSP.
>
>
>          Attila Kinali
>
> --
> <JaberWorky>   The bad part of Zurich is where the degenerates
>                 throw DARK chocolate at you.
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