On Mon, 31 Dec 2018 12:00:02 -0500, [email protected] wrote:
> time-nuts Digest, Vol 173, Issue 44 > Message: 7 > Date: Mon, 31 Dec 2018 04:04:22 -0800 > From: "Tom Van Baak" <[email protected]> > To: "Discussion of precise time and frequency measurement" > <[email protected]> > Subject: Re: [time-nuts] More ES100 WWVB Measurements > Message-ID: <96BB388753294278A9CDE96C1EA7D9AE@pc52> > Content-Type: text/plain; charset="UTF-8" > > Hi Graham, > > That's very nice work. And you have uncovered several unusual effects > in the ES100. Bugs? Features? If we time nuts keep up the good work > to evaluate this chip, we are likely at some point to get an > informative response from the guys who designed it. They read > time-nuts. I didn't see this mentioned, but I think I have found the relevant US patent application: US20130051184A1, Real-time clock integrated circuit with time code receiver, method of operation thereof and devices incorporating the same, Oren Eliezer et al, Oren Eliezer et al, filed 2013-02-28. .<https://patents.google.com/patent/US20130051184> Found this by chasing stuff from the EverSet website: .<http://everset-tech.com/wp-content/uploads/2014/11/ReceiverRadioClocks.pdf>. Joe Gwinn > So now both you and Tim have observed the off-by-one-second (or > off-by-N-seconds) effect in the ES100. I wonder if this explains why > some of my ES100-based La Crosse 1235UA Ultratomic wall clocks are > off by a second sometimes. > > My main question: in your "Time Plot.PNG" plot, what is the cause of > the sawtooth pattern? The points are almost all on a clear negative > slope, though bounded by roughly +/- 75ms. Looking on the far left, I > see a time drift of +50 ms to -25 ms over an hour, which is > equivalent to a -20 ppm frequency offset; about -2 seconds/day. > > Do you think this is due to the 16 MHz onboard xtal? If so, how about > changing the temperature of the eval board by a lot (say, several > tens of degrees) for an extended time (say, 4 hours) and see if the > sawtooth slope changes convincingly. > > Also, just to be sure, can you put a known independent timing signal > (e.g., GPS/1PPS) into your complex BeagleBone Black / Debian 9.4 / > ntpd time server / Python 3 / Excel stack to establish the validity > of your measurement methodology? Very likely you did it right, but I > always cringe when I hear "Linux" or "NTP" and "precise time" in the > same sentence. Yes, sorry, forgive me; I grew up in the "trust, but > verify" generation [1]. It applies pretty well to metrology also ;-) > > /tvb > > [1] https://en.wikipedia.org/wiki/Trust,_but_verify > > > End of time-nuts Digest, Vol 173, Issue 44 > ****************************************** _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
