[time-nuts] Using a UBlox NEO-6 GPS module for calibrating a PIC microprocessor based timer.

Brian Inglis Brian.Inglis at SystematicSw.ab.ca
Mon Dec 2 10:00:12 EST 2013


On 2013-12-01 15:52, Attila Kinali wrote:
> On Sun, 1 Dec 2013 13:57:56 -0500
> "Dale J. Robertson" <dale at nap-us.com> wrote:
>
>> A unidirectional error of 1/100th of a second would accumulate around a
>> minute and a half per day. It's been a long time since I laid eyes on a
>> mechanical pendulum clock. I remember the clock in my childhood home kept
>> better time than that. ( I became odd very early. I compulsively compared
>> the clock time to WWV time at least once a day. I had been using the time
>> service from the phone company. I felt defrauded when I discovered (via WWV)
>> that the time from the local telco's dialup time service was just a rough
>> (very rough) approximation of the time.
>
> IIRC 10^-6 was "easily" acheivable with mechanical clocks, with the
> best going to 10^-8 or so (timescale IIRC 1 day).

Hi,
Many clocks and watches were tuned for years before being submitted for rating.

Astronomical regulators (accurate pendulum clocks) kept time within .01s/day, and
were improved down to about 1s/year, with the help of electromagnets, before being
replaced by quartz oscillators in the 1930s; regulators in other areas were
replaced by electric clocks timed from the grid during that same period.

The best of these had Q ~110,000, with variations in the hundreds of us/day,
better than network synced NTP servers which vary in the low ms.

Mechanical marine chronometer movements are expected to vary only about 0.1s/day.
Quartz wristwatch COSC certified chronometer movements are rated within .2s/day.
Railroad chronometer movements were expected to stay within 30s/week or ~4s/day.
Mechanical wristwatch COSC certified chronometer movements are rated within +6/-4s/day.
The "Geneva Standard" certifies movements stay within 60s/week or ~8s/day.

The certifications and standards (including ISO 3159) also require drift in multiple
orientations and across a range of temperatures ~0-~40C should remain constant.

So with 1 PPM ~ 1 s/11.5 day about 1-10 PPM or 10^-5 to 10^-6 range is expected.

Most modern quartz wristwatches will be in this range and be more accurate than all
but the best, custom mechanical timepieces.

-- 
Take care. Thanks, Brian Inglis


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