[time-nuts] Time source for indoor standalone PC

[Bob Camp]

Hi

Given the temperature coefficient of the device, performance is going to be very dependent on correcting it for the local thermal environment. That may or may not be practical in this case. Correcting it and then moving it probably isn't going to work very well.

Bob

On May 17, 2013, at 6:32 PM, Eric Williams <wd6cmu at gmail.com> wrote:

> Right, that's why I brought up the GPS sentences.  You'd need a small micro
> to read the chronodot registers and output formatted serial, the 1pps can
> go directly to the PC.
> 
> 
> On Fri, May 17, 2013 at 3:24 PM, mike cook <mc235960 at gmail.com> wrote:
> 
>> 
>> 
>> 
>> Le 17 mai 2013 à 22:52, Eric Williams a écrit :
>> 
>>> That's based on my experience, but I did go in and tweaked the offset
>>> register in mine over the course of a month or so.  I think it has gotten
>>> off 3-4 seconds in a year.
>>> 
>> 
>> I have found the same, BUT, they are not a solution to the issue. The
>> reason is that the OS doesn't read the RTC after initial boot sequence,
>> when the system clock is initialised. All clock references are to the
>> system clock from there on until orderly shutdown when it is updated from
>> the system clock value.
>> So it will give an accurate time at boot, but the system clock stability
>> will predominate from there. My Raspberry Pi which has one of these
>> installed has a 40ppm clock drift even though the RTC does better. I need
>> NTP to get correct it.
>> 
>>> 
>>> On Fri, May 17, 2013 at 1:33 PM, Tom Van Baak <tvb at leapsecond.com>
>> wrote:
>>> 
>>>>> Even something as simple as a Chronodot will hold to a few seconds a
>>>> year.
>>>> 
>>>> Eric,
>>>> 
>>>> Are you sure? My understanding is that the Chronodot is based on the
>>>> DS3231. Quoting http://datasheets.maxim-ic.com/en/ds/DS3231.pdf we
>> read:
>>>> 
>>>>   The DS3231 is a serial RTC driven by a temperature compensated 32kHz
>>>> crystal oscillator. The TCXO provides a stable and accurate reference
>>>> clock, and maintains the RTC to within ±2 minutes per year accuracy from
>>>> -40°C to +85°C.
>>>> 
>>>> /tvb
>>>> 
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