[time-nuts] Re: Power and heat re: Heathkit WWV clock / where are the good oscillators?

[Bob kb8tq]

Hi

Backing up a bit:

Any oscillator ( RTC or not ) is going to age. As it ages, the rate it looses 
or gains time speeds up. A device that is dead on today might well age
a ppm ( or more ….) per year. 

Oscillators all are going to have a temperature spec. That’s going to apply
over some range of temperatures *and* up to some (often unstated) rate
of change. 

You then have a set accuracy. When the device leaves the factory, it’s 
within tolerance of “dead on”. That might be 0.1 ppm, it could easily
be something else. Solder the device into a board via a typical reflow 
process and it’s not set where the factory put it any more … 

Past that, you have all of the other nasty little factors. Supply voltage
moves things around. Shock / vibration / acceleration move things. 
On a module that is not hermetic, humidity will get into the act. How much
do any of these contribute? That depends ….. could be tenths of a ppm.

The accuracy of any oscillator at any point will be driven by the sum of
all this “stuff”. The bold print number in that flashy ad likely puts one of 
the numbers in focus and pretty much ignores the rest ( …. in a constant
environment ….). Parsing all the advertising talk often is more than a bit
difficult. 

Do most oscillators do pretty well? Sure they do. This or that goes one 
way today and the other way tomorrow. Net at the end of the week is some
sort of cancelation. If the aging spec is a max, you can bet that most will
do better than that limit. However if you have to be *sure* the device will 
do this or that  ….. hmmm …..

If you make wrist watches, the most common solution to this is to set them
so they typically go a bit fast. Apparently folks don’t seem to mind arriving 
a bit early. They get bothered when they show up late. Back in the day, 
that set target was 10 seconds a month. These days, it’s not quite that much.

Fun !!

Bob

> On Aug 7, 2022, at 1:56 PM, Hal Murray via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> 
> Azelio Boriani said:
>> The Swiss MicroCrystal claims +/- 1ppm accuracy and +/- 0.09 seconds per day
>> for their RTC modules. <https://www.microcrystal.com/en/products/
>> real-time-clock-rtc-modules/> 
> 
> Note that the slots in that table with 1ppm are for 25C.
> 
> I looked at the data sheet for the top slot: 2.5ppm over -40 to +85C.
> 
> There is a graph for the temperature of the crystal that goes to over 100 ppm 
> so I assume there is some trickery to add/drop pulses.  That is probably OK if 
> you are driving a watch but may be "interesting" in other applications.
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
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