Re: PSA: Clock drift and pkgin

> On Dec 13, 2023, at 5:10 PM, Johnny Billquist <[email protected]> wrote:
> 
> On 2023-12-13 22:52, Mouse wrote:
>>>> But a drift of a couple of % would not be unexpected.
>>> Um, yes, it would be unexpected.
>>> The crystal spec in that era was 0.01%, [...]
>>> If you see a couple % drift, that's definitely not the crystal.
>> I'm not so sure.
>> My experience is that older machines keep worse time than newer ones,
>> even high-quality older machines and cheapo newer ones.  I suspect that
>> crystal frequencies drift with time (or perhaps with something that
>> tends to correlate positively with time, such as wide temperature
>> ranges in storage).
> 
> Chrystals age, and over time get farther from the nominal frequency. They also deviate based on temperature. And a bit on load. So I would say more than 100ppm is definitely more or less to be expected.
> 
> But I might have exaggerated a little when I said "several percent". :-)
> 
> But just pull up the data sheet for any modern crystal, and you'll find what the expected deviation will be based on both time and age.
> (Well, actually, for age they usually just say what to expect the first year, after that there isn't much...)

I pulled up a random modern manufacturer, Crystek.  Their HC49 (through hole, metal can) crystals are specified at 50 ppm calibration tolerance, 100 ppm frequency stability, and aging less than 3 ppm for the first year.  That's the basic spec; they offer better specs as an option.

And for grins I found a 1972 catalog from International Crystal Mfg., perhaps the best known supplier for many decades.  Their "general purpose" crystals in the MHz range have a calibration spec of 100 ppm, frequency within 50 ppm from -30 to +60 C, and no aging spec that I can see.

	paul