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Crystal oscillator frequency stability?

Hi guys,

I'm using a cheap, can-type clock oscillator in a project as a frequency standard. It's 10 MHz. Here's the specs:

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What I don't understand is that in the literature they say that the frequency stability is only +/-100 ppm. If I'm figuring right, that means that the clock can vary per second by as much as +/-1000 clock ticks. But when I connect the output to a frequency counter it reads

10,000,060 Hz and only fluctuates maybe one or two ticks over time, which is orders of magnitude better than what they claim.

Did I just get lucky, or am I misunderstanding the specs? Is this an average error over a batch of many parts? Are they taking the entire temperature range into account? What gives?

Thanks.

Sid

Reply to
sylvestersn
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youl find it varies with many things :- temperature at a certain rate, supply voltage at a certain rate and ageing over long time at a certain maximum rate, plus the initial accuracy, all this in total will probably be less than +-100ppm. (and also acceleration too ! but this probably isnt included) so dont expect to see any such wild variations in the space of a second or two.

Colin =^.^=

Reply to
colin
** Groper alert !

** That last option is the one.

Crystal stability is normally quoted over the specified operating temp range.

So, +/- 100 ppm over the range from 0 to 70 C equates to roughly +/- 3 ppm per degree C. This is an average figure and it may well be that it is much better at a particular temperature - like around 20C.

Don't forget the initial accuracy figure too and the fact you can usually tweak a crystal onto its marked frequency with a little capacitive loading.

It follows, that if you can keep the temp of the crystal stable, its frequency is very stable.

....... Phil

Reply to
Phil Allison

That's typical for a cheap can oscillator; they're usually within 10 ppm of dead-on. But they only guarantee +-100 PPM.

But from that initial value, expect a few PPM drift per year and a good fraction of a PPM per degree C (much less if you're lucky) and some more power supply voltage influence. But short-term, stability should be better than 0.1 PPM, even for a cheap rock.

John

Reply to
John Larkin

On Feb 18, 8:33?pm, snipped-for-privacy@yahoo.com wrote: But when I connect the output to a frequency counter it reads

Do not forget, your counter also has a timebase. You must consider the drift and age of that timebase (probably crystal derived?) on your quoted measurement. It could be that the crystal is dead-on, and the instrument is 60 Hz "off".

In reality, it is highly likely that they are both "off", at least a little...

Convert these numbers to percentages and you will discover that for most circuits, the accuracy is plenty sufficient.

-mpm

Reply to
mpm

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