[time-nuts] Is a crystal likely to change frequency by 3% ?

[David McGaw]

The battery probably was going weak and the oscillator coming out of 
full control by the crystal.  The tuning-fork crystal used in RTCs is 
not as high-Q as a MHz crystal.  I have noticed clocks using these can 
go quite slow at low voltage.  The crystal acts more like an inductor in 
this case and resonates with the increased junction capacitance at low 
voltage.

David


On 9/12/14 6:52 PM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:
> Dr David Kirkby
> Managing Director
> Kirkby Microwave Ltd
> Registered office: Stokes Hall Lodge, Burnham Rd, Chelmsford, Essex, CM3
> 6DT, United Kingdom
> Registered in England and Wales as company number 08914892
> http://www.kirkbymicrowave.co.uk/
> Tel 07910 441670 / +44 7910 441670 (0900-2100 GMT)
> On 12 Sep 2014 12:18, "Bob Camp" <kb8tq at n1k.org> wrote:
>> Hi
> Hi,
>
>> If this is an RTC, it’s probably running off of a battery when the
> machine is powered down. It is far more likely that the oscillator is
> dropping out (stopping) rather than shifting frequency.
>
> Good point,  I never thought of that. I have however noticed that analogue
> quartz clocks slow as the battery goes flat. But maybe too they stop and
> start. It would make an interesting experiment to check it, but one would
> need some method of logging the time from the hands.  Conceptually that is
> not difficult,  but it needs more work than I want to do. One could do it
> with a video camera and a fair bit of work writing the software. Probably
> easier is logging battery voltage and current as that should show if it
> starts and stops.
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