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" <kb...@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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