[time-nuts] Can a quartz crystal go off by 2% ?

ALAN MELIA alan.melia at btinternet.com
Mon Dec 28 23:37:29 UTC 2009


It is possible the crystal has succumbed to a mechanical fatigue. To check I used an old relay coil with a ferrite rod stuffed through it and tuned to 32.6khz. If you have a sensitive enough counter you may be able to measure this without an amp in line. (2% is a long way out !) It could also be the trimmer capacitor that has failed. I doubt there is much more mechanical, other than a dodgy solder joint. 

In all probability it will be the bane of all lovers of old electronics....the power supply electrolytic capacitors......remember battery quartz clocks run slow or fast as the batt runs out.

Alan G3NYK

--- On Mon, 28/12/09, Dr. David Kirkby <david.kirkby at onetel.net> wrote:

> From: Dr. David Kirkby <david.kirkby at onetel.net>
> Subject: [time-nuts] Can a quartz crystal go off by 2% ?
> To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
> Date: Monday, 28 December, 2009, 23:22
> I'm on the so-called 'Economy 7'
> electric in the UK, where I'm supposed to get cheap electric
> from 0030 to 0730 - i.e. a 7 hour period when electricity
> demand is low. I'm no longer heating by electric, but do run
> some computers 24/7. It's not totally clear whether this
> saves me money or costs me money, as I pay a higher price
> per unit during the expensive period, to compensate for the
> fact I get it cheap for 7 hours. But I run some computers
> 24/7. I guess I should do the maths and work it out. Apart
> from some heaters in the garage, which are very rarely used,
> I no longer heat with it.
> 
> The time when the electric is cheap is set by a clock,
> which rotates once/day. It says on it "quartz" somewhere, so
> it must be regulated by a crystal and not from the 50 Hz
> supply, which would be pretty useless, as the clock would go
> wrong if there was ever a power failure. The clock has not
> been changed in the 17 years I've lived at my house, though
> the meter has on a couple of occasions.
> 
> The clock used to keep accurate, but now it looses time
> about 30 minutes/day. I wrote a computer program to predict
> when the electric is cheap, so we can schedule when things
> like the washing machine, dishwasher, Hoover etc are used.
> Even cooking to a certain extent, if it's convenient, though
> our life does not revolve around the cheap electric.
> 
> I'm wondering if this is a mechanical fault in the clock,
> or whether the crystal has developed a fault. It's clearly
> well outside any tolerance or aging process of any crystal -
> even the cheapest ones.
> 
> I've not done any very extensive tests, but the error does
> not appear to be constant. Hence every month or so I need to
> produce a new table, as my predictions get less accurate
> with time. Since one can only read the clock to an accuracy
> of about 15 minutes, it's not easy to know how far it is
> out. Sometimes we hear the contactor go over, as this is
> supposed to then power the storage heaters, which we no long
> use.
> 
> Dave
> 
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