From: Dr. David Kirkby <david.kir...@onetel.net>
Subject: Re: [time-nuts] Can a quartz crystal go off by 2% ?
To: "Discussion of precise time and frequency measurement" <time-nuts@febo.com>
Date: Monday, 28 December, 2009, 23:58
ALAN MELIA wrote:
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
It could be the battery is low. There clearly is a battery
backup, and there is
something on the clock which implies the holdover period is
about 4 days. (I
forget the exact wording). Clearly if there is a power
failure, the clock must
still rotate to keep accurate.
I assume the battery is constantly charged by the incoming
supply. Given the age
of the battery (> 17 years), it is unlikely to be in
good condition! But it
should be charged all the time. But perhaps even when
charged, its voltage is
very different to what it should be.
I would not have thought a trimmer cap going open-circuit
could have induced a
2% change. That seems an awful lot.
Thanks for the idea of the ferrite rod.
Dave
--- On Mon, 28/12/09, Dr. David Kirkby <david.kir...@onetel.net>
wrote:
From: Dr. David Kirkby <david.kir...@onetel.net>
Subject: [time-nuts] Can a quartz crystal go off
by 2% ?
To: "Discussion of precise time and frequency
measurement" <time-nuts@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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