Hi
Even with a tuning fork crystal, anything past about 0.2% is a very large
changel. That's true for tuning and also true for normal aging.
I suspect that something mechanical has happened.
1) A cracked crystal - unlikely
2).An electro magnet in the driving circuit no longer firing fully.
a) Due to a bad magnet
b) Due to low power
c) Due to a dying chip
3) A worn escarpment.
Time to get it replaced ....
Bob
On Dec 28, 2009, at 6:22 PM, Dr. David Kirkby wrote:
> 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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