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

Bob Camp lists at cq.nu
Tue Dec 29 00:47:41 UTC 2009


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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