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

Dr. David Kirkby david.kirkby at onetel.net
Tue Dec 29 01:33:12 UTC 2009


ALAN MELIA wrote:
> Hi David at 17 years the probably NiCd batts may have one at zero volts and the charge is constant curent so the clock supply will not be held up by the charger. My timer used alkalines and I replaced every 5 years.
> 
> Alan G3NYK

A recent power failure did not cause the clock to stop, so some battery power 
must exist, but I believe the clock may have run a bit slower during that 
period, as there was a bit of a kink in the graph, but due to the limited amount 
of data, its hard to be precise about this. But I believe the power failure did 
throw my estimates off a bit more than usual.



Dave


> --- On Mon, 28/12/09, Dr. David Kirkby <david.kirkby at onetel.net> wrote:
> 
>> From: Dr. David Kirkby <david.kirkby at onetel.net>
>> Subject: Re: [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, 23:58
>> 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.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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