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

[Dave Baxter]

Hi....
 
My guess, is it's a mechanical failure, as unless you've had a series of long power cuts, the battery/quartz backup won't kick in.  AFIK, the Quartz clock only is in effect, if the 50Hz supply fails.   The utility 50Hz is maintaind to a close tolerance and "tweaked" to maintain a very good 24 hour clock, though it may wander one way or t'other during the day.
 
A good friend a while back, had the imersion heater fail, in such a way that it welded the E7/Normal relay in the E7 position.
 
It was some weeks (in the summer, so heating not in use) before he noticed that the "Normal" meter clock was not incrementing!   Much hand wringing later, he phoned the electric co, who without question replaced the E7 clock/changeover unit and DIDN'T sting him for the cheap electricity he had used, instead of the full price stuff.
 
Two choices, and I didn't say this(!)
 
1) ignore it, and reap the benefit of a wandering 7 hour cheap electric period :-)   (But that could be seen as Fraud by some)
 
2) call the electric co, and they will probably change the clock/changeover unit for free, as after all, it is to their benefit, not yours!
 
If they do change it, I doubt they will let you keep the old one (your might re-fit it, in their eyes) and I doubt the tech who does the job will know the details of it's internal workings.
 
As you use little of the E7 facility, it may pay to have the clock etc removed and go onto a "standard" tarrif.   But, as you say, have to do the math first.
 
I did sit down one time, and worked out that taking into account inverter and battery charge/discharge efficiency (or lack of) it is not worth putting together a large UPS for the PC's I run 24/7 (4 of the blighters at present) that would charge up overnight, and run them on battery during the day.   At least, not with the level of technology currently available to the likes of us.   It is close, but excluding the cost of buying/building the thing, the resulting running costs would not be worth having.  It would not even pay for itself in my lifetime!
 
Best Regards.
 
Dave B.
 
PS:  Does anyone else miss the odd digest mail at times?
 
------------------------------

Message: 4
Date: Mon, 28 Dec 2009 19:47:41 -0500
From: Bob Camp <lists at cq.nu>
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>
Message-ID: <A0C20146-6482-45AB-B219-BB76BA5FA527 at cq.nu>
Content-Type: text/plain; charset=us-ascii

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
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>

-------------- next part --------------
A non-text attachment was scrubbed...
Name: winmail.dat
Type: application/ms-tnef
Size: 8148 bytes
Desc: not available
URL: <http://febo.com/pipermail/time-nuts_lists.febo.com/attachments/20091229/83076478/attachment.bin>