Quartz oscillators

  Covergirl 12:27 11 Aug 10

I always understood that quartz watches / clocks etc run off a quartz crystal which vibrated at so many gazillion vibrations per second, thus creating an extremely accurate timing mechanism for timepieces.

The reason for this poser is that some watches appear to gain or lose time in an unexplicable manner.

For instance, a fairly new novelty pocket watch style (about 4" diameter) running on battery gains about 5 minutes in 3 months, yet an ancient Ferguson clock radio running off mains keeps near enough perfect time to the second over a period of years.
Another item, a video recorder, gains a few minutes every couple of months.

I wondered what else had an influence on why some of these clocks are accurate and others aren't. I've included battery and mains operated devices to eliminate mains voltage fluctations or stabilisation.

What do you know?

  ashdav 12:34 11 Aug 10

The quartz based oscillator is "accurate" in that it is consistent.
If it has not been adjusted properly at manufacture it may gain or lose over a period of time but that gain/loss will be consistent.

  Covergirl 12:40 11 Aug 10

How do you adjust a piece of quartz? Surely they are all the same therefore all consistent.

I've seen the little aluminium cylinders they come in connected by two wires to the main circuit. What else is in that cylinder - electronics to compensate for an over or under oscillating piece of quartz?

Or what?

  wiz-king 13:20 11 Aug 10

You can change the frequency of a crystal with a trimmer capacitor or inductance in series or in parallel.

Quartz oscillators are affected by both temperature and atmospheric pressure so the accuracy of a simple watch may vary day on day but average out over say a year.
The temperature may be held more constant if it is worn 24 hours per day.
More expensive watches utilise electronic circuits to compensate for temperature/pressure variations.

  peter99co 15:02 11 Aug 10
  ashdav 16:24 11 Aug 10

The circuit is trimmed by adjusting a small capacitor. C1 in the circuit shown on peterco's link.
In a cheap device there won't be one so you are stuck with a time drift.

  BT 16:51 11 Aug 10

I can never understand why they can't make the timers in mains operated equipment more accurate. Video recorders and the like always seem to drift, and my Microwave rarely manages to show the correct time.
I would have thought that a mains operated timer could be more accurate. My bedside clock keeps perfect time so it can be done.

  sunnystaines 18:06 11 Aug 10

had an quartz watch when they first came out in early 70's a seiko kept excellent time for about 15 or so years then packed up and was not repairable.

  octal 18:58 11 Aug 10

You can adjust the frequency of the quartz element, but at the end of the day they are made to a cost and one of the problems is the stability is going to suffer.

Mains driven clocks are synchronised to the mains frequency which is held to a tight tolerance, so they won't drift very far from 50Hz.

Modern video equipment is usually synced to the clock transmitted by the transmitter and that is extremely accurate. If its not then its not being synced to the transmitter for some reason and relying on that nasty little quartz crystal element, the cheap and nasty one.

  morddwyd 20:45 11 Aug 10

"make the timers in mains operated equipment more accurate. "

Many mains timers are still controlled by the AC frequency, a nominal 50Hz.

This can be affected by any badly corrected inductive load, such as a vacuum cleaner or refrigerator, and will drift off synch.

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