Bad timekeeping - is it adjustable?

[Scylla]

I have a Novus LED that I bought as NOS, and it seems to be gaining about 30 seconds every few days. Is there a way of fixing this, ie slowing it down?

Thanks.

[bruce wegmann]

Every quartz watch has a means of adjusting the frequency of the quartz crystal that supplies the timing signals to the watch circuitry. This is necessary because quartz oscillators, while very stable, aren't absolutely stable; the natural frequency of the quartz drifts gradually over time [even in the absense of temperature changes], due to "aging" effects in the structure of the crystal. The drift rate is initally relatively high, then diminishes gradually over a period of years [assuming the watch is always under power, and can go in either direction, up or down]. This drift in frequency is the reason Time Computer always recommended the watch be adjusted at every battery change [roughly annually], to compensate for this effect. Overall, this means that old quartz watches keep better time [long term] than new ones, because their crystals have more fully stabilized. Sort of aging like fine wine, getting better with age. Anyway, there will be somewhere on the module what is called a "trimmer", or variable capacitor, that is used to bring the resonant frequency of the circuit to some ideal value. Depending on the design of the circuit, this will typically be 32.768KHz, although different manufacturers used others, including 786.432KHz. Once the ideal frequency is known, it can be compared to a high-resolution frequency standard, and the deviation [in seconds per month, + or -] can be calculated. The gadgets that do all this are called Quartz Monitors [Time Computer called theirs the "Analyzer"], and they are a "must", if you want to do really accurate timing adjustments. ZanTech also made a very good machine; examples show up on eBay every so often. Note: severe cases of off-frequency crystals may require replacement, if the trimmer cannot fully compensate. Again, the use of a Monitor is essential to making that determination. Adjusting the new crystal to proper frequency is then a simple matter.

[Majestyk]

Well, I wish every quartz watch had a trimmer. :) There are many vintage LED's that didn't, like some Texas Instruments and Litronix, etc. Then the last generation Frontier modules did away with them. Non of the modern LED or LCD watches have them these days. I'm having an LED watch produced and even the company that is making it has never heard of a trim capacitor (or trimmer). :) Of course, QC's these days are more reliable and cheaper so just replacing it isn't a big deal but the trimmer is so much nicer.

30 seconds every few days may warrant a QC change.

QC = Quartz Crystal, of course.

MJ

[bruce wegmann]

You're right; I should have qualified my statement as "every vintage led watch", but I guess I would still have been a bit wrong there, anyway. Fact is, manufacturing techniques have improved tremendously in the last thirty years. By todays' standards, the quartz crystals used in the early digitals were crude and unstable. All quartz used in watches is synthetic, but the growth conditions are much more tightly controlled now [growth cycles timed to the fraction of a second, temperatures to the fraction of a degree, purity of materials to parts-per-billion]. It comes as no real surprise to me that, given superior stability, and initally trimmed in frequency to previously unattainable precision, something as primitive as a trimmer capacitor could be dispensed with. Just part of the evolution of the technology, which was already well underway in Time Computers' era... BTW, there must be a capacitor in a resonant quartz circuit; the old variable ones have simply been replaced with one of a specific fixed value; much smaller and cheaper...

[rewolf]

... It comes as no real surprise to me that, given superior stability, and initally trimmed in frequency to previously unattainable precision, something as primitive as a trimmer capacitor could be dispensed with...

Well, that would be fine, but it is not the whole truth. The main reason why the trimmer capacitor disappeared is simply production cost. A trimmer is difficult to adjust automatically - and manual adjustments are way too expensive considering the total production cost of a simple watch module.
Electronic calibration as part of the production test can be a solution. This is done automatically via "test" connections on the chip. These procedures are normally not documented, so recalibration is not possible for the end user. However, I don't know if this type of ajdustment is done in any modern watch.

Standard 32kHz watch crystals have an initial tolerance of 20ppm = 53 sec/month. Plus aging and temperature effects. Cheaper ones have 30 or even 50ppm.
I have about 30 modern digitals I keep running and wear regularly. None of them has a trimmer. They range from -2min/month to +2min/month. Most are within +/-10sec/month. The cheaper ones usually have the biggest deviation, but there are exceptions - e.g. the US$80 DKNY is more accurate than the Ventura d_sparc px which cost over 20 times more. Just a matter of luck (for the DKNY).

[bruce wegmann]

A critical question we forgot to ask is: Does the Novus module have a timing trimmer? If so, a few seconds on a quartz monitor will tell the story. Theoretically, you could have this watch running perfectly in less than a minute. Also, does the Novus use a standard 32Khz crystal? Most timing machines will only read the 32K and 786K frequencies. Worst-case situation is you might have to replace the quartz, but that is a minor repair. The watch would still have to be re-adjusted to bring the timekeeping back to within spec, but that would only take another minute. Also, just for fun, doing some number-juggling on the frequency tolerances... There are a little over 31 million seconds in a year, so a frequency error of 1ppm = 31 sec/year, half the total tolerance Pulsar specified [60sec/year]!. They were therefore guaranteeing a better-than 2ppm frequency accuracy. Not bad for a vintage watch; it's more than an order of magnitude [factor of ten] better than modern ones. A final thought; if you want to see what really precise timekeeping looks like, go to leapsecond.com, and see a clock that goes off the mark a single second in a million and a half years; outside of the National Bureau of Standards, he has the most accurate clocks on the planet...

[Scylla]

Higgie has very kindly offered to calibrate not only my Novus (he says it will probably require that the crystal be changed), but also the NOS P3
I'm negotiating on, which the seller tells me is deviating by 10 seconds a day....

In fact, this particular P3 grows less attractive the more I think about it.

[Majestyk]

I don't think I've ever come across an N.S. module that didn't have a trimmer. I once had a rare Hughes module from 1974 that didn't have one though. :)