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Temperature and Timing Covariance?

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grenchat

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Temperature and Timing Covariance?

Post04 Sep 2014, 07:48

Has anyone noted any timing variance when wearing vintage LED watches outside on very hot/cold days? Granted, these circuits were designed to be stable over a wide range of anticipated temperature fluctuations, though back in my college electronics days we built a digital clock with a series of 7 segment LED displays for a laboratory experiment. We adjusted the circuit’s potentiometer and trimmer capacitor so that the seconds digits would advance at the rate of 60s/m by way of a frequency counter and a wristwatch. Once the circuit was adjusted correctly, we blasted the circuit with freeze spray and noted an instantaneous change on the frequency counter. Likewise, heating the circuit with a heat gun would also induce a change in output frequency. Of course, a watch that a person is wearing would likely never be subject to such extreme temperature fluctuations, though I would expect that a vintage LED watch worn outdoors by someone in Greenland would vary significantly with the same watch being worn outdoors by someone in Mexico. The watch would have to be tuned (if possible) by way of the trimmer capacitor to achieve optimal accuracy in these extreme environments.

Has anyone moved to a warmer or colder environment and needed to make adjustments accordingly?

Just curious…
Jason
"We are showroom dummies"- Kraftwerk
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Ole Joe

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Re: Temperature and Timing Covariance?

Post04 Sep 2014, 19:55

When Motorola was manufacturing XY-Bar cut crystals for the LED watch manufactures back in the early '70's, they did a study on the time keeping ability/accuracy of various electronic wristwatches. They concluded from their study that the best environment was when the watch was in contact with the human body. Why?, beacuse the bodies constant temperature of 98.6 F provided a constant temperature to the watch case and contents therein providing some temperature stablization. The XY-Bar cut crystals have what is known as a "negative parabolic temperture coefficient". When manufactured, they were designed to be spot on center frequency at about 20 C. Any variation from the 20 C temperture, either higher or lower, caused the quartz frequency to decrease by so many parts per million. The frequency of the "total" oscillators integrated circuit also exhibits a similar temperature dependence. When I worked for Frontier Semiconductor in the '70's, our modules were tuned to be within 3 parts per million of 32.768KHz in a 68-70 F temperature enviroment. We also did the best we could to temperature compensate the over-all oscillator circuit by using a trimmer capacitor that had a "positive parabolic temperature coefficient" in the pi feedback network of the oscillator circuit to offset the "negative parabolic temperature coefficient" of the quartz crystal. This scheme, along with the temperature stabilization from the "body" did a pretty good job of holding the oscillator to the set frequency. We were unable to compensate for quartz crystal aging which was spec'd by the manufactures to be from 2-5 parts per million for the first year an essentially no aging thereafter.

Joe
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767Geoff

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Re: Temperature and Timing Covariance?

Post04 Sep 2014, 20:28

You would be amazed at the consistent micro environment afforded to a watch. This discussion goes all the way back to temperature compensation at the turn of the 18th century. Clocks being temperature compensated for about two hundred years prior to the 18th century.

Pocket watches and subsequent wristwatches have bimetallic balances to compensate for steel hair springs. New metals created in the early twentieth century (elinvar and glucudur) were stable from -20 to plus 100 degrees Fahrenheit. However the wristwatch and pocket watch worn next to the skin (wrist) vary only a few degrees off body temperature while worn. In the hot sun or cold day.

Shock freezing and heating of the crystal and trimming capacitor will alter the timing response but does not occur while on the wrist under the sleeve. If you wore your watch around the sleeve as WWI pilots did, in November at 2000' in the air, open cockpit, yes there would be a response, but very little over the time period the watch was exposed. And it was compensated from -20 to plus 100 so again no effect under normal conditions.

So getting back to your experiment, both the trimming cap and the crystal are affected by extremes in temperature. The cap more so, which is why the synchronar and the HP41CX calculator do not have trimming caps but instead have an ability to adjust the count.

So I don't think under normal winter to summer cycles you will see a temperature effect on your timing unless there is something wrong with the cap or crystal as they age.

Hope this is interesting enough to read.

Geoff

As usual an EXPERT got there before me. Joe, ever consider a PDF version of your experiences and knowledge with regard to your time at Frontier. It would make for fascinating reading!

And Joe, thanks for all the help with my modules. All the best, Geoff
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grenchat

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Re: Temperature and Timing Covariance?

Post04 Sep 2014, 22:58

Thank you both for your most informative replies!

Joe, it’s great to learn that we have an industry professional on board. I’ve sure heard of Frontier Semiconductor, but am unsure about which companies produced modules for which watches. I also realize that some overlap is to be expected. For instance: I’ve learned that Hughes Aircraft produced most of the Compu Chron modules, though was replaced by Sanyo when production ceased. I understand that Sanyo also produced the same module for the latter generation Pulsars – presumably with the more standard 32.8KHZ crystal.

Motorola would be an excellent choice for crystal manufacture as they produced quite a few for their quite extensive line of radio transceivers – back when radios still used them. In fact, my very first VHF/UHF scanner held only 5 RX Xtals and also featured some of the niftiest red bubble LEDs. I’m sure you remember these well.

Geoff, thank you for the historical horology information. The stainless steel case back serves as a great heat conductor and I would assume is far more effective if the watch is worn snuggly on the wrist. I recall how in the truly mechanical (not capacitor driven) automatic and hand wound watches, non-ferrous parts were also used to make the watch anti-magnetic. While I owned several hand wound watches when I was young, I never upgraded to automatics because I was opposed to having all those moving parts that require ultrasonic cleaning, lubrication and adjustment when quartz was accurate, reliable and almost maintenance free. Antique hand wound and weighted pendulum clocks, on the other hand, do appeal to me. Back in the ‘80s, I spent a fair amount of time ( :mrgreen: pun intended) soaking mechanisms, lubricating pivots, bushings, and making gradual escape adjustments over long periods.

Regards,
Jason
"We are showroom dummies"- Kraftwerk

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