[time-nuts] Casio Watches 13 Year Drift in Seattle
Tom Van Baak
tvb at LeapSecond.com
Sun Jun 28 10:33:38 UTC 2015
> I think there may be a new Time-Nut in the Seattle area, , ,
> John, KM6QX
Thanks for posting that. I will have to look this person up.
Given typical tempco plots for 32 kHz crystals I would assume the lost time is due to temperature: wall or room temperature is lower than wrist temperature. Someone on the list with that model watch should do a quick test to confirm. Also a measure of voltco would be interesting.
Note the days of quartz being adjusted with a trimmer capacitor are long gone. It's done digitally now. See, for example, paragraph 8.3 of http://www.nxp.com/documents/data_sheet/PCA2003.pdf
It's much more convenient to periodically delete pulses than have to add them so that's why wristwatch oscillators are designed to run fast rather than slow.
32 kHz watch circuit with programmable output period and pulse width
The Principle of Digital Trimming
Digital trimming for frequency adjustment
Method for digital frequency trimming an oscillator in an electronic timepiece
AVR4100: Selecting and testing 32kHz crystal oscillators for Atmel AVR microcontrollers
Quartz Crystal Theory
MSP430 32-kHz Crystal Oscillators
Introduction to the quartz tuning fork
The Accuracy and Stability of Quartz Watches
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