Explanation Quartz clock

first european quartz clock consumers astrochron , junghans, schramberg, 1967 (german clock museum, inv. 1995-603)



first quartz wristwatch movement, used in seiko astron, caliber 35a, nr. 00234, seiko, japan, 1969 (german clock museum, inv. 2010-006)

chemically, quartz compound called silicon dioxide. many materials can formed plates resonate. however, quartz piezoelectric material: is, when quartz crystal subject mechanical stress, such bending, accumulates electrical charge across planes. in reverse effect, if charges placed across crystal plane, quartz crystals bend. since quartz can directly driven (to flex) electric signal, no additional transducer required use in resonator. similar crystals used in low-end phonograph cartridges: movement of stylus (needle) flexes quartz crystal, produces small voltage, amplified , played through speakers. quartz microphones still available, though not common.

quartz has further advantage in size not change temperature fluctuates. fused quartz used laboratory equipment must not change shape along temperature. quartz plate s resonance frequency, based on size, not rise or fall. similarly, since resonator not change shape, quartz clock remain relatively accurate temperature changes.

in 20th century, radio engineers sought precise, stable source of radio frequencies, , started @ first steel resonators. however, when walter guyton cady found quartz can resonate less equipment , better temperature stability, steel resonators disappeared within few years. later, scientists @ nist (then u.s. national bureau of standards) discovered crystal oscillator more accurate pendulum clock.

the electronic circuit oscillator, amplifier output passes through quartz resonator. resonator acts electronic filter, eliminating single frequency of interest. output of resonator feeds input of amplifier, , resonator assures oscillator howls exact frequency of interest. when circuit starts up, single shot can cascade bringing oscillator @ desired frequency. if amplifier perfect, oscillator not start.

the frequency @ crystal oscillates depends on shape, size, , crystal plane on quartz cut. positions @ electrodes placed can change tuning, well. if crystal accurately shaped , positioned, oscillate @ desired frequency. in quartz watches, frequency 32,768 hz, , crystal cut in small tuning fork shape on particular crystal plane. frequency power of 2 (32,768 = 2), high enough people cannot hear it, yet low enough permit inexpensive counters derive 1-second pulse. 15-bit binary digital counter driven frequency overflow once per second, creating digital pulse once per second. pulse-per-second output can used drive many kinds of clocks.

although quartz has low coefficient of thermal expansion, temperature changes major cause of frequency variation in crystal oscillators. obvious way of reducing effect of temperature on oscillation rate keep crystal @ constant temperature. laboratory grade oscillators oven-controlled crystal oscillator used, in crystal kept in small oven held @ constant temperature. method impractical consumer quartz clock , wrist watch movements.

the crystal planes , tuning of consumer grade clock crystal designed minimal temperature sensitivity in terms of effect on frequency , operate best @ 25 28 °c (77 82 °f). @ temperature crystal oscillates @ fastest. higher or lower temperature result in -0.035 parts per million/°c (slower) oscillation rate. ±1 °c temperature deviation account (1) x -0.035 = -0.035 parts per million (ppm) rate, equivalent -1.1 seconds per year. if, instead, crystal experiences ±10 °c temperature deviation, rate change (10) x -0.035 ppm = 100 x -0.035 ppm = -3.5 ppm, equivalent -110 seconds per year.

quartz watch manufacturers use simplified version of oven-controlled crystal oscillator method recommending watches worn regularly ensure best performance. regular wearing of quartz watch reduces magnitude of environmental temperature swings, since correctly designed watch case forms expedient crystal oven uses stable temperature of human body keep crystal in accurate temperature range.