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KF5JRV > TECH     02.05.22 01:37z 13 Lines 1384 Bytes #16 (0) @ WW
BID : 33390_KF5JRV
Subj: Observatory Quartz-Crystal Clock
Sent: 220502/0135Z 33390@KF5JRV.#NWAR.AR.USA.NA BPQ6.0.19

In 1929 the quartz crystal was first applied to timekeeping; this invention was probably the single greatest contribution to precision time measurement. Quartz crystals oscillating at frequencies of 100,000 hertz can be compared and frequency differences determined to an accuracy of one part in 1010.

The timekeeping element of a quartz clock consists of a ring of quartz about 2.5 inches (63.5 mm) in diameter, suspended by threads and enclosed in a heat-insulated chamber. Electrodes are attached to the surfaces of the ring and connected to an electrical circuit in such a manner as to sustain oscillations. Since the frequency of vibration, 100,000-hertz, is too high for convenient time measurement, it is reduced by a process known as frequency division or demultiplication and applied to a synchronous motor connected to a clock dial through mechanical gearing. If a 100,000 hertz frequency, for example, is subjected to a combined electrical and mechanical gearing reduction of 6,000,000 to 1, then the second hand of the synchronous clock will make exactly one rotation in 60 seconds. The vibrations are so regular that the maximum error of an observatory quartz-crystal clock is only a few ten-thousandths of a second per day, equivalent to an error of one second every 10 years. 	  	 

73 de Scott KF5JRV


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