1945/06/01 by Paul Sollenberger, Alfred H. Mikesell, A. H. Mikesell
Materials Science · Physics and Astronomy · #Solid-state spectroscopy and crystallography #X-ray Diffraction in Crystallography #Historical Astronomy and Related Studies
paper · doi:10.1086/105851
The construction of a precision clock utilizing a vibrating quartz crystal as the time determining mechanism requires consideration of the following factors: (i) selection of a low frequency crystal orientation having low temperature coefficient and good activity; (2) chemical and physical treatment of the crystal, after dimensioning, to minimize and stabilize aging; (3) a stable low-loss mounting; (4) an oven and thermostat combination producing only very small and uniform variations of crystal temperature regardless of ambient temperature; (5) a vacuum tube oscillator that drives the crystal at low, constant amplitude and phase despite variations of voltage and circuit elements. A number of crystal clocks, rated for mean and sidereal time, which have been constructed since 1938 are now operating at the U. S. Xaval Observatory with accuracies depending upon the perfection attained in handling these factors. The least accurate is as precise as the poorest of t'~e three Shortt clocks at the Observatory. One of the better clocks is equipped with a 48 kilocycle (sidereal rate) DT-type crystal which is operating 250 C. away from its temperature of compensation in an oven that allows variations of as much as o?i C. in 24 hours. The power supply is nOt regulated. The oscillator, multi- vibrator, and amplifier tubes are all standard radio receiving set types and brands. This clock has been run without stopping since September, 1943, and without adjustment since December, 1943. Its daily rate changed ~. 0002 per day in the period December, 1943, to April, 1944, probably due to aging of the new crystal. Another total change of about SOlO during December, 1944, to March, 1945, perhaps is associated with age of electrical components (the tubes). From April to December, 1944, it ran with an average daily fluctuation of daily rate of less than ~.ooi, as indicated by time sights. This precision is higher than that of the best Shortt clock at the Observatory. U.S. Naval Observatory, Washington, D. C.