In telecommunications, a primary time standard is a time standard that does not require calibration against another time standard.
Examples of primary time, (i.e., frequency standards) are caesium standards and hydrogen masers.
The international second is based on the microwave frequency (9,192,631,770 Hz) associated with the atomic resonance of the hyperfine ground state levels of the caesium-133 atom in a magnetically neutral environment. Realizable caesium frequency standards use a strong electromagnet to deliberately introduce a magnetic field which overwhelms that of the Earth. The presence of this strong magnetic field introduces a slight, but known, increase in the atomic resonance frequency. However, very small variations in the calibration of the electric current in the electromagnet introduce minuscule frequency variations among different caesium oscillators.
Famous quotes containing the words primary, time and/or standard:
“It was the feeling of a passenger on an ocean steamer whose mind will not give him rest until he has been in the engine-room and talked with the engineer. She wanted to see with her own eyes the action of primary forces; to touch with her own eyes the action of primary forces; to touch with her own hand the massive machinery of society; to measure with her own mind the capacity of the motive power. She was bent upon getting to the heart of the great American mystery of democracy and government.”
—Henry Brooks Adams (1838–1918)
“The pressures of being a parent are equal to any pressure on earth. To be a conscious parent, and really look to that little being’s mental and physical health, is a responsibility which most of us, including me, avoid most of the time because it’s too hard.”
—John Lennon (1940–1980)
“A dwarf who brings a standard along with him to measure his own size—take my word, is a dwarf in more articles than one.”
—Laurence Sterne (1713–1768)