When Did Digital Clocks Start?
We see digital time displays in various applications worldwide, in our homes, in airports, along the highways and many other places. But this has not always been the case. For years, an approximate analog display was good enough. But as our lives became more precise, so did our dependence on accurate time. And science, which is always struggling to keep abreast of demands, complied by developing the digital clock. But don't confuse digital clocks with digital displays.
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Atomic/Digital Time
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Science has known for a long time that atoms have a resonance, which means that their electrons will circle their nuclei an exact number of times per second. In 1949, the National Institute of Science and Technology (NIST) developed the first atomic clock, based on the number of revolutions in an atom of ammonia. But even though it was not very accurate, it was digital because it was based on a number of events rather than fractions of time of the Earth's rotation. Researchers soon replaced ammonia with cesium to find ways to be more accurate.
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Early Cesium Clock
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In 1955 the National Physical Laboratory in England, along with the U.S. Naval Observatory built the first cesium atomic clock, in the form of a frequency standard measure, relative to astronomical time based on the motion of stars. In 1960, NIST's development of cesium standards reached a point refined enough to incorporate cesium into their official time-keeping system, thus making the national standard for time digital. Other laboratories began accepting cesium as the new time-keeping standard.
Cesium and Other Clocks
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In 1967, the second became formally defined as exactly 9,192,631,770 cycles of a cesium atom's resonant frequency, replacing the old definition of the second, which was 1/86,400th of a day. Thus, the definition of a second became digital instead of analog. By January of 2002, NIST was able to measure a second to the accuracy of 30 billionths of a second per year, in their eighth series of cesium clocks using the "fountain" principle. Today, some atomic clocks use hydrogen and rubidium vapor because of more compact size, lower cost and less power consumption.
Digital Display
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Digital clock displays have used LEDs, LCDs or printed flaps or wheels moving to show hours and minutes. Analog displays use hands. Many microwave ovens, clock radios, regular ovens, kitchen timers, alarm clocks and many other appliances use digital displays for time and other information. In many cases the circuitry that runs them are indeed digital. So the term digital clock in common usage could be confusing, once we learn a more scientific use of the word "clock." The trend to use digital displays began around 1972, for clocks, watches, calculators and various types of meters.
Digital Watches
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A digital watch, of course, is technically just a small digital clock. But its history is a bit different. The first watch called "digital" was actually an electric watch developed by Hamilton in 1957. In 1960, Bulova came out with the Accutron, for a breakthrough in accuracy. The Swiss developed the quartz crystal movement in 1967. But all these small clocks had analog displays. The first digital display came out in 1972 in the Hamilton Pulsar P1, using light emitting diodes (LED,s). A few months later, Gruen came out with the Teletime, using a liquid crystal (LCD) display. Today, most digital watches use a quartz movement with an LCD display.
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- Photo Credit Image by Flickr.com, courtesy of Rob and Stephanie Levy
