Basic Information About Digital Atomic Clocks

Digital atomic clocks are extremely accurate in timekeeping. They automatically synchronize themselves, usually every night, and have an accuracy of better than one second off ever 80 million years. Because of this high level of accuracy, they are used for scientific purposes as well as convenient for the individual.

The Very Basics

All clocks keep track of time by counting “ticks”. In a pendulum clock, the “ticks” are the swings back and forth of the pendulum. In a traditional digital clock, the “ticks” are the oscillations of the power line or the quartz crystal. How accurate the clock or watch is, is determined by the accuracy of the “ticker.”

The same holds true for atomic clocks, whether digital or analog. For an atomic clock, it uses atoms as its “ticker” (resonance). The explanation is long and complex, and beyond the reach of this article, but suffice it to say that various types of atoms have been found to resonate at the right frequency to be able to maintain a clock, watch, etc.

Since atoms are extremely consistent, resonating at exactly the same frequency each and every time, they can be relied upon implicitly. To compare, for a quartz clock, the quartz crystal (which used to seem very accurate!) is made so the oscillator frequency is close to a standard, but the manufacturing tolerances make it impossible to be perfectly accurate. Also, temperature will change the frequency in a quartz crystal. Using atoms, they are precise simply because they always resonate at the exact same frequency.

Types of Atomic Clocks – What Can Run ‘Em

The principle of how an atomic clock works (whether digital or analog) remains the same, though there are three types. The difference is in which element is used and how changes in energy level are detected.

First, most accurate are the cesium atomic clocks. They use a beam of cesium atoms. Using a magnetic field, the clock separates out the cesium atoms of different energy levels.

Hydrogen atomic clocks are another type. They keep the hydrogen atoms confined in a container with walls of a special material so that they stay at the high energy state.

Rubidium atomic clocks are the smallest and simplest. They use a glass container of rubidium gas. It absorbs light at a certain frequency when the microwave frequency around it is just right. All of these are used in various capacities, and our own digital atomic clocks rely on synchronizing with the atomic clock in Boulder, Colorado. We can buy digital atomic clocks in almost any size and with many features, to a large wall clock to a small atomic digital alarm clock for travel.

How They Came To Be

In the 1930’s, professor Isidor Rabi from Columbia University found a technique that he called atomic beam magnetic resonance. In 1945, he suggested that a clock could be made using it. By 1949, the NIST (National Institute of Standards and Technology) first made one, using ammonia molecules. In 1952, they first used cesium atoms for resonance. It was called NBS-1. Over time, they’ve made more advanced forms. Variations were released with significant improvements in 1955 (the first cesium-beam clock), 1967 (defining the second based on the vibration of the cesium atom, rather than the movement of the earth and sun), and 1968 (NBS-4, world’s most stable cesium clock). In 1999, NIST-FI was released. It is accurate to one second in 20 million years, being the most accurate clock ever invented. Currently, analog and digital atomic clocks are available with this type of accuracy.