Timekeeping devices usually contain or are connected to a machine that swings back and forth or oscillates at a constant rate to control the movement of hands or the rate of change of digits. Mechanical or analog clocks use balance wheels, pendulums and tuning forks as well as quartz crystals as their oscillating machinery for time measurement.

Atomic clocks operate in much the same way – except that they use the frequency of the oscillation of atoms or molecules to measure time – thus the name 'atomic clocks'.

How an Atomic Clocks Works

A typical atomic clock consists of a cavity in which the core element (usually Cesium-133) is heated to release its atoms. The atoms released have varying electrical charges. The atoms are passed through a vacuum tube then through a magnetic field where only atoms with the correct energy state are allowed to pass through.

The selected low-energy atoms then pass through a concentrated microwave field which is produced by a transmitter controlled by a quartz crystal oscillator that's set to vibrate at 9,192,631,770 Hertz or cycles per second. The frequency of the microwave field isn't always exact and varies from the required vibration, but the variation is always minimal and the correct frequency is cyclically attained.Atomic Clock

An atom changes to a high energy state only if it passes through exactly at a time when the microwave field is at the correct frequency. Atoms which have changed energy states are detected and monitored by a device at the end of the vacuum tube.

At this point, another magnetic field sorts and filters the atoms out to identify atoms with the correct energy state. If the atoms counted go below a set threshold level, then the crystal oscillator is not functioning properly and is adjusted so that it is transmitting at the proper frequency. A separate device then converts the oscillation frequency to pulses of exactly one second each.

Uses of Atomic Clocks

The high accuracy of atomic clocks is an essential element in many modern-day applications. The Global Positioning System (GPS) is a cluster of twenty-seven satellites and each satellite carries three atomic clocks. The atomic clocks are crucial in precise measurement of exact location. A ground-based GPS unit receives signals from a minimum of four of these satellites and position is measured using the time differences of the signals from the four satellites.

Communications companies also make use of atomic clocks. Multiple data or voice transmissions can be carried over the same wires if computers at both ends can shift from one transmission to another several thousands of times a second. If the clocks controlling the shifts are out of sync, the transmissions become jumbled and data corrupted. Mobile communications, Internet services and digital television transmissions use the same basic approach.

The various sciences also make use of atomic clocks. Geologists use them in measuring shifts in the earth's crust; astronomers need them to plan their galactic explorations. Other uses are being developed, ranging from consumer applications to scientific ones.