Quartz Clock Function

Quartz analog clocks use a traditional stepper motor to advance the hands.

Quartz clocks calculate time by counting the vibrations of a quartz crystal that has an electric current passing through it. Quartz has a property known as piezoelectricity that causes it to vibrate or oscillate when an alternating electric current is run through it. Quartz clocks and other quartz timepieces are augmented with semiconductors for greater accuracy and different functions.

Background

Quartz is a relatively common naturally occurring mineral.

The piezoelectricity of quartz has been known to scientists since the nineteenth century. Physicists developed and analyzed this attribute through the twientieth century, with commercial clock makers refining quartz technology to use quartz as the center mechanism of watches starting in the 1970s. Quartz clocks tend to be much more accurate than clocks with purely mechanical movements.

Principles

Vibrations per second are counted to keep time.

Applying AC current across a quartz crystal will produce steady vibrations at a certain frequency. When the frequency is counted by a digital processor, the processor will advance the time display by one second when the appropriate number of vibrations have been reached. The number is typically 32,768 vibrations per second. Accuracy largely depends on how carefully and accurately the quartz crystal is manufactured to produce the exact number of vibrations per second.

Precision Manufacturing

Crystals are made from fused silica and have electronics applied by photolithography.

For extreme accuracy, the quartz crystals used in clocks have to be manufactured to exact dimensions. Electrodes to carry the AC current across the crystal have to be placed in exactly the same place for different crystals intended to produce the same vibration rates. Mass-produced quartz clock crystals are typically accurate to within plus or minus 30 counts per million vibrations. This makes quartz clocks accurate to within about a second per day.

Temperature

The quartz crystal can be temperature controlled for extreme accuracy.

The number of vibrations per second for a given crystal is slightly dependent on temperature. High-end clocks and watches may have devices that correct for temperature or keep the crystal at a constant temperature, thus increasing the accuracy of the timepiece. Quartz wrist watches often use a heater or oven for the quartz crystal to compensate for different temperature environments.

Self Adjustment

A "thinking" semiconductor adds more functions and accuracy to a quartz clock.

Clocks or watches that periodically check "real" time by accessing the Atomic Clock can calculate their rates and adjust the number of vibrations to count per second for more accuracy. These clocks actually become more accurate with longer use. The quartz clock will evaluate whether it gained or lost time over the interval between the last two times it checked "real" time. If it lost time during that period, it will use fewer vibrations per second to calculate time until the next time it evaluates its own accuracy.

References

• Physlink: How do quartz watches work?
• Geyer Electronic: Model-KX-327XS