Quartz Watches

Intro to Quartz Watches

This section will answer many of your questions about quartz crystals and how they form the heart of a quartz watch; such as "why are they called quartz watches?" Or, "why are quartz watches so much more accurate than wind-up mechanical watches?"

The quartz analog watch is an electronic watch that uses a piezoelectric quartz crystal as its timing element, coupled to a mechanical movement that drives the hands.

While the first prototype quartz watches were made by CEH research laboratory in Switzerland in 1962, and the first quartz watch to enter production was the Seiko 35 SQ Astron which appeared in 1969, it was in the 1970s that quartz watches widely emerged as the latest high-tech gadgets in the marketplace.

In the beginning these watches had red LED displays and cost in the area of $500. Since then, quartz watches have evolved to feature either an LCD display or a traditional mechanical (hour and minute hand) movement to display the time, and prices have fallen significantly. It's even common these days to find quartz watches given away as promotional items!

TAG Heuer Men's Quartz Link Watch

Before Quartz Watches

A mechanical watch (or wind-up watch) is an amazing piece of technological achievement. It is part of a continuous research-and-development effort that began at the end of the 14th Century. Over the years several innovations have made mechanical wind-up watches smaller, thinner, more reliable, more accurate and even self-winding.

The components that you'll find in today's mechanical watches have been around for centuries:

· A spring to provide the power
· Some sort of oscillating mass to provide a time base
· Two or more display hands
· An enumerated dial on the watch face
· Gears to reduce the ticking rate of the oscillating mass and connect the mass and spring assembly to the hands on the dial

By the end of the 1960s Bulova Watch Company took the first step away from the oscillating balance wheel by using a transistor oscillator that maintained a tuning fork. This watch hummed at hundreds of hertz (Hz, cycles per second) rather than ticking. Cogs and wheels still converted the mechanical movement of the tuning fork to the movement of the hands, but two major steps had been taken:

1. The replacement of the balance wheel and spring with a single-material resonator: the tuning fork

2. The replacement of the wind-up main spring with a battery

Watch manufacturers in the late 1960s were looking to take the next step - finding a technology that would give even better time keeping than the tuning fork. Integrated circuits were very new at the time, but the price was dropping rapidly and the number of transistors was growing. LEDs were also new on the scene. A couple of problems remained to be solved: finding a new timing element and designing an integrated circuit that would use very little power to allow the watch to run on a tiny internal battery.

The Quartz Crystal

There was no problem with the choice of a timing element. The quartz crystal is possibly thousands of times better for timing than the tuning fork, and quartz crystals had been around for many years. Only the type and the frequency of the crystal needed to be chosen. The difficulty was in the selection of the integrated circuit technology that would function at sufficiently low power.

Quartz crystals have been in regular use for many years to give an accurate frequency for all radio transmitters, radio receivers and computers. Their accuracy comes from the fact that quartz - which is silicon dioxide like most sand - is unaffected by most solvents and remains crystalline to hundreds of degrees Fahrenheit. The property that makes it an electronic miracle is the fact that, when compressed or bent, it generates a charge or voltage on its surface. This is a fairly common phenomenon called the piezoelectric effect. In the same way, if a voltage is applied quartz will bend or change its shape very slightly.

If a bell were shaped by grinding a single crystal of quartz, it would ring for minutes after being tapped. Almost no energy is lost in the material. A quartz bell, if shaped in the right direction to the crystalline axis, will have an oscillating voltage on its surface and the rate of that oscillation is unaffected by temperature fluctuations. If the surface voltage on the crystal is picked off with plated electrodes and amplified by a transistor or integrated circuit, it can be re-applied to the bell to keep it ringing.

A quartz bell could be made, but it is not the best shape because too much energy is coupled to the air. The best shapes are a straight bar or a disk. A bar has the advantage of keeping the same frequency provided the ratio of length to width remains the same. A quartz bar can be miniscule and oscillate at a relatively low frequency (32 kilohertz (KHz) is usually chosen for watches not only for size, but because the circuits that divide down from the crystal frequency to the few pulses per second for the display need more power for higher frequencies). Power was a large problem for early watches, and the Swiss spent large sums of money developing integrated-circuit technology to solve this problem.

Modern quartz watches now use a low frequency bar or tuning-fork-shaped crystal. Often, these crystals are made from thin sheets of quartz plated like an integrated circuit and etched chemically to shape. The major difference between good and indifferent time keeping is the initial frequency accuracy and the precision of the angle of cut of the quartz sheet with respect to the crystalline axis. The amount of contamination that is allowed to get through the encapsulation to the crystal surface inside the watch can also affect the accuracy.

The electronics of the watch initially amplifies noise at the crystal frequency. This builds or regenerates into oscillation - it starts the crystal ringing. The output of the watch crystal oscillator is then converted to pulses suitable for the digital circuits. These divide the crystal's frequency down and then translate it into the proper format for the display. Or, in a quartz watch with hands, the dividers create one-second pulses that drive a tiny electric motor, and this motor is connected to standard gears to drive the hands.