The introduction of the quartz watch in the 1970s revolutionised the way we tell time. The technology gave us watches that were more accurate over a year than most mechanical watches were over a week, and quartz watches did not require winding or even wearing to keep them going.Quartz watches have a small piece of quartz crystal inside them that vibrates continuously at 32,768 vibrations per second. (Compare this to some high-grade mechanical watches, which may have a frequency of 36,000 vibrations per hour.) Cut like a tuning fork, the vibrations of such a high-frequency device are immune from the normal disturbances a watch is subjected to in wear.
The high frequency of the quartz crystal limits errors due to external influences (vibrations, shocks, temperature and air pressure). Accuracy in the order of 0.30 sec in 24 hours is the norm for quartz watches.
The prime reason for the inherent accuracy of quartz watches lies in the crystal, which is cut from highly refined silicon crystals grown under laboratory conditions. It is cut in such a way as to be relatively free from temperature effects and pre-aged to maintain its natural frequency over a long period. Any small remaining error is minimised by the division process.
What keeps the quartz vibrating
The battery in a quartz watch supplies a current to the quartz crystal that makes it bend. When the current is not flowing, the crystal returns to its rest position. The characteristic that causes the quartz crystal to bend is ‘piezoelectric property’: this is the reason a quartz crystal is used in the watch. This same physical property results in the quartz producing an electric current as it bends. The speed or frequency with which the quartz vibrates is a result of its physical size. The smaller the crystal, the higher the speed.
(You can experiment with any vibrating string, pendulum, yoyo, or a speaker; you will find the shorter or smaller the object, the higher the frequency.) The hands are driven via an integrated circuit which receives electric pulses from the quartz crystal. It processes these pulses to send a signal to a step motor. The step motor drives a simple wheel train which drives the hands.
Digital displays
Digital watches process the output signal from the quartz crystal like a series of calculators - they divide, add, amplify, and divide again and then translate the signal into something that will drive the segments in a display panel.
The display panel itself is a liquid crystal display panel, which is operated by the presence of voltage in controlled areas of the panel.
Mechanical watches
Mechanical watches undertook significant development during the latter half of the 19th century through to the 1960s, when technology reached its zenith and production numbers were at their peak. The use of better materials, automated manufacturing techniques and synthetic lubricants contributed to the most significant advances in the timekeeping capabilities of mechanical watches. As the technology improved, their performance and available options also improved. Watches became smaller, their cases became water-resistant, shock resist systems were developed, and automatic winding and calendar mechanisms became common.
How do they work?
Mechanical watches use a balance wheel fitted with a spring (hairspring) as the oscillating element (compared to quartz watches which use tuning fork crystals).
The balance of the watch is kept oscillating by power from the mainspring, instead of a battery. In most of these watches, the balance vibrates between 18,000 and 36,000 times per hour or five to 10 vibrations per second (5 - 10 Hz).
In many mechanical watches, the mainspring is wound manually by turning the crown. A wheel train and escapement to the balance transmit the power of the mainspring. The hands are attached to a wheel in the train; since the balance controls the speed of the train, it controls the speed at which the hands rotate around the dial.
Automatic winding
Auto-winding models draw their power from the wearer’s wrist movements. The power is stored in a coiled spring and applied through a precision gear train to indicate the time. The controlling element that makes this possible is the ‘balance’ which, in conjunction with a hairspring, allows the stored power to escape at the precise rate needed to accurately measure time. In a typical watch, this escaping or unlocking occurs five times per second or 18,000 times per hour, day in day out, with minimal attention other than servicing every year or so. If this regular servicing is not carried out, the watch will gradually lose its ability to keep time as the lubricants thicken or disperse and friction increases. In common with any mechanical device, wear will also occur. Poor case sealing will hasten this if dust particles or moisture are allowed to penetrate. This is eliminated by water-resistant cases, but these are not always practicable in dress or small ladies watches designed more as jewellery or items.
Timekeeping of mechanical watches
Compared to the faster moving quartz crystal, the balance oscillator of a mechanical watch makes only three to four oscillations per second. The slower frequency means the oscillator is more prone to external influences - vibrations, shocks, temperature, air pressure changes - as well as the knocks and bumps of everyday living. These all have some effect on the balance as it oscillates to and fro, despite inbuilt compensation, achieved by making the balance and its spring from materials that are not affected by temperature and by using shock-proof jewelling systems.
Today’s good quality mechanical wrist watches meet quality standards and can be relied on to keep time to within at least one minute per day. They can, and often are, adjusted to much closer standards if this is needed.
Additional functions
Quartz analogue watches can have additional functions; these usually involve additional motors and programmed circuits. Generally, a quartz watch with additional functions does not rely on sophisticated mechanical design and therefore is easier to service than a comparable mechanical watch. The fewer mechanical components in the quartz watch have enabled designers to produce slim and elegant models.
The incorporation of a digital display adds significantly to the possibilities for further functions, such as alarms, programmed date mechanism, timers, and alternate time zones.
Mechanical watches also have many other features in addition to the automatic winding already mentioned - chronograph, alarm, day, date, and the moon phase functions are but a few.
These additional mechanisms make the watch more complicated and therefore increase servicing time and cost significantly. Digital quartz watches offer a wider range of functions than analogue watches. As programmed computers, they can be fitted with most computer functions, though the size of the product restricts options.
The timekeeping performance of digital watches is the same as that expected of analogue watches. However, many digital watches on the market are lower-grade products and will not perform as well as the higher-grade models.
Sales and serviceability
The large majority of watches sold today are quartz watches; they offer much greater accuracy as timekeepers and are very reliable in service. Improvements in design and battery technology have resulted in watches now being able to run for up to five years on a battery. Power-generating systems have resulted in quartz watches, which virtually require no battery. Brands such as Citizen and Seiko now make watches that generate their own power. Developments in technology have made it possible to produce thin, elegant and very small watches and, at the other end of the scale, very complicated sports watches with a never-ending list of features.
A problem with quartz watches is that no matter how much trouble the manufacturer goes to in producing a quality product, a poor-quality battery fitted to it can ruin the watch. Watch batteries contain corrosive chemicals necessary for their function. If left standing for long periods, or if batteries are of poor quality, they are prone to leakage.
The proliferation of models and the nature of electronic components make the long-term serviceability of quartz watches an issue also. When first produced, it was believed that the circuits would only last for 10 years. The attachments used on quartz watches may make it difficult to service a 20-year-old quartz watch, compared to servicing mechanical watches of the same age that do not present the same problems.
The manufacturers of high-grade mechanical watches have concentrated on mechanical products because of their intrinsic quality and the fact that all components can be made to the manufacturer’s own quality standard. Service procedures are more specialised than those for quartz watches. Mechanical watches are often marketed as the ‘battery-less’ watch because of the inconvenience in having to fit a battery. These watches are generally reliable in operation, with automatic watches offering the convenience of not requiring daily attention. Wear is a problem in mechanical watches because of the torque generated by the mainspring, which is transmitted through its components.
Higher-grade watches are better protected against this wear by jewelled bearings and higher quality components, and if treated with care and regular maintenance, they can last for many generations. Mechanical watches can be stored for years without the worry of internal damage, an advantage for dress watches or those not worn regularly. A good watchmaker can make new parts and keep a quality watch running indefinitely - some collectable watches and clocks have been running for 700 years or more.
When assisting a customer in making a watch purchase, it can be helpful to point out that while the initial cost of a good mechanical watch is likely to be high, and ongoing maintenance will be essential for optimum performance, the investment potential is significant. And that’s not only if the watch is cased in expensive metals with jewels but also because the watch’s mechanical complexity is so elegantly executed.
These considerations should be weighed against the superior timekeeping capabilities of quartz watches, which will easily outstrip the mechanical units. Quartz watches will hold this performance under adverse conditions and, apart from cell changes, require little ongoing maintenance. Their investment potential, other than as items of jewellery, is vastly increased now that technology has the capacity to make them obsolete. As yet, however, there are no signs of this happening and quartz watches remain as popular as ever.