Optimal for time measurements – frequency-stable pendulum movements

During experiments, Galileo Galilei found in 1632 that for the period of oscillation of a pendulum, the weight is insignificant and the amplitude of the oscillation is secondary. The latter applies in particular to small oscillations. The length of the pendulum, on the other hand, is influential. For example, pendulums that are just under one meter long need one second to move from one side to the other.

In addition, pendulum movements are comparatively stable in frequency, which is important for timekeeping. Everyone can see this for themselves, because the children’s swing is a pleasurable interpretation of the pendulum: The composition of the suspension and the seat determines the frequency at which one swings. Doomed to failure are attempts to influence it significantly. Galileo recognized the importance of his investigations for time-measuring devices without elaborating on the idea.

Centerpieces of clock history: gravity pendulum and balance wheel

Christiaan Huygens was inspired by Galileo’s law of the pendulum and discovered that an oscillator in clocks must be designed in such a way that it can develop its natural oscillation for a long time and constantly. Fittingly, he designed the gravity pendulum with its now familiar design and had the first pendulum clock built in 1657. The astronomer realized that his concept was only suitable for stationary grandfather clocks. He therefore tinkered with a rotating wheel, which was ready for the market in 1674. Since then, this so-called balance wheel has served as a vibration generator in clocks that are intended to be used regardless of their position. With improved materials, tools and techniques, the component was reduced in size until it fitted into wristwatches.

Watch connoisseurs know that, strictly speaking, Huygens’ invention is made up of the rotating oscillating body and a spiral spring, which is used to regulate the oscillation frequency. Such an oscillating system is called an oscillator. The technical term is also used for classic clock pendulums, because they also combine several tasks of an oscillating system.

Oscillators that can hardly be influenced

The core objective of clock making is to reproduce standard time as accurately as possible. In the 17th century, Huygen’s pendulum clock was groundbreaking in that it showed deviations of only 10 seconds every day. The inventors were not satisfied with this. They experimented with oscillating bodies such as torsion pendulums, which made it possible to achieve enormous power reserves in torsion pendulum clocks. More than 80 years ago, the special alloy Nivarox brought great progress in optimizing the material of the oscillators. Temperature, air resistance or humidity: the more effectively external influences were counteracted, the more accurate the clocks became.

Ambitious watchmakers also quickly realized that increasing the rate has a positive effect on accuracy. This is especially true for wristwatches that are confronted with influences such as vibrations. The goal of integrating high-frequency oscillators into watches that are also small and have low deflections was therefore clear.

Tiny frequency miracles: tuning fork oscillators in watches

Mechanical wristwatches now elicit 18,000 to 36,000 vibrations per hour from the balance wheel. This corresponds to frequencies of 2.5 to 5 hertz (Hz). Traditional brands continue to drive mechanical precision timekeeping to this day. This is exemplified by Slimline watches from Frederique Constant, which impressed with its beat frequency of 40 Hz when it debuted in 2021.

This increase in frequency is remarkable in the segment of mechanical regulation. If you compare it with visionary watch legends, it seems manageable. In 1921, Max Hetzel had the brainwave to bring oscillators with a tuning fork shape into play. It took forty years before the concept was ready for the market and characterized Bulova’s Accutron. It impressed with an oscillation frequency of 360 Hz, narrowing deviations to 60 seconds per month. The electrically powered tuning fork watch sold millions of copies, but was quickly supplanted by the next innovation.

Quartz fast oscillator

In 1880, Jacques and Pierre Curie discovered that the electrical poles of quartz crystals shift in the course of elastic deformation, resulting in an electrical voltage. Conversely, they deform when an electric voltage is applied to them. The whole thing is called the piezoelectric effect and explains why quartz crystals are used as oscillators in watches. They oscillate at high frequency for the benefit of rate accuracy and save space. Warren Marrison introduced a working quartz watch in 1928. Ten years later, laboratories could buy the first precision watches with quartz.

The quartz wrist watch

The performance of oscillating crystals increased when, due to scarce natural crystals, synthetic production with quartz sand was introduced. This made it possible to influence the crystal structure in such a way that it became, for example, pressure-insensitive and temperature-stable. Further challenges were mastered until quartz wristwatches ready for series production were presented in the early 1970s. Debutants with oscillators from the laboratory, such as the Seiko Astron, the Astro-Quartz Junghans or the Hamilton Pulsar watch, were greeted with applause.

For technology fans, it was astonishing that the first quartz luxury watches almost cracked the 10,000 hertz mark with their oscillation frequency. Soon after, conceptual improvements and practical considerations resulted in tuning fork-shaped oscillating crystals with 32,768 Hz being defined as the standard. If they meet a high level of production competence at the watch manufacturer, the deviations are limited to 60 seconds per year. In comparison, mechanical luxury watches are already celebrated when their rate deviation is limited to 2 seconds per day.

Beyond wristwatches, quartz is surpassed as an oscillator only by the chemical element cesium, which characterizes the conventional atomic clock. Their development gathered momentum in 1940, when essential findings on magnetic resonance imaging were obtained for nuclear magnetic resonance. Its low error rate was sensational, amounting to one second in 30 million years. The cesium clock, which incidentally also contains a quartz, has since been surpassed by atomic clocks with laser light pulses. Their rate deviation is one second in 100 trillion years.

No convincing performance without perfect ensemble

Every oscillator is slowed down by damping. It therefore needs energy to get going and stay going. This is provided by weights, spiral springs or batteries. The energy supply would simply fizzle out without another ingenious invention for the movement: the escapement. Only in conjunction with numerous components do oscillators become the clock whose transmitted impulses correspond to one second. Pendulum, balance and oscillating quartz: Their quality is only revealed when all components are brilliant and perfectly matched to each other. Oscillators of various types are thus found in mechanical as well as quartz wristwatches, albeit quite different ones.

What does the oscillator do in watches?

This question would be inadequately answered if one were to focus on oscillations. With its recurring deflections, it not only keeps watches in motion, but also controls their processes. That’s why watchmakers also call it the rate regulator.

Der Beitrag What does the oscillator do in watches? erschien zuerst auf Uhrinstinkt Magazine.

Although electric timepieces are out of the question for many mechanical enthusiasts, they reveal an immense technical fascination upon closer inspection. Above all, the heart of the clock, the oscillator, is a delicate marvel on the wrist. Read on to find out how the mechanism works and why quartz oscillators surpass the precision of mechanical alternatives many times over.

Definition: Oscillator explained simply

According to the physical definition, oscillators refer to systems capable of oscillating. In watches, they act as clock generators and appear either as a balance-spring combination (hand-wound and automatic watches) or in the form of an oscillating quartz (quartz watch). The central task of the oscillator is to generate a steady beat, so that the energy stored in the mainspring barrel or in the battery is not arbitrarily passed on to the hand movement. Simply put: Without an oscillator, there is no correct seconds rhythm. Mechanical watches follow a quickly explained principle: The energy stored in the wound barrel is passed on to a wheel system, at the end of which is the so-called assortment (combination of pallet, escape wheel, balance, hairspring) including the oscillator. The oscillator regulates the energy before it is passed on in a finely timed manner to the movement. The development of functional assortments was one of the most demanding achievements of horology and made the world of watches as we know it today possible in the first place.

Quartz oscillators: A crystal sets the pace

Even the explanation of a quartz oscillator is not witchcraft. Analogous to the mainspring of a mechanical movement, the battery serves as an energy store. The quartz oscillator is used to ensure that it does not pass its current on to the gear train unregulated: looking like a small tuning fork, the crystal is made of synthetic material and is made to oscillate by the battery’s electrical voltage. The basis of this process is the piezoelectric effect, which was discovered in 1880 by the famous physicists Pierre and Jacques Curie. It states that certain crystals change their shape when a surface voltage is applied. The crystal vibrates exactly 32,768 times per second (32,768 Hertz).

Why exactly 32,768 hertz?

Whether it’s TW-Steel, Tag Heuer or Breitling, the standard frequency of 32,768 hertz can be found in all price ranges and at all manufacturers. The reason for this uniformity is not a physical law, but a standard first defined by Girard-Perregaux in 1971 and subsequently adopted by the entire industry. To understand this, we need to consider the goal of a quartz watch: In the end, the second hand should move exactly once per second, that is, at a frequency of one hertz. However, an oscillating crystal whose natural frequency is one hertz according to piezoelectric laws would be huge and would not fit into any wristwatch. The smaller the crystal, the higher the frequency.

Watch manufacturers use the following trick: they use a much smaller quartz crystal (a few millimeters) that oscillates at 32,768 hertz when electricity is applied. Of course, the second hand must not tick at this speed. To reduce the frequency, a T-flipflop circuit is used between the oscillator and the gear train, consisting of 15 individual T-flipflops. These components each halve the incoming frequency. If you divide 32,768 hertz 15 times by 2, you get exactly 1 hertz. Now the oscillations are translated into the duration of one second and are finally passed on to a stepper motor, which transfers the energy to the gear train and thus the hands of the Junghans, Bruno Söhnle or other quartz watch. Each time the oscillator (the quartz crystal) completes 32,768 oscillations, the stepper motor transmits exactly one pulse to the gear train, resulting in a tick of the hands.

Quartz oscillator: Many times more precise compared to automatic watch

You see: A quartz oscillator is easy to explain. The important question is: What advantages does this modern-looking system, which was developed back in the 1920s, offer over mechanical timekeeping? The strongest argument lies in the massively increased precision. While a mechanical Junghans, Omega, or Tag Heuer typically clocks in at three to five hertz with its balance spring oscillator, the disproportionately higher frequency of the quartz movement provides a massive increase in accuracy. COSC-certified mechanical watches deviate between -4 and +6 seconds per day from atomic time, while average quartz calibers allow only 30 seconds of rate error per month.

High-end versions such as Breitling’s SuperQuartz movements increase this precision tenfold. For the wearer, this means that the time only needs to be readjusted every few months at most. Four other advantages of quartz technology are also strong selling points for many watch fans:

Robust, easy to clean and flat: other advantages

• Resistance: Compared to their mechanical counterparts, quartz oscillators are noticeably less sensitive to shocks, vibrations and pressure. An extreme example, the Sinn UX diver’s watch with an incredible 5,000 meters of pressure resistance from its quartz movement, illustrates the argument.
  
• Maintenance effort: Apart from battery changes (usually every two years), quartz watches typically require no special care, while mechanical movements need serious maintenance (oil changes, revision, etc.). The more complex the caliber, the more expensive and lengthy the process.
• Flat construction: although mechanical movements can now be wafer-thin, quartz models on average allow for the flatter construction. This is a clear advantage, especially for delicate ladies’ watches.
• Price: Even high-quality quartz movements require significantly less manufacturing effort than mechanical calibers, which translates into more affordable prices.

Disadvantages: Where does the quartz movement need to pass?

The percentage of quartz models in the product portfolio varies depending on the manufacturer: while TW-Steel, Bruno Söhnle and Maurice Lacroix are brands that offer a high level of choice, electronic timekeeping is a rarity at Omega. Rolex, Patek Philippe, Audemars Piguet and other high-end manufactures, on the other hand, have now completely abandoned quartz technology. The reason is simple: luxury watches are emotional products. Although the quartz movement convinces with rational arguments, it lacks the technical fascination of a handmade automatic movement made of hundreds of finely decorated components. Complexity, mechanical know-how and the joy of being able to admire dozens of filigree-tuned components through a glass window are THE reason for many buyers to purchase a timepiece at all in the 21st century. The aspects of a long tradition, the inheritability of a “forever” lasting value and the differentiation from digital everyday life are missing from the quartz model. For enthusiastic mechanics lovers, quartz watches are cool commodities that do not differentiate themselves decisively from other electrical devices.

Practical disadvantages should also be mentioned: First, quartz watches require more frequent visits to the watchmaker (two-year battery life versus five-year maintenance interval for mechanical watches); second, their durability is considered lower. However, we dare to doubt whether this argument stands up to the progressiveness of modern quartz oscillators.

Der Beitrag What is an oscillator? erschien zuerst auf Uhrinstinkt Magazine.