Oscillator

The oscillator is the name for the balance wheel and hairspring viewed as a single sub-system. The balance carries the mass, the hairspring provides stiffness; together they form a harmonic oscillator with a defined natural frequency. Everything we perceive as accuracy in a watch derives from the properties of this oscillator.

Mechanical oscillator

In a mechanical watch the oscillator always consists of two main components:

• Inertial body. The balance wheel — a weighted circular wheel that rotates around its axis.
• Restoring force. The hairspring, which returns the system to its rest position after every displacement.

Energy input keeps the oscillation alive: the escapement delivers a small impulse from the gear train each half-swing, compensating for friction losses. Without this impulse the oscillator would settle in a few minutes — like a struck tuning fork dying away.

The typical beat rate of modern oscillators is 4 Hz (28,800 vibrations per hour). That number is an industrial compromise: high enough for good shock resistance and positional stability, low enough to keep lubrication demand and wear manageable.

Measurement quantities

Three measurements describe the behaviour of a mechanical oscillator:

• Rate. The number of vibrations per hour. Constancy of this rate across positions, temperatures and winding states is the principal accuracy criterion.
• Amplitude. The displacement angle of the balance from its rest position. A healthy amplitude is 270 to 310 degrees at full wind; substantially less points to lubrication or escapement problems.
• Beat error. The asymmetry between the two half-swings. Values below 0.4 milliseconds are considered good.

These three quantities are read on the timegrapher and form the basis of every regulation we perform at our atelier in Munich.

Quartz and other oscillators

The term oscillator is not restricted to mechanical watches. In quartz watches a quartz crystal serves the same function — driven electrically, it vibrates at typically 32,768 Hz and provides a much more precise time reference. Atomic oscillators in research environments reach accuracies of fractions of a second per billion years. In watchmaking the word "oscillator" almost always refers to the mechanical balance-hairspring assembly.

Innovation at the oscillator

Most mechanical watchmaking innovation of the last two decades has centred on the oscillator. Silicon hairsprings (Patek Philippe Spiromax, Omega Si14), Rolex's Parachrom alloy, fully integrated silicon oscillators at certain independents, magnetic-field resistance to 15,000 gauss at Omega Master Chronometer — all of these are attempts to improve the accuracy, stability and magnetic resistance of this core component.