Superlatives are tricky things but we feel safe in saying the MikropendulumS, a new concept watch from TAG Heuer, and developed by their Vice President of Science and Engineering Guy Semon and his R&D team, is perhaps the most radical departure from conventional watchmaking solutions we’ve seen yet, keeping company with such bleeding edge experiments in chronometry as Cartier’s ID One and Two, or the exotic double tourbillon systems developed by Greubel Forsey.
The MikropendulumS is a double tourbillon chronograph –the timekeeping train is controlled by a 12 hertz tourbillon, while the chronograph train is controlled by a 50 hertz tourbillon (and no, that’s not a typo.) The real punch line, though, is that both have oscillators –balance wheels –where the conventional balance spring has been done away with and replaced with the Pendulum system, in which powerful permanent magnets are the restoring force on the balance, rather than a spiral spring.
A little review: a mechanical oscillator like a pendulum moves because it’s pushed by something –in a pendulum clock, that something might be a Graham deadbeat anchor escapement, powered by a falling weight, or a spiral mainspring. The pendulum keeps time because it has a natural frequency, determined by its length. Because gravity –the “restoring force” in technical terms –always pulls back with a strength directly proportional to the degree the pendulum swings, the time it takes for the pendulum to complete a swing is a function of its length only, not how hard it’s pushed. We call such an oscillator “isochronous.” This is an indispensable property of any oscillator in a timekeeper.
In a watch there is a balance rather than a pendulum, and instead of gravity, the spiral balance spring is the restoring force. Balance springs are susceptible to magnetism, temperature error, and most significantly rate variations caused by the fact that the center of equilibrium of the system needs to be exactly at the center of the balance, which is physically impossible as the balance is mounted on an axis –the balance staff –to which the spring has to be attached.
Guy Semon and his team decided to use powerful permanent samarium-cobalt magnets to provide the restoring force. These are not only strong, but show little variation over time in magnetic field strength. They do however have a serious flaw in a watch –the field strength of a samarium-cobalt magnet varies considerably with temperature and using such magnets, variations in rate in early prototypes were as much as 45 seconds per degree centigrade per day –clearly not an acceptable situation.
The solution was found in another rare element –gadolinium, an exotic rare-earth metal. Gadolinium-cobalt magnets have the opposite field strength temperature curve of samarium cobalt magnets –within a certain range GdCo magnets increase in field strength as temperature increases. By adding a small amount of gadolinium to an SmCo magnet, the two opposed temperature curves cancel each other out nearly perfectly –making an SmCoGd magnet one with excellent field strength stability over typical operating temperatures.
It’s thanks to this ingenious solution that the MikropendulumS could be brought into existence. It’s fascinating to watch –the 12 hertz tourbillon on the left would be gripping enough but activate the chronograph and the 50 hertz chronograph springs into action. While it’s a great intellectual treat to understand the basics of how the watch works and what problems have to be solved, it’s also important, Guy Semon pointed out, to remember that this watch still has to be hand assembled and adjusted by a watchmaker, and it’s a very demanding task, both for its complexity and unfamiliarity.
REVOLUTION and I would like to thank Guy Semon for his wonderfully clear and concise explanation of how the MikropendulumS system developed –and congratulate him, his team, and TAG Heuer for creating one of the most intellectually exciting watches we’ve ever seen.