A&S5219 – Constant Force Tourbillon

The A&S5219 movement is equipped with two identical barrels mounted in series, giving a 100-hour power reserve. These barrels alternate in driving the mechanism, the second being activated when the torque of the first falls below optimum output. To guarantee the isochronism of the regulating group over 100 hours of operation, the movement’s designers incorporated a patented constant force mechanism between the going train and the tourbillon. Visible on the dial side, its purpose is to smooth out the energy delivered by the barrels so as to prevent excessive or insufficient torque from affecting the oscillations of the balance in the tourbillon carriage. This constant force mechanism is held in place by an 18-carat yellow gold bridge and rotates over the course of one minute. In the Constant Force Tourbillon 11, it replaces the fusee-and-chain configuration used by John Arnold in his chronometers. As well as supplying a constant force, the system chosen for this timepiece also allows for a ‘dead-beat seconds’ indication, in which the direct-drive hand does not advance seamlessly, but instead makes successive jumps of exactly one second – much like the direct-drive seconds of marine chronometers, which also made very similar jumps (detent chronometers generally beat every half-second).