Phonic wheel
The phonic wheel or tone wheel called is one of Poul La Cour invented in 1875 synchronous motor .
construction
The motor consists of a ferromagnetic gear wheel that rotates slightly around a vertical axis in front of an electromagnet , with the teeth very close to the magnetic pole without touching it. On top of the gear wheel is a can that acts as a flywheel , in the ring-shaped cavity of which there is mercury . If an intermittent electric current is passed through the electromagnet , the wheel starts rotating, which is extremely uniform if the current is interrupted regularly. This is done using a tuning fork , the prongs of which lie between the poles of a horseshoe-shaped electromagnet. If the latter attracts the fork ends, the current is interrupted, the attraction ceases, the fork ends swing back, closing the current again, the fork ends are attracted again, etc. This self-interruption of the current depends on the pitch of the tuning fork; the more vibrations it makes in one second, the faster the phonic wheel rotates, the number of teeth of which must match the corresponding phonoelectric current.
use
Phonic wheels that are as similar as possible, connected in one and the same phonoelectric current, have the same speed; they are therefore suitable for producing very precise isochronism and synchronism . The phonic wheel was used to mark astronomical, ballistic and physical observations, to graphically mark continuous curves, to count very fast movements of a tuning fork (number of vibrations of a tone) or rotating axes (in machines), as a tachytoscope, to determine the magnitude of the speed at every moment to see directly or to obtain an exact match of the rate of two or more distant clocks.