Accutron watches are unique in that they were the first electronic watches to dispense with the traditional "balance wheel and hairspring" as used in mechanical watches and other early battery powered watches. Hence they are of great historical interest, as well as still being a very practical and accurate means of timekeeping. Departing from tradition, they use a tuning fork, not unlike those used by musicians for tuning an instrument. They are inherently more accurate than balance wheel watches for a number of reasons.
The accuracy of a traditional balance wheel watch is dependant on many factors. Friction in the pivots (bearings) due to changes in the quality of the lubricating oil play a significant part in the ability of a mechanical watch to maintain accuracy and consistency of rate. Also, the condition of the mainspring and gear train driving it is very important. The rate of Tuning Fork watches is affected much less by lubrication, though it is still necesary for the correct functioning of the watch. The other major factors affecting accuracy of any mechanical watch are temperature changes and errors due to position (ie. how gravity effects it's operation in different orientations). Tuning fork watches are inherently far less affected by these problems. The fork has no bearings. It is far easier to "build in" temperature compensation into a Tuning Fork than into a circular balance wheel and it's hairspring. Gravity affects Bulova tuning forks in only 2 orientations (tines up and tines down) compared with the usual 5 positions of good quality balance wheel watches. (dial up, dial down, winder up, winder right, winder left). The tuning forks of the ESA movements have virtually zero positional error.
A balance wheel vibrates at usually 2 1/2 times a second, whereas the tuning fork hums at 300-720 times a second, depending on the model. Modern mechanical watches vibrate as fast as 5 times a second, in an attempt to improve their accuracy by making the balance wheel lower in mass and size, thus reducing their susceptibility to external influences.
Only Watchmakers of the highest skill can adjust a balance wheel watch for its best possible performance under all conditions. Repairing and adjusting tuning fork watches is considerably easier, as there are no adjustments apart from the index mechanism, which converts the vibrations of the tuning fork into rotary motion. Of course, skill and experience is still needed to adjust the index mechanism correctly.
Another interesting difference between Tuning Fork watches and Balance Wheel watches is the flow of mechanical power in the mechanism. A traditional watch has a mainspring which stores the energy to drive the gears. This energy starts off strong at the mainspring and is slowly diminished in torque through the train of gears until it is suitable for use by the balance wheel. How much loss of energy occurs in this process is again a function of the quality of the bearings and the state of lubrication. The accuracy of the conventional watch is strongly dependant on the constancy of the power which finally arrives at the balance wheel.
In a Tuning Fork watch the power flow is the other way around. The fork drives the gear train, as opposed to a balance which is driven by the gear train. The forces on the gear train of the tuning fork watch are far less, and the quality of the bearings and lubrication are of much less consequence to its accuracy than is typical for a balance-wheel watch. Neverthless, they are still susceptible to problems due to dirt and poor lubrication as any precision mechanical item is, and maintenance of an Accutron is often overlooked because of their inherent accuracy and reliabiliy. If maintained correctly, they could be expected to last a long time, as the forces on the bearings are so small.
In summary, we can see that the gear train of a conventional watch performs two functions: it drives the hands and transmits power to the balance wheel. In a tuning fork watch, it only drives the hands.
The tuning fork is kept vibrating by an electronic circuit, powered by a battery. While the electronics required to do this are not considered remarkable by today's standards of modern electronics, when taken in historical perspective it is a different story.
When the Accutron was first released, not only was it the first watch to be controlled by a transistor, it was one of the first consumer items of any kind to use this device. Up till then, all battery-powered watches had a balance wheel and hairspring which operated a small set of contacts. These mechanical contacts momentarily supplied electrical current to a coil which in turn gave a magnetic impulse to the balance, keeping it moving.
The transistor itself was still in its infancy, hardly even heard of by the general public, who considered it a novelty of scientific interest only. So it was remarkable not only to use such a device in a consumer item, but to achieve standards of miniaturisation previously unheard of. Remember in those days, nearly all electronic devices, such as radios and TV's were based on vacuum tubes.
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