Clocks

I recently discovered the phenomenal qualities of synchronous electric clocks, and decided to replace all my crapulous quartz/battery clocks.

Synchronicity

A synchronous electric clock is driven by a synchronous motor, and how this works is not obvious. The speed at which a synchronous motor rotates is determined precisely by its design and the frequency of the AC supply, hence the use of the adjective synchronous. If a running synchronous movement is examined all that can be seen is a rotating rotor which drives the hands through the reduction gear.

In British made synchronous clocks the motor often, but not always, rotates at 200 rpm. Electric motors, including synchronous electric motors, are driven by magnetic forces produced by interacting magnetic fields. These magnetic fields are invisible. By contrast, a mechanical clock has an escapement which can be seen operating. How a synchronous motor works is described in detail, including the magnetic impulses which drive the motor. A synchronous motor is not inherently self starting. In a non self starting clock there is a manually operated device which runs the motor up to the synchronous speed in the correct direction, whereas in a self starting clock this is done automatically.

The British company Smiths was the leader in the field, and made electric clocks from the early 1930’s until the early 1970’s for both commercial and home use. The best clocks were made prior to the mid 1950’s when they started to use plastics in the mechanisms instead of brass. Unfortunately the plastic has not proven to be very durable.

Mains Frequency

The utility frequency, (power) line frequency (American English) or mains frequency (British English) is the nominal frequency of the oscillations of alternating current (AC) in a wide area synchronous grid transmitted from a power station to the end-user. In large parts of the world this is 50 Hz, although in the Americas and parts of Asia it is typically 60 Hz.

During the development of commercial electric power systems in the late-19th and early-20th centuries, many different frequencies (and voltages) had been used. Large investment in equipment at one frequency made standardization a slow process. However, as of the turn of the 21st century, places that now use the 50 Hz frequency tend to use 220–240 V, and those that now use 60 Hz tend to use 100–127 V.

In practice, the exact frequency of the grid varies around the nominal frequency, reducing when the grid is heavily loaded, and speeding up when lightly loaded. However, most utilities will adjust generation onto the grid over the course of the day to ensure a constant number of cycles occur. This is known as Time error correction.

This 50Hz is used by Smiths clocks to accurately maintain their time - and indeed the clocks are incredibly accurate. All with a five star energy rating of ~2W.