Pendulum Clock - Mechanism

Mechanism

All mechanical pendulum clocks have these five parts:

• A power source; either a weight on a cord or chain that turns a pulley or sprocket, or a mainspring
• A gear train (wheel train) that steps up the speed of the power so that the pendulum can use it
• An escapement that gives the pendulum precisely timed impulses to keep it swinging, and which releases the gear train wheels to move forward a fixed amount at each swing. This is the source of the "ticking" sound of an operating pendulum clock.
• The pendulum, a weight on a rod
• An indicator or dial that records how often the escapement has rotated and therefore how much time has passed, usually a traditional clock face with rotating hands.

Additional functions in clocks besides basic timekeeping are called complications. More elaborate pendulum clocks may include these complications:

• Striking train – strikes a chime on every hour, with the number of strikes equal to the number of the hour. More elaborate types, technically called chiming clocks, strike on the quarter hours, and may play tunes, usually Westminster quarters.
• Calendar dials – show the day, date, and sometimes month
• Moon phase dial – Shows the phase of the moon, usually with a painted picture of the moon on a rotating disk.
• Equation of time dial – this rare complication was used in early days to set the clock by the passage of the sun overhead at noon. It displays the difference between the time indicated by the clock and the time indicated by the position of the sun, which varies by as much as ±16 minutes during the year.
• Repeater attachment – repeats the hour chimes when triggered by hand. This rare complication was used before artificial lighting to check what time it was at night.

In electromechanical pendulum clocks such as used in mechanical Master clocks the power source is replaced by an electrically powered solenoid that provides the impulses to the pendulum by magnetic force, and the escapement is replaced by a switch or photodetector that senses when the pendulum is in the right position to receive the impulse. These should not be confused with more recent quartz pendulum clocks in which an electronic quartz clock module swings a pendulum. These are not true pendulum clocks because the timekeeping is controlled by a quartz crystal in the module, and the swinging pendulum is merely a decorative simulation.