Pendulum clock

The pendulum clock is a clock, the clock is a mechanical pendulum ( also outdated: pendulum ) is. It was invented by Galileo Galilei in his last years ( around 1640 ), but it was built by his son Vincenzo. At the same time, Christian Huygens also dealt with the theory and design of the pendulum clock.

• 5.1 longcase clocks
• 5.2 Drehpendeluhr
• 5.3 moving eyes
• 5.4 Mysterieuse

Description

The principle of the pendulum clock based on the fact that an oscillating or rotating pendulum at each passage at a certain point of its travel in the movement triggers an action by which the time indicator is switched (most often this is done by escapement wheel and anchor escapement ). Further, the pendulum movement of the or another drive receives a pulse ( lift ), so that the oscillation is maintained, despite the energy loss due to friction.

The symmetry of the pendulum movement is decisive for the accuracy of the clock, which is why the design of the pendulum and the triggering of the action in the movement widespread attention. The pendulum friction was soon reduced by agate bearings, snaking reduced by pendulum springs, improved the uniform transfer of force to the pendulum of a pendulum rod and the air resistance reduced by sleek pendant lenses. Changing external factors on the period of oscillation, such as temperature, air density and humidity can be offset by compensation. A low-friction triggering of the movement and a uniform momentum transfer from the movement of the pendulum are essential ingredients for good precision results.

The adjustment of the oscillation period of pendulum clocks is done by changing the effective length of the pendulum - see main article seconds pendulum.

Brief History

Accuracy of the vibration

The oscillations coherent, stable built pendulum, which rotate about a horizontal axis, have a higher uniformity than other fishtailing. Such processes are inaccurate, for example, the vertically oscillating spring pendulum ( see harmonic oscillation) or a simple pendulum. Both surpass difficult to accuracies of 0.01 percent, whereas, for example, a shielded compensating pendulum can reach 0.0001 percent ( 10-6 ± 0.1 seconds per day). Special designs come in the range of a few milliseconds per day.

In classic pendulum clocks, the oscillation of the escapement in a stepwise rotation of the escape wheel is converted, which in turn is driven by a gear train, for example, by the watch weight, to submit a metered pulse to the pendulum can.

The pendulum electric clocks receives its power through a coil which is supplied at the right moment on the pendulum contacts or other controller with electric current. The coil moves the purpose of a permanent magnet made ​​spherical. The coil can also be used themselves for the production of the control signal, by their mutual induction voltage is used. The lower damping in such watches and more accessible constant amplitude of the pendulum improves the accuracy considerably.

One of the most accurate clocks count the largely freed of interference Shortt clock. In the master clock a nearly free pendulum is swinging in a vacuum. A second synchronized to the master clock Clock contains all the other moving parts, which would interfere with the master clock. The error of this clock is a few milliseconds per day. This accuracy was only surpassed in 1933 by the temperature-stabilized quartz watches.

Special forms

Astronomical clocks

The second shock allows for measurements of stellar passages - as in the telescope of a meridian circle - the precise correlation of time with the pulling through the field star ( up to 15 " / s) with the so-called eye -ear method time measurements to 0.05 to to 0., 1 seconds are performed accurately.

The rate adjustment (calibration) of pendulum clocks by means of screws at the lower end of the pendulum or weight plates.

The temperature compensation of good clocks by means of three-rod pendulum or mercury pendulums. Thereby the center of gravity, or the rod length of the pendulum are influenced, to compensate for the thermal expansion of the pendulum and thus caused the temperature dependence of the oscillation frequency. The dependence of the oscillation period on the air pressure can be reduced with the help of Aneroiddosenkompensation or compensated by encapsulation of the pendulum.

Reversible pendulum for gravimetry

A pendulum, which can be turned over and around two axes (usually agate cutting) has the same period of oscillation, the reversible means. This technique allows the precise measurement of the length of the pendulum and therefore by the above formula pendulum and the acceleration due to gravity.

Similarly we explored the Earth's gravity in the 18th century. The shape of the earth was determined and the meter defined by combining gravimetric and geometric measurement of a degree.

Today we used for highly accurate spring scales, the so-called gravimeters.

Private clocks

Private pendulum clocks pendulum usually have lengths of 15 to 25 cm; The latter corresponds to about 1 [s ] oscillation period. They reach about an accuracy of a few seconds per day. Shorter, swinging front of the dial pendulums have the so-called Zappler, with two swinging pendulums is called Doppelzapplern. They are table - or short wall clocks whose case is closed only on the face side. Their accuracy is about 10 seconds per day.

Longcase clocks

Longcase clocks, grandfather clocks for short or house clocks, have weight drive and longer pendulum with small amplitude and therefore good conditions for higher accuracy.

Drehpendeluhr

Torsion pendulum clocks use instead of a pendulum oscillating back and forth a torsion pendulum as a time base. Torsion pendulum are very low loss because they move slowly and therefore air friction is low. Torsion pendulum clocks can therefore with an elevator very long run ( eg one year ). Torsion pendulum clocks can - as well as ordinary clocks - including even their own pendant form (that is, to rotate as a pendulum mass or resonate ). For three clocks but this leads to Inaccuracies due to the expanding spring. Torsion pendulum clocks require so little power that they can be driven only by the air pressure and temperature variations in their environment ( Atmospheric clock ). Such watches have a lift mechanism that operates similarly to a pressure cell as in pressure gauges.

The decorative clocks nowadays offered as a commodity with a torsion pendulum (often imitated brass balls ) or small, fast commuting per se are quartz watches - they have only an ornament to an additional electric drive for the movement of the pendulum.

Moving eyes

A " moving eyes " is a clock in which the pendulum move with the eyes of the statue.

Mysterieuse

This is a Schwingpendeluhr, form a unit with the pendulum and movement.