Working principle of pendulum

Pendulum clock measures time by using the periodic vibration (swing) process of pendulum, and time = vibration period of pendulum × vibration times. The vibration period of the pendulum is t = 2π (L/G) 0.5.

Generally speaking, the weight of the pendulum is fixed, and the vibration period of the pendulum can be adjusted by adjusting the reference length (L) of the pendulum. The reference length of pendulum is shortened and the clock is faster; On the contrary, it slows down. For precision pendulum clocks, the additional weight method is also used to fine-tune the vibration period of the pendulum.

When the pendulum clock is placed in different geographical locations (different latitudes and heights of the earth), the gravitational acceleration of the pendulum will change, thus affecting its vibration period. The pendulum clock placed in different temperature and air pressure environment will also cause the change of vibration period. Temperature changes will cause changes in the dimensions of all parts of the pendulum, including the reference length of the pendulum.

Generally, the temperature rises, the pendulum elongates and the clock slows down; On the contrary, the pendulum is shorter and the clock is faster. Therefore, precision pendulum clocks are usually made of materials with different linear expansion coefficients to compensate for the influence of temperature. The change of air pressure will cause the change of air resistance and air density, thus causing the change of vibration period. Therefore, precision pendulum clocks often install the pendulum in a constant pressure shell to eliminate the influence of air pressure.

The amplitude of the pendulum affects the synchronization of the clock. The smaller the amplitude, the smaller the change of the daily difference (see the daily difference of clocks and watches) caused by the amplitude change, that is, the better the synchronization, so the precision pendulum clock often adopts a long pendulum with a small swing. However, the small swing is very sensitive to external vibration and impact, so it requires a high installation environment. The time difference of pendulum clock can generally reach less than 20 seconds/day, and the precision pendulum clock can reach a few thousandths of a second.

The pendulum clock is a mechanical clock. Although some electronic clocks are also equipped with pendulums or torsion pendulums, they only play a decorative role.

Extended data:

Pendulum structure

The structure of pendulum clock can be roughly divided into travel time part, dot part, pointer part and dot control part.

1. Travel time section

It consists of a head wheel (that is, a box wheel with a spring inside), two wheels, three wheels (central wheel), four wheels, an escapement wheel, an escapement fork and a pendulum.

2. Dot part

It consists of a box wheel, a second wheel, a third wheel, a fourth wheel, a fifth wheel and a wind wheel.

3. Pointer part

It consists of a minute wheel, a straddle wheel and an hour wheel. The structural principle is basically the same as the alarm clock.

4. Point control part

The pendulum clock strikes the time every half hour, and the times of striking the time must be the same as the time indicated by the hour hand. Therefore, its impact must be controlled by walking time. There is a mechanism for controlling the number of dotting between walking and dotting, which consists of dihedral angle cam, dodecahedral angle cam, sector teeth, brake lever, switch lever, gear shifting cam and so on.

Baidu encyclopedia-pendulum clock-working principle