Working of Clock

Working of Analog Clock

Importance of time keeping is recognized ever since the life came into existence. From just days and nights demarcating the time to using sundials for time keeping in the days in medieval period to balanced wheels and pendulum clocks in 15 and 16^th century, time keeping had always remained a challenge to the scientists.

  

The first electric clock was patented in 1840 and since then there has been a lot of advancement in this sphere. Digital Clocks have capture the 21^st century world however analog clocks still remains a part of almost all the houses.

This post is dedicated to explaining the working of these analog clocks.

  

Analog clock consists of:

• Oscillator
• Driving circuit for the oscillator
• Coil
• Ferrous Core
• Magnet
• Cogs (gears)
• Battery
• Hour hand
• Minute hand
• Second hand

 

The oscillator is a tuning fork shaped quartz crystal of 32 kHz. 

Circuitry attached to it performs three main tasks:

1. Resonates the tuning fork at 32 kHz.
2. Bringing the frequency the output end (coil) to 1Hz by using a series of divide by 2 circuits.
3. To prevent damping of the oscillation by providing positive feedback.

 
 

When this voltage signal of 1Hz is fed to the coil it creates a saw tooth alternating magnetic flux. This flux travels through the magnetic core which is asymmetric. The circular space along the shorter limb of the core is used to mount the circular magnet. 

 

The produced magnetic flux interacts with that of the permanent magnet and exerts a torque on it. The rotation produced is as accurate as a stepper motor.

The cog mounted on the magnet connects it to the second hand cog. With the help of gears (cogs) these torque is transported to minute hand and hours hand simultaneously. The teeth and the radius of gears are so adjusted that the frequency ratio of hr: min: sec remains 1: 60: 3600.

The battery provides the driving force required by the circuit. Many DIY’s talk about reverse clocking (anticlockwise rotation). This can be achieved by flipping the metal core. Changing the terminals of the coil however won’t have any effect (it may not tick even). Actually it’s the magnetic core that is responsible for the direction of rotation of the clock. This magnetic core being asymmetric changes the flux at the end of the core (around the magnet) which imparts direction to the stepper motor (magnet).