How does a quartz watch work? - The quartz movement explained in detail
The quartz watch, accurate, reliable, and affordable. – A thorn in the side of mechanical watchmakers.
The further development of the quartz watch in 1980 made quartz watches affordable. This made it possible for everyone to wear a watch. However, quartz movements are not only found in inexpensive watches. This new development plunged the entire watch industry into a real quartz crisis.
Due to their excellent quality, compactness and accuracy, they are also present in the watches of renowned manufacturers such as Rolex.
How does the quartz movement of a quartz watch work?
In a quartz movement, a quartz crystal is used as a reffrence. Due to the piezo effect, the quartz oscillates at 32,768 vibrations per second, which are counted, resulting in the time. The hands of the quartz clock are driven by a small motor. The energy for this comes from a small battery, which should be replaced annually.
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How exactly does a quartz watch work in detail?
Unlike an automatic watch, the hands of a quartz watch are not powered by mechanically stored energy, but by electronically stored energy. Essentially, the functioning of quartz movements is simpler than the functioning of a mechanical movement.
To explain it understandably, I divide the quartz movement into two parts: the drive and the time-measuring mechanism.
The Power Unit
In a quartz watch, the gear train is driven by a small electric motor. The gear train translates the speed of the second hand to the speed of the minute and hour hands. The translation works like a mechanical movement via a series of gears.
The energy for the electric motor comes from a small button battery, which should be replaced annually.
Alright, you now know how the quartz watch moves its hands, but the unique thing about a quartz watch is the mechanism that measures time and thus regulates the speed of the hands.
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The time measuring mechanism of a quartz watch in detail
Quartz is a piezoelectric material.
This means that the electrical poles shift when elastic deformation takes place. The displacement of the poles subsequently leads to an electrical voltage.
Conversely, the inverse piezoelectric effect states that when a voltage is applied to a material, the material deforms due to the displacement of the poles.
This sounds complicated, therefore once again more understandable:
"A quartz crystal deforms when an electrical voltage is applied."
The quartz is now moving, but where does the resonance and the exact number of oscillations per second come from?
The frequency at which the quartz crystal vibrates is largely determined by the shape.
A square quartz oscillates at an extremely high frequency. This is so high that the power consumption for reading out the frequency would exceed the capacities of a wristwatch.
With the tuning fork design, the frequency of the oscillating crystal could be reduced to 32,768 Hz, resulting in much lower power consumption.
Watchmakers had to trade off between a higher frequency, which results in a more accurate watch, and a lower frequency, which consumes less power.
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So now we clarify how the tuning fork swings back and forth!
An electrode is fixed to each side of the tuning fork, and an oscillator is applied to it to produce any alternating field.
Thanks to the inverse piezoelectric effect, the applied alternating field causes the quartz crystal to start vibrating.
With the help of a feedback loop, the frequency of the alternating field is adapted to the mechanical natural frequency of the quartz crystal.
This causes the quartz crystal to become an electrical resonance circuit, which has a so-called low damping, meaning that the vibrations of the quartz crystal can be maintained for a very long time without losing much energy. The vibrations are then converted into electrical impulses.
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An electronic counter counts the pulses and calculates the time from them. As soon as the counter reaches a certain number of pulses, it sends a command to the electric motor, which moves the hands of the quartz clock.
The accuracy of the quartz watch is ensured by the precise frequency of the quartz crystal and the high stability of the electrical resonant circuit. Therefore, quartz watches are usually more accurate than mechanical watches.
In summary, the quartz movement works because of the combination of a piezoelectric quartz crystal, an electric resonant circuit and an electronic counter. These components allow the quartz watch to measure time very accurately and move the hands precisely.
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Count the vibrations
The quartz oscillates and the gear train is moved with the help of the electric motor. - Now we can still clarify in detail how the number of oscillations are counted.
To evaluate the frequency, the AC voltage, which is 32,768 Hz, is applied to a series of T flip-flops.
A T-flip-flop is a circuit with two inputs that can switch from 0 to 1 like a switch.
Connecting 15 T-flipflops in series results in 2^15 possible combinations.
2^15 gives 32,768, which is exactly one thousand times the oscillation rate.
Thus, if the frequency of 32.768 Hz is applied to the 15 T flip-flops, a second pulse can be derived.
Now we know the exact time intervals and can control the stepper motor that moves the hands according to this second pulse.
Previously, I mentioned that more energy is needed at a higher frequency. This has to do with the fact that at a higher frequency more T-flipflops are needed, which require more current in total.
Like this! You have just understood how a quartz watch works in detail.
If you have any questions or comments, feel free to express them in the comments.
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Conclusion
I have to be honest, a guartz movement is more complicated than we thought.
But the basics are then quickly understood.
We have to take into account that we did not go into how the frequency of the AC voltage is synchronized with the natural frequency of the quartz crystal. Furthermore, there is a lot more to know about the T-flipflops than I have touched on here.
For reasons of relevance, I have not gone into these two areas in more detail, but I have linked to the appropriate Wikipedia articles.
I would really appreciate a note or comment if you have another question.
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Q&A
How accurate is a quartz watch?
Quartz watches shine with their accuracy of less than one second per month. Calculated over the year, that's about 10 seconds. So quartz watches are so accurate that it is not necessary to adjust them regularly.
How long does the battery of the quartz watch last?
The button battery of the quartz watch usually lasts for one year. To change it, you need to take the watch to a watchmaker, who will open it and replace the battery. For inexpensive watches, you can also change the battery yourself. Changing the battery costs between 15 and 50 €, depending on the watch and the watchmaker.
About the author
Maio Rosatzin
My passion began with a Breitling Premier B01. Since then, I've been sharing my fascination for watchmaking here on my blog. Let's dive into this fascinating world together!
