Quartz Watches - Some Information Some May Find Interesting

I wanted to make a post about quartz watches, and although I realize not everyone here is a fan, but hopefully after reading this you will at least understand how sophisticated they are, and at least appreciate them as something more than a “dumb” stepping motor and dividing circuit.

So the modern quartz watch offers a lot of technology to increase accuracy and extend battery life, that most people have no idea are included inside these movements. But first let’s talk about what these movements look like, and how well they are made.

The image most people have in their mind of a quartz movement is one made of thin metal or plastic, and a very low count for the jewels, if any at all. In addition, there is probably a well deserved reputation of very small and cheap movements, in very large cases, like this:



Note this is a Diesel that I swapped a battery in a while back - the owner had sent it in to the company twice to have the battery changed and they refused to do it. They gave him a certificate on a discount for a new watch instead. Amazing...

Anyway, not all quartz watches look like the one above. Here are some very old photos (my photography was certainly lacking back then, so excuse the poor quality) of my wife’s Cartier quartz - took these when I was changing the battery for her:



The finishing was quite nice, with rhodium plating and well done Cotes de Geneve:



Now it’s not all that often that they look quite as nice as this one does. To give a more typical example from Omega, here is a shot of a Cal. 1538 - a movement that I deal with often - it is also rhodium plated, and has perlage decoration:



So although not as nice as the Cartier, it’s way nicer than the movements I can buy for $5 from the local material house. Some are even cheaper than the one in the Diesel above, made with all plastic gears. There are also middle of the road movements that have metal plates, are well jeweled, and those certainly can be serviced. Not all quartz watches are "disposable".

So they can be well finished, but they are also much more sophisticated than a simple quartz oscillator and dividing circuit. To illustrate this, I’ll use my timing machine, as it can be used to time both mechanical and quartz watches. In this photo I have another quartz SMP with a Cal. 1538 that I have removed the battery from, and I am powering the watch using my timing machine. This allows me to perform more diagnostic checks on the movement that I can’t perform when it’s being powered by a battery:



Here is a closer look at the screen and the results, and to explain things I have added some letters beside some of the readings on the screen:



Now most people are aware that modern quartz watches tell you when the battery is getting low on power. That feature is called the EOL - End Of Life indicator. On the Cal. 1538, it makes the hands tick once every 4 seconds. But the features do not stop there....

So looking at the labels on the screen, let’s look at B first. It reads the average daily rate in seconds per day, and it’s currently running 0.32 seconds fast per day. But beside it at A, there is another rate “Q” that shows 4.18 seconds fast per day, so what does that mean? Well it’s related to letter F down below, and that is labeled as “Inhibition” with the number 60 after it. The number that is 4.18 seconds per day fast is the rate of the quartz crystal, and it is intentionally set fast. The inhibition number is the frequency that the movement corrects it’s own timing.

So in this example in a typical 60 second period, the watch is running +4.18 s/d for 59 out of the 60 seconds. Then on the 60th second, it corrects itself and slows the watch down for one second. It then resumes it’s fast rate for the next 59 seconds. This results in a very stable actual rate, and this watch can be as accurate as 2 minutes per year.

You will notice under the A and B section up top and their corresponding numbers, there is a line with a scale on it, and on the right side there is a green arrow pointing down at just past the 4 second mark. This is indicating the instantaneous rate that the movement is running at, so for 59 seconds that arrow will be in this location. Then when the correction happens, the arrow will jump to a negative number to the left of the zero on that scale for one second, and turn red, then go back to where you see it now - this is a visual indication to show you that the inhibition is happening in real time. Inhibition period can be different for different movements, and 60 seconds is common, as well as 10 second intervals.

Now there are some other numbers we can get out of the way at this point, and those are C and D. C shows the consumption of the movement, measured in micro-amperes, and overall the movement is consuming 0.877 uA, which is well within the allowed standard by Omega. At D, this is showing the consumption of just the circuit, so not counting the power needed to actually drive the hands. These consumption numbers are the most critical things to check when a working quartz movement comes in the shop, as this will tell me if the movement is using too much power, and possibly needs servicing.

I also check some other things not shown here, such as the coil resistance. Also, by powering the watch with the machine, I can vary the voltage that is supplied to the movement, so that allows me to check things like the EOL indicator. I lower the voltage until it kicks into the 4 seconds pulses, and check to make sure this feature is triggering at the correct voltage. I also keep lowering the voltage until the movement stops completely, which is the LWL or Lower Working Limit. All of these features have specifications that are checked when a watch comes in, even for just a simple battery change.

So I’ve covered most of the letters I added to the screen, but there are 2 left. For me this is where these movements really do get amazing. Now looking at G, this is labeled as “Pulse width” and here the pulse is 7.8 milliseconds. So what this tells me is that the pulse of the motor inside the movement is only 7.8 ms long. So unlike a mechanical watch that has force/pressure on the pivots of the watch from the time the mainspring is wound until it unwinds, in this watch there is only a very short period each second (pulses every seconds as shown by the motor period at E) that there is any force on the movement parts. But here’s the thing - these pulses are not just one long pulse, but a chopped pulse. So the 7.8 ms pulse is divided further into smaller pulses, and the percentage of time that the rotor is actually being powered is represented by the number at H called drive level, which in this case is at 50%. So what does this mean? Well this is part of the feature called “asservissement” in French, and what I simply refer to as the motor management.

So here is how this works...when the movement sends it’s pulses to the motor, it expects to move the second hand. In a “dumb” quartz movement this is an open loop system, and the movement does not actually know if the hand moved or not. With asservissement, the loop is closed. When that hand moves, and comes to a stop, it will wiggle back and forth a bit due to the inertia of the hand, and this creates a feedback signal to the movement. The movement looks for this signal, and if it sees it and all is well, it keeps on ticking. At this time the movement is only using 50% of the 7.8 ms pulse in several smaller pulses, and this conserves energy compared to a situation where it is “on” the whole 7.8 ms. Now if it sends a signal to the movement to pulse the motor, and does not see that feedback signal it knows the hand has not moved, it then increases the percentage of the pulse, and tries to overcome whatever is causing the hand not to move - could be a small piece of debris on the tooth of a wheel for example. It will continue to have this increased pulse percentage for a while, then it will return to it’s and shorter length pulses.

This feature is one of the main reasons why watches that used to have a 2 year battery life, now have multiples of that.

Now my machine does not have to power the watch to do some more simple diagnostic checks, and I can use the induction sensor on the left side of the machine to check the timing and some other basic functions if a watch comes in and it’s actually running. I simply have to lay the watch on the sensor - it does not have to be opened even. It will tell me if the watch has inhibition, and I can also usually tell if it has asservissement as well. Here is a shot of a watch on that sensor, and it has both those functions. You can see that the inhibition period is noted at 60 seconds, that the quartz crystal is running at almost +5 seconds per day, but the watch is running at +0.23, and also see the green bar that shows it has chopped pulses and is only using 75% of the pulse time.





Now here is a “dumb” quartz watch, and it’s my own CWC British issued military watch - issued in 1989. I usually wear this for playing tennis....





So here you can see that the quartz crystal rate and the watch rate are the same, so no inhibition on this one. Also the drive level is always at 100% so no asservissement either. I’ll be honest that even most cheap modern quartz watches I get in here at least have inhibition, and many have asservissement as well.

So as you can see, these movements have a lot going on inside. So I expect everyone to rush out and buy several quartz watches now! Okay not really, but hopefully you have learned something. 😉

Thanks to everyone who has read this far.

Cheers, Al

Very cool post, regarding the diesel I'd suspect its probably a result of diesel outsourcing their watch production and not having facilities to service/maintain.

Thank you for this - all most interesting if not quite as engrossing and accessible (for me) as mechanical movements.

One of those well-meaning relatives who knows only that I like watches in the general sense gave me a quartz chronometer containing a "thermocompensated" movement (ETA 251.233)that had passed quartz COSC testing. What technology makes it thermocompensated?

...and put on some Gawd-ugly footwear...yes, we know. http://omegaforums.net/threads/my-first-ug.5440/

Thanks for this Al, its always interesting seeing the insides of our watches from the professional side.

How do the 2.4Mhz Omegas fit into the equation, its a dramatically higher frequency than the regular 32khz of quartz watches

Too late now. 🤦. Is it small, like the watch ones (I've heard that about Gov't workers)?

Glad you all found this useful. To answer a few questions....

1 - How does it work - yes there is programming on the circuit.

2 - Adjusting of time - depends on the specific movement. Some are done with a trimmer (older movements usually) and some are set at the factory, and some can be reprogrammed using a special machine - eeprom basically.

3 - Thermocompensating - Dennis has the basics down. There's not much more to it than that. Note that higher or lower temps will cause a slower rate, not just lower temperatures.

4 - Higher frequencies - the higher the frequency, the more accurate the rate can be.

5 - Thickness of quartz - the gears inside the movement still require space, as does the date mechanism, etc. so if you are looking for an analog time display with hands, it can only be so thin. Most quartz movement are in fact very thin to begin with, and typically much thinner than the average mechanical watch.

6 - What can go wrong - most common things would be debris in the movement from battery changes or possibly damaged coils again from battery changes. Like any watch, they require maintenance, but unlike mechanical watches it's not often, and if you let it go beyond the point where it needs service, there won't be any damage done to the movement through wear - it will simply stop. One big thing though - when the battery is dead, don't leave it in the watch as a leaking cell can lead to corroded contacts or other movement parts being damaged.

7 - Replacement parts - this is the rub. Not that long ago ETA stated that they will no longer sell circuits separately for their quartz movements, so if you have a bad circuit for some reason, you have to change the whole movement. In my experience with Japanese quartz watches, they tend to discontinue the movements fairly quickly, and when supplies dry up the watch sits if you can't somehow make another movement work in it. I don't think this is the sort of problem you would run into with major Swiss brands, at least not to the same extent. For some Omega movements you can't buy many replacement parts, but have to buy a whole new movement.

Cheers, Al