Everything You Wanted To Know About A Quartz Watch But Were Afraid To Ask



Posted by Walt A. on December 03, 1997 at 3:34:23:
In Reply to: Quartz v. Mechanical - A Technical Analysis posted by RFC on December 01, 1997 at 12:28:16:

Since this discussion has already been under way for a couple of days, there will inevitably be some duplications in the topics covered and ideas presented. I apologize to anyone who has beaten me to some of the points I present. My transgression is unintentional.

Durability:

A quartz watch has a slight edge on shock resistance over the mechanical, but it is certainly not invulnerable. Low mass of the vital components helps protect them from shocks. Most vulnerable spots in a quartz watch are the stepper motor and the quartz crystal package. Most vulnerable in mechanical watch is the balance wheel's cap jewels, the balance staff, the rotor bearing (in an automatic) and from there, various other parts of the escapement, especially cap jewels. The case and crystal are equally vulnerable in both kinds of watches.

No contest in the low-temperature sweepstakes: A well-maintained mechanical watch will keep on ticking long after the battery of a quartz is temporarily immobilized. High temperature durability is less clear. Accuracy of both degrades rapidly at temperatures well above skin temperature.

Given everything the same, a quartz watch should be able to maintain its water-resistance better than a mechanical, simply because of its far less frequent need to have its crown unscrewed for time setting. But there are many other variables here,including the robustness of the individual watch.

Vulnerability to strong magnetic fields: A mechanical watch is generally more readily affected by a strong magnetic field, but the effect is reversible although a nuisance. Not so with the quartz: A strong enough magnetic field can depolarize or partly reorient the permanent magnets in the stepper motor. This can't be reversed.

A mechanical watch is for all practical purposes invulnerable to strong electrostatic discharges and RF electromagnetic fields. The quartz watch's CMOS logic chip and stepper drivers can be destroyed by just the right (or we should say wrong) zap. The EMP (Electromagnetic Pulse) effect associated with nuclear detonations can also be fatal to any microcircuit, but let's not worry about that - a nuke can do more to you and me than it can to your watch. In fact, it can ruin your whole day.

Resistance to mechanical wear in the movement is much better in the quartz watch because the gear train of a mechanical watch is under constant load from the mainspring. This load is particularly heavy at the mainspring barrel. Further down the line, the wear is increasingly due to friction between gear tooth surfaces and between gear staffs and their jewels. Obviously, the better maintained the watch, the less significant the wear. In a quartz watch, the gear train is under no load. For this reason, it doesn't need frequent (in some case ANY) servicing to maintain proper lubrication.

Resistance to aging is definitely far superior in the mechanical watch, providing it is well maintained and protected from mosture and chemical contaminants. There are watches today that are still running after 200 years of service. While quartz watches have not been around long enough to establish reliable longevity data, some of the mechanisms that contribute to a watch's deterioration with time are known. They are the normal aging of discrete electrical components, solder and spot-weld connections, damage from dead batteries left to deteriorate and/or leak in the watch, etc. Still, quartz watches have the potential for decent longevity. My oldest quartz watch (a Seiko) is 21 years old and is just now starting to show occasional signs of senility. My oldest mechanical watch (a Ball Official RR Standard) is 37 years old and still runs flawlessly. However, it has over the years suffered some repairable insults, like a broken balance staff. So here is a major difference: For most old quartz watches, if they suffered this level of damage, I would pitch them. Mechanical ones I would have repaired. Why? Nothing logical -- I get bored more readily with a quartz watch. Go figure.

Convenience:

This is hard to separate from accuracy, because the two complement each other. Here is the gist of the matter: A quartz watch can be put into a drawer, kept there 3 months, then taken out, put on the wrist and worn. It would still show the right time (unless there was a change from Standard to Daylight time or vice versa in between) and the adjustment for the date needed to account for the short months in the intervening period is very simple. Further, you can do this with 20 watches in your drawer. Any of them can be taken out at any time and worn. The minus side of that is that out of those 20 watches there will likely be at least one that needs a battery. Unlucky you if you chose that one to take on your 2-week fishing trip!

A manually wound watch can be kept going at the price of a 30-second-per-day manual winding; no need to wear it. The same goes for 20 such watches in your drawer. However, because of the relative inaccuracy of these watches compared to the quartz, you will probably have to set the watch to the right time after 3 months of disuse. We owners of such watches will argue that it doesn't take much longer to set the watch than it does to adjust the quartz above for changes in time and date.

Automatic watches can be used as above only if they are on winders. And 20 winders can be quite an outlay of cash you could use more pleasurably buying that Lange Saxonia.

Reliability:

The reliability of mechanical watches is legendary. This can be true of the quartz, but for one little item: Its battery. Battery life is highly unpredictable. My own record goes to a Lassale dress watch that ran on a battery (a Varta, I believe) for 7 years! But then, it ticks only once every 20 seconds, advancing 1/3 minute each time. My experience with batteries is that much depends on its age when you bought it and a variety of other factors, so you can rarely be absolutely sure when this temperamental power source will unpredictaly find itself shedding the last coulomb in its reservoir, leaving you timeless out there on the Continental Divide, where you plan to stay another week. Small wonder, then, that 'survival' watches are usually mechanical.

Obsolescence:

Replacement parts for mechanical watches are widely available, including for watches dating back to the '40s and earlier. Also, they can always be made if they are no longer available, albeit at considerable cost. Not so with quartz watch needs, particularly batteries. What about all those mercury batteries from the early days of the quartz era (e.g., the infamous 388) with their vile cargo of toxins, now outlawed? (So what if the dosage I'd get from them is negligible compared to what I get regularly at the fish market and at the sushi bar? It's the Principle of the thing!) In time, many of the batteries in common use today will no longer be available. Since it is the voltage and capacity that counts, it may be possible to use newer batteries with a suitable adapter, but if the voltage requirements are different, its Adios to that dear old Seiko or Raymond Weil your mom gave you as a graduation gift.

The Boredom Factor:

I won't go into this touchy subject, but you all know what I mean. I will let YOU decid which type of watch more readily falls prey to this phenomenon.

I am looking forward to hearing more on all these topics from you in this discussion.

Regards,
Walt




Posted by Walt A. on December 04, 1997 at 13:08:16:
In Reply to: Great Info.. some questions on quartz..more.. posted by John Toh onDecember 04, 1997 at 10:55:43:

Hi, John,

While I have no experience with quartz watch electronic circuit design, I have spent many years in designing similar systems, i.e., low voltage CMOS circuitry implemented on high density PC board assemblies. My fellow engineers on this Forum, many with direct watch experience, may add some valuable points to what I will attempt to summarize.

On most quartz watches, the logic microcircuit, consisting of the 15 stage counter and a variety of control and interface circuitry, is potted in epoxy or similar material but is in fact not hermetically sealed. Also, the quality of the initial assembly process varies widely in practice. Residual mechanical and thermal stresses are often left in the microscopic bonding wires and resistance welds, leading to stress cracks developing. Crystallization of the joints is also common; it may lead to cracks developing in time. Chemical contamination from the outside can seep into the circuit due to poor hermetic integrity. That is one common failure mechanism.

A general problem with all PC assemblies of this scale is hairline-cracks developing in the tiny traces due to warping of the glass-epoxy or other board materials, or even simple oxidation of the trace material.

Battery contacts tend to oxidize -as do the surfaces of the batteries themselves- and become non-conducting due to the ultra-low operating current, meaning the contacts are not self cleaning (as were the points in the ignition systems in old cars, before electronic ignition). This problem can be solved by cleaning the battery contacts, but many shopping-mall battery-swappers who call themselves watchmakers don't know that.

Even the finest capacitors (especially the trimmers in the oscillator's tank circuit) do age and change their characteristics over long time periods. On many watches, these components are anything BUT first-class. In that sense, the cheapest watches may have an advantage, not having trimmers. (Trimmers are among the most expensive components in a typical quartz module) They use laser-trimmed resistors instead, in combination with cheap fixed capacitors.

Finally -and most significantly- there is progressive damage done to the microcircuit and stepper drivers (usually included in the microcircuit) by the hundreds and thousands of little electrostatic discharges, each one doing just a BIT of damage to the CMOS circuits but not enough to stop it in its tracks. My fellow engineers will recognize this as a common affliction of high-density chips in microprocessor-based subsystems (especially ROMs and FPGAs) that operate in hostile environments. This kind of progressive damage can actually be seen under a microscope if a chip is carefully cut open after a few months of use. Well, there is always that straw that finally breaks the camel's back! Replacing the logic chip in a quartz watch is generally not economically feasible even if the module is still in production.

This is what we face with the quartz modules of the current generation. Future designs may prove to be more robust.

Does anyone care to supplement this very brief list? Your contribution would be most sincerely appreciated.

Regards,
Walt



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