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Importance of amplitude.


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  • 2 weeks later...

What's high amplitude?

 

I like to see (and companies I do work for) a healthy 270 flat at full wind. Drop in vertical amp hopefully not much more than 30 degrees. This helps ensure that the rate will still be good at 24h. John has more technical documentation he can quote, but looking at a sheet from one company they spec 300 to 320 max amplitude (but no minimum) horizontal at 0h, and generally around 200 minimum in vertical at 24h.

 

Some watches are very stable though; for example the Lemania 5100 chronograph might only lose 10 degrees in 24h. On one of those I don't mind if I have 250 at full wind, as it will still rate terrifically at 24h.

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37 minutes ago, nickelsilver said:

one company they spec 300 to 320 max amplitude (but no minimum) horizontal at 0h, and generally around 200 minimum in vertical at 24h..

ETA? They like to run 300-320°. I read somewhere that Rolex do not like more than 280° - I think it was because, if you run at higher amplitudes, you get a bigger drop after 24 hours. At 270-280° the idea is that a lower drop over 24 hours gives better timekeeping.

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The higher the amplitude, the more stable is the swing regarding timing. Shocks have less influence on timing, and escapement action is a series of pos. and neg. shocks, too.

With standard value 270° flat you will get near 220° vertical, at least after some hours. This is a magical number, as poise errors have zero influence at 220. So choosing 270/220 was quite clever.

bessel.jpg.185212badc11ec4e92e0110a71a63cac.jpg

Frank

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1 hour ago, nickelsilver said:

but looking at a sheet from one company they spec 300 to 320 max amplitude (but no minimum) horizontal at 0h, and generally around 200 minimum in vertical at 24h.

I would be curious as to whose sheet that is.

Yes I'm all sorts of interesting technical  documentation but just trying to find it all in one place can be a challenge. Witschi will take up to 330° but watch companies tend to get nervous if he gets too high and usually are more concerned about at 24 hours. Then of course the big thing most companies are concerned about is his timekeeping.

I'll just attach a few interesting things slightly different version of the above chart Posted by praezis.  With this chart shows is amplitude and poising errors is a concerns of the higher the amplitude the less effect poise is.

Something from Seiko 4006 service instructions actually gives you a numeric number for amplitude.

Eta Is interesting because typically you don't Get timing specifications in the service information. For that you need to manufacturing information sheets that's for all the nifty specifications are. Then there is sort of consistency and then sort of non-consistency in the various manufactures sheets. Universally 200 is the minimum I've snipped out an image of one of them but the maximum seems to very 304 one 324 another so that seems to very As to what the maximums going to be.

That Omega has interesting for their amplitude specifications typically they would only give you a minimum mom. But I noticed something right now that I hadn't seen before they actually do specify the maximum so I snipped that out. The minimum depends upon the particular watch and the lowest I'm seeing is 160°. Also have an image of timing specifications for watches that aren't listed anywhere else the rest of the document. Of course at these low amplitudes the watch still has to keep time.

 

 

 

amplitude versus position witschi.JPG

poise of balance wheel versus amplitude.JPG

Seiko 4006a amplitude 180° fully wound up.JPG

ETA 2826-2 timing.JPG

Omega amplitude specifications general.JPG

older Omega timekeeping.JPG

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4 hours ago, praezis said:

The higher the amplitude, the more stable is the swing 

So given the same amplitude    !!!            do big and small balances enjoy the same stability? 

or other parameters such as balance radius factor in.

TIA 

 

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1 minute ago, Nucejoe said:

So given the same amplitude    !!!            do big and small balances enjoy the same stability? 

or other parameters such as balance radius factor in.

TIA 

 

Considering something like a standard 18,000 beat watch, it's very hard to get a smaller balance to perform as well as a larger one. I mean like an 11 or 13 ligne movement compared to a 5x7 ligne. Generally the proportions of the balance pivots doesn't quite scale; the larger watch might have 0.09 or 0.08 pivots, while the smaller balance might have the same or in a high grade piece maybe a hundredth less- but a far smaller balance and inertia.

 

Another big factor is the hairspring- again, proportions. You can have a proportionally smaller hairspring collet on the larger balance, which gets the spring end closer to the balance center. This is a big deal for timing. Then there's the escapement; on something like an AS 1012, the escape wheel and fork and pretty much the same size as the escapement in a larger 11 or so ligne watch, so more effort for the tiny balance to unlock, more mass in the parts, etc. etc. There are some very high grade small movements that perform very well, but they are relatively rare. An example, while not super small in diameter but ultra thin is the JLC 838; these can give surprisingly good rates, stably, while having a very light balance and tiny escapement (and suspended barrel too!). JLC also made some really impossible to rate small movements...

 

In higher beat watches the balance does become smaller than a similar size movement at 18K. These do tend to rate very well, as the higher beat is a huge help, it's a different escapement geometry that's suited to the higher beat, and by and large the hairspring collet is a Greiner or similar which are poised and also help with the rate.

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In 18000/ hr beaters, big balance was preffered, later,  high frequency was achieved, So, is the linear distance a balance travels per unit time significant?    that is;  the balance rim travels more distance with higher frequency and bigger balance radius.  

Rgds

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3 hours ago, Nucejoe said:

In 18000/ hr beaters, big balance was preffered, later,  high frequency was achieved, So, is the linear distance a balance travels per unit time significant?    that is;  the balance rim travels more distance with higher frequency and bigger balance radius.  

Rgds

It's more of a power issue. Higher beat rates need more power, but there's only so much room for the barrel, so the inertia of the balance is reduced.

 

The distance the balance travels from perspective of a point on the rim is the same for a given balance diameter at a given amplitude; it just travels that distance more quickly at a higher beat. So for a given time, yes, it travels more distance, which means a higher power input required.

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One of the things that amplitude means is the greater the amplitude the less affect the escapement has on timekeeping. Escapement's always produce a loss and will interfere with timekeeping. So the greater the amplitude the smaller the effect the escapement will have. That is a reason to have a higher amplitude.

 

Just now, nickelsilver said:

inertia of the balance is reduced.

Thinking of the inertia of the balance wheel I have a PDF attached. This is where the physics of the balance wheel isn't necessarily just simply increasing the amplitude is good there may be other things that also affect that. Like the diameter the balance wheel or even how heavy it is.

So the attached document Omega's talking about changing their balance wheels. On the second page we see where it says greater rating stability. Explained because of the inertia because the larger balance rim.

sine wave watch what does it really mean.JPG

Omega-have-adopted-the-screwless-balance.pdf

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 Ok,   rate becomes more stable as the wheel's inertia is increased, and we can increase inertia by increasing the radius of gyration which can be done whilst reducing the weight of the wheel.  so far so good. 

But Inertia can also be increased by increasing frequency of the wheel to a point that amplitude is no longer a predominate parameter, so big amplitude is not of intrinsic significance in achiving stability. Its just a way to increase inertia. 

Pivots attached to big wheels are more vounerable to shocks, not so with small wheels, in fact wheel with  high frequency absorbs most of the shock rendering pivot less vounerable. 

I made up most of this, best go hide myself before Frank or Nickesilver catch me. 

 

 

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17 hours ago, Nucejoe said:

But Inertia can also be increased by increasing frequency of the wheel to a point that amplitude is no longer a predominate parameter, so big amplitude is not of intrinsic significance in achiving stability. Its just a way to increase inertia. 

6 hours ago, Nucejoe said:

Correction to the above, 

Moment  of inertia is increased when increasing velocity. 

I don't think this is correct. A pendulum's moment of inertia depends solely on how its mass is distributed around the pivot point, not its velocity.

It's an interesting question though, why are high-beat movements usually preferred? There's the obvious advantage of a smoother seconds hand of course. I've also heard that high-beat movements recover faster from shocks and are therefore more accurate.

But the balance spins faster in a high-beat movement which increases friction. Is this the reason why you need more power? In my mind, if you disregard friction for a moment, a high-beat movement shouldn't need more power to operate compared to a low-beat movement, but I'd love to be corrected on that. Of course, adding friction forces means you need larger impulses to the balance to maintain a given amplitude, but then again, you're giving more impulses per second in a high-beat movement, so each impulse could conceivably be smaller. Lots of tradeoffs, lots of misconceptions, looking forward to hear the expert opinions...

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18 minutes ago, fellerts said:

I don't think this is correct. A pendulum's moment of inertia depends solely on how its mass is distributed around the pivot point, not its velocity.

It's an interesting question though, why are high-beat movements usually preferred? There's the obvious advantage of a smoother seconds hand of course. I've also heard that high-beat movements recover faster from shocks and are therefore more accurate.

But the balance spins faster in a high-beat movement which increases friction. Is this the reason why you need more power? In my mind, if you disregard friction for a moment, a high-beat movement shouldn't need more power to operate compared to a low-beat movement, but I'd love to be corrected on that. Of course, adding friction forces means you need larger impulses to the balance to maintain a given amplitude, but then again, you're giving more impulses per second in a high-beat movement, so each impulse could conceivably be smaller. Lots of tradeoffs, lots of misconceptions, looking forward to hear the expert opinions...

It's easy to get confused with angular units, as we aren't used to using them.

The moment of inertia isn't increased with velocity. It's how the mass is distributed.  The moment of inertia is the sum of the mass x radius² - which is why the radius is so important.

image.png.280f3a0e2382369733c8eb68effbeefa.png

What does increase with rotational rate is the "angular momentum", 

L = I x w          (where w is the angular speed in rad/s)

So yes, a high beat does give higher angular momentum, so the friction forces will be relatively lower than a low beat.

Edited by mikepilk
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33 minutes ago, Nucejoe said:

I was wrong, good you noticed that,  I mixed up moment of inertia with angulare momentum, when translating from Farsi to English. 

So,  angular momentum increases as anglure velocity increase.

I always forget the terminology for angular motion - I had to read up on it to remind myself.

In linear motion we have mass and momentum, and angular motion the equivalents are moment of inertia and angular momentum.

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Interesting thread.  From an electrical engineering point of view, there is the signal, and there is the noise.  The higher the ratio of signal to noise (SNR) the better.  You achieve this by increasing the signal with fixed noise, or decreasing the noise with fixed signal.  So for a watch, it makes sense to me that the larger the amplitude, the less impact noise has on the output (the tics in the case of timekeeping).  The noise, is anything in the going train that has random errors (systematic errors have been adjusted to zero).  Considering the signal as the sine wave, you want the rate of change as fast as possible as it crosses "around" zero which causes the next tic.  Higher rate is achieved by greater amplitude. 

Some of the earlier posts in this thread have touched on these points in different ways.

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A massive body tends to resist change in its motion. 

 Disturbance ( due to shocks ) to motion of the oscilator is a instantly transiant one, so ( as Framk said )  its effect on timing is negligible.

Selfwinders generate abundance of power, paving the way for high beat, yet we have to chase high amplitude in every piece. 

Rgds

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  • 3 months later...

DISCLAIMER 1: The following is certainly obvious for 99% of forum members, but maybe it's still worth writing down for the remaining 1%.

DISCLAIMER 2: This may not be the intention of the question and everyone else provided impressive answers on the importance of amplitude for the good functioning of the watch...  but there's also another much simpler, but practically valuable, perspective:

Movements are built to achieve a certain amplitude (and it's good to know how these vary by brand/movement!!).... and if you movement doesn't reach that amplitude after your service, then something is wrong and you should go troubleshooting. Simple as that.

Amplitude is the most commonly used indicator for a movement's "health" for good reason:

1. it's simple to measure (with a timegrapher, of course)

2. it's a very good indicator: As it measures the functioning of the very last element (=the swing of the balance), it implicitly tests the proper functioning of all other elements all the way to the first element (the mainspring).

Sure, there may be something wrong with a movement/service even if amplitude is high. Not all problems manifest in amplitude. But probably 90% (don't pin me down on that number, hahaha!!!) of potential problems impact amplitude.

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1 hour ago, Knebo said:

Movements are built to achieve a certain amplitude (and it's good to know how these vary by brand/movement!!).... and if you movement doesn't reach that amplitude after your service, then something is wrong and you should go troubleshooting. Simple as that.

But if you have a watch that's 50, 60, 100 years old and has been used extensively, there will inevitably be wear in all components. So you cannot expect to get the amplitude the watch had when new. 

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2 hours ago, Knebo said:

Movements are built to achieve a certain amplitude.

Does this    certain amplitude     have any technical significance.

Praezis makes lots of sense here,

On 1/25/2023 at 2:30 PM, praezis said:

The higher the amplitude, the more stable is the swing regarding timing.

 

 Yet I am still not clear what makes 220 degrees majical, if I understand this part then I can easily agree amplitudes between 220 - 270 are clever to choose at the drawing board.

 

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4 hours ago, Knebo said:

Amplitude is the most commonly used indicator for a movement's "health" for good reason:

one of the places were amplitude would be more interesting and useful is. New watch you got it for the first time you run a timing cycle six positions you record all the amplitudes and rates. His service the watch you should see better amplitude.

if you look at technical specifications from the Swiss for instance you will see that they typically do not tell you what a good amplitude is they've only tell you what a unacceptable yes. They usually have a maximum because of you go over 300 depending upon the watch that is undesirable but other than that they don't care about a high amplitude they only care about a low amplitude typically at 24 hours sometimes they'll specify which crown position it is other times it's more generic. Then it depends upon the watch watches can vary as to what is good and bad I think the lowest I've ever seen Omega have some other movements would go 260°.

so how about an example this is a Rolex it was incoming know of valuation was done on the inside yet. We know for 3035 Rolex that and attends you little variation here currently it seems to be 200° at 24 hours is unacceptable some other tech sheets had 190.

so first image dial-up fully wound up looks pretty good

image.png.aa06ce854dd308fc45287406b9c8b163.png

next we have crown down now here we can see the amplitude has dropped by quite a bit

image.png.63a03415f50e5d08d997e1ca1e9f9a92.png

24 hours later dial up and by the way this shows why when looking at a watch you should look at more than one positions the person who gave me the images actually had all of the images I only snipped out a couple of them because they were too many.

image.png.b7b465763efe9e43c31eb03610b7c8db.png

crown down at 24 hours is looking below the 200 that we typically see but above the 190 that some of the tech sheets have

image.png.400c491aed03500c5965dfa74d837392.png

all the other interesting thing with the obsession with amplitude on this group is often times people don't look at does the watch keep time?

Then yes amplitude is a measure of performance but unfortunately each watch can be different. This means spending lots and lots of time trying to get something to do 300° conceivably is almost a waste of time because the factory never designed it that way. Look at Seiko watches typically lay have pathetic amplitude and they oil the pallet fork pivots which makes it worse.

oh and the Rolex watch above a 3035 as an issue can you tell me what it is? all we know is the current owner wears it occasionally.

Oh and this is where amplitude also has a problem if it's a watch you serviced if you documented your watch properly especially when you're learning. Example incoming watch check it in six positions write all the numbers down when it's fully wound up just for the fun of it wait 24 hours do it again service the watch see if you have an improvement. A year from now another year another year keep checking see how your watches doing. But is a minor problem to this?

oh and is amplitude a problem on hundred-year-old watches what about out of beat? One of the watch keeps time are those other things important well they are where I work my boss gets annoyed if the beat is too extreme or the amplitude looks low I tenderly worry about if it runs overnight keeps time.

2 hours ago, mikepilk said:

But if you have a watch that's 50, 60, 100 years old and has been used extensively, there will inevitably be wear in all components. So you cannot expect to get the amplitude the watch had when new. 

one of the problems is what exactly was the amplitude when these watches were new? The theories of horology have changed with time for a variety of reasons things basically today more efficient. Back then there were more concerned about keeping time than amplitude. they didn't have a timing machine to please. 

then there is a problem of all the people who worked on the watch over time. All the strange things that have happened to certain degree it's a miracle if you gave it to get these watches running again.

1 hour ago, Nucejoe said:

Yet I am still not clear what makes 220 degrees majical,

maybe a picture would help.

if you look at the image below you'll notice something interesting poise of the balance wheel. the purpose the chart is it shows what happens when you have a heavy spot on the balance wheel. At various amplitudes depending upon where the heavy spot is the watch with a run fast or slow its how we do dynamic poising for instance. But as the amplitude increases hitting approximately 220° you no longer will observe any poising errors at all. Then as you go faster in noticed that the errors aren't as big. Which is why dynamic poising is easier at a  low amplitude as it's much much more noticeable. So this is what makes 220° kind of a magical number as no poising errors suggest think if you watch could run a perfect 220° no poising errors.

 

image.png.d1fe0659547ccae66b4b4abe6390e826.png

 

image.png

Edited by JohnR725
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