# Query pendulum amplitude

#### NEW65

##### Registered User
I just have a query... its regarding someone's movement that has been bushed.
Rear/front escape wheel and verge done.
I have had the clock running and sometimes although slight, the amplitude of the pendulum varies. I gauge the amplitude as the end of the threaded bar moves between the chains. Some days the pendulum amplitude is slightly greater. Can pendulum amplitude vary in clock movements? I am only talking a variation of 5 mm, nothing striking.
Thanks chaps.

#### NEW65

##### Registered User
Also I meant to add (if I’m correct), that amplitude has nothing to do with a clock being in beat...so, in beat or out of beat would result in same amplitude ? Am I correct?

#### bruce linde

NAWCC Member
Donor
is it possible the chains move, or turn to present a different angle/perspective?

do you hear any changes at all in the ticking over time?

since that's less than a 1/4"... is there a correlation between the amplitude and if the minute hand is coming down the right side of the dial or heading up the left side?

NEW65

#### shutterbug

##### Moderator
Staff member
NAWCC Member
With weight driven clocks you should see little change over time. If you have new bushings, it just might need a little time to adjust.

NEW65

#### R. Croswell

##### Registered User
When the clock is about to strike/chime the process of unlocking and initiating the "warning run" the time train is called on to provide the power to unlock. If the pendulum amplitude drop always happens at the same time before the hour, and every hour, that could be a factor. What kind of movement is this, and how much total pendulum swing does it have? Can we see a video of this movement running?

RC

NEW65

#### Bruce Alexander

NAWCC Brass Member
NEW,

We're talking about 0.2" across a total of what amplitude?

RC's suggestion sounds to be the most likely although, upon re-reading your post, I notice that you said nothing is striking....

I wonder if variations in atmospheric pressure might also have a slight effect on amplitude. We know it can have an affect on rate. I don't know.

I'll normally place a Yardstick behind a pendulum (for a Tall Case) and try to make sure that my point of view is always the same to avoid parallax reading errors.

Regards,

Bruce

NEW65

#### NEW65

##### Registered User
Thanks everyone for your thoughts. The amplitude may vary a little more than 5mm. I'll do what you say Bruce and put a measure at the rear of the disc and ensure I stand in same position every time I view the pendulum. The chains have helped me gauge the swing and definitely there has been days when the amplitude has been greater than other days. I will check what RC has mentioned just to see if the amplitude lessens at a time when the long lever is being lifted. I can see how a loss in power in the time train can slightly lessen the amplitude of the pendulum. I guess if you want a mechanical clock and excellent time keeping, its best to forget the chime and/or strike, and buy a regulator!
Shutt - that had crossed my mind too. I also thought that maybe the verge pivot holes needed opening a fraction as they have been bushed too. IF the amplitude begins to remain consistent over the next few days I will just leave things as is. I have seen changes in amplitude on a few clocks over the years and I am beginning to think RC may have solved the mystery or not so much of a mystery now its been explained. I will measure the amplitude and report back and probably add the video as requested.
One thing for sure though - a changing amplitude no matter how small ( for whatever reason), will affect time keeping.

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#### kinsler33

##### Registered User
Thanks everyone for your thoughts. The amplitude may vary a little more than 5mm. I'll do what you say Bruce and put a measure at the rear of the disc and ensure I stand in same position every time I view the pendulum. The chains have helped me gauge the swing and definitely there has been days when the amplitude has been greater than other days. I will check what RC has mentioned just to see if the amplitude lessens at a time when the long lever is being lifted. I can see how a loss in power in the time train can slightly lessen the amplitude of the pendulum. I guess if you want a mechanical clock and excellent time keeping, its best to forget the chime and/or strike, and buy a regulator!
Shutt - that had crossed my mind too. I also thought that maybe the verge pivot holes needed opening a fraction as they have been bushed too. IF the amplitude begins to remain consistent over the next few days I will just leave things as is. I have seen changes in amplitude on a few clocks over the years and I am beginning to think RC may have solved the mystery or not so much of a mystery now its been explained. I will measure the amplitude and report back and probably add the video as requested.
One thing for sure though - a changing amplitude no matter how small ( for whatever reason), will affect time keeping.
Couple of thoughts: (1) Does the 'threaded rod' you mentioned in the first post have a pendulum bob on it? If not, it should, because a light or non-existent pendulum can't give an accurate indication of a clock's performance.

(2) The presence of a strike and chime train doesn't affect the accuracy of a clock, at least not much.

(3) A properly-designed pendulum swings at precisely the same rate regardless of its amplitude, which is why we use a pendulum for a 'time base.' It's been shown that at small amplitudes a 'practical' pendulum approximates an 'ideal' pendulum, which is one that describes a parabolic instead of a circular path as it swings.

I'm generally happy if a long pendulum (e.g., German grandfather clock) has a 7 cm total swing, but many clocks have a far smaller swing than that by design.

Mark Kinsler

#### NEW65

##### Registered User
Thanks Mark - I have only just seen this post! Yes it has a bob.
I always thought amplitude was the distance the bob travelled but amplitude is also the angle from equilibrium position.. as below:

#### John MacArthur

NAWCC Member
Amplitude of the pendulum is the total swing angle from end to end, not from center. If this is a weight driven clock, it will likely lose a little amplitude when the weights are slightly below the level of the pendulum bob (i.e. where their cables are nearly the same length as the pendulum), due to absorbing a tiny bit of its energy due to parasitism.
Johnny

#### John MacArthur

NAWCC Member
Upon looking at various definitions, I see that many show the amplitude as being only half the swing. This may be related to electronic theory - it doesn't have much to do with the actual behavior of a pendulum except in mathematical analysis. Semantics and pendulum construction are quite different beasts.
Johnny

#### Ralph

NAWCC Member
Another thought, if your clock is not isochronous and is affected by weight, as the weight descends, the chain weight adds to the total weight and might affect the amplitude.

Ralph

#### kinsler33

##### Registered User
---
i
Upon looking at various definitions, I see that many show the amplitude as being only half the swing. This may be related to electronic theory - it doesn't have much to do with the actual behavior of a pendulum except in mathematical analysis. Semantics and pendulum construction are quite different beasts.
Johnny
Yep. In math, physics, electric power engineering, and electronics, amplitude is the excursion of an oscillator from the neutral to one extreme or the other. In some electronics repair and clock repair, it is the distance between the extremes. The latter is easier to see and measure, but is problematic in physics because the peaks occur at different times.

M Kinsler

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