Re: Temperature compensating a pendulum clock?

dAz wrote:

On 13/01/12 07:23, jeff_wisnia wrote:


We have a very nice pendulum wall clock in our kitchen which has the
type of movement where a battery powered electric motor winds the spring
of a traditional type pendulum movement.

The clock keeps excellent time in the summer, but during the cold months
of our New England weather, when we let the temperature in the part of
the haouse where the clock is located drop into the 50s during the
night, the clock gains about 3 minutes a day.

I presume this is due to the pendulum shaft shortening with temperature
and I can sort of compensate for it by adjusting the bob downwards a
bit, but it's still not accurate enough to suit my taste.



what is the pendulum rod made of?

the other thing to consider is the suspension spring in cold temps will stiffen the spring and make the rate faster,



I was wondering if I could fasten one end of a strip of bimetal
scavengened from an old thermostat onto the back of the bob in such a
way that the free end moved downward as the temperature dropped and with
some trial and error tuning end up with a "temperature compensated
pendulum."


hmm I think you find will that won't make much of difference, better to improve the pendulum, if for example it's a brass rod brass/lead bob, then simply fitting a steel rod will help or a timber one, if you could get your hands on it invar would make a better rod as it won't vary much in length.


If I decide to take on the challenge (Just for Ss & Gs) I'll keep my eye open for a glass rod of the right length and shape. I know the thermal coefficient of glass is quite low. I should be able to replace most of the length of the pendulum rod with a glass rod with epoxied on metal ends, maybe then sprayed with bronze paint so it doesn't look so odd.

It's been a while since I've mucked around much with clocks, the most interesting one I did about 45 years ago had a "verge" escapement. It's still hanging on a wall in our home but don't even think about asking me how good a timekeeper it is. <G>

http://home.comcast.net/~jwisnia18/jeff/clock.html

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10e12 furlongs per fortnight.


Comments appreciated, I'd really like to keep the existing movement in
that clock rather than jump to a quartz movement.

Thanks guys,

Jeff




.

Relevant Pages

  • Re: Temperature compensating a pendulum clock?
    ... The clock keeps excellent time in the summer, ... I presume this is due to the pendulum shaft shortening with temperature ... hmm I think you find will that won't make much of difference, better to improve the pendulum, if for example it's a brass rod brass/lead bob, then simply fitting a steel rod will help or a timber one, if you could get your hands on it invar would make a better rod as it won't vary much in length. ...
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  • Temperature compensating a pendulum clock?
    ... We have a very nice pendulum wall clock in our kitchen which has the type of movement where a battery powered electric motor winds the spring of a traditional type pendulum movement. ... The clock keeps excellent time in the summer, but during the cold months of our New England weather, when we let the temperature in the part of the haouse where the clock is located drop into the 50s during the night, the clock gains about 3 minutes a day. ... I presume this is due to the pendulum shaft shortening with temperature and I can sort of compensate for it by adjusting the bob downwards a bit, but it's still not accurate enough to suit my taste. ...
    (alt.horology)
  • Re: Hybrid wall clock
    ... The clock was destroyed by a fire in 2001, but between 1957 and 2001, it ran flawlessly, and without repair or maintenance. ... The clock used a single D cell, which drove an electric motor with gearing. ... I fiddled a bit with the coupling of the escapement to the pendulum, but I guess I wasn't smart enough to figure out a way to reduce the amplitude of the pendulum swing so I took the cheater's way out and routed about 1/4" off the inside of the case on both sides, at the spots ... My clock is a little temperature sensitive and changes rate about 15 seconds a day summer/winter here in New England, where our kitchen goes down into the 50s at night during the winter and up into the low 80s on hot summer days when were at work and the AC is off. ...
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  • Re: Temperature compensating a pendulum clock?
    ... The clock keeps excellent time in the summer, ... I presume this is due to the pendulum shaft shortening with temperature ... and I can sort of compensate for it by adjusting the bob downwards a ...
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  • Re: Evidences for the ether
    ... by projecting a length onto another coordinate axis. ... IRT says that the physical length of a rod remains the same in all frames. ... frame in order to measure the rate of a moving clock, ... "Preferred" in the sense that the laws of physics ...
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