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Pendulum Clock with Atomic Precision
u19925 writes "Now you can get atomic clock precision out of your grandma pendulum clocks. Here is how it works: There is a camcorder fitted inside the clock which monitors the pendulum swing. It has an atomic clock signal receiver. It compares the pendulum swings with the atomic signal hearbeat. The camcorder also has an arm. If the pendulum clock drifts, then it uses its arm to push or pull the pendulum to make correction." It's not an April Fool's joke, but it is rather impractical.
heres a revised version of the article:
Now you can get atomic clock precision out of your grandma pendulum clocks. Here is how it works: There is a camcorder fitted inside the clock which monitors the pendulum swing. It has an atomic clock signal receiver. It compares the pendulum swings with the atomic signal hearbeat. The camcorder also has an arm. If the pendulum clock drifts, then it uses its arm to push or pull the pendulum to make correction. " It's not an April Fool's joke, but it is rather impractical.
Well, it may not be what they meant, but a pendulum atomic clock is impractical simply because many of the experiments that require atomic precision, would have an adverse effect on a pendulum...
. ht ml
Here is a good link with examples of why pendulum (gravity) based systems wouldn't be too practical.
http://media4.physics.indiana.edu/~kostelec/mov
Doesn't anyone read the friggin articles?
Nowhere in the article are the words 'camcorder', 'grandma', 'arm', etc.
It wasn't designed to fit into a grandmother clock and it certainly doesn't use a camcorder. It uses an infared sensor to sense pendulum location and a 'piston' to modify pendulum swing, and it is being used to automate maintenance on large clocks in churches, etc. It can also set the clock ahead and back an hour for daylight savings time.
Gotta be the worst case of can't be bothered to RTFA I've ever seen.
Now, anyone who thinks it would be better to replace the clocks in Big Ben with some modern electronic thing... well... probably ought to be shot. This doesn't seem like a bad way to get those big clocks to operate a good long time without human intervention.
I feel that some informed comments are required for this topic. I am a clockmaker, yes I work on 200 year old clocks all the time; and I have to say that this is a really neat merging of modern and antique technology.
The clocks that are being regulated are tower clocks, they are observed by hundreds if not thousands of people a day. It would be nice to know that they are on time. It would also be a crime to rip out the old pendulum movement and replace them with an electric movement. Another feature is that the old antique system can run for several days in the event of a power failure, it just won't be quite as accurate.
The movements in these clocks are heavy cast iron units with large gears and very heavy pendulums. Using a magnet system to attempt to influence the timing rate would probably prove ineffective. However using some sort of system to raise or lower the pendulum by just a couple of millimeters will affect the timing rate by several seconds a day.
These clocks used to be wound once a week by hand and the time would have been reset at that time. These days most of these clocks have been converted to an automatic winding system, thus they see much less hands on maintenance, automatic systems for regulating the clock become much more attractive.
As a side note, the tower clock in London, commonly known as "Big Ben" ("Big Ben" is really the name of the bell that is used to count the hours) is regulated by adding or removing one or two old English Pennies, the one that were about the size of an old American Silver Dollar. The clock is regulated to be as on time as possible on the Queens Birthday and on New Years Eve.
Going even further afield some of you might get a kick out of the elaborate astronomical clocks that were designed in the 1800's. These were astonishing pieces of engineering that have been known to take an astronomer to figure out all of the settings required to set the clock.
I guess my passion for my vocation is showing, I hope that I was able to add something of interest.
Chronos
Ah you cry, but the time taken by a pendulum does not depend on the weight, well yes but the pennies slightly raise the center of gravity of the bob you see...
Slightly off-topic, but interesting none the less: a normal pendulum does not take the same time to reach the bottom no matter where it is released, contrary to popular belief. The correct curve is actually an inverted cycloid, and the finding of this curve was deemed the 'tautochrone problem.' Obligatory mathworld linkage: Tautochrone Problem.
Of course, this is an example of where reality and theory conflict: constructing a clock with a tautochronic (a made up word?) pendulum wouldn't matter enough due to friction etc.; the semi-circle is just fine for pendulum based clocks. =)
This statement is false.
Camcorder - where on earth did he get that from?! Did the guy that submitted that actaully read the article he was submitting?! It doesn't mention that in the article - mainly because it would be a stupid idea. That's maxiumum overkill if I've ever heard of it. That would be like using a camcorder to 'look' and see if the fridge door is shut!
And why use a piston to change the swing? What's wrong with an electromagnet which wouldn't need to actually touch the pendlum?
Nick...
Consider where I work - we have a very accurate 10 MHz reference to sync all our RF gear to. We need that ref to be tracable to the National Bureau of Standards. Now, it would be somewhat impractical to check with the Bureau 10 million times a second (anybody want to run a fiber from Boulder to Wichita just for the time sync?).
Before I go on, let me point out the difference between precision, accuracy, and repeatability.
From a metrological standpoint, having more accuracy than repeatability is useless. Having more precision than accuracy is also useless. (Ignoring tricks like averaging for the moment.)
Back to the example. What we do is to have a very high precision and stable oscillator (we used to use a rubidium standard). It has a long term stability of about 10E-9 and a short term stability of 10E-12. In other words, over a short period of time the thing will drift not more than one part per trillion, and over the long term (days) it will drift about one part per billion.
Now, that is running next to a GPS receiver that gives us a time tick synced to the Bureau. Every second the GPS time is compared to the local time standard, and an error value is computed. That error value is averaged over a long period of time, and used to gently tweak the rubidium standard. Thus, over the long run the drift is reduced to level of the cesium clocks, about 10E-13.
So we have atomic clock accuracy but rubidium clock precision and repeatability.
Now, if you used the same sort of technique on a pendulum clock - measure the error between the clock and the GPS, average, filter, and apply - you would have atomic clock accuracy with pendulum clock precision. Granted, I would not want to use the clock's time for reporting astronomic phenomena where the precision must be very high, but for normal use this would be quite good enough.
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