[time-nuts] Three subjects, one selected.
swbenn at gmail.com
Thu Jan 5 11:37:15 EST 2006
I remember this article. A pendulum clock was made more accurate by "
harmonic locking " the pendulum to a crystal oscillator.
A small magnet was attached to the pendulum and fitted to pass
through a solenoid at one end of the pendulum's swing. The solenoid
was driven with a signal that was a harmonic of the pendulum's
frequency. If the pendulum arrived a little out of phase with the
signal driving the solenoid, it was given a small kick. If the
pendulum was in phase, no net kick was given. It's a simple and
somewhat effective method of locking two oscillators together.
Unfortunately it can be a bit fussy to set up.
In high school my Physics instructor had a setup with two pendulums
suspended from a common beam. If the pendulums where started up with a
small difference in phase, they would soon be swinging together.
Pendulums who's frequency was related harmonically could also be "
locked". This was a grand time sink and no doubt influenced my
interest in oscillators and PLL circuits.. The amount of energy
transferred was small but over time it would be enough to lock up the
two pendulums. Ah, the power of integration.
I have never built a harmonically locked pendulum but I have used
harmonically locked oscillators a number of times with mixed results.
It can provide dead simple circuits but one often finds ones self in a
corner fighting the lock in range of the system, feed through of the
reference signal and all the usual trade offs found in PLL systems.
That said, I would love to give it a hack someday. Perhaps a pendulum
locked to a GPS 1PPS signal driving a nixie display........
There are also a number of " perpetual motion" toys on the market,
they are in the form of a pendulum of some sort passing over a plastic
base with a battery and circuitry concealed inside. As the magnet in
the pendulum passes over the circuit's coil, it begins to oscillate
and the pendulum is given a small kick as it passes by. Cheap fun,
usually no more than one transistor a coil and a couple of passives.
Teasing one apart on the bench can provide a pleasant afternoon's
distraction when you just can't make your self do anything useful.
Search Amazon for "the amateur scientist" there is an article
collection available on CD ROM and there was a dead tree collection
printed. Great time sink, great gift for the geeky kid in the family.
Date: Wed, 04 Jan 2006 23:11:07 -0800
From: Hal Murray <hmurray at suespammers.org>
Subject: Re: [time-nuts] Three subjects.
To: Discussion of precise time and frequency measurement
<time-nuts at febo.com>
Message-ID: <20060105071108.28A23BDE1 at ip-64-139-1-69.sjc.megapath.net>
Content-Type: text/plain; charset=us-ascii
I think we had one like that back in grade school. That was a long time ago.
There was an article in Scientific American 20 or 30 years ago. The idea was
to make an old grandfather clock keep very good time by adding a magnet to
the pendulum so you could gently push/pull it.
Anybody remember that one? Anybody build one?
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