By Robert James Matthys
The Shortt clock, made within the 1920's is the main well-known actual clock pendulum ever identified, having an accuracy of 1 moment according to 12 months while stored at approximately consistent temperature. just about all of a pendulum clock's accuracy is living in its pendulum. If the pendulum is exact, the clock could be actual. during this e-book, the writer describes many clinical facets of pendulum layout and operation merely with experimental information, and little arithmetic. it's been written, the entire diverse components and points of the pendulum in nice element, bankruptcy via bankruptcy, reflecting the measure of consciousness beneficial for creating a pendulum run thoroughly. the themes coated contain the dimensional balance of other pendulum fabrics, sturdy and negative suspension spring designs, the layout of mechanical joints and clamps, impact of quartz on accuracy, temperature reimbursement, air drag of alternative bob shapes and making s sinusoidal electromagnetic force. One entire bankruptcy is dedicated to uncomplicated methods of enhancing the accuracy of normal inexpensive pendulum clocks, that have a special building to the costlier designs of considerably well-made ones. This booklet will turn out valuable to somebody who desires to understand how to make a extra exact pendulum or pendulum clock.
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652] and then hedges by saying the optimum method depends on the oscillator’s noise characteristics. 01 1 2 5 10 20 50 100 200 500 Time interval (days) actual measured time error of the clock over an 18-month period . Curve B shows the leveled time error with the average slope of curve A removed. 4. 3. 3. 3, all to the same scale, for easy comparison. 3) both cover 18 months. 6 months, because of the statistical need for a minimum of five samples to obtain a reasonably accurate Allan variance.
5 days to make sure the pendulum is stabilized at the higher temperature. Removing the electric blankets and the front side of the clock case then provides a Ϫ17 ЊC step down in temperature to the pendulum inside which has a 2 s period. The pendulum’s time error response to the step input of temperature is monitored by recording over a 12–16 h interval the time difference between the pendulum’s ends-of-swing and WWV, the radio time standard in the United States. A moving magnet on the pendulum and a fixed coil on the clock case give a polarity-reversing voltage null at each end of the pendulum swing that accurately defines (electrically) the two ends of the pendulum’s swing.
0. 5). 5) at the 3–6-month interval, because of the frequent appearance of a step change in clock rate (frequency) at about that interval of time. 4 because the plot ends at 3 months. What does the Allan variance give us? It gives us two things: (1) a normalized curve representing a clock’s random variation in frequency and time over a range of time intervals, and (2) the slope of the curve describes what type of modulation is represented by the clock’s variance over different time intervals. But knowing what modulation type that a clock’s variance represents is useless information to the clockmaker.