Sweep or continuous second hand on a watch means this
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March 26, 2008
What does a "Sweep" action watch or second hand on a watch or clock really mean? Well most people think of sweep as a continuous movement. There is really no continuous moving second hand on clocks or watches. Being based on some sort of regular timing or oscillation, even AC motor driven clocks have a movement that is not continuous. The AC motor clock has a 60 hertz sine wave it runs on and will slow at the crossing of the sine wave at 0 volts. Due to momentum the human eye can not detect this slow and fast movement. On watches most are now based on a quartz timed stepper motor. The quartz circuit gives the stepper motor one kick every second and you will see the second hand move once each second. On quartz watches with no second hand or dual digital analog watches such as the T-Touch by Tissot and Hamilton, the minute hand will move a bit every three to twenty seconds (a number that evenly devides into 60). So what is being called continuous is usually a mechanical (wind up) movement in makes such as Rolex and Omega and many others. These too are not really continuous. A mechanical wind up, whether manual wind or automatic wrist movement wind up are really pulsing 5 to 7 times a second. They look almost continuous but are not. They are rated in beats per minute and are not continuous. I am not familiar with a true continuous watch movement as of yet. But there are some premium quartz clock movements that could be. It goes back to the stepper motor and if they pulse faster than once a second and look continuous or are really running at a high motor speed like the old AC clocks and spin at an almost constant rate. You have to look at the specifications and see if they use an oscillator and stepper motor and are pulsing fast or if they use a fly wheel on a motor. Only a DC motor can approximate a continuous action but would be hard to make accurate. An AC motor clock runs at the line frequency of the AC power, in the USA, South America and Canada that is 60 times a second and in Europe that is 50 times a second. Because the AC line frequency has to be exact (to prevent generators fighting each other which would cause a power outage) an AC clock motor is synced to the power grid and is always adjusted to be accurate. So if you want a watch that looks like a continuous movement second hand go for one that has a high beat rate, but be aware that the faster a beat rate the faster the wear too. A quartz movement running at 1 pulse a second can last indefinitely. Usually the quartz circuit, motor coil or more likely the capacitor dries out long before the mechanical components wear out. Also be aware that mechanical movements need to be cleaned and oiled every 5 years if used every day. At least that is what Rolex states and at $500 for each average servicing that can add up.
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