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Alarm clock (clock) is a clock with an alarm device. Both can indicate the time, but also according to people's predetermined time to send sound signals or other signals. Alarm clock movement structure mainly mechanical and quartz electronic two categories.
Other types such as transistorized balance-spring type, tuning fork type has been rarely used, usually placed on the desktop alarm clock, mainly for travel use called travel alarm clock. Daily mechanical alarm clocks are generally within 120 seconds / day error, quartz electronic alarm clocks are generally within 0.2 seconds / day error.
There are many kinds of alarm clocks, mechanical, quartz, since it was invented using the principle of pendulum has become an indispensable item in people's lives.
(1) first check the appearance: the clock shell color bright and even, no paint, discoloration and scuff marks. The clock face should be clean, the scale is even, and the handwriting is clear.
(2) check the sensitivity: slightly open the clockwork, the second hand will begin to move, proving that the sensitivity is high. High sensitivity of the clock, the continuation of the time longer.
(3) check the time sound: the clock face left and right before and after the up and down placed, if the four sides of the direction of the time sound is the same, uniform and no noise, it is normal.
(4) check whether to touch the needle: toggle the hour and minute hands, so that the hour and minute hands and second hand overlap (three needle overlap), the three needles should maintain a certain gap between them, do not allow friction. At the same time, the needle and the clock face, the glass should also be appropriate clearance.
(5) check the alarm difference: respectively, the alarm face dial to 3, 6, 9, 12, and then dial the hour and minute hands to these places, such as alarm error are within 5 minutes, alarm difference is normal.
(6) check the alarm sound; alarm sound should be clear, bright, no mute, no empty sound.
(7) check the key to the needle, to the alarm key tightness: tightness should be moderate. If the key to the needle is loose, indicating that the center wheel on the spring spring force is insufficient, will produce the second hand to go while the minute hand does not go or go slow phenomenon.
If the alarm key is loose, the alarm dial face will follow the hour and minute hands. But if all too tight, it is not convenient to use.
Reference: Baidu Encyclopedia-Alarm Clock