◆ What are the causes for watches showing inaccurate time? What is the normal range of time error (discrepancy between the time shown and the actual time)?
A: Mechanical watches: Time accuracy of the watch differs according to the type of watch movement. The normal range for international standard mechanical watches is within ± 30 seconds / day; some movements with a higher degree of precision, such as chronograph watches, the range can be -4 + 6 seconds / day. The following are major reasons for mechanical watches to show time errors and inaccurate time:
(1) Insufficient motion power: You need to check first whether motion power is adequate. If the amount of activity for an automatic mechanical watch is too little, this may result in insufficient power storage. Power can be replenished by manual winding. After winding, observe whether the speed is too slow or too fast.
(2) Magnetisation: If the balance spring in the watch is magnetised, or the swing cycle of the rotor is interfered with by a magnetic force, the time shown on the watch will not be accurate. In most cases the mechanical watch will go very fast, but in others cases, the watch stops running. Computers, microwave ovens, audio systems, magnetic buckles, electric mah-jong machines, card readers for car park access and so on, are examples of places where it is easy for your watch to get magnetised. It is normal for watches to be magnetised and degaussing is very simple. Maintenance technicians will degauss by using a professional degaussing machine. After adjusting to the right time, observe the watch for a certain period. If the time shown is normal, then the problem is solved.
(3) Impacts and vibrations: Parts are packed very closely inside any watch movement. If you wear a watch while you are playing sport, or if you subject your watch to soft impacts by casually tossing it on the bed or a sofa, or your watch receives an impact or hit, the vibration period of the rotor may be affected, damaging the axle hub dowel or gossamer, or causing lateral displacement, deformation, or hanging of the balance wheel, or causing other internal parts to come loose and become damaged. All these will lead to problems with timekeeping.
(4) Constantly spinning and shaking the watch: constantly spinning and shaking the watch in effect applies an external force to the watch, especially when the watch is in place on a level surface. The resulting swing amplitude of the rotor will become bigger and bigger, ultimately causing a collision swing. Collision swing is when the rotor swings with great amplitude and the impact needle hits the outer side of the anchor escapement. The result is a greatly shortened oscillation cycle of the rotor, which is accompanied by the second hand making a rapid sound like horses galloping. The second hand runs visibly faster, resulting in increased error.
(5) The effect of the regulator on a balance spring: the regulator serves to facilitate the calibration of timekeeping accuracy, but because there is a gap between the regulator and the balance spring, the existence of this gap undermines the precision timing of mechanical watches and increases their position.
(6) The effect of position change: this is the so-called position error of a watch. Before a watch leaves the factory, tests are done at three temperatures and at five positions. The five positions are: on the surface (dial facing up), below the surface (dial facing down), below the crown (below the 3:00 position), left of the crown (below the 12:00 position) and above the crown (below the 9:00 position). Only the right of the crown position (below the 6:00 position) is not commonly used (unless you wear the watch on the palm or on your right wrist). Statistics show most people, in a single day, wear their watch about 35% of the time at a “surface” location, 30% to the “left of the crown” position, 25% at the “below the crown” position, and 10% elsewhere. Therefore, a position change results in an increase in surface friction on the rotor axle tenon, as well as the gravity role of the balance spring. Both will enable the escapement speed regulation system in each location to be affected by the size of the impact of different oscillation cycles.
(7) Amplitude effect: spring tightness, torque transmission will directly affect the size of the rotor amplitude, and therefore also affect the precision timing of mechanical watches.
(8) Temperature changes: a change in temperature will induce a change in the physical size of the rotor and the balance wheel, directly affecting the oscillation cycle. Temperature will also change the viscosity of the lubricant oil, in turn inducing a change in torque transmission and swinging in the wheel system in the movement, leading to time errors.
(9) Maintenance required: a lack of lubricant oil in the movement, or the wear and tear of aging internal parts, can cause time errors. Maintenance in the form of removing the lubricant oil is needed.
(10) Mechanical malfunctioning of the watch: Common situations include missing hands, transmission system malfunction, first wheel malfunction, partial two-wheel malfunction, transmission gear disengagement, if the teeth on the transmission gear are worn away, or there is only shallow engagement of teeth, or the gear is not round in shape, or the gear, the tip or teeth are damaged and so on … these situations may result in periodic faster rotations.
(11) Other factors: Mainly because the case cover on a mechanical watch is not sealed tight, changes in moisture and changes in atmospheric pressure will affect time accuracy, and also allow small dust particles and foreign matter to enter the watch, affecting the operation of the parts of the mechanical watch.
Quartz watches: Generally speaking, quartz watches are more accurate. The normal range for international standard watches is within ± 15 seconds / month. Reasons for quartz watches not showing the accurate time include:
(1) Battery is running out: If the quartz watch suddenly runs slow, it could be caused by the battery being nearly used up; or if the second hand jumps every four seconds, it is a sign that the battery needs to be replaced.
(2) Magnetisation: If the watch is subjected to magnetic interference from a magnetic field, the time shown will be inaccurate, and in most cases the hands will go fast. Computers, microwave ovens, audio systems, magnetic buckles, electric mah-jong machines, card readers for car park access, etc. are examples of instanes where it is easy for your watch to get magnetised. As long as the quartz watch leaves the magnetic field, it can effectively self-demagnetise. However, the time error caused by the magnetic field cannot automatically be corrected and requires manual adjustment to the correct time.
(3) Temperature changes: The environment in which the watch is used has an important impact on the time it displays. Quartz watches are less susceptible to changes in the environment than mechanical watches, but are still affected by them. If the environment in which the watch is used is too cold or too hot, the time error will greatly exceed the normal error range.
(4) Changes in component parameters: If time errors caused by quartz resonator parameters, circuit parameters and capacitance changes are significant, adjust the fixed capacitance and then fine-tune the capacitance.
(5) Problems with the quality of the quartz resonator: If there are problems with the quality of the quartz resonator, the watch will run slower than normal.
(6) Damaged integrated circuit board: If a fault occurs in the divider circuit, the output signal frequency is either greater than or smaller than the normal value by many multiples, and the time will be faster or slower by multiples.
(7) Other failures: The watch runs slow because the rotor and the rotating shaft have skidded; if the centre wheel and the centre gear shaft have skidded the same will occur.