Frequency Deviation of Crystal Oscillator Leads to Inaccurate Time of Electronic Clock/Clock Crystal

Electronic clocks/clock crystal used for timing the key electronic components for the quartz crystal oscillator, the nominal frequency of 32.768KHz. With the aging of the quartz crystal oscillator, its frequency will be with the Q quality factor down and drift phenomenon. In the actual circuit application of the clock crystal 32.768KHz, the capacity of the external capacitor can be fine-tuned or rely on the CMOS integrated circuit in the logic frequency adjustment method to actively compensate for the purpose of adjusting the time day difference.

External Capacitor Adjustment Method

If the electrical capacity increases, the time slows down; if the electrical capacity decreases, the time speeds up. Electronic clock / quartz clock crystal selected by the quartz crystal oscillator frequency deviation (adjustment frequency deviation) should be ≤ 10PPM. If the crystal oscillator frequency deviation itself exceeds the specification requirements. In other words, the use of the above approach is still unable to meet the time day difference specification, it is recommended to use qualified quartz crystal oscillator to replace the existing crystal oscillator, fundamentally eliminate the problem of inaccurate time.

Clock Crystal oscillator 32.768KHz frequency accuracy and the amount of time error variation

±10PPM:

The frequency deviation : 32.736KHz~32.800KHz

The time error :0.864×1=0.864 seconds per day

The total time deviation : 5.256 minutes per year

±20PPM:

The frequency deviation : 32.703KHz~32.833KHz

The time error : 0.864×2=1.728 seconds per day

The total time deviation: 10.512 minutes per year.

±30PPM:

The frequency deviations: 32.670KHz~32.866KHz

The time error: 0.864×3=2.592 seconds per day

The total time deviation : 15.768 minutes per year

If the clock crystal oscillator 32.768KHz accuracy is ±10PPM, the time of day error calculation formula is as follows：

10 (PPM) x 24 (1 day = 24 hours) x 60 (1 hour = 60 minutes) x 60 (1 minute = 60 seconds) = 864,000 * 1/100,000 = 0.864 seconds

The time error of this RTC crystal is no more than 0.864 seconds per day. If it is +10PPM, it is at most 0.864 seconds faster per day; if it is -10PPM, it is at most 0.864 seconds slower per day.