BSWA 308 - Page 50

BSWA 308/309 BSWA Technology Co., Ltd
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★Note: The RTC of sound level meter has calibrated to a reference clock with average error
2ppm (maximum error 3ppm). The time accuracy keep <10ppm (<26s within 30 days) at
room temperature. The maximum time error is approx. 5s~8s at 25℃ in internal test.
The RTC accuracy may vary by the
temperature due to no temperature
compensation. As the figure show the
typical temperature curve, the RTC
keep its basic frequency at 25 ℃ .
When the temperature increase or
decrease, RTC frequency change
according to -0.04ppm/℃
2
. Therefore,
when the temperature is 0 ℃ , the
change value of RTC is -0.04 x (0-25)
2
= -25ppm, equal to slow 2.16s daily. when the temperature is 40℃, the change value of RTC
is -0.04 x (40-25)
2
= -9ppm, equal to slow 0.78s daily.
The maximum error (<10ppm) given by user manual can be calculated as approx. 16℃
difference to reference temperature (25℃). Therefore, the RTC can keep every 30 day the
error <26s at 9℃~41℃ which can be recognized as room temperature. Notice that the real
RTC error may beyond the value shown in user manual if exceed the temperature range.