RTC accuracy

natsnats
Posts: 1
Joined: Fri Aug 11, 2017 3:41 pm

RTC accuracy

Postby natsnats » Thu Nov 23, 2017 11:37 pm

Using the sntp example from

https://github.com/espressif/esp-idf/tr ... /sntp/main

While in deepsleep, the RTC time is wrong by 76 seconds after 3.5 hours. Is this the best that can be expected?

ESP_igrr
Posts: 870
Joined: Tue Dec 01, 2015 8:37 am

Re: RTC accuracy

Postby ESP_igrr » Fri Nov 24, 2017 1:15 am

Internal RTC clock frequency error is about 5%. With external 32k XTAL the error will be determined by the XTAL, usually about 20-30ppm.

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Gfast2
Posts: 107
Joined: Fri Aug 11, 2017 1:52 am

Re: RTC accuracy

Postby Gfast2 » Fri Nov 24, 2017 3:47 pm

ESP_igrr wrote:Internal RTC clock frequency error is about 5%. With external 32k XTAL the error will be determined by the XTAL, usually about 20-30ppm.

Hi ESP_igrr,

Cool stuff!

https://www.dataq.com/blog/data-logger/whats-all-this-ppm-stuff/ :o

The de facto standard in the industry for crystal inaccuracy is 20 PPM

You can also express PPM as a percentage: ±20/1,000,000 = ±0.002%. So after 30 days (2,592,000 seconds) we can expect the clock to drift about ±52 seconds; after 60 days about ±104 seconds, and so on.


Cheers

Gfast2

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