AT+QLTS to get the accurate time for PPM correction

Technical Subjects
1

Hi,

I am working on a product where I use the microcontroller’s internal RTC for time-related functionality. The crystal used for the RTC has an error of approximately ±20 ppm. However, the application does not allow a time deviation of more than 0.2 to 0.5 seconds per day.

The product includes a Quectel EG912 module, which is always attached to the device.

We have used the EG912U module with the command AT+QLTS to synchronize the internal RTC time every 5 seconds, in order to maintain accurate time for all processes. However, after some time — like 1 or 2 days — the time returned by the AT+QLTS command becomes incorrect and starts leading by approximately one second each day. This issue occurs randomly and not on every device.

My question is simple:
Can I rely on the AT+QLTS command for accurate time reference?
Also, I would like to understand why the time returned by AT+QLTS drifts forward by about one second per day, randomly.

Any help and information would be appreciated.

Regards,
JBR

2

This returns is related to the base station.It is reported by the operator cell. Maybe it is problem from the network cell around you. You can check what is the NITZ.
If you need more precise time, I suggest another GNSS module.

3

AT+QLTS Is Quectel customized AT command. AT+CCLK and AT+CTZU is 3GPP standard AT command.

4

So you are saying that “AT+QLTS” is not the right solution for time accuracy?
Also Is there any possibility for “AT+CCLK” for getting accurate time? or can I replace “AT+QLTS” with “AT+CCLK”?.

5

I mean that the NITZ cannot give you the accurate time. It might be someting wrong from the network side.