The following table lists problem situations and their remedies related to GNSS time synchronization.
If the problem you have is not listed, you have a problem related to other time synchronization methods, or if the proposed solution does not fix the problem, contact Vaisala technical support.
| Problem | Possible cause | Action |
|---|---|---|
| GNSS time synchronization is not working. | GNSS signal is lost. | Make sure that GNSS receiver has a clear view of the sky. |
| It may take up to 15 minutes before GNSS time synchronization begins adjusting the system clock. | Wait long enough after setting up GNSS time synchronization. | |
| High CPU load. | GNSS device sends data too quickly. |
Adjust the receiver settings to limit the transmission rate. Alternatively, modify the application with Kaiku Designer and increase the Nominal transmit interval of the gnss_device component to make the software‑based rate limiting more efficient. |
| I do not know if the GNSS time synchronization is functioning or not. | If the system clock is already accurate when setting up GNSS time synchronization, no changes between system clock and GNSS time will be visible. |
Modify the application with Kaiku Designer and add the GNSS component to the Web UI's Measurements view to quickly verify whether the receiver is active and receiving a signal. |
| GNSS component shows an error state in the Web UI's Measurements view. | GNSS device does not see any satellites | Make sure that the GNSS device can acquire satellite fix. Check the antenna and antenna cabling, if any. Try connecting the GNSS device to a computer or other such device to make sure that it is sending the expected NMEA messages (at least RMC message, for example GPRMC for GPS, is required). |
| GNSS device is not connected to DMU801 | Make sure that the GNSS device is powered up and properly connected to the correct serial port of DMU801. If the problem persists, try with another device and/or cable set. | |
| GNSS device is not properly configured | Make sure that the GNSS device is sending at least the NMEA RMC message with a send interval that is not equal or less than the nominal transmit interval configured for DMU801. Check that the typical NMEA serial port settings are being used, for example 4800‑N‑8‑1. The method to configure GNSS device is manufacturer- and model-specific. For further instructions, see manufacturer documentation. | |
| GNSS device is not sending messages often enough | Make sure that the send interval in the GNSS device and nominal transmit interval in the DMU801 match. |
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