Timing

In the Sixaola, data packet time stamps are defined by either GPS or NTP. Either will suit the needs of earthquake monitoring institutions like yours.

Note

OSOP recommends using NTP mode.

Related Topics

• Why does seedlink.log sometimes show a gap after startup?

How it works

NTP

When no GPS lock ever exists, time stamping is done with NTP time.

In the web-interface and blueconf command-line driven program, NTP servers are configured under “Networking”.

The end user is able to configure as many as 5 NTP servers. Additional NTP servers are hard-coded to ensure NTP functionality and to guarantee that the system can always tell time. These fixed DNS servers include 3.ubuntu.pool.ntp.org and ntp.ubuntu.com. We recommend configuring a minimum of 3 NTP servers, the last 2 are optional.

Note

Blinking Red LED: No GPS/ NTP timing, No data

Note

NTP is not run on port 123 but on 1025-65535 as: iptables -t nat -A POSTROUTING -p udp –sport 123 -j MASQUERADE –to-ports 1025-65535

GPS

When a GPS antenna is connected and there is lock, time stamping is done using GPS time. In GPS mode, the GPS clock is connected to the STM32 processor. The firmware checks the drift that happens between GPS and the STM32 clock. Drift is accounted for in real-time, all the time, where the clocks remain forever in sync.

Warning

The Sixaola3’s Linx GPS module requires a minimum of 4 satellites to perform properly (4 satellites are required to attain PPS lock) and looks at only USA-hosted satellites. Therefore, OSOP recommends installing the GPS antenna with a full view of the sky. Affixing the antenna to the window or placing it on the side of the building may result in timing issues. Similarly, Sixaola4’s uBlox GPS module requires 3 satellites. The uBlox does, however, look at more than just USA GPS constellations. It also looks at GLONASS and QZSS.

Warning

When testing multiple Sixaolas, OSOP recommends placing the antennas at least 1 meter apart from one another to avoid RF interference.

Note

Solid Red LED: GPS not in lock

Blinking Red LED: No GPS/ NTP timing, No data

Timing Quality

At startup,

GPS is to the msec accurate.

NTP is accurate to within 2 sample intervals.

NTP timing quality remains within 1 sample of accuracy versus startup accuracy. This means:

+/- 10 ms @ 100 sps

For a P-wave velocity of 6000 m/s, this translates to location uncertainties of:

+/- 10 ms = maximum +/- 30 meters

For lower P-wave velocities, the uncertainties diminish. At all sample rates, these uncertainties are within a reasonable margin of error for locating earthquakes.