The System Time can be configured to operate in one of several timescales, such as UTC, GPS and TAI (Temps Atomique International). These timescales are based on international time standards, and are offset from each other by varying numbers of seconds.
When configuring VersaSync, in most cases, UTC will be the desired timescale to select.
Note: UTC timescale is also referred to as “ZULU” time. GPS timescale is the raw GPS time as transmitted by the GNSS satellites (in 2017 the GPS time is currently 18 seconds ahead of UTC time. UTC timescale observes leap seconds while GPS timescale does not).
Note: The TAI timescale also does not observe leap seconds. The TAI timescale is fixed to always be 19 seconds ahead of GPS time. As of January, 2017 TAI time is 37 seconds ahead of UTC.
VersaSync's System timescale is configured via the MANAGEMENT > OTHER: Time Management screen, see System Time.
Some of the inputs may not necessarily provide time to VersaSync in the same timescale selected in the System Time’s timescale field. These inputs have internal conversions that allow the timescale for the inputs to also be independently defined, so that they don’t have to be provided in the same timescale. For example, the System timescale can be configured as “UTC”, but the IRIG input data stream can provide VersaSync with “local” time, with no time jumps occurring when the reference is selected.
If an output reference is using the GPS or TAI timescale, and the System Time is set to “UTC”, then the GPS Offset box in the Edit GPS Offset window must be populated with the proper timescale offset value in order for the time on the output reference to be correct. Some references (like GNSS) provide the timescale offset to the system. In the event that the input reference being used does not provide this information, it must be set in through the Offsets panel of the Time Management page.
Since the GPS and TAI offsets have a fixed relationship, only the GPS offset can be set. If only the TAI offset is known, subtract 19 from it to get the GPS offset.
Note: If the System Time is set to the UTC timescale, and all output references either use the UTC or “local” timescale, then it is not necessary to set the GPS and TAI timescale Offsets.
Caution: It is imperative to configure any input reference’s timescales appropriately. Otherwise, a System Time error may occur!
Some of the available VersaSync outputs (such as the ASCII data module’s outputs, etc.) won’t necessarily output in the same timescale selected in the System Time’s timescale field. These outputs have internal conversions that allow the timescale for the outputs to also be independently defined, so that they don’t have to be provided in the same timescale.
Other VersaSync outputs will be provided in the same timescale that is selected in the System timescale field. The NTP output for network synchronization and the time stamps included in all log entries will be in the same timescale as the configured System timescale. For example, if “GPS” is selected as the System timescale, the log entries and the time distributed to the network will all be in GPS time (time broadcasted directly from the GNSS constellation).