Manually Setting The Time - Spectracom PRISMA VelaSync User Manual

3.2 System Time
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 ref-
erences (like GNSS) provide the timescale offset to the system. In the event that the input ref-
erence 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.
Output timescales
Some of the available VelaSync 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 out-
puts 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 VelaSync 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).
3.2.1.3 Manually Setting the Time
For some applications, it may not be necessary to synchronize VelaSync to a UTC-based ref-
erence. Or, a GPS reference is not available yet (e.g., because the antenna is not yet installed),
but the system has to be setup and tested.
In such cases, the System Time can be hand-set, and then used as a User [x] -set System Time. For
more information on when to use this functionality, see "The "User/User" Reference" on
page 108.
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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 appro-
priately. Otherwise, a System Time error may occur!
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