Timescales - Spectracom PRISMA VelaSync User Manual

4.
5.
3.2.1.2 Timescales
The System Time can be configured to operate in one of several timescales , such as UTC, GPS
and TAI
standards, and are offset from each other by varying numbers of seconds.
When configuring VelaSync, in most cases, UTC will be the desired timescale to select.
VelaSync's System timescale is configured via the MANAGEMENT > OTHER: Time Management
screen, see "System Time" on the previous page.
Input timescales
Some of the inputs may not necessarily provide time to VelaSync in the same timescale selected
in the System Time's timescale field. These inputs have internal conversions that allow the times-
cale 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 VelaSync with "local" time, with no time jumps occurring when
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TAI : International Atomic Time (Temps Atomique International).
The TAI time scale is based on the SI second and is not adjusted for leap
seconds. As of October 2017, TAI is ahead of UTC by 36 seconds. TAI is
always ahead of GPS by 19 seconds.
GPS : The Global Positioning System time is the timescale maintained by the
GPS satellites.
Global Positioning System time is the time scale maintained by the GPS
satellites. The time signal is provided by atomic clocks in the GPS ground
control stations. The UTC–GPS offset as of October 2017 is 17 seconds.
For more information on Timescales, see "Timescales" below.
If you want to override the system time with a manually set User Time , check the Manual
Time Set checkbox. For information, see "Manually Setting the Time" on the next page.
Click Submit to update the System Time and close the window.
(Temps Atomique International)
Note: UTC timescale is also referred to as "ZULU" time. GPS timescale is the raw
GPS time as transmitted by the GNSS satellites (in 2018 the GPS time is currently
18 seconds ahead of UTC time. UTC timescale observes leap seconds while GPS
timescale does not).
The timescale also does not observe leap seconds. The TAI timescale is
Note: TAI
fixed to always be 19 seconds ahead of GPS time. As of January, 2017 TAI time
is 37 seconds ahead of UTC.
. These timescales are based on international time
3.2 System Time
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