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8.3
Time acceptance
System startup:
After finishing the boot procedure, the time reception from any source usually takes 10
minutes or more. The first source available will be taken to set system time even if it
does not have priority 1.
Outputs activation:
As soon as the system time was set successfully within nanosecond accuracy to its
source, the outputs are activated.
Source changes:
Time source change decisions are either done automatically or manually, depending
on user settings.
Automatic mode:
The priority is based on deviation estimations of each source. The
source with lowest deviation has highest priority.
Manual mode:
Uses the user defined source priority list.
Source failures:
The active source is permanently supervised. If it fails for more than 1 minute, DTS will
choose the next best source (e.g. from priority 1 to priority 2). Source changes happen
immediately but maximal once per 10 minutes, which prevents source hopping.
Holdover accuracy:
The specified holdover accuracy is reached after a minimum of 7 days of continuous
synchronization to an accurate source such as GNSS or PTP. The lower the source
accuracy, the longer it takes to reach high holdover accuracy. Holdover accuracy
increases over time, hence the longer synchronized the higher is the accuracy in
holdover.
Short-term time/frequency stability:
When the specified holdover accuracy is reached, a source failure of less than 1 hour
has no effect on output accuracy.
Long-term source failure (> 1 hour):
Longer source failure puts the DTS into holdover. When the holdover accuracy is
reached, a long-term source failure can be bridged with accuracy according to the built-
in oscillator.
At the moment of the resumption of the source signal, a possible time drift is adjusted
with a speed of a few ns/sec.
A correction can take up to 1 hour plus 1 hour per day of source absence.
Example: Loss of GPS during 2 days:
Duration of time correction = 1 hour + 2 x 1 hour
Total: approx. 3 hours
Variants of time synchronization:
•
Adjusting slowly (Adjust Mode = follow):
After starting the DTS, the time is set for a first time (from a source). Afterwards,
the time will only be aligned with maximum adjusting speed of a few ns / sec. if
deviating from the source.
Configuration: see chapter “6.5.10 Time adjustment / Time-keeping“
•
Adjust immediately (Adjust Mode = set):
this mode is currently not
implemented!
Manual time set:
The time is always set immediately. The stratum is set to 1.
Notice:
Manual time setting is intended to use only for testing purposes.
