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Add Internal GPS/Oscillator

In the standard configuration, TimeKeeper distributes the time provided by VelaSync's high-quality oscillator. The oscillator is disciplined by the GPS time. When no GPS is available e.g., because the signal is lost temporarily, the oscillator will transition into Holdover mode (by default, for 7200 seconds [2 hours]), before TimeKeeper starts using other previously configured timing sources e.g., a PTP server.

Configuring the "Internal GPS/Oscillator" timing source may become relevant in the following situations:

  1. If you accidentally deleted your GPS timing source (0)), and need to create a new one.
  2. To add the oscillator to the list of permitted timing sources, using it as the lowest priority source. This will allow TimeKeeper to distribute the time and 1PPS signal provided by the un-disciplined oscillator in the event that the GPS and all other configured timing sources are lost.

  3. To disable GPS steering for timing source (0), thereby allowing TimeKeeper to use the time provided by the oscillator, even if GPS is not available. In other words, the oscillator is not disciplined by any reference, i.e. it is in Freerun mode, and yet TimeKeeper is allowed to broadcast its time/1PPS signal. This may be useful for system testing (e.g., if no GPS antenna is yet installed), or for other, special use cases if the time distributed does not need to be linked to UTC.

See Configuring Timing Sources to learn how to configure these use cases.

Window "Add a new Source: Internal GPS/Oscillator"

The menu items under Internal GPS/Oscillator are:

  • TimeKeeper GPS device: [checkbox, default: checked] En-/Disable GPS input: This must be checked in order for TimeKeper to use VelaSync's GPS time. If unchecked, and Disable GPS steering checked, TimeKeeper will use the time and 1PPS signal provided by the oscillator indefinitely, even though the oscillator is at no point in time disciplined by a GPS signal.
  • Disable GPS steering: [checkbox, default: unchecked] Only check this box in conjunction with the TimeKeeper GPS device disabled, so as to allow TimeKeeper to use the time and 1PPS signal provided by the free running oscillator, i.e. in the absence of a GPS signal.
  • Sync error threshold: If the sync quality (offset) exceeds this floating point value, emit trap/syslog messages.
  • Cable delay: Bias the clock to account for cable delays or asymmetries. With a long cable run that delays signal by 1ms, use a value of 0.001. TimeKeeper will subtract this value from the incoming timing signal.
  • Holdover Limit: Determine for how long TimeKeeper is allowed to use the time and 1PPS signal provided by the free running oscillator, before TimeKeeper cross-checks time against other sources (in seconds). For more information on Holdover, see Holdover.