Dac; First Time Lock; Time Error And Time Threshold - Symmetricom XLi User Manual

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DAC

Status: OK or Fault
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The DAC indicator reports "OK" when the DAC that steers the XLi's internal oscillator is operating nor-
mally. The DAC indicator reports "Fault" when the DAC is operating at or near its limits. This can occur if
the oscillator is near its aging rate, has been exposed to extreme temperatures, or if the reference
source is intermittent, in error, or changes phase significantly.
If the DAC indicator reports a continuous fault, contact Symmetricom Global Customer Assistance.
This indicator can be enabled for troubleshooting oscillator, environmental, and reference source prob-
lems.

First Time Lock

Status: OK or Fault
First Time Lock reports "OK" when the clock has locked one or more times since the unit was powered
on. It reports a "Fault" if the clock has not locked once since the unit was powered on.
If this fault persists, contact Symmetricom Global Customer Assistance. While operating with a First
Time Lock fault, all outputs from the XLi are unreliable and should not be used.
This indicator can be enabled for troubleshooting to determine if the unit locks at all during an extended
testing period.

Time Error and Time Threshold

Status: OK or Fault
Time Threshold sets a limit, measured in nanoseconds, for the XLi clock's accumulated time error. While
the accumulated time error remains below the Time Threshold limit, the Time Error indicator reports
"OK". If the accumulated time error exceeds the Time Threshold limit, the Time Error indicator reports
fault.
Typically, the XLi doesn't experience Time Error faults while locked to a reference source and steering its
oscillator. When XLi comes unlocked from its reference source(s) the system clock uses the internal
oscillator to keep time. It also starts calculating an estimate of the worst case time error from the last
reference. The length of time before this condition triggers a Time Error fault depends on the Time
Threshold setting and type of internal oscillator, as well the DAC setting and the estimated worst case
time error at the time the reference source became unavailable.
The accumulated time error typically remains below the default values for the given reference source,
but may exceed the Time Threshold for brief periods of time. These 'excursions' are usually non-critical
and can be ignored. For this reason, it is good practice to set the Time Threshold at the maximum time
error value that can be tolerated for each application.
The Timeout indicator and Timeout Delay setting can be used to suppress alarms that are caused by
'excursions' while still allowing more significant Time Error to trigger an alarm.
100 XLi Time & Frequency System
XLi-man, Issue 8, 6/17/2008, Rev. H
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