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097-55501-01 Revision M – January 2009
TimeHub 5500 User’s Guide 217
Chapter 5 Maintaining the TimeHub 5500
Troubleshooting the TimeHub 5500
SNDRIFT Events
In addition to the LEDs, the events and alarms are useful in diagnosing Clock card
issues. One event, SNDRIFT, provides an indication that the frequency relationship
between the indicated input and clock module internal reference oscillator is
exhibiting a larger amount of drift (frequency change vs. time) than would normally
be expected. For example, the event shown below indicates that the frequency
relationship between the CLK2 internal reference oscillator (CLK2 indicated in
beginning of response) and input 1 (this is the 1 in CLK2-1) is drifting more than
expected.
"CLK2-1,T1:MN,SNDRIFT,NSA,10-17,06-56-57:\"Drift Exceeds Limits\""
The drift limits are based on GR-1244 holdover frequency stability requirements
(see section 5 in GR-1244). These requirements are specifications for the stand-
alone stability of the internal reference oscillator, which cannot be self-measured by
the TimeHub shelf during normal operation. The TimeHub measures the drift
relationship between every input and the internal reference oscillator, which is what
is measured and used in the SNDRIFT assessment. Since this measurement is a
combination of both the drift of the input and the internal reference oscillator, it is not
a direct assessment vs. the GR-1244 specification described above (which is only
about the internal reference). However, if the combined relative drift of input and
internal oscillator exceeds these thresholds it could be an indication that there is an
issue with either the input or internal reference oscillator. The Timehub does not
disqualify the input when this condition is reported since it doesn't necessarily
indicate that anything is out of spec.
Standby
Off
This card is not generating an
output that is phase-locked to
the output of the other (active)
Clock card.
If the Active LED on this card is lit,
none required. If the Active LED on
this card is also off:
1.
If the Fail LED is lit, replace the
card; if the Fail LED is off,
remove, then insert the card as
described in
2.
If the Standby LED is still off,
replace the card as described in
Green
This card is generating an
output that is phase-locked to
the output of the other (active)
Clock card.
None required.
Force Active
(Pushbutton)
–
When pressed, this
pushbutton forces the card to
be the active card.
–
Table 5-1. Troubleshooting the Clock Card Front Using the LEDs (Continued)
Name
State
Description
Action
Содержание TimeHub 5500
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