96 XLi Time & Frequency System
XLi-man, Issue 8, 6/17/2008, Rev. H
SSSSSSSSSSSS SSSSSSSSSS SSSSSSS S SSS S SSSSS S
1
Note:
• *A: This indicator is enabled when the XLi is purchased with the corresponding option. Enable this
indicator if performing a field installation of the corresponding option.
• *B: Enable this indicator when configuring the XLi with the corresponding reference source.
• *C: Enable this indicator for troubleshooting purposes.
Clock Status
Status: Locked or Unlocked
The Clock Status indicator reports “Locked” when the XLi clock is locked to a reference source (e.g.,
GPS, IRIG, AUX REF, etc.). This is the normal operational state of the clock. While locked, the XLi clock
steers its internal oscillator to the reference source.
The Clock Status indicator reports “Unlocked” when the XLi clock is not locked to a reference source.
This may be because the reference source is unlocked or unstable. While unlocked from a reference
source, the XLi uses its internal oscillator to keep time until a reference becomes available again.
Note: There are two uses of the word “unlocked” here: one refers to the XLi system clock when it doesn’t
have a reference source, the other refers to the reference source (e.g., GPS, IRIG) when it doesn’t have
a valid signal.
The XLi can provide stable and accurate time while the Clock Status indicator is “Unlocked”. How long
depends on a number of factors including the stability of the internal oscillator and the acceptable
amount of time error for the application. The Time Error indicator and the Time Threshold setting can be
used to trigger an alarm when the time error exceeds customer-defined limit.
To prevent the Clock Status indicator from coming unlocked, apply the following recommendations:
• Configure the XLi with multiple reference sources. For example, two GPS receiver cards and/or an
Aux Ref input from a Cesium primary frequency reference.
• Follow the standard procedures and guidelines for installing and configuring the reference sources
(such as for GPS antenna installation).
To investigate and solve a persistent “Unlocked” Clock Status indicator, perform the following steps:
First Time Lock Disabled - *C OK or Fault
Time Error Enabled OK or Fault
Time Threshold 350 nS (Range 0 to 99,999 nS)
Alarm LED Blink Enabled (Enabled or Disabled)
Timeout Disabled OK or Fault
Timeout Delay 300 sec. (Range 0 to 86,400 sec.)
Power-On Alarm Suppress 300 sec. (Range 0 to 86,400 sec.)
NTP Fault Disabled - *A OK or Fault
Clear Alarm Latch No Yes or No
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