Other Information 9-2
9.1 Time Quality
A 4-bit time quality indicator is used by several manufactures of satellite controlled clocks. It is an
indicator of time accuracy or synchronization to UTC and is based on a clock’s internal parameters. Per the
IEEE 1344 standard, the code recommended is by order of magnitude relative to 1(ns). The 1ns basic
reference is adequate to accommodate present industry requirements now and into the foreseeable future.
With present GPS technology at 100ns accuracy level, a 0000 code indicating locked will change to 0011
or a 0100 unlock code. The following table contains the IEEE 1344 quality indicator codes.
APP-601 clock accuracy/alignment with the 1PPS is 0.6 µsec with an
un-modulated IRIG-B input. The accuracy with a modulated IRIG-B
input is 1msec.
If the satellite-controlled clock does not output a time quality code, APP-601 keys off the clocks synch/un-
sync signal. If the clock is synchronized then the fault record tag will show locked. If the clock is un-
synchronized then the fault record tag will show unlocked.
If there is no signal connected to the APP-601 IRIG input, then the fault record tag will display “No
Signal”.
Table 18: IEEE 1344 Time Quality Values
fault –unknown – clock fail
Normal Operation Clock Locked
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