LIGO Document T1900799-v2

aLIGO Timing System Checks During O3A

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T - Technical notes
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Advanced LIGO (aLIGO) data is recorded by a data acquisition system (DAQ) that is driven entirely by the GPS-backed aLIGO Timing Distribution System. Several independent clocks’ 1PPS signals are used in timing diagnostics studies as witness signals. At each site, a Microsemi 4310b Cs-III Cesium-standard atomic clock checks for transient or short-term timing problems (see LIGO-T1700298 for details), and two CNS Clock II GPS clocks and a GPS-backed NTP server check for long-term/absolute timing problems.
We measured the time delay between aLIGO Timing Distribution System 1PPS and the aforementioned Timing Diagnostic System’s CNS Clock II GPS clock’s and a GPS-backed NTP server’s 1PPS signals for the first half of aLIGO’s third observation run (O3A). We also checked the atomic clock’s calibration during O3A. We also performed checks throughout O3A which can be found in LIGO-T1900671 on the DuoTone time delays, which probe timing performance on the sub-microsecond level, and the IRIG-B outputs at both sites for all Open Public Alert candidates.
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