LIGO Document E1500355-v1

ECR: Add independent absolute time marker to frame files

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E - Engineering documents
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In initial LIGO we had and absolute and independent time marker in the frame files. It was an IRIG-B signal digitized in one of the end stations. We lost this feature as part of the timing upgrades in Advanced LIGO. We propose to add the IRIG-B channel back to the science frame, derived from an independent GPS clock.
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ECR timing
Notes and Changes:
The existing aLIGO Timing GPS modules (D1002546) brings out the serial port of the Trimble GPS receiver through a Lantronix Serial->Ethernet adapter to an Ethernet port on the front-panel. It is now desired to read out the GPS module directly from the serial port to a port on the Beckhoff system Serial Concentrator. To do this cleanly, modify the GPS module to bring the embedded serial port on a DB9 cable to a DB9 feed through, mostly likely on the back panel D1002555. This change needs to be reflected in drawings and likely requires updating the
test procedure (T1000659) to use a direct serial port. In addition, this change requires updates to the Beckhoff EtherCAT software (already completed at LHO). All of this work is (implicitly) part of this ECR.

Issue tracker:
for associated changes to get the serial output of the GPS receiver, see also

approved by Dennis Coyne
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