aLIGO LHO Logbook

H1 PSL (PSL)

peter.king@LIGO.ORG - posted 11:58, Thursday 14 July 2016 - last comment - 13:12, Thursday 14 July 2016(28406)

Laser trip

The laser tripped this morning.  The status screen red flagged the following:
 - Xtak chiller flow
 - Interlock OK
 - Frontend Power error (WD)
 - Oscillator Power error (WD)

    Initial thought was that a water leak occurred.  That was not the case.

    Suspect that the power watchdog was tripped because the injection locking was lost.
When the injection locking servo loses lock, the laser power drops and sets off the
watchdog.

    The laser restarted without any problems, other than the alignment into the pre-modecleaner
was off a little.  Upon recovery, the pre-modecleaner had some problems locking.  Went into the
PSL Enclosure to adjust the alignment but by the time we got inside, the pre-modecleaner was locked.
Tweaked the alignment a little.

    Closed the other loops successfully.  After deliberately bringing up and down the input
modecleaner a couple of times, the FSS seemed fine with the occasional PZT oscillation.




  JeffB/Ed/Peter

Comments related to this report

peter.king@LIGO.ORG - 12:45, Thursday 14 July 2016 (28407)

Link

Before the alignment tweak the output of the locking photodiode was ...
 - unlocked -1.017 to -1.024 V
 - locked -0.148  -0.161 mV
This corresponds to a visibility of ~85%.

    After the alignment tweak ...
 - unlocked -1.017 to -1.024 V
 - locked -0.142 mV to -0.155 mV
This corresponds to a visibility of ~86%.

Images attached to this comment

peter.king@LIGO.ORG - 13:12, Thursday 14 July 2016 (28409)

Link

Measured the DC output of PDA - the first loop out of loop photodiode - with a digital multimeter (DMM).

DMM reading (V)    MEDM value (V)    REFSIGNAL slider
===============    ==============    ================
-8.76              10.62             -2.15
-9.01              10.86             -2.20
-9.21              9.14              -1.85

   There is a mis-match between the value reported by MEDM and that measured with a voltmeter.  The
level of disagreement varies over time, for reasons unknown.  A known "unknown" still.