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Entry  Mon May 6 19:04:30 2013, Jamie, Update, IOO, mode cleaner not locking 
    Reply  Mon May 6 21:05:06 2013, rana, Jamie, KOji, Update, IOO, mode cleaner not locking 
       Reply  Fri Sep 20 20:27:18 2013, rana, Update, IOO, mode cleaner not locking 
          Reply  Sun Sep 22 22:54:28 2013, rana, Update, IOO, mode cleaner not locking 
          Reply  Sat Nov 30 23:50:28 2013, rana, Update, IOO, mode cleaner not locking mcdrift.png
Message ID: 8531     Entry time: Mon May 6 21:05:06 2013     In reply to: 8530     Reply to this: 9148
Author: rana, Jamie, KOji 
Type: Update 
Category: IOO 
Subject: mode cleaner not locking 

As it turned out, the setting of +26dB for the FSS Fast gain was making the NPRO PZT / Pockels cell crossover too unstable. This was the cause of the large ~30 kHz peak that Jamie was seeing in his spectra (more to follow in the morning).

After recovering the locking, etc. by fiddling with the gains, we went about systematically setting all of the gains/offsets. Jamie's elog will show all of the various spectra with different FSS gains.

For offset setting, this was the procedure:

  1. We want the MC servo board to have zero voltage on its MCL and MCF outputs (aka MC_SLOW_MON and MC_FAST_MON) with the Boosts ON, so we switched ON the 40:4000 and the 2 Super Boosts and put the VCO gain into its nominal +25 dB setting. This saturates the outputs and makes them impossible to use as readbacks so you have to be careful. Get the outputs close to zero as you turn on each boost. Finally, you will see that +/- 1mV of input offset (aka MC_REFL_OFFSET) will flip the FAST output between +/- 10V. This is the right setting.
  2. With the MC board adjusted to send 0 V into the FSS error point, adjust the FSS input offset (with the Common and Fast gains at the nominal values) so that the FAST output voltage goes to +5.5 V. This is the middle of the range for the high voltage driver which drives the NPRO.
  3. Let the MC lock and go through the UP script. When the MCL comes on with the integrator, the FAST voltage will shift from +5.5 V to something else. Use the following line: ezcaservo -r C1:PSL-FSS_FAST -g -1 -s 5.5 C1:SUS-MC2_MCL_OFFSET, to automatically tune the MCL offset.

     

    That's all. I have left the FSS common gain at +10.5 and the Fast gain at +23.5. These seem to be close to the optimum. Jamie will have more tuning tomorrow.
     
    I have also changed the 'mcup' script to set the MCL offset and set the FSS Slow setpoint to shoot for +5.5 V of FSS_FAST.
     
    MC_REFL_OFFSET = +1.176 V
    MC2_MCL_OFFSET = +47.8 counts
    FSS_INOFFSET   = -0.85 V
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