H1 PSL

sheila.dwyer@LIGO.ORG - posted 22:25, Saturday 05 November 2016 - last comment - 18:10, Tuesday 16 March 2021(31245)

ISS second loop offsets, DBB, PSL rack grounding problems?

Travis, Sheila

Tonight we saw more pathological behavoir in the PSL electronics.

Robert wanted to do a test of powering down the DBB, so he switched the power supply that sits on top of the DBB chassis off and unplaggued the DIN connector from the back. After this, engaging the ISS second loop caused the diffracted power to drop from almost 5% to less than 0.5%, which caused locklosses as we tried to increase power.

We tried to let the offset adjustment servo (30932) run for a while, but this didn't help.

We plugged back in the DBB so we could get back to locking, but doing so tripped the PSL external shutter.

Comments related to this report

sheila.dwyer@LIGO.ORG - 01:48, Sunday 06 November 2016 (31248)

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We've continued having trouble with the ISS second loop introducing a large offset into the ISS, although it is not as bad with the DBB plugged back in.

The attached screenshot shows the AC coupled ISS second loop moving the diffracted power by almost 2% as we power up, so we need to be able to keep the diffracted power high enough that we don't saturated while powering up. Right now turning on the second loop decreases the diffracted power by about 4%, so we are just setting it high to start with.

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robert.schofield@LIGO.ORG - 08:17, Sunday 06 November 2016 (31252)

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In addition to electronics problems, there is also a chance that there might be alignment differences in the beam path next to the DBB when it is shut off since it is 4 degrees warmer than the table.

daniel.sigg@LIGO.ORG - 12:57, Sunday 06 November 2016 (31262)

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How to adjust the diffraction power (when out of lock):

Make sure the second loop is in its down state. This means only the input switch is off. The output switch is on as well as its input into the first loop board.
Make sure the excitation input is enabled and the AC coupling servo switch is on (shouldn't do anything, since the input switch is off).
In this state, the output offset should be continuously zeroed by the offset servo. Just check that the second loop output readback reads near zero.
Adjust the REFSIGNAL of the first ISS loop, so that you roughly have 4% diffracted power.
Turn second loop on with the input switch (the IMC needs to be locked).
In the AC Coupling medm screen there is an input offset (top left). Adjust it so that the diffracted power stays at 4%.
Toggle the input switch and make sure that the diffracted power doesn't change.

jeffrey.kissel@LIGO.ORG - 18:06, Monday 28 November 2016 (31942)IOO, OpsInfo

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 How to adjust the diffraction power (when out of lock) -- translated with screenshots of the relevant MEDM screens, and with the language color coded to match the colored highlighted boxes on the screenshots:

   - Make sure the second loop is in its down state. This means only the input switch is off. The output switch is on as well as its input into the first loop board.
   - Make sure the excitation input is enabled and the AC coupling servo switches are on (shouldn't do anything, since the input switch is off).
   - In this state, the output offset should be continuously zeroed by the offset servo. Just check that the second loop output readback reads near zero.
   - Adjust the REFSIGNAL of the first ISS loop, so that you roughly have 4% diffracted power.
   - Turn second loop on with the input switch (the IMC needs to be locked).
   - In the AC Coupling medm screen there is an input offset (top left). Adjust it so that the diffracted power stays at 4%.
   - Toggle the input switch and make sure that the diffracted power doesn't change.

Images attached to this comment

jenne.driggers@LIGO.ORG - 18:10, Tuesday 16 March 2021 (58265)

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These instructions are outdated. The ISS second loop board has been modified since these were written. Please see new instructions at alog 58264.