sheila.dwyer@LIGO.ORG - posted 18:55, Tuesday 14 February 2017 - last comment - 12:45, Wednesday 15 March 2017(34154)
Installation of bullseye detector (mostly done)
Sheila, Jenne, Mark, Richard, Fil, Daniel
We made some progress on installing a prototype of the bullseye detector that Mark has been building in the PSL today.
- Jenne and I went into the PSL and realized that the location I ha orignally thought of for the diode wouldn't work. After dicussing it with Jason we deicded to move aside the beam profiler in the DBB HPO path and put the diode there. There was about 0.65 mW of power in this path. Jenne added a steering mirror (Y1) and a diverging lens (PLCC-25.4-103.0-UV-1064). To install the diode we had to remove the rail that was on the table, we placed it on the portable cart on the oposite side of the enclosure.
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We used a temporary adapter cable that Mark made that allows us to power the diode from the power strips under the table and get the signals out onto a DB9. We used a breakout board to display the segments on a scope while we were in the enclousre. Based on watching the signals while we steered the beam around, we think that the segments are arranged like this:
- pin1 pin6 (seg 1) side of the diode closer to the anteroom
- pin 2 pin 7 (seg 2) center
- pin 3 pin 8 (seg 3) side of diode closer to HAM1
- pin 4 pin 9 (seg4) bottom of diode
- We decided to use the unused half of the MC2 trans QPD whitening chassis for this diode. Fil made an adapter cable that we could use to get the MC2 signals from the 25 pin Dsub from the transimpendance amplifier and the bullseye signals off the 9pin Dsub that comes out of the PSL into the whiteing chassis. (The 9 pin cable reaches, but next time someone is in the PSL we could uncoil a little more from under the table).
- The whitening chassis already had BIO, but there was no beckhoff code for the spare hardware. Daneil added this, and named the whitening PSL-SPARE_QPD. Dave did a DAQ restart for this change.
We will hopefully get the whitened signals into the ADC channels that are already set aside and connected to AS_D in the ASC model tomorow.
Important note! The segment numbers I wrote above are incorrect
This morning I checked the signals from the bullseye detector using a scope in the ISC rack, and saw that all 4 channels had a large oscialltion at 52kHz. I got it off the table and Mark Richard and Fil spent some time in the EE shop, and saw that indeed, attaching a long cable to the detector made it oscillate. Mark changed the 50 Ohm series resistors to 100Ohms, which fixed the problem. While we were there Mark also confirmed with a laser pointer that the middle segment is on pin 2 of the connector.
While the detector was in the shop, Vaishali and I went back to the rack and checked which pins on the input to the whitening chassis showed up as which segments in the digital system. This was not as I had expected, the correct mapping is in this table:
Robert and I went back into the PSL and put the detecor back on the table, and removed the lens so that we now have close to equal amounts of power in the center of the bullseye and in the outer ring. By the time we came out, the alignment seems to have shifted a little.
Keita checked on the whitening, and it seems to be working OK. We set dark offsets with the diode unplugged, one stage of whitening on and 24dB of whitening gain. We didn't measure the dark noise, so if anyone gets a chance to go back in it would be good to both measure the dark noise and try to readjust the alignment.
I went in to the PSL yesterday, the 14th, during the maintenance period as described in WP6522. I have done the following activities.
By the way, here is a picture of the bullseye setup.