[Kiwamu with a help from Christina@AEI remotely]
Today I made some efforts to bring the ISS back on by following an instruction by Christina and made it sort of running --- the loop can be closed by the autolocker but the diffraction power seems bit too high and also the gain seems too low. Certainly the ISS needs further investigations.
-
Reference signal
-
Initially I tried to set it to be 1/5 of the DC signal of PDA which was 8.5 V.
-
-1.7 V at the reference signal didn't work -- it unlocked the ISS loop because of a too big signal at OSCILLATION_MON_LP.
-
I empirically ended up with a reference of -1.62 V which seems giving us a stable lock.
-
However this gave me a big diffracted power of about 16 % and I guess this needs to be about 10 % according to the strip chart in the ISS medm screen.
-
GAIN
-
Initially this was set at 7 dB.
-
I increased the gain by 6 dB but it seems that a higher gain induces an unknown oscillation at about 100 kHz. This was clearly visible at the outer loop PD output in an oscilloscope.
-
Toggling the noise eater didn't change the situation.
-
So the gain was set back to 7 dB.