SudarshanK, GabrieleV, PeterK.
The modifications was made on the ISS second loop power stabilisation board to change the variable gain represented by H1:PSL-ISS_SECONDLOOP_GAIN form 0 to 40dB to -11 to 31dB. This is on top of the addition 20dB gain that was added and reported in alog 14291, and controlled by H1:PSL-ISS_SECONDLOOP_ADD_GAIN.
We also made some modifications on the Guardian scripts that engages the second loop. Now the second loop can be engaged from the IMC guardian window although some fault checking will need to be implemented.
The in-loop and out-of-loop RPN measurement with the loop closed, gain set at maximum, boost and integrator engaged is attached below. The loop performance looks on-par with our past measurements, about 1E-8 at 10Hz.
Two modifications were implemented in the board:
- the variable gain stage was tuned to the range [-11dB, 31dB] instead of [0dB,40dB]
- the additional gain stage was changed from inverting to non-inverting. In this way we can now switch it on or off without breaking the ISS loop.
- the sign switch was flipped accoridngly to modification 2
In this way we can acquire the lock of the ISS second loop with in total 20 dB less gain than before. This solved our old problem of a second loop correction railing just before engagement of the loop. Now we can simply turn on the loop with -11 dB of global gain, then engage the +20dB stage and increase the gain to the maximum +31 dB.
The ISS lock acquisition is much simpler and much more robust than before.