I removed one of two SR560s used for ISS 3rd loop and reshuffled connections so we can directly go to the 2nd loop error point.
First attachment shows the new configuration, second attachment the old one.
PD58 path is used as the injection point of the 3rd loop.
Since we're injecting to a different point, you need to figure out a new gain/filter.
Kiwamu says that you cannot increase power while the 2nd loop is on. The setpoint voltage for the second loop needs to be changed as the power goes up, otherwise the loop hits the rail, but there's a pair of 0.1Hz hardware poles in the offset voltage path and you cannot update the voltage fast enough. You might want to put digital double zero-poles, e.g. zpk([0.1, 0.1], [5, 5], 1, 'n') or something in H1:PSL-ISS_SECONDLOOP_REF_SIGNAL_ANA_CALI to mitigate this effect.
Anyway, this might mean that you need to use different gain/filter configurations for the 3rd loop while powering up without the 2nd loop, and once you reach the final power you enable the 2nd loop and switch to the final configuration for the 3rd loop.
Possible switch combinations:
| PD select = 1-4 | PD select = 5-8 | |
| ADD SUM5-8 = ON |
2nd loop ON, |
2nd loop OFF, 3rd loop ON with twice the gain |
| ADD SUM5-8 = OFF |
2nd loop ON |
2nd loop OFF 3rd loop ON |
We're not losing the out of loop sensor, as PD5-8 analog summation output is NOT used as such.
Use H1:PSL-ISS_SECONDLOOP_SUM58_AC_OUTPUT and H1:PSL-ISS_SECONDLOOP_SUM58_REL_OUTPUT instead, these are digital sum and digital RIN.