Yesterday, somebody started implementing DC-coupled PR3 OL servo actuating on M2 stage, so I made it usable.

Right now it's only for PIT (H1:SUS-PR3_M2_OLDAMP_P), and the filter is a simple 1mHz pole with 0dB DC gain, a 0.6Hz-ish elliptic low pass, and a 74dB gain (this gain is the inverse of the measured DC gain from the M2 OLdamp filter output to the OL PIT,  about +2E-4 rad/count).

With all filters on, the filter gain is equal to the DC gain, and the UGF is equal to 1mHz multiplied by the filter gain.

For the moment the filter gain is set to -10, so the UGF is 10mHz.

To turn it off, turn the filter output off, not the input.

To change the set point, change the filter offset.