[Changed the power level on PDA]
I went into the PSL today and changed the ND filter that was screwed on the PDA photodetector module (30415) in order to change the power level of the photo diode. Before the change the PDA DC singal read a relatively small value of 2.2 V. After the change, the DC signal became 3.8 V which is close to what PDB says 3.9 V. Indeed, the voltage readouts for the two diodes shown in the medm became close to each other (~ 4.5V). The new ND filter is actually a stuck of 0.2 and 0.5 abrorptice ND filters. It was an ND1 before.
[New setting for ISS inner loop]
The gain slider now should be 18 dB (which used to be 30 dB, 30415). This gain gives us a UGF of 54 kHz. This means that the open loop transfer function is almost identical to the one with PDB used as the in-loop sensor (29942) as expected. In fact, we can now switch the sensor between PDA and PDB without changing the reference offset or gain while keeping the loop closed. Though this typically changes the diffraction power by a few %. The new gain is now accepted in SDF.
The attached is a plot of the measured open loop transfer function with PDA. Also the raw data is attached. Also, I attach a noise spectrum seen at one of the analog output for measuring the transfer function.
