As a part of temperature actuator characterization, today Eric Q and I made some measurements for the open loop TF of both the X-arm and Y-arm  thermal actuators. 

For this, we gave an input  of random excitation for the temperature offset input( since we faced some serious issues when we gave in Swept sine yesterday) and observed the PZT actuation signal keeping the arm to be locked all the time of our measurements and ensuring that the PZT signal doesn't saturate.

The  channels used for the measurement were  C1:ALS-X_SLOW_SERVO2_EXC as the input and C1:ALS-X_SLOW_SERVO1_IN1  as the output.

The random noise used for the measurement :

Y-ARM:  Gain- 6000;  Filter - butterworth-first order - band-pass filter with start frequency= 1 Hz stop frequency = 5 Hz.

X-ARM: Gain -3000; Filter - butterworth- first order- band-pass filter with start frequency 3 Hz and stop frequency = 30 Hz and  notch(1,10,20).

The Y-ARM measurement was stable but for the X-ARM, the PZT was saturating too often so Eriq Q went inside the lab and placed a 20dB attenuator in the path of the  X-ARM PZT signal readout to carry out the stable measurements.

The units of the TF of these measurements are not calibrated and are in count/count. I will have to calibrate the units by measuring the PZT count by changing the cavity length so that I can get a standard conversion into Hz/count. I will elog the calibrated TFs in my next elog after I take the cavity length and PZT TFs.

The attached are the bode plots for both the X-ARM and Y-ARM thermal actuators(non-calibrated). I will work on finding the poles and zeroes of this system once I finish calibration of the TF measurements.