[Zach / Koji]

Measurement of the primary (CCW) cavity openloop TF.

Method:

- Inject the actuation signal from the PZT sweep input
- Take after-the-sum signal and before-the-sum signal from TP6 and the output mon, respectively.

Result:

- UGF: 10kHz (this is OK)
- Phase margin: 14deg (this is too small)

Thought:

- The phase compensation between 5k to 20k is not enough.
- The phase delay above 10k seems too big. Possibly come from not-so-fast opamps (op27)?

To Do:

• Make the model of the openloop tf in alll frequency range (1mHz-100kHz).
  • The cavity cut-off has already been measured fc=98kHz (elog 9062)
  • Measure and characterize the low pass (fc=1.9MHz) just after the demodulator
  • Update the circuit diagram to show the latest condition
  • Make the filter transfer function with dial gain of 2.5
  • Check the gain dependence on the gain dial
  • Measure and characterize the notch filter (utilize earlier measurements?)
  • What is the calibration of the laser fast PZT and the transfer function?
  • Is the low frequency boost useful? (The boost may eat up our phase margin and make the servo unstable.)
  • How to construct the model of the temperature loop?
• Design and implement better phase compensation.
• Make a new custom servo circuit.