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Entry  Mon Jan 24 18:13:20 2011, Zach, Electronics, GYRO, PDH servo basic_design.png
    Reply  Tue Jan 25 00:05:57 2011, Koji, Electronics, GYRO, PDH servo 
       Reply  Tue Jan 25 01:30:01 2011, Zach, Electronics, GYRO, PDH servo PDH2.pdf
          Reply  Tue Jan 25 01:39:00 2011, Koji, Electronics, GYRO, PDH servo 
             Reply  Tue Jan 25 02:09:16 2011, Zach, Electronics, GYRO, PDH servo 
                Reply  Tue Jan 25 02:18:17 2011, Koji, Electronics, GYRO, PDH servo 
                   Reply  Wed Jan 26 01:20:10 2011, Zach, Electronics, GYRO, PDH servo PDH2.pdf
                      Reply  Wed Jan 26 06:20:03 2011, Koji, Electronics, GYRO, PDH servo 
                         Reply  Wed Jan 26 12:42:36 2011, Zach, Electronics, GYRO, PDH servo 
                            Reply  Wed Jan 26 18:10:37 2011, rana, Electronics, GYRO, PDH servo 
                               Reply  Wed Jan 26 19:47:42 2011, Zach, Electronics, GYRO, PDH servo PDH2.pdf
                                  Reply  Wed Jan 26 20:01:31 2011, Zach, Electronics, GYRO, PDH servo 
Message ID: 1261     Entry time: Mon Jan 24 18:13:20 2011     Reply to this: 1262
Author: Zach 
Type: Electronics 
Category: GYRO 
Subject: PDH servo 

 I have been thinking about how the dedicated PDH servo for the gyro should look. Here is a cartoon.

basic_design.png

It is essentially the same basic setup as the universal box, but with four switchable true integrator stages, so that we can turn the boost up to f-4 at low frequencies. Following the lead of the MC servo, I am planning to use AD829s instead of the slower OP27s.

For the variable gain stage, I'm not sure if we want to do something fancy like the multiplexer deal that the MC servo has (so that we can switch between several gain setting remotely) or if a local gain adjust will be enough. My guess is that a multiplexer and an additional set of 6-8 op amps is a bit overkill, since we'll probably not change the gain setting that often anyways. What's more, we will probably want to have finer control of the gain so that we can increase it just up to the point before the servo becomes unstable, which is easier to do with a potentiometer anyhow.

For the integrator switches, I imagined putting a relay on each one so that we can switch between flat DC response all the way up to f-4 with EPICS, and eventually write an autolock script to do this for us. We might want to use something like a multiplexer for this so that we can specify the frequency response with one DAC channel.

We will also probably like to have a way to remotely engage the sweep input and inject excitation signals from the digital system. I think this should be implemented separately from a local sweep option (which will disconnect the signal pathway) that we will use in an open-loop configuration for things like signal optimization. Maybe we can just have it so that there is an "EXC" input that is always live (which we will hook up to the DAC) and a "SWEEP" input that must be engaged and that will kill the signal loop.

For the inverter, I think we can afford to just have a local switch.

I am working on the basics of the servo in Altium and I will wait for some input regarding the more advanced stuff. Remember that the current idea is to just make a board that we will mount into a NIM module and directly into our crate. The REFL PD signals will be sent to the crate where they will be mixed and then put into the servo. The PZT actuation signal will go back to the laser from here via BNC. There will be BNC inputs for the remote boost control, EXC, and local SWEEP.

 

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