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Entry  Thu Aug 1 22:58:45 2013, Charles, Update, ISS, CTN Servo - Explicit Requirement and Proposed Servo CTN_Servo_TF_-_Proposed_v_Req.pngCTNServo_v3.fil
    Reply  Mon Aug 5 11:53:45 2013, Evan, Update, ISS, CTN Servo - Explicit Requirement and Proposed Servo 
Message ID: 8959     Entry time: Thu Aug 1 22:58:45 2013     Reply to this: 8964
Author: Charles 
Type: Update 
Category: ISS 
Subject: CTN Servo - Explicit Requirement and Proposed Servo 

 In PSL elog 1270, Evan elucidated the explicit requirements for the CTN ISS board. Essentially, the transfer function of the ISS should be something like:

     TF_mag = (Unstabilized RIN) / (Calculated RIN Requirement)

I took Evan's data and did exactly this. I then designed a servo (using the general design I proposed here) to meet this requirement with a safety factor of ~10. By safety factor, I mean that if the ISS operates exactly according to theory, it should suppress the noise by a factor of 10 more than what is necessary/set out by the requirement. Below is a plot of the loop gain obtained directly from the requirement (the above expression for TF_mag) and the transfer function of the servo I am proposing.


I don't have the actual schematics attached as I was working with a LISO file and have yet to update the corresponding Altium schematic. The LISO file is attached and I will add the schematics later, although one can reference the second link to find a simple drawing.

Attachment 2: CTNServo_v3.fil  642 Bytes  | Hide | Hide all
# Stage 1
r R31 1.58k in n_inU3
op U3 ad829 p_inU3 n_inU3 outU3
r R35 1k p_inU3 gnd
c C33 1u p_inU3 gnd
c C32 10n n_inU3 outU3
r R34 158k n_inU3 outU3

# Stage 2
#r R41 15.8 outU3 n_inU4U5
... 24 more lines ...
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