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Message ID: 3303     Entry time: Tue Jul 27 23:46:45 2010
Author: Jenne 
Type: Update 
Category: SUS 
Subject: Q measurements of 2 TTs 

[Koji, Jenne]

We took measurements of the Q of all the modes that we could think of for TT#4, and then repeated several of the same measurements for TT#2.  We noticed that when we took off the backplane and then replaced it on TT#4, the pitch pointing had changed, so we had to repeat the balancing procedure by slightly shifting the position of the wire clamps relative to the mirror holder. No fun. We decided to quit removing the backplanes. 

The main conclusion of this evening's measurements of TT#4 is that everything looks very close to the design ideas.  Good work team!

TT#4:

'Free Swinging' values (just for interest)

Vert, no damping:   Q = 31.4

Pitch, no damping (ECD backplane removed): Q = ~700

Yaw, no ECDs: Q = ~900

Pos, no ECDs (no measurement) - we had already put the backplane back on, and didn't want to take it off again.

 

Damped Values:

Vert, with damping: Q = 14.3

Pitch, with ECDs: overdamped, so Q < 1/2

Yaw, with ECDs: Q = 2.3

Pos, with ECDs: Q = 1.4

Side, with ECDs: Q = 1.9

 

We also measured the resonant frequency of each of the ECDs for this TT (since we had the backplane removed anyway...)

ECD UL: 10.05Hz

ECD UR: 10.15Hz

ECD LL: 10.21Hz

ECD LR: 10.21Hz

 

TT#2:

Yaw, with ECDs: Q = 7.0

Pitch, with ECDs: overdamped, so Q < 1/2

Vert: Problematic.  No damping, f = 25.9Hz, Q = 36.  With rubber dampers, f = 20.0Hz, Q = 42.   Yes, you read that right.  The frequency is lower, and the Q is higher *with* the damping.  Perhaps our brains are fried.  Perhaps we've discovered new, inconsistent physics (awfully unlikely....). We'll revisit this again tomorrow to figure out what mistake we're making.

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