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 Thu Dec 4 17:42:23 2008, caryn, Update, IOO, drum modes observable without excitation 
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 Fri Dec 5 09:29:59 2008, rana, Update, IOO, drum modes observable without excitation
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Fri Dec 5 21:31:11 2008, Yoichi, Update, IOO, drum modes observable without excitation
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Message ID: 1182
Entry time: Fri Dec 5 21:31:11 2008
In reply to: 1179
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| Author: |
Yoichi |
| Type: |
Update |
| Category: |
IOO |
| Subject: |
drum modes observable without excitation |
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The calibration of the MC_F feedback is posted in elog:1032.
I'm not sure where Caryn took MC signal, but if you take the signal from the servo out BNC on the MC board, it
directly corresponds to the voltage sent to the FSS VCO.
The DC calibration of the VCO is 1.75MHz/V. Since the AOM is the double-pass, the PSL frequency
change is 3.5MHz/V. At frequencies above 40Hz, the VCO calibration drops by a factor of 39/1000,
because of the pole/zero at 1.6Hz/40Hz in the VCO box.
So at the frequencies of interest (around 30kHz), the servo out voltage can be converted to the PSL frequency
change by 0.137MHz/V.
Since 30kHz is still within the bandwidth of the MC servo, the feedback signal should correspond to the actual
length change of the MC. So the above calibration factor can be used to calibrate Caryn's measurement and check
what Rana suggested. |