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Message ID: 2130     Entry time: Mon Aug 13 21:37:58 2018
Author: aaron 
Type: Notes 
Category: Cryo Q 
Subject: Temperature Sensitivity of Eigenfrequency Tracking 

I keep giving these deeply unsatisfactory answers in group meetings when asked about the temperature sensitivity of this scheme of using the disk's eigenmode frequency as a temperature probe. I've put together a doc that hopefully will let me answer with a much more satisfactory and marginally more useful "I made an elog about that back in..."

Big takeaway: the sensitivity near 123K is 0.38Hz/K

Gautam and I talked about one way to improve this sensitivity by going to a higher frequency mode and downconverting to DAQ-friendly frequencies with a lock in amplifier. Our sensitivity will scale linearly with temperature, so it is only a matter of how high a frequency we can reliably excite the disk at. I wonder...

  • if we could send the temperature-probe excitation to the HV driver through some bias-T, so we can drive with the DAC and some lock in TTL simultaneously
  • we'd also have to check the high frequency rolloff of the HV driver.
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