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 Wed Dec 19 17:47:02 2018, anchal, DailyProgress, TempCtrl, Cavity Temperature Sensor Circuit v1.1 Mon Dec 24 16:52:26 2018, rana, DailyProgress, TempCtrl, Cavity Temperature Sensor Circuit v1.1 Tue Jan 29 17:47:14 2019, anchal, DailyProgress, TempCtrl, Cavity Temperature Sensor Breadboard Circuit Noise Analysis Wed Jan 30 12:17:05 2019, rana, DailyProgress, TempCtrl, Cavity Temperature Sensor Breadboard Circuit Noise Analysis
Message ID: 2298     Entry time: Tue Jan 29 17:47:14 2019     In reply to: 2269     Reply to this: 2299
 Author: anchal Type: DailyProgress Category: TempCtrl Subject: Cavity Temperature Sensor Breadboard Circuit Noise Analysis

Here are the noise spectrum and time series plots that were asked of me ages ago. Apologies for the delay. I've also attached the analysis files in .zip.

### Noise Spectrum:

• I took noise spectrum by hooking the output of circuit directly into SR785.
• 100 rms averages were taken at AC coupling with BMH window.
• The RTD (I guess) was still getting into equilibrium as the DC voltage was higher after some time. So the noise spectrum includes low-frequency drift due to RTD self-heating.
• I calculated effective input referred noise of temperature sensing assuming no noise from 5V ref, no noise from instrumentation amplifier, no current source noise and no inherent temperature noise.
• So the input referred value is simply output divided by the theoretical transfer function.

### Time series data:

• I took time series data by SR785's Time1 function under FFT for 32 seconds.
• This data was taken in the end and RTD was already at equilibrium.
• While taking data, I set coupling to DC and units to Volts peak.
• Again, I calculated sensed temperature assuming all components working ideally.

Even with a breadboard circuit and different opamps (see PSL:2268 for changes), the circuit has less than $0.1\,mK/\sqrt{Hz}$ of input referred noise almost in all frequency range. The time series data also fluctuates less than $3\,mK_{pkpk}$  during 32 seconds of data, so worst case, this circuit would be precise to at least 5mK. However, since this circuit has no bypassing capacitors and high drift resistors, the PCB version should perform even better. I'll do same analysis with a stuffed PCB board soon.

 Quote: post a plot of the times series and noise spectrum Here is a link on how to choose R and C: https://dcc.ligo.org/LIGO-T070016