Slides/Talking Points for October 2007 Consortium Meeting C. Darren Dowell Draft: 2007 October 17

Topics Microphonics characterization plans Photometer PCAL response Spectrometer PCAL response High flux mode for photometer Simpler approach to Section 4.2.6 in Pipeline document

SPT Microphonics Characterization: Minimal Approach Photometer: Quiet bias frequency settings from PFM5 (to demonstrate good SPIRE performance): 126.01 Hz Noisy settings from PFM5 (which are most sensitive for “accelerometery”): 171.33 Hz, 156.25 Hz Spectrometer: Quiet settings from PFM5: 175.96 Hz Noisy settings from PFM5: 279.02 Hz

Photometer Microphonics

Spectrometer Microphonics Note change of scale from photometer microphonics. SLW is similar to photometers.

SPT Microphonics Characterization: Thorough Approach Many features apparently enter the system at higher harmonics of the demodulation frequency (=bias frequency). Since the demodulation is square wave, the low odd harmonics are relevant. Given the 5 (24) Hz post-demodulation bandwidths of the photometer (spectrometer): Bias frequency searches stepped by 5 (24) Hz only find all of the first harmonic microphonics. New features from higher harmonics could appear at in-between frequency settings. Searches stepped by 1.6 (8) Hz find all of the third harmonic features, etc.

“Proof” of Higher Harmonics (Include a plot here)

PCAL Photometer Calibration PCAL response follows trend to ≤5% precision.

PCAL Photometer Calibration Bolometer model is fairly good at recovering the PCAL power regardless of detector conditions (SUBKTEMP).

PCAL&SCAL Spectrometer Calibration Data analysis to do… Hopefully a demo that base temperature drifts and loading changes both follow the same curve of responsivity vs V(detector).

High Flux Mode for Photometer The typical photometer pixel readout saturates at 200, 360, 310 Jy/beam for 200, 350, 500 m, but interesting regions of the Galaxy are brighter than this. (Especially a problem at 200 m.) References:

Three Solutions Decrease bias to decrease responsivity: Responsivity can be made arbitrarily small Significant variation from pixel to pixel Maximum flux nonlinearity Increased NEP Enhanced microphonic, temperature fluctuation, and bias fluctuation sensitivity Thermistors usable Increase bias to decrease responsivity: Factor of 3 decrease possible (90 mV vs. 15 mV) Low flux nonlinearity Lowest temperature fluctuation sensitivity Thermistors saturate  no temperature drift correction Raise detector operating temperature to decrease responsivity: Factor of 3 by going from 310 mK to 420 mK Increase NEP Best solution? Fixed heat on charcoal pump? However, slow to switch normal  high flux modes. References:

High Flux Mode for Photometer Whatever the high flux mode is, it needs its own set of calibration tests: PCAL responsivity with the new bias + range of loading Temperature drift correlations Transfer function References:

Calibration Strategy See Pipeline document, Section 4.2.6, option 2 The “linearized voltage” idea I proposed didn’t catch on. Still, I think this section could be improved. Hopefully I’ll have a draft to review.