Analysis of PCSS Timing Handling

Introduction

Herschel/PACS FM-IST measurements at the He-II cryo stage have been carried out between 24th and 28th August 2008. These comprised SFT, SPT, EMC test, FFT. During the analysis of the data obtained during these measurements, the time key of the diagnostic HK data turned out to be unreliable. Here, I summarise some the most important issues of this finding.

Data Analysis

For the check of the synchronisation of the PACS chopper trigger with the SPEC detector readout, we used a diagnostic HK sampling frequency of 256 Hz and 1000 Hz. I selected measurement with the lower frequency for this summary. The TM file is FIST_SPT_Spec707a_choppDetecSync_redundant_20080828_03.tm. Furthermore, the Chopper SFT carried in open loop is used during this investigation. The referring TM file is FIST_SFTHeII_Chopper_002_20080824.tm. I also investigate the impact on the time keys of the two PCSS HK import classes getRawMeasures and ValuesExtractor.getDiagnosticValues. Finally and as a comparison, I investigated the time keys extracted from the data DECMEC header.

Chopper SFT

attachment:Comp_TimeHK_Interp_FIST_SFTHeII_Chopper_002_20080824.png

This Figure demonstrates the time information extracted from the 1kHz diagnostic HK for every data point and separated into the two available PCSS import classes. It shows that ValuesExtractor.getDiagnosticValues produces a non-continuous sequence time information. At some point, even two following data points have a negative time progression. The time jumps backwards. This can lead to confusing results when analysing the HK data. The (deprecated) class getRawMeasures does not seem to have this problem.

attachment:Diff_TimeHK_Interp_FIST_SFTHeII_Chopper_002_20080824.png

attachment:Comp_TimeHK_Interp_FIST_SPT_Spec707a_choppDetecSync_redundant_20080828_03.png

attachment:Diff_TimeData_Interp_FIST_SPT_Spec707a_choppDetecSync_redundant_20080828_03.png

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