GLAST Large Area Telescope Gammaray Large Area Space
- Slides: 7
GLAST Large Area Telescope Gamma-ray Large Area Space Telescope Engineering Meeting 23 November 2004 Charge Injection Calibration James Swain Stanford Linear Accelerator Center jswain@slac. stanford. edu 650 -926 -2721 23 November 2004 Engineering Meeting - Charge Inj. Calibration
Goal • To gather enough information to produce – DAC -> ADC curves for each discriminator in the front ends – Measurements of cross-talk between front end channels – Time over threshold curves • Need subsystem input – How should we collect TOT data? One channel at a time? – What pulse patterns do we need to make available? • FSW is proposing providing two pulse patterns, each of which can optionally be masked 23 November 2004 Engineering Meeting - Charge Inj. Calibration 2
Operation • Configure – Use LATC to perform initial configuration. – Perform reconfiguration (DACs, thresholds etc) within calibration loops as determined by LCI configuration files. • Pulse – Number of times determined by LCI configuration files • Read • Accumulate • Package – Preserve as much of the raw data as possible. • Send • Don’t Analyse • Don’t Apply 23 November 2004 Engineering Meeting - Charge Inj. Calibration 3
Calibration Styles Subsystem Calibrations ACD PHA (ADCs) CNO Accepts Hits Pedestals CAL TKR 23 November 2004 Bit scan ADC scan X X X ADCs Low Energy Trigger High Energy Trigger Accepts Pedestals X X X Accepts Time over Threshold X X Engineering Meeting - Charge Inj. Calibration 4
Calibration Styles (cont’d) • Bit scan – For charge injection DAC setting – For each of threshold setting – Pulse N times and record the number of accepts. • Simple version just uses a fixed number of DAC settings • Intelligent version focuses around the interesting threshold region. • ADC scan – Fixed number of injection DAC settings – Record ADC response to injection N times. 23 November 2004 Engineering Meeting - Charge Inj. Calibration 5
Volume and Time Estimates Subsystem Projected Time Uncompressed Volume CAL 10 s 420 Mbits 150 Mbits TKR 640 s 8 440 Mbits 420 Mbits ACD 10 s 30 Mbits 10 Mbits • Assumptions – Pulsing at 10 k. Hz – Pulsing 1 channel per TFE, 12 TFE per TRC • Cross-talk measurements will take longer – Auto-range readout for the CAL • Intend to use auto-ranging for most of the DAC values • Use four-range readout for overlap regions and keep two ranges so the overlap regions will increase data volume 23 November 2004 Engineering Meeting - Charge Inj. Calibration 6
FSW needs • What results would FSW like to be uploaded after calibration? – ACD pedestals • Might be nice, but not necessary – CAL linear correction • Two values per range per log end required. 23 November 2004 Engineering Meeting - Charge Inj. Calibration 7