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Ecal / Hcal monitoring

Ecal / Hcal monitoring. Yu. Guz (IHEP, Protvino), I. Machikhiliyan (ITEP, Moscow). Outline: ECAL/HCAL monitoring with LEDs (short reminder) Summary from discussion 13/12/07 + some examples Comments on monitoring procedures Hardware status. Monitoring with LEDs (I). Why?

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Ecal / Hcal monitoring

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  1. Ecal / Hcal monitoring Yu. Guz (IHEP, Protvino), I. Machikhiliyan (ITEP, Moscow) • Outline: • ECAL/HCAL monitoring with LEDs (short reminder) • Summary from discussion 13/12/07 + some examples • Comments on monitoring procedures • Hardware status

  2. Monitoring with LEDs (I) • Why? • for quick identification / masking of malfunctioning channels; • to trace the stability of readout chains; • to correct on PM gains drift if any in-between (“physical”) calibration cycles; To account for LEDs drift, the system of very stable PIN-diodes is foreseen, therefore PM gain correction factors have the form of ratios: where <PM_current> and <PIN_current> are responses of PM and corresponding PIN to LED and <PIN_ref> is the reference value of PIN response

  3. Monitoring with LEDs (II) • How? • during routine data taking LEDs are fired with the frequency 50-100 Hz synchronously with one of “empty” accelerator bunches; • LED events are delivered to dedicated “calibration” farm (most probably made of single node), where • dedicated code (Orwell) produces: • summary histograms for N, sum, sum^2,.. (LED,PINs, pedestals) for each 100-200 LED flashes / cell  to perform fast quality check, generate alarms and (may be) produce gain correction factors; • histograms with LED / pedestal spectra for each individual cell and PIN on the basis of higher statistics  to perform full quality check, identify malfunctioning channels and produce refined peaks positions and widths;

  4. Monitoring with LEDs (III) Picture is taken from: Yu Guz: 14 Mar 2007 / Calo online monitoring For details of Orwell implementation: see Olivier talks PVSS/ROOT Histogram viewer Calibration Farm Histogram producer Analysis node ROOT histograms CondDB updates Histogram Analyzer Histogram adder Histogram Analyzer Saver Histogram Database Alarms to ECS

  5. Discussion 13/12/07 (I) • Agenda: • Orwell tutorial by Olivier (including installation under lxplus accounts) • Discussion on LED DQ summary histograms for quick detection of problems: The same for PINs Summary histogram for PM channels

  6. Discussion 13/12/07 (II) # of channels with bad pedestals # of channels with bad LEDs (r.m.s) # of “empty” channels # of channels with no LED seen Number of histograms

  7. Discussion 13/12/07 (III) <LED> for PM channels Also: <PIN> PIN r.m.s. Also: <Ped> Ped r.m.s. LED r.m.s. for PM channels

  8. <LED> as function of unique PM/PIN id LED r.m.s. as function of unique PM/PIN id Discussion 13/12/07 (IV) <Ped> as function of unique PM/PIN id Ped r.m.s. as function of unique PM/PIN id

  9. Discussion 13/12/07 (V) <LED> as function of unique FEB id (1 r/o crate, Outer section) LED r.m.s. as function of unique FEB id, (1 r/o crate, Outer section) Also: <Ped> as function of unique FEB id Also: Ped r.m.s. as function of unique FEB id

  10. Discussion 13/12/07 (VI) Number of channels with LED present vs FEB id (1 r/o crate, Outer section)

  11. LED r.m.s. as function of X/Y (Outer) <LED> as function of X/Y (Outer) Discussion 13/12/07 (VII) Ped r.m.s. as function of X/Y (Outer) <Ped> as function of X/Y (Outer)

  12. <LED> as function of X/Y (Inner) LED r.m.s. as function of X/Y (Inner) Discussion 13/12/07 (VIII) <Ped> as function of X/Y (Inner) Ped r.m.s. as function of X/Y (Inner)

  13. Discussion 13/12/07 (IX) • Agenda(cont): • Fast monitoring: • control gain variations using ratio <PIN>/<PM> as it calculated on-line by Orwell • If variation is significant – update condDB with gain correction factors. Thresholds are to be defined from further studies on detector behaviour. • condDB structure to store correction factors: • still under discussion, but • not ratio, but <PIN> and <PM> values separately will be stored • somehow a kind of link to the set of calibration coefficients, which have to be corrected, should be foreseen (each set has to be accompanied with <PIN> reference value)

  14. Agenda (cont): • Slow monitoring: • LED / pedestal histograms are to be stored somewhere on the disk and then analyzed more precise way (at least in the beginning of LHCb operation) • detect dead / hot / noisy / unstable channels • obtain precise LED / pedestal position and width (fit) and foresee place to store them together with channel status (ok/hot/dead/…). They further might be used to study detector performance • List of tasks ( following their priority): • set-up online display to present a set of summary histograms for DQ • develop histogram analyzer • set-up communications with condDB • integration with PVSS / mechanism to deliver alarms Discussion 13/12/07 (X)

  15. Discussion 13/12/07 (XI) NEED MORE DATA FOR DEBUGGING / THRESHOLDS DEFINITION / …

  16. Comments on fast monitoring (I)From Yu Guz: 14 Mar 2007 16:55 / Calo online monitoring LED monitoring: real spectra (pictures from Irina) PM: CW noise on top of PM signal PIN: amplifier noise ~ independent of signal In order to minimize spread: • set LED flash for ~ max possible amplitudes in PM @ working PM gains • tune LED-PIN system to obtain large PIN signal @ working PM gains

  17. Comments on fast monitoring (II)From Yu Guz: 14 Mar 2007 16:55 / Calo online monitoring In presence of the CW noise, the sample RMS is subject to high fluctuations. However the RMS calculated on a sample with omitted (5%) max and min amplitudes is more stable and can be used to produce alarms Quality check Quick quality check routine can produce alarms in the following cases: • on steep (or too frequent) variations of monitored average • on variation of pedestal (with ped. subtr., it should be always ~0) • optionally, on significant increase of RMS of the LED signal or pedestal (this can be done every ~100…200 LED flashes per cell).

  18. Comments on slow monitoring (I) Ideas for the procedure: 1) DQ of the spectrum (PM / PIN): - shape of the LED distribution (gaussian / non-gaussian / more than one peak) - shape of the pedestal distribution (gaussian / non-gaussian / more than one peak) - ADC bit errors (? How could they look with pedestal subtraction?) - …? will learn from the data

  19. ECAL problematic channel, Dec 2007 Comments on slow monitoring (II) HCAL problematic channel, Dec 2007 Pedestal subtraction problem? HCAL problematic channel, Dec 2007

  20. Comments on slow monitoring (III) • 2) If DQ passed: • calculate position / width (fit) of the pedestal • calculate position / width (fit) of the LED • Known problems (for ECAL): • No signal in individual PM: • narrow pedestal – no contact between PM / ADC • “normal” pedestal width –> bad C-W -> or broken optical fiber • Unstable signal (several peaks) • Unstable LED (if instability is seen in all PMs of the grop) ? • Unstable PM ? • Unstable contact somewhere ? Our famous C-W noise can help

  21. Comments on slow monitoring (IV) • So, do we need to store and analyze histograms? • YES! This option MUST be foreseen. • Confident identification of malfunctioning channels • Easing of detector maintenance: in many cases expert can classify the problem source (PM, ADC or contact in between) just looking at the spectrum • In the future: useful stuff for detector performance studies, like: • - stability of pedestal and gains • - modules light yield degradation (e.g. due to rad. damage) • For all these purposes fit parameters are much better than mean/r.m.s. values

  22. Do we need alternative to LED based monitoring? The weakness of the LED system: one LED-to-many channels correspondence, so: • Loose one LED -> loose 9-16 channels (in case of ECAL) • Loose one PIN -> loose 1-4 LED groups • Loose one LED TSB output -> loose one LED • Loose 1 control box LED mezzanine -> loose up to 16 LEDs

  23. Do we need alternative to LED based monitoring? Good solution for backup/cross-check (both ECAL and HCAL): • Monitoring of an individual channel based on raw data (ADC readings) in physical (mbias) events • Parameter to be monitored: raw spectra of not-reconstructed ADC readings; occupancy; • The method is already proved in HERA-B HCAL only: • Monitor average PMT current values, using integrators of radioactive source calibration system • The DQ histogram (1 value per HCAL cell) can be sent to ?calibration node? with a period from several seconds to several minutes

  24. HERA-B experienceFrom: 20 Oct 2006 12:35 / Status of ECAL tests and of LED monitoring software • !! Raw data (ADC readings) !! • LED trigger: • position/width -> readout channel stability trace, dead/hot channels identification • pedestal position/width ( from “empty” bunches, if LEDs are OFF) • Minbias trigger: pedestal position/width • fast data quality check (e.g. ADC bit errors identification) • channel occupancy monitoring->another way of identifying hot/dead cells • Usually: several “monitoring” sets per run -> later used in off-line analysis

  25. Last but not least: HW status • LED system: pulse intensity is adjusted to fit with ADC dynamic range (at nominal PM gain): • HCAL – done • ECAL – done except 11 malfunctioning LEDs on A-side. May be some additional small tuning of several LEDs will be needed • PIN system: • the majority of channels is operational • HCAL: amplifiers gain is adjusted in the way that LED response is well in the ADC dynamic range at nominal LED pulse intensity • ECAL: amplifiers gain tuning should be finished during Jan / Feb 2008

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