Howto:How to calculate livetime with offline information?

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Types of dead time

Dead time can be categorized into the following 3 groups:

  • Reactor-related
    • No reactor thermal power data available
  • Detector-related
    • DAQ-related
      • Detector not included in partition
      • Included but HV was left off or other error
      • Detector being vetoed due to nearby (in space and/or time) muon
      • DAQ dead times (add details)
    • DCS-related
      • Detector undergoing calibration run
      • Off-center port CCD camera operation
      • AD camera operation
  • Offline-related


Offline-Related

Calculating AD and Water Veto livetime from a raw data file

To first order, the livetime of an AD or Water Veto detector can be estimated from the running time of the resulting data file. Under normal running conditions, the trigger system for the AD and Water Veto detectors will introduce a small deadtime. When the data production rate exceeds the ability of the electronics system to transfer and record it, the system will 'block' additional triggers. The number of triggers that were not issued during such a 'blocked' period is written to the first event recorded after such a blocked period. The deadtime can therefore be estimated from the time gap preceding events that have a record of 'blocked' triggers. When operating the trigger at rates greater than 1.5kHz, this deadtime correction can become a significant correction to the livetime.

Additionally, the trigger has a configurable parameter to limit the minimum time between triggers. Under normal running conditions this gap is ~700ns, and is smaller than the readout time window of the event. Under special circumstances this time gap can be increased to introduce deadtime and thereby limit the data flow from a detector. For example, during recent data taking with the 241Am source this gap was set to 500us, limiting the maximum trigger rate to 2kHz. The resulting deadtime can be calculated by multiplying the number of triggers by the minimum time between triggers.

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