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Lima Detector Calibration

Readout time calibration

The aim of calibrating a lima detector is to estimate the readout time needed. Fscan distinguishes 2 cases:

  • internal trigger time : time between 2 exposures in internal trigger mode. Used when scan_mode is set to CAMERA
  • external trigger time : time needed after an exposure before sending next trigger. Used when scan_mode is set to POSITION or TIME

By default lima calibration uses:

  • internal_trigger_time = readout_time
  • external_trigger_time = readout_time + trigger_latency

readout_time is estimated from the detector properties. It depends on the detector type and capabilities. For example, a Frelon detector readout time changes, if the detector is used in frame transfer mode, a Marana detector readout time depends on its overlap mode, ...

trigger_latency uses the following default values defined in the fscan code:

detector
type		 code defined
latency
pilatus 5e-5
andor3 1e-4
pco 4e-4
frelon 1e-4
perkinelmer 1e-4
other detectors 0.

Configuration

Readout time and/or trigger latency can be changed in the configuration. Add the following section to the fscan config:

  lima_calib:
    mymarana:
      trigger_latency: 0.0005
    myfrelon:
      readout_time: 0.026
      trigger_latency: 0.001
    myfrelon2:
      trigger_latency: 0.005

Note that detectors are referenced by name (not $mymarana !!).

Eiger detectors

Eiger detectors' readout_time is different, for both external and internal triggering and is proportional to the exposure time. So for this detector two extra properties are defined:

  lima_calib:
    myeiger:
      internal_time_correction: 0.000041
      external_time_correction: 0.00006

External and internal trigger times are therefore calculated as follows:

  • internal_trigger_time = internal_time_correction * acq_time + 1e-7
  • external_trigger_time = external_time_correction * acq_time + 0.0001 + latency_time

Accessing lima calibration details from bliss

We can access lima calibration details from the scan object as follow:

FSCANTEST [8]: ftimescan.validate()
FSCANTEST [9]: ftimescan.master.lima_calib
      Out [9]: Calibration for exposure_time = 0.1 sec

               Name                Internal    External    Latency Used
               ----------------  ----------  ----------  --------------
               bcu_mpx_tpxatl25      0.0003      0.0003               0

               ==> internal trigger time = 0.0003 sec
               ==> external trigger time = 0.0003 sec