When will dark frame be collected? Clarify some parameters related with this question

[Long Yang]

Hi all,

I am posting this question here because this might be a common question for xpd users. Tim will post his answer and detailed example here. Hope this can help people clarify some related parameters about dark frame, such as frame_acq_time, dk_window, and ct. Thank you!

Long

[Chia-Hao Liu]

That's the content I had with Long over email. Let me post it.

definition: 

  1. frame_acq_time -> inverse of frame rate in seconds. Default is 0.1s and can't be set to more than 5s

  2. dk_window -> dark window in minute. Default to 2000 minutes.

  3. valid dark -> currently a valid dark frame is the dark frame that has the same 1) inverse frame rate 2) total acquisition time as the light frame and 3) it was taken at a time less than ``dk_window`` ago.

Assume you only have use ct_60 (single shot, 60s) for your experiment.

0. beam time just start, frame_acq_time is set to 0.1s and dk_window is set to 2000 mins

1. run ct_60. A dark (dk1) will be collected as no dark has been run.

2. run ct_60 again. No dark will be collected as you have dk1 collected within 2000 mins from current experiment.

3. run ct_120. A dark (dk2) will be collected  as there is no dark with the same total exposure time (120s)

3. change frame_acq_time to 0.5s

4. run ct_120. A dark (dk3) will be collected as there is no dark with same inverse frame rate (0.1s)

5. run ct_60. A dark (dk4) will be collected as no 60s dark with 0.5s inverse frame rate has been collected.

6. change frame_acq_time back to 0.1s

7. run ct_60. No dark will be collected and dk1 will be applied.

8. run ct_120. No dark will be collected and dk2 will be applied.

9. change dk_window to 0.5 min

10. run ct_60. A dark (dk5) will be collected as dk1 was collected more than 0.5 min ago.

11. run ct_120. A dark (dk6) will be collected as dk2 was collected more than 0.5 min ago.

Hope that help clarify some aspects.