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Last modified: 20 July 2010

What does this warning mean?

# hrc_process_events (CIAO 4.2): The following error occurred 2482 times:
  dsHPEEVENTSEQERR -- WARNING: Out of sequence events discovered in hrc_evt1.fits.

There are occasional events that appear in the telemetry stream with time tags that make them seem to have occurred out-of-sequence. One special case where this occurs has been documented (see the Out-of-sequence HRC Time Tags memo); other occurrences are most likely to be caused by hiccups in the HRC or by double-bit errors in telemetry (single-bit errors are corrected).

This warning may be ignored in most cases, as long as the number of events flagged as out-of-sequence is a small fraction of the total number of events in the file. For example:

unix% dmlist hrc_evt1.fits blocks
 
--------------------------------------------------------------------------------
Dataset: hrc_evt1.fits blocks
--------------------------------------------------------------------------------
 
     Block Name                          Type         Dimensions
--------------------------------------------------------------------------------
Block    1: PRIMARY                        Null        
Block    2: EVENTS                         Table        20 cols x 798768   rows
Block    3: GTI                            Table         2 cols x 7        rows

(2482.0 / 798768.0) * 100 = 0.310729

Since there are 798768 events in the file, the 2482 that were flagged as out-of-sequence make up just 0.31% of the total events.

Note that all standard data products are supplied in the decommed order, so you should not run dmsort in an attempt to reorder them. These events are marked as bad by hrc_process_events and are removed by the standard level 2 status filter (see the HRC-S Imaging Observations section of the Create a New Level=2 Event File thread for an example).



Last modified: 20 July 2010