Re: xspress3 Realtime not arrived when set 100s

[Matt Newville via Tech-talk <tech-talk at aps.anl.gov>]

Hi Lynn, 

On Thu, Aug 3, 2023 at 3:05 AM lynn via Tech-talk <tech-talk at aps.anl.gov> wrote:

Dear experts，

    Xspress3 Realtime was 46.31s when set 100s. It was normal when the acquire time less. 

    P.S. It is xspress3 1Chan.

    When use IOC from Github: (macro was: XSP_1Chan)

    The realtime was always 46.31, when acquire time set to 100 seconds. We tried several times, the result was same.

    And "XSPS_1Chan:C1SCA:0:Value_RBV" was 3.70503e+09. ( 3.70503e+09 / 8000000 = 46.31) 

   

   Then we changed IOC from verder:( macro was XSPRESS3-EXAMPLE)   

   The realtime was still 46s, i mean the xspress stop acquire at 46s when set 100s.

    And XSPRESS-EXAMPLE:C1_SCA0:Value_RBV was  -5.89935e+08.

    If you did not have a device, we would like to support.

    teamview or other software was ok.

   

Yes, the xspress3 uses an 80 MHz clock (as far as I know, this has not changed) and the counters are 32-bit.  That means the clock counter for a single frame (acquisition) overflows at 2**32 / (80e6) = 53.687 seconds.   When you ask for a longer count time, say 100 seconds, the clock will report 100 % (53.867)  = 43.613 seconds.  The MCA arrays and other scalar value will continue to count, though eventually, those other SCAs (say, the reset rates or "good events") may also overflow.

So, it's best to consider that a single frame is limited to 53 seconds.  To collect a longer image, you can easily collect multiple frames (say 10 frames of 10 seconds or 4000 frames of 0.025 seconds) and read the sums of the MCAs and SCA values.