[Halld-cal] [New Logentry] Timing of LED pulses taken overnight

[dalton at jlab.org]

Logentry Text:
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Data was taken overnight using the BCAL South crates with the downstream LEDs pulsing at 0.1 Hz.  This was run BCAL 3077, /gluonraid1/rawdata/active/RunPeriod000/BCAL/south/bcal_s4_3077.0.coda

In this entry I analyze the arrival time  (with respect to the trigger) of the pulses in the DAQ.  All times are detemined using the "IU" method (interpolating the time where the pulse crosses half the maximum height) and are quoted in units of sample number (4 ns interval on the f250.)

Figure 1 gives an example of the time determination, with the little black crosses indicating the intersection of the pulse and the half-maximum height.  

Figure 2 is a plot of all the pulse time sfrom the overnight run.  There is a large variation of more than 25 samples (100 ns) between time and there is structure within the distribution.

Figure 3 shows the times for LED puses for all channels for an individual event.  There are clear patterns to the times. The times show distinct variation by quadrant and by channels corresponding to LED "columns" over each quadrant.  It seems that the LEDs are not being pusled at the same time and that the difference is large.  There is also the expected difference between upstream (channels 8-15) and downstream (channels 0-7) due to propagation of the light from one end of the bar to the other, and this can be seen, but it is smaller than the channel to channel variation. 

Even more interesting is the overnight variation of this arrival time.  This is plotted in Fig. 4 and 5 for channels in two ADCs in two different crates (representing quadrants 2 and 3) respectively.  As can be seen, there is a common behavior for a single LED string which can be different from string to string.  The plots for all ADCs in each quadrant look essentially identical.

Figure 6 is a plot of some temparatures within the fan tray of roc 37.  This can also serve as a proxy for the hall temperature until those sensors are installed.  It seems that there is some relationship between temperature (either in the crate or in the hall) and the arrival time of most LED pulses at the DAQ.  However, Fig. 4 column 3 demostrates that the timing of 1 of the 8 LED distributions observed herein is insensitive.


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This is a plain text email for clients that cannot display HTML.  The full logentry can be found online at https://logbooks.jlab.org/entry/3286760
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