[Eg6_analysis] Data Acquisition System

[Dupré Raphaël]

Hello guys,

The system of data acquisition is set up such that it stocks the data over
a long time. When the trigger signal arrives the DAQ system takes data for
8.5 micro seconds more and keeps values from -1.5 to 8.5 relative to the
trigger. TDC slots are of 100 ns and there you have 100 of them with the
trigger time at TDC = 15.

Pedestals for the ADC values are calculated from a larger window taken from
previous data. I do not remember the time window used for these pedestals,
but it is probably documented somewhere (it might be interesting to try to
find it). Finally the DAQ send some data, the data are sent by clusters of
consecutive TDCs. In order to define a cluster you need to have 3 (?)
consecutive hits with ADCs higher than 45 (?). Then the cluster is defined
by all these consecutive hits plus the 3 before and the 3 after in term of
TDC, so you have a minimum size of clusters of 9 (except on the edges of
the time sample). These additional 6 hits can be of any ADC value and can
eventually be used in order to make an additional pedestal, either by using
a mean value of them or the 2 extremes (or any other combination that would
be most appropriate) and subtract this to all the hits of the cluster.

I am not completely sure of the final values we used in the run, so the
numbers followed by a "(?)" should be checked. It should be straight
forward to find them by looking into data.  The minimum size of clusters
will give the number of consecutive hits needed and the ADC distribution
has a discontinuity at the threshold level.


Best,

-- 
Raphaël Dupré
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