This page descibes the Zero Suppression study undertaken on the X-Y table at CERN. The point of the study was to verify that the software Zero-Suppression (in CMSSW) and the Hardware Zero Suppression were doing the same thing, and more specifically to make sure that the FED's algorithm was not suspect. We trust the software insofar as it is easily understandable, since reading the code is all one has to do to understand it.
I will not describe the set-up here in detail. I used a rod with its data split using an optical splitter. The data was simultaneously fed into 2 different FED cards. I will refer to the FEDs as FED 7 and FED 15 because slots 7 and 15 in the VME crate were used to house the FEDS. For technical reasons, it turned out that I could only use the data from one module on the rod. The X-Y table was chosen because it has a radioactive source which could be positioned anywhere above the detector. I chose to position it at the center of the module which provided a good trigger rate and lots of hits and clusters. Data was taken with both FEDS in hardware ZeroSuppressed mode (ZS), both FEDS in Virgin Raw (VR) mode, FED 7 in ZS mode and FED 15 in VR mode and FED 7 in VR mode and FED 15 in ZS mode. The fibers coming from the optical splitter were then switched between the two FEDs and data was retaken. The data in Virgin Raw mode was then zerosuppressed offline using CMSSW version 1_2_0 but with the latest Zero Suppression code. The results of the study are outlined in the following pages, and a tentative conculsion is obtained.
Both FEDS in Virgin Raw mode