I allready mentioned that the scintillator strips in the PES emit light which is collected by WLS fibers. This light is then sent to the cathode of a photomultiplier tube (PMT). PMTs convert light into electrical signals. Currently, we use PMTs that have 16 cathodes and anodes (MAPMT). This means that one MAPMT can handle 16 strips.
The signals coming from the MAPMTs are then sent to a ShowerMax Digitizer (SMD) Board which is part of the front end electronics. It's purpose is to digitize these signals. But recall that bunch crossings can occur every 132 ns. Since the electronics can't work that fast, it gets help from 12 SQUID Cards located on the face of the SMD Boards. The SQUIDs allow us to store events until they're ready to be read out.
The ShowerMax Receiver (SMXR) Board is what tells the SMD Module to send the data onward. Since not every event is interesting and there is only a limited a mount of disk space, the SMXR must know what to keep and what to throw away. It must also get the timing right so that it agrees with the other detectors sending data.
Once the SMXR gives the thumbs up, data is sent to the Data Acquisition (DAQ) System. This is where the data is written out into the proper banks. All PES data is written to the PESD bank. For information on how to use these banks, consult the offline section.
