How the Trigger Works

The trigger recieves a 4 bit nsum from each LBL electronics card (this is the number of PMTs connected to that card whose signal went above the discriminator level). The nsum signal from each card is stretched to 125ns. The total nsum from different regions of the detector is used for the issuing of many different nsum triggers.

The trigger also recieves signals from some calibration devices such as the PLED or Laser, which can issue many different triggered source triggers. These input signals must be timed to arrive apropriately with the scintillation light.

At the start of each run the trigger can take some LBL electronics calibration triggers such pedestals and clocks.

The trigger also recieves input signals from a GPS unit which can be used to issue triggers.

For each trigger issued, a record of the trigger condition is kept.