Each station contains 8 PWC planes--4 x-y pairs. A plane has 80 cells; each cell has an amplifier, shift register, and summer used in coincidence to form a self-trigger for the station. The station trigger is a coincidence of the x OR y signals from the top 3 pairs of planes. This trigger stores the station's 640 cells of information in the local shift register memory.
The data acquisition system (DAS) in the trailer at the center of the array receives a timing signal from each hut which triggered. A coincidence circuit is set for N huts, where N is 1, 2, 3,... A DAS coincidence sends a train of clock pulses to all stations shifting their data serially to the trailer in 70 microseconds. The time of the trigger, accurate to 1 millisecond, is also recorded.
With a N=1 trigger (sensitive to single muon tracks from primaries 30 to 300 GeV) the data acquisition system "computer" records the data. A pattern of one-and-only-one hit in each of the 8 planes of a station is a muon track candidate. The wire coordinates are stored in memory for a successful muon. Each computer stores 900 tracks in its memory which are then written to disks. Single muon data are stored at a rate of 2400 muons per sec; one disk holds several months of data.