The electronics behind SNO is very complex. The signals from each of the 10,000 photomultiplier tubes need to be individually processed, involving charge amplification and
discrimination, analogue to digital conversion, time to digital conversion, analogue and digital buffering and multiplexing I/O tasks. Each photomultiplier tubes channel must have a very large dynamic
range (0.1 to 1000 photoelectrons), timing precision to better than 1 nano-second, have a very fast reset time and be able to buffer data to handle event burst rates of hundreds of kHz.
There is also the need to have
low power consumption. The heat sink capacity of the mine is too low to allow for high power consumption.
Groups of 32 photomultiplier tubes connect to a Front End Card, designed at University of Pennsylvania, to
process the PMT signals and distribute the high voltage.
At the heart of the Front End Card is the analogue/digital storage array, an in-house chip design using the latest CMOS technology.
Sixteen of
these Front End Cards then plug into a VME ( a hardware module) crate controlled by a single board computer (SBC). The SBC handles crate monitoring, on-line diagnostics and local event trigger logic.
There
are 20 of these VME crates which in turn are controlled by the data aquisition computer (DAQ) via a custom highspeed data protocol. The DAQ serves as the master trigger controller and event builder. The DAQ writes data
out to several mass storage devices both in the mine and on the surface by fibre-optic links. The DAQ also communicates to the calibration computer, water systems and the CMA computer. The DAQ system is being developed
at the University of Washington with assistance from other SNO institutions
