The "old" system brings all of the antennas into a set of Discriminators that produce
trigger pulses whenever the signal on the antenna exceeds a threshold. Those digital signals
are processed by a "Majority Logic Unit" that determines if multiple antennas detected the event. If the event
passes that screening, the result would be used to trigger the digitizing oscilloscopes. If the event is valid,
the data will be read (slowly) from the scopes into computers.
The HSV board is inserted in the trigger path to determine if the order in which antenna signals arrive matches
some known pattern for spurious data. In about 100 nanoseconds, the HSV board compares the pattern of arrival of antenna signals
and compares them with at least 25 known "bad" patterns; it can then trigger the scope only on non-vetoed patterns.
This operation is far too intensive to be handled by a computer, so
an FPGA (Field Programmable Gate Array) with several hundred
thousand gates is programmed into a massive logic system.
In addition, data on the rates at which antennas are hit and on
how often the "bad" patterns show up are sent from the FPGA every
100 ms to a microcontroller. From there, they are passed to
the Data Collection computer every second. |
