VME Crates

VME crate on Gammasphere and a closeup of what the front of a crate can look like.

VME (Versa Module Extension) crates house the digitizers, triggers, and IOC modules for Gammasphere's DAQ system. The crate has specific connectors that plug into a standard backplane for power and communication. VME backplanes are mounted into mechanical assemblies referred to as “crates” or “subracks” that in turn mechanically mount into larger mechanical objects called “racks” or “relay racks”.

Each VME crate contains 3 individual VME backplanes, and each of them act as an individual VME system. Each of these VME systems has four digitizers, for a total of up to 12 digitizers per crate. One of the 12 VME systems is reserved for housing the System Trigger and the associated electronics. The System Trigger is then connected to all routers in the system. However, whereas the original setup used short copper cables to make these connections, the new distributed system uses optical connections between the System Trigger and the Routers. The required the designing of a VME Fiber Expander to provide a fully optical interface to the System Trigger.