Tuesday, November 9, 2010

Linac Control System

The current Linac control system is based on a VME computer with custom I/O components. A custom scanner card in the VME crate using a dual-port memory map protocol communicates with the I/O cards via a 50-pin ribbon cable using a CGR-Mev in house protocol. Each I/O card is homogenous in that all digital I/O is a TTL signal, and all analog I/O utilizes a 0-10V signal. Each card is given it address via external TTL voltages. The cards have ribbon cable connector on one side, and connect to a 3U Eurocard backplane that handles all incoming and outgoing control signals. This backplane then connects to any signal specific hardware necessary, such as TTL to 24V contact relays, voltage to frequency converters, or directly to the devices controlled.

As all I/O is homogeneous at the Eurocard backplane, this is the point at which the conversion from the old control system to the new PLC system will take place. Special cables have been fabricated to connect D-shell DIN-rail breakout boxes to the 96-pin backplane connectors. Using this setup, the new control system can be tested, and the Linac can be reverted to the old control system simply by removing the adapter cables, and reinserting the I/O cards as before.

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