The University of Toronto Solid State Linac Interlock Systems

The linac safety interlock system is based on solid state computer logic modules. This approach eliminates many of the problems associated with conventional relay interlock circuits and also make unauthorized tampering more difficult. The system incorporates duplicate logic on all functions and an error check section which senses logic malfunction. The various interlock operating modes are programmed by means of plug-in printed circuit boards which allow operation only in a specific mode. Selector switches provide logic level signals to inputs for test purposes but in so doing break the main interlock chain to ensure that interlocks are not overridden. Authorized bypassing of minor interlocks can be effected by the use of one key--vital interlocks require the use of an additional key held by the Radiation Safety Officer.