Sunday, August 7, 2011

Safety Interlock Systems of PLC





Programmable systems are appropriate the standard of de facto for Safety Interlock Systems, permitting for personnel protection growing complexity. The National Accelerator Laboratory of SLAC has realized a system of programmable safety interlock utilizing a graded advance to protect personnel from contact to prompt radiation.

The architecture of personnel protection system is according to two tiers of programmable systems doing safety interlocks and access control. The strategy contains in isolating the functions of safety from the control of access and system monitoring presented through EPICS. The isolation enables the functions of safety to be ensured even in the fully working control system absence. The functions of safety are made by redundant certified of PLC for safety applications. Every PLC was programmed by a self-determining engineer to give some diversity level and protection from errors of coding. Functional testing was did during a test bench and, after operation through a procedure of field checkout designed to verify the operation system for New Data are saved in an array on the PLC Access Control and recovered by the system of control via TCP/IP. Commands from the Master Control Center are transmitted throughout an interface of EPICS via TCP/IP. Controls are disregard by the PLC Access Control unless they are authenticated by a Hardware Enable, it’s mean a signal that is hardwired to PLC from the center of control.

The processes were built to handle the integration and the life cycle with obtainable installations. Control signals necessary for operation safely are hardwired from a card output on the Access Control Operators distantly control access into the hazardous zone using a workstation of EPICS. The PLC Access Control is an IOC on the network of controls which controls the keybank release keys and releases the locked door magnetically. The PLC Access Control also gives status to the Station of Operator and personnel at the Entry Door.

The redundant of Safety PLCs check the switches of interlock and restrain the operation of the hazards. The Safety PLCs are cross interlocked such that if either PLC detects a fault, and the other PLC will also restrain.

The cross Interlock hazard, the path of communication between the Access Control and the Safety PLCs lets the Safety PLCs to transmit a status bit to each other of PLC. The status bit is a signal that the controller is in a Station of Operator to observe the status of interlock.


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