Wednesday, November 3, 2010

Developed System for SNS Linac Cooling & Vacuum with PLC

External contractors are developing the vacuum control and the local cooling systems for the Spallation Neutron Source (SNS) linac. Soon these systems will be integrated into the facility wide controls system. Allen-Bradley Logic5000 series programmable controllers, populated with appropriate input and output modules, were selected as the local controllers. These controllers is interfaced to the facility wide control system via VME systems with PowerPC processors running the Wind River VxWorks operating system and EPICS (Experimental Physics and Industrial Control System) front end controller software.

Through much of the SNS, PLC (Programmable Logic Controller) will be used for the local controller systems. The EPICS IOC (Input/Output Controller) provide alarm functions, supervisory control and serve as the interface point for the PLC to global controls, the machine protection system and the event link system.

The local control integration systems to EPICS require resolution of interface issues preferably during design but in some cases issues are discovered during integration and development. The more significant issues identified during design and development of the DTL (Drift Tube Linac) and CCL (Coupled Cavity Linac), RCCS (Resonance Control and Cooling System) and vacuum systems. The issues examined were:
Interface between IOC and PLC; selection of protocol communication, creating and reaching agreement on signal lists, mapping process variables, optimizing data transfer between IOC and PLC.

Serial based devices; use of serial ports on PLC, serial types and network layout, device driver development, and distributed control.
Control loops over Ethernet, PID loops dispersed over PLC and IOC on non dedicated networks.

EPICS Operator displays and control vs PLC displays; development and maintenance of local PanelView displays, cost, redundant control screens on different platforms.

Alarm checking and management; the IOC as the appropriate location for checking the alarm functions versus the PLC, alarm limit parameter maintenance. Each of these integration and interface issues follow but first a brief background of the CCL RCCS and SNS DTL and vacuum systems.

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