Modernization of PLC-Based Control Systems at SNS
When the SNS site was built around 20 years ago, the Conventional Facilities (CF) control systems were de-signed using 2 communication protocols to allow pro-grammable logic controllers (PLCs) to interface with motors, variable frequency drives (VFDs), and remote input and output (I/O) devices. The protocol chosen to control motors and VFDs is DeviceNet, a CANbus-based protocol developed by Allen-Bradley, a subsidiary of Rockwell Automation. The protocol chosen to communi-cate with remote I/O is ControlNet, another protocol developed by Allen-Bradley. Both of these protocols are obsolete and present reliability and maintainability is-sues, particularly DeviceNet. As the Control Systems Section at SNS is working to modernize control systems throughout the machine, a major goal for PLC-based systems is to remove the obsolete communication proto-cols in favor of standard, ubiquitous Ethernet. To this end, any new VFDs installed use Ethernet communica-tion. Many VFDs are currently being replaced in the Central Utilities Building (CUB) and the Central Exhaust Facility (CEF) and are being removed from DeviceNet in favor of Ethernet communication. Planning is underway to retrofit Eaton Intelligent Technology motor control centers (MCCs) in the Target Building to remove particu-larly troublesome DeviceNet adaptors and replace them with Ethernet adaptors for each motor starter. The Con-trolNet network in the CUB has been demolished, with I/O drops integrated into a local Ethernet network, im-proving sustainability and maintainability.