by Dan Hebert, Control magazine
OPC is playing a significant role in allowing plants to bridge the gap between process control and building automation systems, according to an article in the November issue of Control magazine by senior technical editor Dan Hebert.
Whether users and integrators choose a single control system or multiple systems depends on the degree of sophistication required to control the process, according to Hebert, as well as other key factors such as upfront costs, operating expenses and staffing requirements.
“All plant subsystems should be integrated into one overall monitoring and control solution,” says Dennis Runno, president of Custom Automation, a system integrator in Mesa, Arizona. “Successful plant processing is inextricably linked to the supporting building facilities. With two separate systems, information can be made to bridge the gap, but it’s much easier when you have a unified system.” Why combined systems are better:
- One system to learn and maintain
- Same HMI displays
- Similar control programming
- Single-vendor responsibility
- Simplified maintenance, spare parts stocking
- Easier integration of data between systems
- More open than using proprietary building automation systems
The author points to an example, the U.S. Department of Energy’s Waste Isolation Pilot Plant (WIPP) in the Chihuahauan Desert of southeastern New Mexico. The plant processes radioactive waste and safely entombs it in deep underground chambers. Thirteen critical subsystems are managed in the control room on a single system that handles everything including ventilation, electrical distribution and energy monitoring, HVAC, fire protection, radiation monitoring and plant protection.
The WIPP site uses redundant KEPServerEX servers with OPC and OPC UA to communicate with numerous subsystems using BACnet and other protocols. The interconnected subsystems talk to each other and accept commands from the operators on duty. The system is also designed to act independently to maintain a safe environment.
Of course, there’s another view that says it’s better to keep process and building automation systems separate. Matrix Technologies, a system integrator in Maumee, Ohio, prefers using two systems, according to Charles Sheets, director of the industrial systems division. “Since standard automation components can perform many functions, the same hardware and software can be used to control many different devices.“
Sheets adds that physical separation is beneficial for maintenance, security and to ensure that a problem with one system won’t affect the other, but he wants to use the same components such as PLCs in both systems for easier maintenance, spare parts and troubleshooting. Reasons to keep them separate:
- Lower upfront costs because building automation systems are cheaper
- Building automation systems have built-in building-oriented control schemes
- Each system is simpler than a combined alternative
- A failure in one system doesn’t take the entire plant down
Adds Erik Dellinger, product manager at Kepware Technologies in Portland, Maine, “There’s no idea solution here, but a good one we routinely see is two separate systems that only share the data they need,” with the process control system using industrial Ethernet and the building automation system using BACnet. “These are two different systems, but an OPC server can communicate with both BACnet ad Ethernet/IP and provide access and translation of only the data needed between the systems.”
To read the complete article, go to http://www.controlglobal.com/articles/2014/combining-building-and-process-automation-systems-is-it-better/. In a companion article, Hebert discusses how the two systems can be linked using the BACnet/IP protocol and OPC at either the HMI or controller level: http://www.controlglobal.com/articles/2014/use-bacnetip-to-connect-building-automation-and-process-systems Excerpted with permission from Control magazine.