Foundation fieldbus tested for nuclear plant, safety applications
When the managing director of British Nuclear Fuels' (Warrington, U.K.) BNFL Engineering division challenged its staff to cut costs by 25%, they decided to examine fieldbuses for savings and future platform growth. Tom Nobes, BNFL's senior systems engineer, says he and his colleagues were attracted to using a fieldbus by its simplified cabling; reduced installation costs; more flexible ordering...
When the managing director of British Nuclear Fuels' (Warrington, U.K.) BNFL Engineering division challenged its staff to cut costs by 25%, they decided to examine fieldbuses for savings and future platform growth. Tom Nobes, BNFL's senior systems engineer, says he and his colleagues were attracted to using a fieldbus by its simplified cabling; reduced installation costs; more flexible ordering due to programmable instruments; and improved diagnostics for optimized production and targeted maintenance.
"We can keep an eye on instruments that are more critical to the process, rather than simply calibrating them all at regular intervals, whether they need it or not," says Mr. Nobes. "Anything we can do to avoid visiting instruments is an advantage."
Mr. Nobes says BNFL began evaluating fieldbus at its small pilot plant at BNFL Springfields, near Preston, U.K. The plant uses mostly inert materials, such as water and Fullers Earth, to test filter efficiency. "We saw that rig as having virtually no safety implications, and we decided to outfit that system with fieldbus products, rather than conventional instruments. In this way, this system became a test rig for filters, as well as a fieldbus test rig."
BNFL also formed an internal committee to ensure that all divisions signed up for the same fieldbus for the same reasons. The committee eventually produced an internal standard, or code of practice, to prevent unauthorized systems from being introduced at any of its sites.
"We listed all the protocols available, and stopped when they reached 26," says Mr. Nobes. "We chose FOUNDATION fieldbus because we felt it most suited our requirements for speed, deterministic operation and time synchronization. A big advantage of FOUNDATION fieldbus to BNFL is its use of function blocks." Function blocks are uniform pieces of device description language used to carry out control functions in devices, and are standardized to ensure interoperability.
The filter test rig at BNFL Springfields was fitted with 30 loops and FOUNDATION- based products . The control systems, pressure transmitters, electromagnetic flowmeters and vortex flowmeters are from Yokogawa; level-measuring instruments are from Endress & Hauser; temperature transmitters are from Smar, and its control valves are from Flowserve.
Mr. Nobes says the project's first objective is to determine if a FOUNDATION fieldbus-based basic plant control system (BPCS) has demand rates and risk reduction factors that are no worse than existing, conventional DCS-based BPCS. Its second task is to assess implications of possible future use of FOUNDATION fieldbus in safety related applications up to SIL 1, which equals 85% of all trips at BNFL.
"Before trying to use fieldbus in active plants for safety, we're seeking to prove that fieldbus is no less reliable than a conventional 4-20 mA system," says Mr. Nobes. "BNFL works under the regulatory supervision of the Nuclear Installations Inspectorate (NII). Safety is BNFL's No. 1 priority. Safety in our plant is enhanced by instrument systems with alarms and trip actions. Before we approach the NII to let them know that we want to start using FOUNDATION fieldbus in our main plants, we need to establish a track record in simpler plants. Using small plants, we can gain experience; graduate upwards from there; and, in a few years, we could look at fitting FOUNDATION as our first choice."
So far, the filter test rig has operated for 12 months without any significant failures, and Mr. Nobes says it has logged every scrap of data from its instruments. This information will be used to build the performance statistics for a mean time between failure (MTBF) argument supporting eventual use of fieldbus in larger and more critical settings. In fact, BNFL is already designing a sump monitoring system with 230 FOUNDATION fieldbus loops.
However, to serve in safety settings, FOUNDATION fieldbus-based equipment will also have to survive failure mode effect analyses (FMEA) that break devices into component parts, and proactively try to determine how they might fail.
For more information, visit www.fieldbus.org .
Jim Montague, news editor firstname.lastname@example.org
Use this 'To Do' List for Fieldbus Projects
MSet up a fieldbus awareness group or committee that includes everyone with input on the plant, such as designers, installers, users, maintainers and buyers.
Decide on an internal fieldbus standard, policy or procedure that meets the needs of the organization's application.
Test potential fieldbus candidates in small, less-critical settings that appropriately simulate the applications in which they may eventually serve.
Seek to ensure that the fieldbus selected also fits into the company's quality assurance system.
Provide enough fieldbus training to potential users.
Source: Control Engineering with information from British Nuclear Fuels